Update contrib/restricted/abseil-cpp to 20220623.0

47 files changed, 2083 insertions, 1507 deletions

diff --git a/contrib/restricted/abseil-cpp/absl/strings/CMakeLists.txt b/contrib/restricted/abseil-cpp/absl/strings/CMakeLists.txt
index 748356eb0b..778460e63d 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/CMakeLists.txt
+++ b/contrib/restricted/abseil-cpp/absl/strings/CMakeLists.txt
@@ -25,6 +25,8 @@ target_sources(abseil-cpp-absl-strings PRIVATE
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/ascii.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/charconv.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/cord.cc
+  ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/cord_analysis.cc
+  ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/cord_buffer.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/escaping.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/charconv_bigint.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/charconv_parse.cc
@@ -33,6 +35,7 @@ target_sources(abseil-cpp-absl-strings PRIVATE
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_consume.cc
+  ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_crc.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_ring.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_functions.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_handle.cc
diff --git a/contrib/restricted/abseil-cpp/absl/strings/ascii.h b/contrib/restricted/abseil-cpp/absl/strings/ascii.h
index b46bc71f35..42eadaea6c 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/ascii.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/ascii.h
@@ -133,7 +133,7 @@ inline bool ascii_isdigit(unsigned char c) { return c >= '0' && c <= '9'; }
 
 // ascii_isprint()
 //
-// Determines whether the given character is printable, including whitespace.
+// Determines whether the given character is printable, including spaces.
 inline bool ascii_isprint(unsigned char c) { return c >= 32 && c < 127; }
 
 // ascii_isgraph()
@@ -197,7 +197,7 @@ ABSL_MUST_USE_RESULT inline std::string AsciiStrToUpper(absl::string_view s) {
 ABSL_MUST_USE_RESULT inline absl::string_view StripLeadingAsciiWhitespace(
     absl::string_view str) {
   auto it = std::find_if_not(str.begin(), str.end(), absl::ascii_isspace);
-  return str.substr(it - str.begin());
+  return str.substr(static_cast<size_t>(it - str.begin()));
 }
 
 // Strips in place whitespace from the beginning of the given string.
@@ -211,13 +211,13 @@ inline void StripLeadingAsciiWhitespace(std::string* str) {
 ABSL_MUST_USE_RESULT inline absl::string_view StripTrailingAsciiWhitespace(
     absl::string_view str) {
   auto it = std::find_if_not(str.rbegin(), str.rend(), absl::ascii_isspace);
-  return str.substr(0, str.rend() - it);
+  return str.substr(0, static_cast<size_t>(str.rend() - it));
 }
 
 // Strips in place whitespace from the end of the given string
 inline void StripTrailingAsciiWhitespace(std::string* str) {
   auto it = std::find_if_not(str->rbegin(), str->rend(), absl::ascii_isspace);
-  str->erase(str->rend() - it);
+  str->erase(static_cast<size_t>(str->rend() - it));
 }
 
 // Returns absl::string_view with whitespace stripped from both ends of the
diff --git a/contrib/restricted/abseil-cpp/absl/strings/cord.cc b/contrib/restricted/abseil-cpp/absl/strings/cord.cc
index 854047ca98..85a67a0810 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/cord.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/cord.cc
@@ -34,9 +34,12 @@
 #include "absl/base/port.h"
 #include "absl/container/fixed_array.h"
 #include "absl/container/inlined_vector.h"
+#include "absl/strings/cord_buffer.h"
 #include "absl/strings/escaping.h"
+#include "absl/strings/internal/cord_data_edge.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_btree.h"
+#include "absl/strings/internal/cord_rep_crc.h"
 #include "absl/strings/internal/cord_rep_flat.h"
 #include "absl/strings/internal/cordz_statistics.h"
 #include "absl/strings/internal/cordz_update_scope.h"
@@ -52,7 +55,7 @@ ABSL_NAMESPACE_BEGIN
 
 using ::absl::cord_internal::CordRep;
 using ::absl::cord_internal::CordRepBtree;
-using ::absl::cord_internal::CordRepConcat;
+using ::absl::cord_internal::CordRepCrc;
 using ::absl::cord_internal::CordRepExternal;
 using ::absl::cord_internal::CordRepFlat;
 using ::absl::cord_internal::CordRepSubstring;
@@ -64,56 +67,6 @@ using ::absl::cord_internal::kMinFlatLength;
 using ::absl::cord_internal::kInlinedVectorSize;
 using ::absl::cord_internal::kMaxBytesToCopy;
 
-constexpr uint64_t Fibonacci(unsigned char n, uint64_t a = 0, uint64_t b = 1) {
-  return n == 0 ? a : Fibonacci(n - 1, b, a + b);
-}
-
-static_assert(Fibonacci(63) == 6557470319842,
-              "Fibonacci values computed incorrectly");
-
-// Minimum length required for a given depth tree -- a tree is considered
-// balanced if
-//      length(t) >= min_length[depth(t)]
-// The root node depth is allowed to become twice as large to reduce rebalancing
-// for larger strings (see IsRootBalanced).
-static constexpr uint64_t min_length[] = {
-    Fibonacci(2),          Fibonacci(3),  Fibonacci(4),  Fibonacci(5),
-    Fibonacci(6),          Fibonacci(7),  Fibonacci(8),  Fibonacci(9),
-    Fibonacci(10),         Fibonacci(11), Fibonacci(12), Fibonacci(13),
-    Fibonacci(14),         Fibonacci(15), Fibonacci(16), Fibonacci(17),
-    Fibonacci(18),         Fibonacci(19), Fibonacci(20), Fibonacci(21),
-    Fibonacci(22),         Fibonacci(23), Fibonacci(24), Fibonacci(25),
-    Fibonacci(26),         Fibonacci(27), Fibonacci(28), Fibonacci(29),
-    Fibonacci(30),         Fibonacci(31), Fibonacci(32), Fibonacci(33),
-    Fibonacci(34),         Fibonacci(35), Fibonacci(36), Fibonacci(37),
-    Fibonacci(38),         Fibonacci(39), Fibonacci(40), Fibonacci(41),
-    Fibonacci(42),         Fibonacci(43), Fibonacci(44), Fibonacci(45),
-    Fibonacci(46),         Fibonacci(47),
-    0xffffffffffffffffull,  // Avoid overflow
-};
-
-static const int kMinLengthSize = ABSL_ARRAYSIZE(min_length);
-
-static inline bool btree_enabled() {
-  return cord_internal::cord_btree_enabled.load(
-      std::memory_order_relaxed);
-}
-
-static inline bool IsRootBalanced(CordRep* node) {
-  if (!node->IsConcat()) {
-    return true;
-  } else if (node->concat()->depth() <= 15) {
-    return true;
-  } else if (node->concat()->depth() > kMinLengthSize) {
-    return false;
-  } else {
-    // Allow depth to become twice as large as implied by fibonacci rule to
-    // reduce rebalancing for larger strings.
-    return (node->length >= min_length[node->concat()->depth() / 2]);
-  }
-}
-
-static CordRep* Rebalance(CordRep* node);
 static void DumpNode(CordRep* rep, bool include_data, std::ostream* os,
                      int indent = 0);
 static bool VerifyNode(CordRep* root, CordRep* start_node,
@@ -135,75 +88,6 @@ static inline CordRep* VerifyTree(CordRep* node) {
   return node;
 }
 
-// Return the depth of a node
-static int Depth(const CordRep* rep) {
-  if (rep->IsConcat()) {
-    return rep->concat()->depth();
-  } else {
-    return 0;
-  }
-}
-
-static void SetConcatChildren(CordRepConcat* concat, CordRep* left,
-                              CordRep* right) {
-  concat->left = left;
-  concat->right = right;
-
-  concat->length = left->length + right->length;
-  concat->set_depth(1 + std::max(Depth(left), Depth(right)));
-}
-
-// Create a concatenation of the specified nodes.
-// Does not change the refcounts of "left" and "right".
-// The returned node has a refcount of 1.
-static CordRep* RawConcat(CordRep* left, CordRep* right) {
-  // Avoid making degenerate concat nodes (one child is empty)
-  if (left == nullptr) return right;
-  if (right == nullptr) return left;
-  if (left->length == 0) {
-    CordRep::Unref(left);
-    return right;
-  }
-  if (right->length == 0) {
-    CordRep::Unref(right);
-    return left;
-  }
-
-  CordRepConcat* rep = new CordRepConcat();
-  rep->tag = cord_internal::CONCAT;
-  SetConcatChildren(rep, left, right);
-
-  return rep;
-}
-
-static CordRep* Concat(CordRep* left, CordRep* right) {
-  CordRep* rep = RawConcat(left, right);
-  if (rep != nullptr && !IsRootBalanced(rep)) {
-    rep = Rebalance(rep);
-  }
-  return VerifyTree(rep);
-}
-
-// Make a balanced tree out of an array of leaf nodes.
-static CordRep* MakeBalancedTree(CordRep** reps, size_t n) {
-  // Make repeated passes over the array, merging adjacent pairs
-  // until we are left with just a single node.
-  while (n > 1) {
-    size_t dst = 0;
-    for (size_t src = 0; src < n; src += 2) {
-      if (src + 1 < n) {
-        reps[dst] = Concat(reps[src], reps[src + 1]);
-      } else {
-        reps[dst] = reps[src];
-      }
-      dst++;
-    }
-    n = dst;
-  }
-
-  return reps[0];
-}
-
 static CordRepFlat* CreateFlat(const char* data, size_t length,
                                size_t alloc_hint) {
   CordRepFlat* flat = CordRepFlat::New(length + alloc_hint);
@@ -229,21 +113,7 @@ static CordRep* NewBtree(const char* data, size_t length, size_t alloc_hint) {
 // The returned node has a refcount of 1.
 static CordRep* NewTree(const char* data, size_t length, size_t alloc_hint) {
   if (length == 0) return nullptr;
-  if (btree_enabled()) {
-    return NewBtree(data, length, alloc_hint);
-  }
-  absl::FixedArray<CordRep*> reps((length - 1) / kMaxFlatLength + 1);
-  size_t n = 0;
-  do {
-    const size_t len = std::min(length, kMaxFlatLength);
-    CordRepFlat* rep = CordRepFlat::New(len + alloc_hint);
-    rep->length = len;
-    memcpy(rep->Data(), data, len);
-    reps[n++] = VerifyTree(rep);
-    data += len;
-    length -= len;
-  } while (length != 0);
-  return MakeBalancedTree(reps.data(), n);
+  return NewBtree(data, length, alloc_hint);
 }
 
 namespace cord_internal {
@@ -258,22 +128,6 @@ void InitializeCordRepExternal(absl::string_view data, CordRepExternal* rep) {
 
 }  // namespace cord_internal
 
-static CordRep* NewSubstring(CordRep* child, size_t offset, size_t length) {
-  // Never create empty substring nodes
-  if (length == 0) {
-    CordRep::Unref(child);
-    return nullptr;
-  } else {
-    CordRepSubstring* rep = new CordRepSubstring();
-    assert((offset + length) <= child->length);
-    rep->length = length;
-    rep->tag = cord_internal::SUBSTRING;
-    rep->start = offset;
-    rep->child = child;
-    return VerifyTree(rep);
-  }
-}
-
 // Creates a CordRep from the provided string. If the string is large enough,
 // and not wasteful, we move the string into an external cord rep, preserving
 // the already allocated string contents.
@@ -306,13 +160,14 @@ static CordRep* CordRepFromString(std::string&& src) {
 // --------------------------------------------------------------------
 // Cord::InlineRep functions
 
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr unsigned char Cord::InlineRep::kMaxInline;
+#endif
 
-inline void Cord::InlineRep::set_data(const char* data, size_t n,
-                                      bool nullify_tail) {
+inline void Cord::InlineRep::set_data(const char* data, size_t n) {
   static_assert(kMaxInline == 15, "set_data is hard-coded for a length of 15");
 
-  cord_internal::SmallMemmove(data_.as_chars(), data, n, nullify_tail);
+  cord_internal::SmallMemmove<true>(data_.as_chars(), data, n);
   set_inline_size(n);
 }
 
@@ -341,7 +196,9 @@ inline void Cord::InlineRep::remove_prefix(size_t n) {
 // Returns `rep` converted into a CordRepBtree.
 // Directly returns `rep` if `rep` is already a CordRepBtree.
 static CordRepBtree* ForceBtree(CordRep* rep) {
-  return rep->IsBtree() ? rep->btree() : CordRepBtree::Create(rep);
+  return rep->IsBtree()
+             ? rep->btree()
+             : CordRepBtree::Create(cord_internal::RemoveCrcNode(rep));
 }
 
 void Cord::InlineRep::AppendTreeToInlined(CordRep* tree,
@@ -349,11 +206,7 @@ void Cord::InlineRep::AppendTreeToInlined(CordRep* tree,
   assert(!is_tree());
   if (!data_.is_empty()) {
     CordRepFlat* flat = MakeFlatWithExtraCapacity(0);
-    if (btree_enabled()) {
-      tree = CordRepBtree::Append(CordRepBtree::Create(flat), tree);
-    } else {
-      tree = Concat(flat, tree);
-    }
+    tree = CordRepBtree::Append(CordRepBtree::Create(flat), tree);
   }
   EmplaceTree(tree, method);
 }
@@ -361,16 +214,14 @@ void Cord::InlineRep::AppendTreeToInlined(CordRep* tree,
 void Cord::InlineRep::AppendTreeToTree(CordRep* tree, MethodIdentifier method) {
   assert(is_tree());
   const CordzUpdateScope scope(data_.cordz_info(), method);
-  if (btree_enabled()) {
-    tree = CordRepBtree::Append(ForceBtree(data_.as_tree()), tree);
-  } else {
-    tree = Concat(data_.as_tree(), tree);
-  }
+  tree = CordRepBtree::Append(ForceBtree(data_.as_tree()), tree);
   SetTree(tree, scope);
 }
 
 void Cord::InlineRep::AppendTree(CordRep* tree, MethodIdentifier method) {
-  if (tree == nullptr) return;
+  assert(tree != nullptr);
+  assert(tree->length != 0);
+  assert(!tree->IsCrc());
   if (data_.is_tree()) {
     AppendTreeToTree(tree, method);
   } else {
@@ -383,11 +234,7 @@ void Cord::InlineRep::PrependTreeToInlined(CordRep* tree,
   assert(!is_tree());
   if (!data_.is_empty()) {
     CordRepFlat* flat = MakeFlatWithExtraCapacity(0);
-    if (btree_enabled()) {
-      tree = CordRepBtree::Prepend(CordRepBtree::Create(flat), tree);
-    } else {
-      tree = Concat(tree, flat);
-    }
+    tree = CordRepBtree::Prepend(CordRepBtree::Create(flat), tree);
   }
   EmplaceTree(tree, method);
 }
@@ -396,16 +243,14 @@ void Cord::InlineRep::PrependTreeToTree(CordRep* tree,
                                         MethodIdentifier method) {
   assert(is_tree());
   const CordzUpdateScope scope(data_.cordz_info(), method);
-  if (btree_enabled()) {
-    tree = CordRepBtree::Prepend(ForceBtree(data_.as_tree()), tree);
-  } else {
-    tree = Concat(tree, data_.as_tree());
-  }
+  tree = CordRepBtree::Prepend(ForceBtree(data_.as_tree()), tree);
   SetTree(tree, scope);
 }
 
 void Cord::InlineRep::PrependTree(CordRep* tree, MethodIdentifier method) {
   assert(tree != nullptr);
+  assert(tree->length != 0);
+  assert(!tree->IsCrc());
   if (data_.is_tree()) {
     PrependTreeToTree(tree, method);
   } else {
@@ -419,7 +264,7 @@ void Cord::InlineRep::PrependTree(CordRep* tree, MethodIdentifier method) {
 // written to region and the actual size increase will be written to size.
 static inline bool PrepareAppendRegion(CordRep* root, char** region,
                                        size_t* size, size_t max_length) {
-  if (root->IsBtree() && root->refcount.IsMutable()) {
+  if (root->IsBtree() && root->refcount.IsOne()) {
     Span<char> span = root->btree()->GetAppendBuffer(max_length);
     if (!span.empty()) {
       *region = span.data();
@@ -428,13 +273,8 @@ static inline bool PrepareAppendRegion(CordRep* root, char** region,
     }
   }
 
-  // Search down the right-hand path for a non-full FLAT node.
   CordRep* dst = root;
-  while (dst->IsConcat() && dst->refcount.IsMutable()) {
-    dst = dst->concat()->right;
-  }
-
-  if (!dst->IsFlat() || !dst->refcount.IsMutable()) {
+  if (!dst->IsFlat() || !dst->refcount.IsOne()) {
     *region = nullptr;
     *size = 0;
     return false;
@@ -448,12 +288,7 @@ static inline bool PrepareAppendRegion(CordRep* root, char** region,
     return false;
   }
 
-  size_t size_increase = std::min(capacity - in_use, max_length);
-
-  // We need to update the length fields for all nodes, including the leaf node.
-  for (CordRep* rep = root; rep != dst; rep = rep->concat()->right) {
-    rep->length += size_increase;
-  }
+  const size_t size_increase = std::min(capacity - in_use, max_length);
   dst->length += size_increase;
 
   *region = dst->flat()->Data() + in_use;
@@ -461,90 +296,6 @@ static inline bool PrepareAppendRegion(CordRep* root, char** region,
   return true;
 }
 
-template <bool has_length>
-void Cord::InlineRep::GetAppendRegion(char** region, size_t* size,
-                                      size_t length) {
-  auto constexpr method = CordzUpdateTracker::kGetAppendRegion;
-
-  CordRep* root = tree();
-  size_t sz = root ? root->length : inline_size();
-  if (root == nullptr) {
-    size_t available = kMaxInline - sz;
-    if (available >= (has_length ? length : 1)) {
-      *region = data_.as_chars() + sz;
-      *size = has_length ? length : available;
-      set_inline_size(has_length ? sz + length : kMaxInline);
-      return;
-    }
-  }
-
-  size_t extra = has_length ? length : (std::max)(sz, kMinFlatLength);
-  CordRep* rep = root ? root : MakeFlatWithExtraCapacity(extra);
-  CordzUpdateScope scope(root ? data_.cordz_info() : nullptr, method);
-  if (PrepareAppendRegion(rep, region, size, length)) {
-    CommitTree(root, rep, scope, method);
-    return;
-  }
-
-  // Allocate new node.
-  CordRepFlat* new_node = CordRepFlat::New(extra);
-  new_node->length = std::min(new_node->Capacity(), length);
-  *region = new_node->Data();
-  *size = new_node->length;
-
-  if (btree_enabled()) {
-    rep = CordRepBtree::Append(ForceBtree(rep), new_node);
-  } else {
-    rep = Concat(rep, new_node);
-  }
-  CommitTree(root, rep, scope, method);
-}
-
-// Computes the memory side of the provided edge which must be a valid data edge
-// for a btrtee, i.e., a FLAT, EXTERNAL or SUBSTRING of a FLAT or EXTERNAL node.
-static bool RepMemoryUsageDataEdge(const CordRep* rep,
-                                   size_t* total_mem_usage) {
-  size_t maybe_sub_size = 0;
-  if (ABSL_PREDICT_FALSE(rep->IsSubstring())) {
-    maybe_sub_size = sizeof(cord_internal::CordRepSubstring);
-    rep = rep->substring()->child;
-  }
-  if (rep->IsFlat()) {
-    *total_mem_usage += maybe_sub_size + rep->flat()->AllocatedSize();
-    return true;
-  }
-  if (rep->IsExternal()) {
-    // We don't know anything about the embedded / bound data, but we can safely
-    // assume it is 'at least' a word / pointer to data. In the future we may
-    // choose to use the 'data' byte as a tag to identify the types of some
-    // well-known externals, such as a std::string instance.
-    *total_mem_usage += maybe_sub_size +
-                        sizeof(cord_internal::CordRepExternalImpl<intptr_t>) +
-                        rep->length;
-    return true;
-  }
-  return false;
-}
-
-// If the rep is a leaf, this will increment the value at total_mem_usage and
-// will return true.
-static bool RepMemoryUsageLeaf(const CordRep* rep, size_t* total_mem_usage) {
-  if (rep->IsFlat()) {
-    *total_mem_usage += rep->flat()->AllocatedSize();
-    return true;
-  }
-  if (rep->IsExternal()) {
-    // We don't know anything about the embedded / bound data, but we can safely
-    // assume it is 'at least' a word / pointer to data. In the future we may
-    // choose to use the 'data' byte as a tag to identify the types of some
-    // well-known externals, such as a std::string instance.
-    *total_mem_usage +=
-        sizeof(cord_internal::CordRepExternalImpl<intptr_t>) + rep->length;
-    return true;
-  }
-  return false;
-}
-
 void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) {
   assert(&src != this);
   assert(is_tree() || src.is_tree());
@@ -581,7 +332,7 @@ Cord::Cord(absl::string_view src, MethodIdentifier method)
     : contents_(InlineData::kDefaultInit) {
   const size_t n = src.size();
   if (n <= InlineRep::kMaxInline) {
-    contents_.set_data(src.data(), n, true);
+    contents_.set_data(src.data(), n);
   } else {
     CordRep* rep = NewTree(src.data(), n, 0);
     contents_.EmplaceTree(rep, method);
@@ -591,7 +342,7 @@ Cord::Cord(absl::string_view src, MethodIdentifier method)
 template <typename T, Cord::EnableIfString<T>>
 Cord::Cord(T&& src) : contents_(InlineData::kDefaultInit) {
   if (src.size() <= InlineRep::kMaxInline) {
-    contents_.set_data(src.data(), src.size(), true);
+    contents_.set_data(src.data(), src.size());
   } else {
     CordRep* rep = CordRepFromString(std::forward<T>(src));
     contents_.EmplaceTree(rep, CordzUpdateTracker::kConstructorString);
@@ -642,14 +393,14 @@ Cord& Cord::operator=(absl::string_view src) {
     // - MaybeUntrackCord must be called before set_data() clobbers cordz_info.
     // - set_data() must be called before Unref(tree) as it may reference tree.
     if (tree != nullptr) CordzInfo::MaybeUntrackCord(contents_.cordz_info());
-    contents_.set_data(data, length, true);
+    contents_.set_data(data, length);
     if (tree != nullptr) CordRep::Unref(tree);
     return *this;
   }
   if (tree != nullptr) {
     CordzUpdateScope scope(contents_.cordz_info(), method);
     if (tree->IsFlat() && tree->flat()->Capacity() >= length &&
-        tree->refcount.IsMutable()) {
+        tree->refcount.IsOne()) {
       // Copy in place if the existing FLAT node is reusable.
       memmove(tree->flat()->Data(), data, length);
       tree->length = length;
@@ -675,6 +426,7 @@ void Cord::InlineRep::AppendArray(absl::string_view src,
   const CordRep* const root = rep;
   CordzUpdateScope scope(root ? cordz_info() : nullptr, method);
   if (root != nullptr) {
+    rep = cord_internal::RemoveCrcNode(rep);
     char* region;
     if (PrepareAppendRegion(rep, &region, &appended, src.size())) {
       memcpy(region, src.data(), appended);
@@ -705,27 +457,11 @@ void Cord::InlineRep::AppendArray(absl::string_view src,
     return;
   }
 
-  if (btree_enabled()) {
-    // TODO(b/192061034): keep legacy 10% growth rate: consider other rates.
-    rep = ForceBtree(rep);
-    const size_t min_growth = std::max<size_t>(rep->length / 10, src.size());
-    rep = CordRepBtree::Append(rep->btree(), src, min_growth - src.size());
-  } else {
-    // Use new block(s) for any remaining bytes that were not handled above.
-    // Alloc extra memory only if the right child of the root of the new tree
-    // is going to be a FLAT node, which will permit further inplace appends.
-    size_t length = src.size();
-    if (src.size() < kMaxFlatLength) {
-      // The new length is either
-      // - old size + 10%
-      // - old_size + src.size()
-      // This will cause a reasonable conservative step-up in size that is
-      // still large enough to avoid excessive amounts of small fragments
-      // being added.
-      length = std::max<size_t>(rep->length / 10, src.size());
-    }
-    rep = Concat(rep, NewTree(src.data(), src.size(), length - src.size()));
-  }
+  // TODO(b/192061034): keep legacy 10% growth rate: consider other rates.
+  rep = ForceBtree(rep);
+  const size_t min_growth = std::max<size_t>(rep->length / 10, src.size());
+  rep = CordRepBtree::Append(rep->btree(), src, min_growth - src.size());
+
   CommitTree(root, rep, scope, method);
 }
 
@@ -746,7 +482,8 @@ inline void Cord::AppendImpl(C&& src) {
     // Since destination is empty, we can avoid allocating a node,
     if (src.contents_.is_tree()) {
       // by taking the tree directly
-      CordRep* rep = std::forward<C>(src).TakeRep();
+      CordRep* rep =
+          cord_internal::RemoveCrcNode(std::forward<C>(src).TakeRep());
       contents_.EmplaceTree(rep, method);
     } else {
       // or copying over inline data
@@ -782,10 +519,50 @@ inline void Cord::AppendImpl(C&& src) {
   }
 
   // Guaranteed to be a tree (kMaxBytesToCopy > kInlinedSize)
-  CordRep* rep = std::forward<C>(src).TakeRep();
+  CordRep* rep = cord_internal::RemoveCrcNode(std::forward<C>(src).TakeRep());
   contents_.AppendTree(rep, CordzUpdateTracker::kAppendCord);
 }
 
+static CordRep::ExtractResult ExtractAppendBuffer(CordRep* rep,
+                                                  size_t min_capacity) {
+  switch (rep->tag) {
+    case cord_internal::BTREE:
+      return CordRepBtree::ExtractAppendBuffer(rep->btree(), min_capacity);
+    default:
+      if (rep->IsFlat() && rep->refcount.IsOne() &&
+          rep->flat()->Capacity() - rep->length >= min_capacity) {
+        return {nullptr, rep};
+      }
+      return {rep, nullptr};
+  }
+}
+
+static CordBuffer CreateAppendBuffer(InlineData& data, size_t capacity) {
+  // Watch out for overflow, people can ask for size_t::max().
+  const size_t size = data.inline_size();
+  capacity = (std::min)(std::numeric_limits<size_t>::max() - size, capacity);
+  CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(size + capacity);
+  cord_internal::SmallMemmove(buffer.data(), data.as_chars(), size);
+  buffer.SetLength(size);
+  data = {};
+  return buffer;
+}
+
+CordBuffer Cord::GetAppendBufferSlowPath(size_t capacity, size_t min_capacity) {
+  auto constexpr method = CordzUpdateTracker::kGetAppendBuffer;
+  CordRep* tree = contents_.tree();
+  if (tree != nullptr) {
+    CordzUpdateScope scope(contents_.cordz_info(), method);
+    CordRep::ExtractResult result = ExtractAppendBuffer(tree, min_capacity);
+    if (result.extracted != nullptr) {
+      contents_.SetTreeOrEmpty(result.tree, scope);
+      return CordBuffer(result.extracted->flat());
+    }
+    return CordBuffer::CreateWithDefaultLimit(capacity);
+  }
+  return CreateAppendBuffer(contents_.data_, capacity);
+}
+
 void Cord::Append(const Cord& src) {
   AppendImpl(src);
 }
@@ -810,7 +587,8 @@ void Cord::Prepend(const Cord& src) {
   CordRep* src_tree = src.contents_.tree();
   if (src_tree != nullptr) {
     CordRep::Ref(src_tree);
-    contents_.PrependTree(src_tree, CordzUpdateTracker::kPrependCord);
+    contents_.PrependTree(cord_internal::RemoveCrcNode(src_tree),
+                          CordzUpdateTracker::kPrependCord);
     return;
   }
 
@@ -837,103 +615,45 @@ void Cord::PrependArray(absl::string_view src, MethodIdentifier method) {
   contents_.PrependTree(rep, method);
 }
 
-template <typename T, Cord::EnableIfString<T>>
-inline void Cord::Prepend(T&& src) {
-  if (src.size() <= kMaxBytesToCopy) {
-    Prepend(absl::string_view(src));
+void Cord::AppendPrecise(absl::string_view src, MethodIdentifier method) {
+  assert(!src.empty());
+  assert(src.size() <= cord_internal::kMaxFlatLength);
+  if (contents_.remaining_inline_capacity() >= src.size()) {
+    const size_t inline_length = contents_.inline_size();
+    memcpy(contents_.data_.as_chars() + inline_length, src.data(), src.size());
+    contents_.set_inline_size(inline_length + src.size());
   } else {
-    CordRep* rep = CordRepFromString(std::forward<T>(src));
-    contents_.PrependTree(rep, CordzUpdateTracker::kPrependString);
+    contents_.AppendTree(CordRepFlat::Create(src), method);
   }
 }
 
-template void Cord::Prepend(std::string&& src);
-
-static CordRep* RemovePrefixFrom(CordRep* node, size_t n) {
-  if (n >= node->length) return nullptr;
-  if (n == 0) return CordRep::Ref(node);
-  absl::InlinedVector<CordRep*, kInlinedVectorSize> rhs_stack;
-
-  while (node->IsConcat()) {
-    assert(n <= node->length);
-    if (n < node->concat()->left->length) {
-      // Push right to stack, descend left.
-      rhs_stack.push_back(node->concat()->right);
-      node = node->concat()->left;
-    } else {
-      // Drop left, descend right.
-      n -= node->concat()->left->length;
-      node = node->concat()->right;
-    }
-  }
-  assert(n <= node->length);
-
-  if (n == 0) {
-    CordRep::Ref(node);
+void Cord::PrependPrecise(absl::string_view src, MethodIdentifier method) {
+  assert(!src.empty());
+  assert(src.size() <= cord_internal::kMaxFlatLength);
+  if (contents_.remaining_inline_capacity() >= src.size()) {
+    const size_t inline_length = contents_.inline_size();
+    char data[InlineRep::kMaxInline + 1] = {0};
+    memcpy(data, src.data(), src.size());
+    memcpy(data + src.size(), contents_.data(), inline_length);
+    memcpy(contents_.data_.as_chars(), data, InlineRep::kMaxInline + 1);
+    contents_.set_inline_size(inline_length + src.size());
   } else {
-    size_t start = n;
-    size_t len = node->length - n;
-    if (node->IsSubstring()) {
-      // Consider in-place update of node, similar to in RemoveSuffixFrom().
-      start += node->substring()->start;
-      node = node->substring()->child;
-    }
-    node = NewSubstring(CordRep::Ref(node), start, len);
-  }
-  while (!rhs_stack.empty()) {
-    node = Concat(node, CordRep::Ref(rhs_stack.back()));
-    rhs_stack.pop_back();
+    contents_.PrependTree(CordRepFlat::Create(src), method);
   }
-  return node;
 }
 
-// RemoveSuffixFrom() is very similar to RemovePrefixFrom(), with the
-// exception that removing a suffix has an optimization where a node may be
-// edited in place iff that node and all its ancestors have a refcount of 1.
-static CordRep* RemoveSuffixFrom(CordRep* node, size_t n) {
-  if (n >= node->length) return nullptr;
-  if (n == 0) return CordRep::Ref(node);
-  absl::InlinedVector<CordRep*, kInlinedVectorSize> lhs_stack;
-  bool inplace_ok = node->refcount.IsMutable();
-
-  while (node->IsConcat()) {
-    assert(n <= node->length);
-    if (n < node->concat()->right->length) {
-      // Push left to stack, descend right.
-      lhs_stack.push_back(node->concat()->left);
-      node = node->concat()->right;
-    } else {
-      // Drop right, descend left.
-      n -= node->concat()->right->length;
-      node = node->concat()->left;
-    }
-    inplace_ok = inplace_ok && node->refcount.IsMutable();
-  }
-  assert(n <= node->length);
-
-  if (n == 0) {
-    CordRep::Ref(node);
-  } else if (inplace_ok && !node->IsExternal()) {
-    // Consider making a new buffer if the current node capacity is much
-    // larger than the new length.
-    CordRep::Ref(node);
-    node->length -= n;
+template <typename T, Cord::EnableIfString<T>>
+inline void Cord::Prepend(T&& src) {
+  if (src.size() <= kMaxBytesToCopy) {
+    Prepend(absl::string_view(src));
   } else {
-    size_t start = 0;
-    size_t len = node->length - n;
-    if (node->IsSubstring()) {
-      start = node->substring()->start;
-      node = node->substring()->child;
-    }
-    node = NewSubstring(CordRep::Ref(node), start, len);
-  }
-  while (!lhs_stack.empty()) {
-    node = Concat(CordRep::Ref(lhs_stack.back()), node);
-    lhs_stack.pop_back();
+    CordRep* rep = CordRepFromString(std::forward<T>(src));
+    contents_.PrependTree(rep, CordzUpdateTracker::kPrependString);
   }
-  return node;
 }
 
+template void Cord::Prepend(std::string&& src);
+
 void Cord::RemovePrefix(size_t n) {
   ABSL_INTERNAL_CHECK(n <= size(),
                       absl::StrCat("Requested prefix size ", n,
@@ -944,14 +664,21 @@ void Cord::RemovePrefix(size_t n) {
   } else {
     auto constexpr method = CordzUpdateTracker::kRemovePrefix;
     CordzUpdateScope scope(contents_.cordz_info(), method);
-    if (tree->IsBtree()) {
+    tree = cord_internal::RemoveCrcNode(tree);
+    if (n >= tree->length) {
+      CordRep::Unref(tree);
+      tree = nullptr;
+    } else if (tree->IsBtree()) {
       CordRep* old = tree;
       tree = tree->btree()->SubTree(n, tree->length - n);
       CordRep::Unref(old);
+    } else if (tree->IsSubstring() && tree->refcount.IsOne()) {
+      tree->substring()->start += n;
+      tree->length -= n;
     } else {
-      CordRep* newrep = RemovePrefixFrom(tree, n);
+      CordRep* rep = CordRepSubstring::Substring(tree, n, tree->length - n);
       CordRep::Unref(tree);
-      tree = VerifyTree(newrep);
+      tree = rep;
     }
     contents_.SetTreeOrEmpty(tree, scope);
   }
@@ -967,68 +694,24 @@ void Cord::RemoveSuffix(size_t n) {
   } else {
     auto constexpr method = CordzUpdateTracker::kRemoveSuffix;
     CordzUpdateScope scope(contents_.cordz_info(), method);
-    if (tree->IsBtree()) {
+    tree = cord_internal::RemoveCrcNode(tree);
+    if (n >= tree->length) {
+      CordRep::Unref(tree);
+      tree = nullptr;
+    } else if (tree->IsBtree()) {
       tree = CordRepBtree::RemoveSuffix(tree->btree(), n);
+    } else if (!tree->IsExternal() && tree->refcount.IsOne()) {
+      assert(tree->IsFlat() || tree->IsSubstring());
+      tree->length -= n;
     } else {
-      CordRep* newrep = RemoveSuffixFrom(tree, n);
+      CordRep* rep = CordRepSubstring::Substring(tree, 0, tree->length - n);
       CordRep::Unref(tree);
-      tree = VerifyTree(newrep);
+      tree = rep;
     }
     contents_.SetTreeOrEmpty(tree, scope);
   }
 }
 
-// Work item for NewSubRange().
-struct SubRange {
-  SubRange(CordRep* a_node, size_t a_pos, size_t a_n)
-      : node(a_node), pos(a_pos), n(a_n) {}
-  CordRep* node;  // nullptr means concat last 2 results.
-  size_t pos;
-  size_t n;
-};
-
-static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) {
-  absl::InlinedVector<CordRep*, kInlinedVectorSize> results;
-  absl::InlinedVector<SubRange, kInlinedVectorSize> todo;
-  todo.push_back(SubRange(node, pos, n));
-  do {
-    const SubRange& sr = todo.back();
-    node = sr.node;
-    pos = sr.pos;
-    n = sr.n;
-    todo.pop_back();
-
-    if (node == nullptr) {
-      assert(results.size() >= 2);
-      CordRep* right = results.back();
-      results.pop_back();
-      CordRep* left = results.back();
-      results.pop_back();
-      results.push_back(Concat(left, right));
-    } else if (pos == 0 && n == node->length) {
-      results.push_back(CordRep::Ref(node));
-    } else if (!node->IsConcat()) {
-      if (node->IsSubstring()) {
-        pos += node->substring()->start;
-        node = node->substring()->child;
-      }
-      results.push_back(NewSubstring(CordRep::Ref(node), pos, n));
-    } else if (pos + n <= node->concat()->left->length) {
-      todo.push_back(SubRange(node->concat()->left, pos, n));
-    } else if (pos >= node->concat()->left->length) {
-      pos -= node->concat()->left->length;
-      todo.push_back(SubRange(node->concat()->right, pos, n));
-    } else {
-      size_t left_n = node->concat()->left->length - pos;
-      todo.push_back(SubRange(nullptr, 0, 0));  // Concat()
-      todo.push_back(SubRange(node->concat()->right, 0, n - left_n));
-      todo.push_back(SubRange(node->concat()->left, pos, left_n));
-    }
-  } while (!todo.empty());
-  assert(results.size() == 1);
-  return results[0];
-}
-
 Cord Cord::Subcord(size_t pos, size_t new_size) const {
   Cord sub_cord;
   size_t length = size();
@@ -1038,9 +721,7 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
 
   CordRep* tree = contents_.tree();
   if (tree == nullptr) {
-    // sub_cord is newly constructed, no need to re-zero-out the tail of
-    // contents_ memory.
-    sub_cord.contents_.set_data(contents_.data() + pos, new_size, false);
+    sub_cord.contents_.set_data(contents_.data() + pos, new_size);
     return sub_cord;
   }
 
@@ -1060,10 +741,11 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
     return sub_cord;
   }
 
+  tree = cord_internal::SkipCrcNode(tree);
   if (tree->IsBtree()) {
     tree = tree->btree()->SubTree(pos, new_size);
   } else {
-    tree = NewSubRange(tree, pos, new_size);
+    tree = CordRepSubstring::Substring(tree, pos, new_size);
   }
   sub_cord.contents_.EmplaceTree(tree, contents_.data_,
                                  CordzUpdateTracker::kSubCord);
@@ -1071,146 +753,6 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
 }
 
 // --------------------------------------------------------------------
-// Balancing
-
-class CordForest {
- public:
-  explicit CordForest(size_t length)
-      : root_length_(length), trees_(kMinLengthSize, nullptr) {}
-
-  void Build(CordRep* cord_root) {
-    std::vector<CordRep*> pending = {cord_root};
-
-    while (!pending.empty()) {
-      CordRep* node = pending.back();
-      pending.pop_back();
-      CheckNode(node);
-      if (ABSL_PREDICT_FALSE(!node->IsConcat())) {
-        AddNode(node);
-        continue;
-      }
-
-      CordRepConcat* concat_node = node->concat();
-      if (concat_node->depth() >= kMinLengthSize ||
-          concat_node->length < min_length[concat_node->depth()]) {
-        pending.push_back(concat_node->right);
-        pending.push_back(concat_node->left);
-
-        if (concat_node->refcount.IsOne()) {
-          concat_node->left = concat_freelist_;
-          concat_freelist_ = concat_node;
-        } else {
-          CordRep::Ref(concat_node->right);
-          CordRep::Ref(concat_node->left);
-          CordRep::Unref(concat_node);
-        }
-      } else {
-        AddNode(node);
-      }
-    }
-  }
-
-  CordRep* ConcatNodes() {
-    CordRep* sum = nullptr;
-    for (auto* node : trees_) {
-      if (node == nullptr) continue;
-
-      sum = PrependNode(node, sum);
-      root_length_ -= node->length;
-      if (root_length_ == 0) break;
-    }
-    ABSL_INTERNAL_CHECK(sum != nullptr, "Failed to locate sum node");
-    return VerifyTree(sum);
-  }
-
- private:
-  CordRep* AppendNode(CordRep* node, CordRep* sum) {
-    return (sum == nullptr) ? node : MakeConcat(sum, node);
-  }
-
-  CordRep* PrependNode(CordRep* node, CordRep* sum) {
-    return (sum == nullptr) ? node : MakeConcat(node, sum);
-  }
-
-  void AddNode(CordRep* node) {
-    CordRep* sum = nullptr;
-
-    // Collect together everything with which we will merge with node
-    int i = 0;
-    for (; node->length > min_length[i + 1]; ++i) {
-      auto& tree_at_i = trees_[i];
-
-      if (tree_at_i == nullptr) continue;
-      sum = PrependNode(tree_at_i, sum);
-      tree_at_i = nullptr;
-    }
-
-    sum = AppendNode(node, sum);
-
-    // Insert sum into appropriate place in the forest
-    for (; sum->length >= min_length[i]; ++i) {
-      auto& tree_at_i = trees_[i];
-      if (tree_at_i == nullptr) continue;
-
-      sum = MakeConcat(tree_at_i, sum);
-      tree_at_i = nullptr;
-    }
-
-    // min_length[0] == 1, which means sum->length >= min_length[0]
-    assert(i > 0);
-    trees_[i - 1] = sum;
-  }
-
-  // Make concat node trying to resue existing CordRepConcat nodes we
-  // already collected in the concat_freelist_.
-  CordRep* MakeConcat(CordRep* left, CordRep* right) {
-    if (concat_freelist_ == nullptr) return RawConcat(left, right);
-
-    CordRepConcat* rep = concat_freelist_;
-    if (concat_freelist_->left == nullptr) {
-      concat_freelist_ = nullptr;
-    } else {
-      concat_freelist_ = concat_freelist_->left->concat();
-    }
-    SetConcatChildren(rep, left, right);
-
-    return rep;
-  }
-
-  static void CheckNode(CordRep* node) {
-    ABSL_INTERNAL_CHECK(node->length != 0u, "");
-    if (node->IsConcat()) {
-      ABSL_INTERNAL_CHECK(node->concat()->left != nullptr, "");
-      ABSL_INTERNAL_CHECK(node->concat()->right != nullptr, "");
-      ABSL_INTERNAL_CHECK(node->length == (node->concat()->left->length +
-                                           node->concat()->right->length),
-                          "");
-    }
-  }
-
-  size_t root_length_;
-
-  // use an inlined vector instead of a flat array to get bounds checking
-  absl::InlinedVector<CordRep*, kInlinedVectorSize> trees_;
-
-  // List of concat nodes we can re-use for Cord balancing.
-  CordRepConcat* concat_freelist_ = nullptr;
-};
-
-static CordRep* Rebalance(CordRep* node) {
-  VerifyTree(node);
-  assert(node->IsConcat());
-
-  if (node->length == 0) {
-    return nullptr;
-  }
-
-  CordForest forest(node->length);
-  forest.Build(node);
-  return forest.ConcatNodes();
-}
-
-// --------------------------------------------------------------------
 // Comparators
 
 namespace {
@@ -1256,7 +798,7 @@ inline absl::string_view Cord::InlineRep::FindFlatStartPiece() const {
     return absl::string_view(data_.as_chars(), data_.inline_size());
   }
 
-  CordRep* node = tree();
+  CordRep* node = cord_internal::SkipCrcNode(tree());
   if (node->IsFlat()) {
     return absl::string_view(node->flat()->Data(), node->length);
   }
@@ -1274,11 +816,6 @@ inline absl::string_view Cord::InlineRep::FindFlatStartPiece() const {
     return tree->Data(tree->begin());
   }
 
-  // Walk down the left branches until we hit a non-CONCAT node.
-  while (node->IsConcat()) {
-    node = node->concat()->left;
-  }
-
   // Get the child node if we encounter a SUBSTRING.
   size_t offset = 0;
   size_t length = node->length;
@@ -1298,6 +835,28 @@ inline absl::string_view Cord::InlineRep::FindFlatStartPiece() const {
   return absl::string_view(node->external()->base + offset, length);
 }
 
+void Cord::SetExpectedChecksum(uint32_t crc) {
+  auto constexpr method = CordzUpdateTracker::kSetExpectedChecksum;
+  if (empty()) return;
+
+  if (!contents_.is_tree()) {
+    CordRep* rep = contents_.MakeFlatWithExtraCapacity(0);
+    rep = CordRepCrc::New(rep, crc);
+    contents_.EmplaceTree(rep, method);
+  } else {
+    const CordzUpdateScope scope(contents_.data_.cordz_info(), method);
+    CordRep* rep = CordRepCrc::New(contents_.data_.as_tree(), crc);
+    contents_.SetTree(rep, scope);
+  }
+}
+
+absl::optional<uint32_t> Cord::ExpectedChecksum() const {
+  if (!contents_.is_tree() || !contents_.tree()->IsCrc()) {
+    return absl::nullopt;
+  }
+  return contents_.tree()->crc()->crc;
+}
+
 inline int Cord::CompareSlowPath(absl::string_view rhs, size_t compared_size,
                                  size_t size_to_compare) const {
   auto advance = [](Cord::ChunkIterator* it, absl::string_view* chunk) {
@@ -1473,42 +1032,6 @@ void Cord::CopyToArraySlowPath(char* dst) const {
   }
 }
 
-Cord::ChunkIterator& Cord::ChunkIterator::AdvanceStack() {
-  auto& stack_of_right_children = stack_of_right_children_;
-  if (stack_of_right_children.empty()) {
-    assert(!current_chunk_.empty());  // Called on invalid iterator.
-    // We have reached the end of the Cord.
-    return *this;
-  }
-
-  // Process the next node on the stack.
-  CordRep* node = stack_of_right_children.back();
-  stack_of_right_children.pop_back();
-
-  // Walk down the left branches until we hit a non-CONCAT node. Save the
-  // right children to the stack for subsequent traversal.
-  while (node->IsConcat()) {
-    stack_of_right_children.push_back(node->concat()->right);
-    node = node->concat()->left;
-  }
-
-  // Get the child node if we encounter a SUBSTRING.
-  size_t offset = 0;
-  size_t length = node->length;
-  if (node->IsSubstring()) {
-    offset = node->substring()->start;
-    node = node->substring()->child;
-  }
-
-  assert(node->IsExternal() || node->IsFlat());
-  assert(length != 0);
-  const char* data =
-      node->IsExternal() ? node->external()->base : node->flat()->Data();
-  current_chunk_ = absl::string_view(data + offset, length);
-  current_leaf_ = node;
-  return *this;
-}
-
 Cord Cord::ChunkIterator::AdvanceAndReadBytes(size_t n) {
   ABSL_HARDENING_ASSERT(bytes_remaining_ >= n &&
                         "Attempted to iterate past `end()`");
@@ -1551,166 +1074,33 @@ Cord Cord::ChunkIterator::AdvanceAndReadBytes(size_t n) {
     return subcord;
   }
 
-  auto& stack_of_right_children = stack_of_right_children_;
-  if (n < current_chunk_.size()) {
-    // Range to read is a proper subrange of the current chunk.
-    assert(current_leaf_ != nullptr);
-    CordRep* subnode = CordRep::Ref(current_leaf_);
-    const char* data = subnode->IsExternal() ? subnode->external()->base
-                                             : subnode->flat()->Data();
-    subnode = NewSubstring(subnode, current_chunk_.data() - data, n);
-    subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
-    RemoveChunkPrefix(n);
-    return subcord;
-  }
-
-  // Range to read begins with a proper subrange of the current chunk.
-  assert(!current_chunk_.empty());
+  // Short circuit if reading the entire data edge.
   assert(current_leaf_ != nullptr);
-  CordRep* subnode = CordRep::Ref(current_leaf_);
-  if (current_chunk_.size() < subnode->length) {
-    const char* data = subnode->IsExternal() ? subnode->external()->base
-                                             : subnode->flat()->Data();
-    subnode = NewSubstring(subnode, current_chunk_.data() - data,
-                           current_chunk_.size());
-  }
-  n -= current_chunk_.size();
-  bytes_remaining_ -= current_chunk_.size();
-
-  // Process the next node(s) on the stack, reading whole subtrees depending on
-  // their length and how many bytes we are advancing.
-  CordRep* node = nullptr;
-  while (!stack_of_right_children.empty()) {
-    node = stack_of_right_children.back();
-    stack_of_right_children.pop_back();
-    if (node->length > n) break;
-    // TODO(qrczak): This might unnecessarily recreate existing concat nodes.
-    // Avoiding that would need pretty complicated logic (instead of
-    // current_leaf, keep current_subtree_ which points to the highest node
-    // such that the current leaf can be found on the path of left children
-    // starting from current_subtree_; delay creating subnode while node is
-    // below current_subtree_; find the proper node along the path of left
-    // children starting from current_subtree_ if this loop exits while staying
-    // below current_subtree_; etc.; alternatively, push parents instead of
-    // right children on the stack).
-    subnode = Concat(subnode, CordRep::Ref(node));
-    n -= node->length;
-    bytes_remaining_ -= node->length;
-    node = nullptr;
-  }
-
-  if (node == nullptr) {
-    // We have reached the end of the Cord.
-    assert(bytes_remaining_ == 0);
-    subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
+  if (n == current_leaf_->length) {
+    bytes_remaining_ = 0;
+    current_chunk_ = {};
+    CordRep* tree = CordRep::Ref(current_leaf_);
+    subcord.contents_.EmplaceTree(VerifyTree(tree), method);
     return subcord;
   }
 
-  // Walk down the appropriate branches until we hit a non-CONCAT node. Save the
-  // right children to the stack for subsequent traversal.
-  while (node->IsConcat()) {
-    if (node->concat()->left->length > n) {
-      // Push right, descend left.
-      stack_of_right_children.push_back(node->concat()->right);
-      node = node->concat()->left;
-    } else {
-      // Read left, descend right.
-      subnode = Concat(subnode, CordRep::Ref(node->concat()->left));
-      n -= node->concat()->left->length;
-      bytes_remaining_ -= node->concat()->left->length;
-      node = node->concat()->right;
-    }
-  }
-
-  // Get the child node if we encounter a SUBSTRING.
-  size_t offset = 0;
-  size_t length = node->length;
-  if (node->IsSubstring()) {
-    offset = node->substring()->start;
-    node = node->substring()->child;
-  }
+  // From this point on, we need a partial substring node.
+  // Get pointer to the underlying flat or external data payload and
+  // compute data pointer and offset into current flat or external.
+  CordRep* payload = current_leaf_->IsSubstring()
+                         ? current_leaf_->substring()->child
+                         : current_leaf_;
+  const char* data = payload->IsExternal() ? payload->external()->base
+                                           : payload->flat()->Data();
+  const size_t offset = current_chunk_.data() - data;
 
-  // Range to read ends with a proper (possibly empty) subrange of the current
-  // chunk.
-  assert(node->IsExternal() || node->IsFlat());
-  assert(length > n);
-  if (n > 0) {
-    subnode = Concat(subnode, NewSubstring(CordRep::Ref(node), offset, n));
-  }
-  const char* data =
-      node->IsExternal() ? node->external()->base : node->flat()->Data();
-  current_chunk_ = absl::string_view(data + offset + n, length - n);
-  current_leaf_ = node;
+  auto* tree = CordRepSubstring::Substring(payload, offset, n);
+  subcord.contents_.EmplaceTree(VerifyTree(tree), method);
   bytes_remaining_ -= n;
-  subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
+  current_chunk_.remove_prefix(n);
   return subcord;
 }
 
-void Cord::ChunkIterator::AdvanceBytesSlowPath(size_t n) {
-  assert(bytes_remaining_ >= n && "Attempted to iterate past `end()`");
-  assert(n >= current_chunk_.size());  // This should only be called when
-                                       // iterating to a new node.
-
-  n -= current_chunk_.size();
-  bytes_remaining_ -= current_chunk_.size();
-
-  if (stack_of_right_children_.empty()) {
-    // We have reached the end of the Cord.
-    assert(bytes_remaining_ == 0);
-    return;
-  }
-
-  // Process the next node(s) on the stack, skipping whole subtrees depending on
-  // their length and how many bytes we are advancing.
-  CordRep* node = nullptr;
-  auto& stack_of_right_children = stack_of_right_children_;
-  while (!stack_of_right_children.empty()) {
-    node = stack_of_right_children.back();
-    stack_of_right_children.pop_back();
-    if (node->length > n) break;
-    n -= node->length;
-    bytes_remaining_ -= node->length;
-    node = nullptr;
-  }
-
-  if (node == nullptr) {
-    // We have reached the end of the Cord.
-    assert(bytes_remaining_ == 0);
-    return;
-  }
-
-  // Walk down the appropriate branches until we hit a non-CONCAT node. Save the
-  // right children to the stack for subsequent traversal.
-  while (node->IsConcat()) {
-    if (node->concat()->left->length > n) {
-      // Push right, descend left.
-      stack_of_right_children.push_back(node->concat()->right);
-      node = node->concat()->left;
-    } else {
-      // Skip left, descend right.
-      n -= node->concat()->left->length;
-      bytes_remaining_ -= node->concat()->left->length;
-      node = node->concat()->right;
-    }
-  }
-
-  // Get the child node if we encounter a SUBSTRING.
-  size_t offset = 0;
-  size_t length = node->length;
-  if (node->IsSubstring()) {
-    offset = node->substring()->start;
-    node = node->substring()->child;
-  }
-
-  assert(node->IsExternal() || node->IsFlat());
-  assert(length > n);
-  const char* data =
-      node->IsExternal() ? node->external()->base : node->flat()->Data();
-  current_chunk_ = absl::string_view(data + offset + n, length - n);
-  current_leaf_ = node;
-  bytes_remaining_ -= n;
-}
-
 char Cord::operator[](size_t i) const {
   ABSL_HARDENING_ASSERT(i < size());
   size_t offset = i;
@@ -1718,6 +1108,7 @@ char Cord::operator[](size_t i) const {
   if (rep == nullptr) {
     return contents_.data()[i];
   }
+  rep = cord_internal::SkipCrcNode(rep);
   while (true) {
     assert(rep != nullptr);
     assert(offset < rep->length);
@@ -1729,16 +1120,6 @@ char Cord::operator[](size_t i) const {
     } else if (rep->IsExternal()) {
       // Get the "i"th character from the external array.
       return rep->external()->base[offset];
-    } else if (rep->IsConcat()) {
-      // Recursively branch to the side of the concatenation that the "i"th
-      // character is on.
-      size_t left_length = rep->concat()->left->length;
-      if (offset < left_length) {
-        rep = rep->concat()->left;
-      } else {
-        offset -= left_length;
-        rep = rep->concat()->right;
-      }
     } else {
       // This must be a substring a node, so bypass it to get to the child.
       assert(rep->IsSubstring());
@@ -1778,6 +1159,7 @@ absl::string_view Cord::FlattenSlowPath() {
 
 /* static */ bool Cord::GetFlatAux(CordRep* rep, absl::string_view* fragment) {
   assert(rep != nullptr);
+  rep = cord_internal::SkipCrcNode(rep);
   if (rep->IsFlat()) {
     *fragment = absl::string_view(rep->flat()->Data(), rep->length);
     return true;
@@ -1807,6 +1189,9 @@ absl::string_view Cord::FlattenSlowPath() {
 /* static */ void Cord::ForEachChunkAux(
     absl::cord_internal::CordRep* rep,
     absl::FunctionRef<void(absl::string_view)> callback) {
+  assert(rep != nullptr);
+  rep = cord_internal::SkipCrcNode(rep);
+
   if (rep->IsBtree()) {
     ChunkIterator it(rep), end;
     while (it != end) {
@@ -1816,44 +1201,13 @@ absl::string_view Cord::FlattenSlowPath() {
     return;
   }
 
-  assert(rep != nullptr);
-  int stack_pos = 0;
-  constexpr int stack_max = 128;
-  // Stack of right branches for tree traversal
-  absl::cord_internal::CordRep* stack[stack_max];
-  absl::cord_internal::CordRep* current_node = rep;
-  while (true) {
-    if (current_node->IsConcat()) {
-      if (stack_pos == stack_max) {
-        // There's no more room on our stack array to add another right branch,
-        // and the idea is to avoid allocations, so call this function
-        // recursively to navigate this subtree further.  (This is not something
-        // we expect to happen in practice).
-        ForEachChunkAux(current_node, callback);
-
-        // Pop the next right branch and iterate.
-        current_node = stack[--stack_pos];
-        continue;
-      } else {
-        // Save the right branch for later traversal and continue down the left
-        // branch.
-        stack[stack_pos++] = current_node->concat()->right;
-        current_node = current_node->concat()->left;
-        continue;
-      }
-    }
-    // This is a leaf node, so invoke our callback.
-    absl::string_view chunk;
-    bool success = GetFlatAux(current_node, &chunk);
-    assert(success);
-    if (success) {
-      callback(chunk);
-    }
-    if (stack_pos == 0) {
-      // end of traversal
-      return;
-    }
-    current_node = stack[--stack_pos];
+  // This is a leaf node, so invoke our callback.
+  absl::cord_internal::CordRep* current_node = cord_internal::SkipCrcNode(rep);
+  absl::string_view chunk;
+  bool success = GetFlatAux(current_node, &chunk);
+  assert(success);
+  if (success) {
+    callback(chunk);
   }
 }
 
@@ -1868,14 +1222,11 @@ static void DumpNode(CordRep* rep, bool include_data, std::ostream* os,
     *os << " [";
     if (include_data) *os << static_cast<void*>(rep);
     *os << "]";
-    *os << " " << (IsRootBalanced(rep) ? 'b' : 'u');
     *os << " " << std::setw(indent) << "";
-    if (rep->IsConcat()) {
-      *os << "CONCAT depth=" << Depth(rep) << "\n";
+    if (rep->IsCrc()) {
+      *os << "CRC crc=" << rep->crc()->crc << "\n";
       indent += kIndentStep;
-      indents.push_back(indent);
-      stack.push_back(rep->concat()->right);
-      rep = rep->concat()->left;
+      rep = rep->crc()->child;
     } else if (rep->IsSubstring()) {
       *os << "SUBSTRING @ " << rep->substring()->start << "\n";
       indent += kIndentStep;
@@ -1912,7 +1263,7 @@ static std::string ReportError(CordRep* root, CordRep* node) {
 }
 
 static bool VerifyNode(CordRep* root, CordRep* start_node,
-                       bool full_validation) {
+                       bool /* full_validation */) {
   absl::InlinedVector<CordRep*, 2> worklist;
   worklist.push_back(start_node);
   do {
@@ -1922,21 +1273,10 @@ static bool VerifyNode(CordRep* root, CordRep* start_node,
     ABSL_INTERNAL_CHECK(node != nullptr, ReportError(root, node));
     if (node != root) {
       ABSL_INTERNAL_CHECK(node->length != 0, ReportError(root, node));
+      ABSL_INTERNAL_CHECK(!node->IsCrc(), ReportError(root, node));
     }
 
-    if (node->IsConcat()) {
-      ABSL_INTERNAL_CHECK(node->concat()->left != nullptr,
-                          ReportError(root, node));
-      ABSL_INTERNAL_CHECK(node->concat()->right != nullptr,
-                          ReportError(root, node));
-      ABSL_INTERNAL_CHECK((node->length == node->concat()->left->length +
-                                               node->concat()->right->length),
-                          ReportError(root, node));
-      if (full_validation) {
-        worklist.push_back(node->concat()->right);
-        worklist.push_back(node->concat()->left);
-      }
-    } else if (node->IsFlat()) {
+    if (node->IsFlat()) {
       ABSL_INTERNAL_CHECK(node->length <= node->flat()->Capacity(),
                           ReportError(root, node));
     } else if (node->IsExternal()) {
@@ -1949,75 +1289,17 @@ static bool VerifyNode(CordRep* root, CordRep* start_node,
       ABSL_INTERNAL_CHECK(node->substring()->start + node->length <=
                               node->substring()->child->length,
                           ReportError(root, node));
+    } else if (node->IsCrc()) {
+      ABSL_INTERNAL_CHECK(node->crc()->child != nullptr,
+                          ReportError(root, node));
+      ABSL_INTERNAL_CHECK(node->crc()->length == node->crc()->child->length,
+                          ReportError(root, node));
+      worklist.push_back(node->crc()->child);
     }
   } while (!worklist.empty());
   return true;
 }
 
-// Traverses the tree and computes the total memory allocated.
-/* static */ size_t Cord::MemoryUsageAux(const CordRep* rep) {
-  size_t total_mem_usage = 0;
-
-  // Allow a quick exit for the common case that the root is a leaf.
-  if (RepMemoryUsageLeaf(rep, &total_mem_usage)) {
-    return total_mem_usage;
-  }
-
-  // Iterate over the tree. cur_node is never a leaf node and leaf nodes will
-  // never be appended to tree_stack. This reduces overhead from manipulating
-  // tree_stack.
-  absl::InlinedVector<const CordRep*, kInlinedVectorSize> tree_stack;
-  const CordRep* cur_node = rep;
-  while (true) {
-    const CordRep* next_node = nullptr;
-
-    if (cur_node->IsConcat()) {
-      total_mem_usage += sizeof(CordRepConcat);
-      const CordRep* left = cur_node->concat()->left;
-      if (!RepMemoryUsageLeaf(left, &total_mem_usage)) {
-        next_node = left;
-      }
-
-      const CordRep* right = cur_node->concat()->right;
-      if (!RepMemoryUsageLeaf(right, &total_mem_usage)) {
-        if (next_node) {
-          tree_stack.push_back(next_node);
-        }
-        next_node = right;
-      }
-    } else if (cur_node->IsBtree()) {
-      total_mem_usage += sizeof(CordRepBtree);
-      const CordRepBtree* node = cur_node->btree();
-      if (node->height() == 0) {
-        for (const CordRep* edge : node->Edges()) {
-          RepMemoryUsageDataEdge(edge, &total_mem_usage);
-        }
-      } else {
-        for (const CordRep* edge : node->Edges()) {
-          tree_stack.push_back(edge);
-        }
-      }
-    } else {
-      // Since cur_node is not a leaf or a concat node it must be a substring.
-      assert(cur_node->IsSubstring());
-      total_mem_usage += sizeof(CordRepSubstring);
-      next_node = cur_node->substring()->child;
-      if (RepMemoryUsageLeaf(next_node, &total_mem_usage)) {
-        next_node = nullptr;
-      }
-    }
-
-    if (!next_node) {
-      if (tree_stack.empty()) {
-        return total_mem_usage;
-      }
-      next_node = tree_stack.back();
-      tree_stack.pop_back();
-    }
-    cur_node = next_node;
-  }
-}
-
 std::ostream& operator<<(std::ostream& out, const Cord& cord) {
   for (absl::string_view chunk : cord.Chunks()) {
     out.write(chunk.data(), chunk.size());
@@ -2035,7 +1317,6 @@ uint8_t CordTestAccess::LengthToTag(size_t s) {
   ABSL_INTERNAL_CHECK(s <= kMaxFlatLength, absl::StrCat("Invalid length ", s));
   return cord_internal::AllocatedSizeToTag(s + cord_internal::kFlatOverhead);
 }
-size_t CordTestAccess::SizeofCordRepConcat() { return sizeof(CordRepConcat); }
 size_t CordTestAccess::SizeofCordRepExternal() {
   return sizeof(CordRepExternal);
 }
diff --git a/contrib/restricted/abseil-cpp/absl/strings/cord.h b/contrib/restricted/abseil-cpp/absl/strings/cord.h
index f0a1991471..18d6ab852f 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/cord.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/cord.h
@@ -70,6 +70,7 @@
 #include <string>
 #include <type_traits>
 
+#include "absl/base/attributes.h"
 #include "absl/base/config.h"
 #include "absl/base/internal/endian.h"
 #include "absl/base/internal/per_thread_tls.h"
@@ -78,9 +79,13 @@
 #include "absl/container/inlined_vector.h"
 #include "absl/functional/function_ref.h"
 #include "absl/meta/type_traits.h"
+#include "absl/strings/cord_analysis.h"
+#include "absl/strings/cord_buffer.h"
+#include "absl/strings/internal/cord_data_edge.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_btree.h"
 #include "absl/strings/internal/cord_rep_btree_reader.h"
+#include "absl/strings/internal/cord_rep_crc.h"
 #include "absl/strings/internal/cord_rep_ring.h"
 #include "absl/strings/internal/cordz_functions.h"
 #include "absl/strings/internal/cordz_info.h"
@@ -100,6 +105,20 @@ template <typename Releaser>
 Cord MakeCordFromExternal(absl::string_view, Releaser&&);
 void CopyCordToString(const Cord& src, std::string* dst);
 
+// Cord memory accounting modes
+enum class CordMemoryAccounting {
+  // Counts the *approximate* number of bytes held in full or in part by this
+  // Cord (which may not remain the same between invocations). Cords that share
+  // memory could each be "charged" independently for the same shared memory.
+  kTotal,
+
+  // Counts the *approximate* number of bytes held in full or in part by this
+  // Cord weighted by the sharing ratio of that data. For example, if some data
+  // edge is shared by 4 different Cords, then each cord is attributed 1/4th of
+  // the total memory usage as a 'fair share' of the total memory usage.
+  kFairShare,
+};
+
 // Cord
 //
 // A Cord is a sequence of characters, designed to be more efficient than a
@@ -214,7 +233,7 @@ class Cord {
   //
   // Releases the Cord data. Any nodes that share data with other Cords, if
   // applicable, will have their reference counts reduced by 1.
-  void Clear();
+  ABSL_ATTRIBUTE_REINITIALIZES void Clear();
 
   // Cord::Append()
   //
@@ -226,6 +245,45 @@ class Cord {
   template <typename T, EnableIfString<T> = 0>
   void Append(T&& src);
 
+  // Appends `buffer` to this cord, unless `buffer` has a zero length in which
+  // case this method has no effect on this cord instance.
+  // This method is guaranteed to consume `buffer`.
+  void Append(CordBuffer buffer);
+
+  // Returns a CordBuffer, re-using potential existing capacity in this cord.
+  //
+  // Cord instances may have additional unused capacity in the last (or first)
+  // nodes of the underlying tree to facilitate amortized growth. This method
+  // allows applications to explicitly use this spare capacity if available,
+  // or create a new CordBuffer instance otherwise.
+  // If this cord has a final non-shared node with at least `min_capacity`
+  // available, then this method will return that buffer including its data
+  // contents. I.e.; the returned buffer will have a non-zero length, and
+  // a capacity of at least `buffer.length + min_capacity`. Otherwise, this
+  // method will return `CordBuffer::CreateWithDefaultLimit(capacity)`.
+  //
+  // Below an example of using GetAppendBuffer. Notice that in this example we
+  // use `GetAppendBuffer()` only on the first iteration. As we know nothing
+  // about any initial extra capacity in `cord`, we may be able to use the extra
+  // capacity. But as we add new buffers with fully utilized contents after that
+  // we avoid calling `GetAppendBuffer()` on subsequent iterations: while this
+  // works fine, it results in an unnecessary inspection of cord contents:
+  //
+  //   void AppendRandomDataToCord(absl::Cord &cord, size_t n) {
+  //     bool first = true;
+  //     while (n > 0) {
+  //       CordBuffer buffer = first ? cord.GetAppendBuffer(n)
+  //                                 : CordBuffer::CreateWithDefaultLimit(n);
+  //       absl::Span<char> data = buffer.available_up_to(n);
+  //       FillRandomValues(data.data(), data.size());
+  //       buffer.IncreaseLengthBy(data.size());
+  //       cord.Append(std::move(buffer));
+  //       n -= data.size();
+  //       first = false;
+  //     }
+  //   }
+  CordBuffer GetAppendBuffer(size_t capacity, size_t min_capacity = 16);
+
   // Cord::Prepend()
   //
   // Prepends data to the Cord, which may come from another Cord or other string
@@ -235,6 +293,11 @@ class Cord {
   template <typename T, EnableIfString<T> = 0>
   void Prepend(T&& src);
 
+  // Prepends `buffer` to this cord, unless `buffer` has a zero length in which
+  // case this method has no effect on this cord instance.
+  // This method is guaranteed to consume `buffer`.
+  void Prepend(CordBuffer buffer);
+
   // Cord::RemovePrefix()
   //
   // Removes the first `n` bytes of a Cord.
@@ -270,11 +333,10 @@ class Cord {
 
   // Cord::EstimatedMemoryUsage()
   //
-  // Returns the *approximate* number of bytes held in full or in part by this
-  // Cord (which may not remain the same between invocations).  Note that Cords
-  // that share memory could each be "charged" independently for the same shared
-  // memory.
-  size_t EstimatedMemoryUsage() const;
+  // Returns the *approximate* number of bytes held by this cord.
+  // See CordMemoryAccounting for more information on the accounting method.
+  size_t EstimatedMemoryUsage(CordMemoryAccounting accounting_method =
+                                  CordMemoryAccounting::kTotal) const;
 
   // Cord::Compare()
   //
@@ -324,7 +386,7 @@ class Cord {
   //----------------------------------------------------------------------------
   //
   // A `Cord::ChunkIterator` allows iteration over the constituent chunks of its
-  // Cord. Such iteration allows you to perform non-const operatons on the data
+  // Cord. Such iteration allows you to perform non-const operations on the data
   // of a Cord without modifying it.
   //
   // Generally, you do not instantiate a `Cord::ChunkIterator` directly;
@@ -372,12 +434,6 @@ class Cord {
     using CordRepBtree = absl::cord_internal::CordRepBtree;
     using CordRepBtreeReader = absl::cord_internal::CordRepBtreeReader;
 
-    // Stack of right children of concat nodes that we have to visit.
-    // Keep this at the end of the structure to avoid cache-thrashing.
-    // TODO(jgm): Benchmark to see if there's a more optimal value than 47 for
-    // the inlined vector size (47 exists for backward compatibility).
-    using Stack = absl::InlinedVector<absl::cord_internal::CordRep*, 47>;
-
     // Constructs a `begin()` iterator from `tree`. `tree` must not be null.
     explicit ChunkIterator(cord_internal::CordRep* tree);
 
@@ -393,17 +449,10 @@ class Cord {
     Cord AdvanceAndReadBytes(size_t n);
     void AdvanceBytes(size_t n);
 
-    // Stack specific operator++
-    ChunkIterator& AdvanceStack();
-
     // Btree specific operator++
     ChunkIterator& AdvanceBtree();
     void AdvanceBytesBtree(size_t n);
 
-    // Iterates `n` bytes, where `n` is expected to be greater than or equal to
-    // `current_chunk_.size()`.
-    void AdvanceBytesSlowPath(size_t n);
-
     // A view into bytes of the current `CordRep`. It may only be a view to a
     // suffix of bytes if this is being used by `CharIterator`.
     absl::string_view current_chunk_;
@@ -416,12 +465,9 @@ class Cord {
 
     // Cord reader for cord btrees. Empty if not traversing a btree.
     CordRepBtreeReader btree_reader_;
-
-    // See 'Stack' alias definition.
-    Stack stack_of_right_children_;
   };
 
-  // Cord::ChunkIterator::chunk_begin()
+  // Cord::chunk_begin()
   //
   // Returns an iterator to the first chunk of the `Cord`.
   //
@@ -437,7 +483,7 @@ class Cord {
   //   }
   ChunkIterator chunk_begin() const;
 
-  // Cord::ChunkItertator::chunk_end()
+  // Cord::chunk_end()
   //
   // Returns an iterator one increment past the last chunk of the `Cord`.
   //
@@ -447,7 +493,7 @@ class Cord {
   ChunkIterator chunk_end() const;
 
   //----------------------------------------------------------------------------
-  // Cord::ChunkIterator::ChunkRange
+  // Cord::ChunkRange
   //----------------------------------------------------------------------------
   //
   // `ChunkRange` is a helper class for iterating over the chunks of the `Cord`,
@@ -461,7 +507,7 @@ class Cord {
   class ChunkRange {
    public:
     // Fulfill minimum c++ container requirements [container.requirements]
-    // Theses (partial) container type definitions allow ChunkRange to be used
+    // These (partial) container type definitions allow ChunkRange to be used
     // in various utilities expecting a subset of [container.requirements].
     // For example, the below enables using `::testing::ElementsAre(...)`
     using value_type = absl::string_view;
@@ -481,9 +527,9 @@ class Cord {
 
   // Cord::Chunks()
   //
-  // Returns a `Cord::ChunkIterator::ChunkRange` for iterating over the chunks
-  // of a `Cord` with a range-based for-loop. For most iteration tasks on a
-  // Cord, use `Cord::Chunks()` to retrieve this iterator.
+  // Returns a `Cord::ChunkRange` for iterating over the chunks of a `Cord` with
+  // a range-based for-loop. For most iteration tasks on a Cord, use
+  // `Cord::Chunks()` to retrieve this iterator.
   //
   // Example:
   //
@@ -549,7 +595,7 @@ class Cord {
     ChunkIterator chunk_iterator_;
   };
 
-  // Cord::CharIterator::AdvanceAndRead()
+  // Cord::AdvanceAndRead()
   //
   // Advances the `Cord::CharIterator` by `n_bytes` and returns the bytes
   // advanced as a separate `Cord`. `n_bytes` must be less than or equal to the
@@ -557,21 +603,21 @@ class Cord {
   // valid to pass `char_end()` and `0`.
   static Cord AdvanceAndRead(CharIterator* it, size_t n_bytes);
 
-  // Cord::CharIterator::Advance()
+  // Cord::Advance()
   //
   // Advances the `Cord::CharIterator` by `n_bytes`. `n_bytes` must be less than
   // or equal to the number of bytes remaining within the Cord; otherwise,
   // behavior is undefined. It is valid to pass `char_end()` and `0`.
   static void Advance(CharIterator* it, size_t n_bytes);
 
-  // Cord::CharIterator::ChunkRemaining()
+  // Cord::ChunkRemaining()
   //
   // Returns the longest contiguous view starting at the iterator's position.
   //
   // `it` must be dereferenceable.
   static absl::string_view ChunkRemaining(const CharIterator& it);
 
-  // Cord::CharIterator::char_begin()
+  // Cord::char_begin()
   //
   // Returns an iterator to the first character of the `Cord`.
   //
@@ -580,7 +626,7 @@ class Cord {
   // a `CharIterator` where range-based for-loops may not be available.
   CharIterator char_begin() const;
 
-  // Cord::CharIterator::char_end()
+  // Cord::char_end()
   //
   // Returns an iterator to one past the last character of the `Cord`.
   //
@@ -589,13 +635,13 @@ class Cord {
   // a `CharIterator` where range-based for-loops are not useful.
   CharIterator char_end() const;
 
-  // Cord::CharIterator::CharRange
+  // Cord::CharRange
   //
   // `CharRange` is a helper class for iterating over the characters of a
   // producing an iterator which can be used within a range-based for loop.
   // Construction of a `CharRange` will return an iterator pointing to the first
   // character of the Cord. Generally, do not construct a `CharRange` directly;
-  // instead, prefer to use the `Cord::Chars()` method show below.
+  // instead, prefer to use the `Cord::Chars()` method shown below.
   //
   // Implementation note: `CharRange` is simply a convenience wrapper over
   // `Cord::char_begin()` and `Cord::char_end()`.
@@ -620,11 +666,11 @@ class Cord {
     const Cord* cord_;
   };
 
-  // Cord::CharIterator::Chars()
+  // Cord::Chars()
   //
-  // Returns a `Cord::CharIterator` for iterating over the characters of a
-  // `Cord` with a range-based for-loop. For most character-based iteration
-  // tasks on a Cord, use `Cord::Chars()` to retrieve this iterator.
+  // Returns a `Cord::CharRange` for iterating over the characters of a `Cord`
+  // with a range-based for-loop. For most character-based iteration tasks on a
+  // Cord, use `Cord::Chars()` to retrieve this iterator.
   //
   // Example:
   //
@@ -671,6 +717,29 @@ class Cord {
     cord->Append(part);
   }
 
+  // Cord::SetExpectedChecksum()
+  //
+  // Stores a checksum value with this non-empty cord instance, for later
+  // retrieval.
+  //
+  // The expected checksum is a number stored out-of-band, alongside the data.
+  // It is preserved across copies and assignments, but any mutations to a cord
+  // will cause it to lose its expected checksum.
+  //
+  // The expected checksum is not part of a Cord's value, and does not affect
+  // operations such as equality or hashing.
+  //
+  // This field is intended to store a CRC32C checksum for later validation, to
+  // help support end-to-end checksum workflows.  However, the Cord API itself
+  // does no CRC validation, and assigns no meaning to this number.
+  //
+  // This call has no effect if this cord is empty.
+  void SetExpectedChecksum(uint32_t crc);
+
+  // Returns this cord's expected checksum, if it has one.  Otherwise, returns
+  // nullopt.
+  absl::optional<uint32_t> ExpectedChecksum() const;
+
   template <typename H>
   friend H AbslHashValue(H hash_state, const absl::Cord& c) {
     absl::optional<absl::string_view> maybe_flat = c.TryFlat();
@@ -686,7 +755,8 @@ class Cord {
   // be used by spelling absl::strings_internal::MakeStringConstant, which is
   // also an internal API.
   template <typename T>
-  explicit constexpr Cord(strings_internal::StringConstant<T>);
+  // NOLINTNEXTLINE(google-explicit-constructor)
+  constexpr Cord(strings_internal::StringConstant<T>);
 
  private:
   using CordRep = absl::cord_internal::CordRep;
@@ -738,12 +808,12 @@ class Cord {
     bool empty() const;
     size_t size() const;
     const char* data() const;  // Returns nullptr if holding pointer
-    void set_data(const char* data, size_t n,
-                  bool nullify_tail);  // Discards pointer, if any
-    char* set_data(size_t n);          // Write data to the result
+    void set_data(const char* data, size_t n);  // Discards pointer, if any
+    char* set_data(size_t n);                   // Write data to the result
     // Returns nullptr if holding bytes
     absl::cord_internal::CordRep* tree() const;
     absl::cord_internal::CordRep* as_tree() const;
+    const char* as_chars() const;
     // Returns non-null iff was holding a pointer
     absl::cord_internal::CordRep* clear();
     // Converts to pointer if necessary.
@@ -831,6 +901,11 @@ class Cord {
     // Returns true if the Cord is being profiled by cordz.
     bool is_profiled() const { return data_.is_tree() && data_.is_profiled(); }
 
+    // Returns the available inlined capacity, or 0 if is_tree() == true.
+    size_t remaining_inline_capacity() const {
+      return data_.is_tree() ? 0 : kMaxInline - data_.inline_size();
+    }
+
     // Returns the profiled CordzInfo, or nullptr if not sampled.
     absl::cord_internal::CordzInfo* cordz_info() const {
       return data_.cordz_info();
@@ -861,9 +936,6 @@ class Cord {
   };
   InlineRep contents_;
 
-  // Helper for MemoryUsage().
-  static size_t MemoryUsageAux(const absl::cord_internal::CordRep* rep);
-
   // Helper for GetFlat() and TryFlat().
   static bool GetFlatAux(absl::cord_internal::CordRep* rep,
                          absl::string_view* fragment);
@@ -901,6 +973,15 @@ class Cord {
   template <typename C>
   void AppendImpl(C&& src);
 
+  // Appends / Prepends `src` to this instance, using precise sizing.
+  // This method does explicitly not attempt to use any spare capacity
+  // in any pending last added private owned flat.
+  // Requires `src` to be <= kMaxFlatLength.
+  void AppendPrecise(absl::string_view src, MethodIdentifier method);
+  void PrependPrecise(absl::string_view src, MethodIdentifier method);
+
+  CordBuffer GetAppendBufferSlowPath(size_t capacity, size_t min_capacity);
+
   // Prepends the provided data to this instance. `method` contains the public
   // API method for this action which is tracked for Cordz sampling purposes.
   void PrependArray(absl::string_view src, MethodIdentifier method);
@@ -938,8 +1019,8 @@ namespace cord_internal {
 // Fast implementation of memmove for up to 15 bytes. This implementation is
 // safe for overlapping regions. If nullify_tail is true, the destination is
 // padded with '\0' up to 16 bytes.
-inline void SmallMemmove(char* dst, const char* src, size_t n,
-                         bool nullify_tail = false) {
+template <bool nullify_tail = false>
+inline void SmallMemmove(char* dst, const char* src, size_t n) {
   if (n >= 8) {
     assert(n <= 16);
     uint64_t buf1;
@@ -976,22 +1057,16 @@ inline void SmallMemmove(char* dst, const char* src, size_t n,
 }
 
 // Does non-template-specific `CordRepExternal` initialization.
-// Expects `data` to be non-empty.
+// Requires `data` to be non-empty.
 void InitializeCordRepExternal(absl::string_view data, CordRepExternal* rep);
 
 // Creates a new `CordRep` that owns `data` and `releaser` and returns a pointer
-// to it, or `nullptr` if `data` was empty.
+// to it. Requires `data` to be non-empty.
 template <typename Releaser>
 // NOLINTNEXTLINE - suppress clang-tidy raw pointer return.
 CordRep* NewExternalRep(absl::string_view data, Releaser&& releaser) {
+  assert(!data.empty());
   using ReleaserType = absl::decay_t<Releaser>;
-  if (data.empty()) {
-    // Never create empty external nodes.
-    InvokeReleaser(Rank0{}, ReleaserType(std::forward<Releaser>(releaser)),
-                   data);
-    return nullptr;
-  }
-
   CordRepExternal* rep = new CordRepExternalImpl<ReleaserType>(
       std::forward<Releaser>(releaser), 0);
   InitializeCordRepExternal(data, rep);
@@ -1011,10 +1086,15 @@ inline CordRep* NewExternalRep(absl::string_view data,
 template <typename Releaser>
 Cord MakeCordFromExternal(absl::string_view data, Releaser&& releaser) {
   Cord cord;
-  if (auto* rep = ::absl::cord_internal::NewExternalRep(
-          data, std::forward<Releaser>(releaser))) {
-    cord.contents_.EmplaceTree(rep,
+  if (ABSL_PREDICT_TRUE(!data.empty())) {
+    cord.contents_.EmplaceTree(::absl::cord_internal::NewExternalRep(
+                                   data, std::forward<Releaser>(releaser)),
                                Cord::MethodIdentifier::kMakeCordFromExternal);
+  } else {
+    using ReleaserType = absl::decay_t<Releaser>;
+    cord_internal::InvokeReleaser(
+        cord_internal::Rank0{}, ReleaserType(std::forward<Releaser>(releaser)),
+        data);
   }
   return cord;
 }
@@ -1069,6 +1149,11 @@ inline const char* Cord::InlineRep::data() const {
   return is_tree() ? nullptr : data_.as_chars();
 }
 
+inline const char* Cord::InlineRep::as_chars() const {
+  assert(!data_.is_tree());
+  return data_.as_chars();
+}
+
 inline absl::cord_internal::CordRep* Cord::InlineRep::as_tree() const {
   assert(data_.is_tree());
   return data_.as_tree();
@@ -1207,10 +1292,15 @@ inline size_t Cord::size() const {
 
 inline bool Cord::empty() const { return contents_.empty(); }
 
-inline size_t Cord::EstimatedMemoryUsage() const {
+inline size_t Cord::EstimatedMemoryUsage(
+    CordMemoryAccounting accounting_method) const {
   size_t result = sizeof(Cord);
   if (const absl::cord_internal::CordRep* rep = contents_.tree()) {
-    result += MemoryUsageAux(rep);
+    if (accounting_method == CordMemoryAccounting::kFairShare) {
+      result += cord_internal::GetEstimatedFairShareMemoryUsage(rep);
+    } else {
+      result += cord_internal::GetEstimatedMemoryUsage(rep);
+    }
   }
   return result;
 }
@@ -1248,6 +1338,31 @@ inline void Cord::Prepend(absl::string_view src) {
   PrependArray(src, CordzUpdateTracker::kPrependString);
 }
 
+inline void Cord::Append(CordBuffer buffer) {
+  if (ABSL_PREDICT_FALSE(buffer.length() == 0)) return;
+  absl::string_view short_value;
+  if (CordRep* rep = buffer.ConsumeValue(short_value)) {
+    contents_.AppendTree(rep, CordzUpdateTracker::kAppendCordBuffer);
+  } else {
+    AppendPrecise(short_value, CordzUpdateTracker::kAppendCordBuffer);
+  }
+}
+
+inline void Cord::Prepend(CordBuffer buffer) {
+  if (ABSL_PREDICT_FALSE(buffer.length() == 0)) return;
+  absl::string_view short_value;
+  if (CordRep* rep = buffer.ConsumeValue(short_value)) {
+    contents_.PrependTree(rep, CordzUpdateTracker::kPrependCordBuffer);
+  } else {
+    PrependPrecise(short_value, CordzUpdateTracker::kPrependCordBuffer);
+  }
+}
+
+inline CordBuffer Cord::GetAppendBuffer(size_t capacity, size_t min_capacity) {
+  if (empty()) return CordBuffer::CreateWithDefaultLimit(capacity);
+  return GetAppendBufferSlowPath(capacity, min_capacity);
+}
+
 extern template void Cord::Append(std::string&& src);
 extern template void Cord::Prepend(std::string&& src);
 
@@ -1274,27 +1389,27 @@ inline bool Cord::StartsWith(absl::string_view rhs) const {
 }
 
 inline void Cord::ChunkIterator::InitTree(cord_internal::CordRep* tree) {
+  tree = cord_internal::SkipCrcNode(tree);
   if (tree->tag == cord_internal::BTREE) {
     current_chunk_ = btree_reader_.Init(tree->btree());
-    return;
+  } else {
+    current_leaf_ = tree;
+    current_chunk_ = cord_internal::EdgeData(tree);
   }
-
-  stack_of_right_children_.push_back(tree);
-  operator++();
 }
 
-inline Cord::ChunkIterator::ChunkIterator(cord_internal::CordRep* tree)
-    : bytes_remaining_(tree->length) {
+inline Cord::ChunkIterator::ChunkIterator(cord_internal::CordRep* tree) {
+  bytes_remaining_ = tree->length;
   InitTree(tree);
 }
 
-inline Cord::ChunkIterator::ChunkIterator(const Cord* cord)
-    : bytes_remaining_(cord->size()) {
-  if (cord->contents_.is_tree()) {
-    InitTree(cord->contents_.as_tree());
+inline Cord::ChunkIterator::ChunkIterator(const Cord* cord) {
+  if (CordRep* tree = cord->contents_.tree()) {
+    bytes_remaining_ = tree->length;
+    InitTree(tree);
   } else {
-    current_chunk_ =
-        absl::string_view(cord->contents_.data(), bytes_remaining_);
+    bytes_remaining_ = cord->contents_.inline_size();
+    current_chunk_ = {cord->contents_.data(), bytes_remaining_};
   }
 }
 
@@ -1324,8 +1439,11 @@ inline Cord::ChunkIterator& Cord::ChunkIterator::operator++() {
   assert(bytes_remaining_ >= current_chunk_.size());
   bytes_remaining_ -= current_chunk_.size();
   if (bytes_remaining_ > 0) {
-    return btree_reader_ ? AdvanceBtree() : AdvanceStack();
-  } else {
+    if (btree_reader_) {
+      return AdvanceBtree();
+    } else {
+      assert(!current_chunk_.empty());  // Called on invalid iterator.
+    }
     current_chunk_ = {};
   }
   return *this;
@@ -1366,7 +1484,11 @@ inline void Cord::ChunkIterator::AdvanceBytes(size_t n) {
   if (ABSL_PREDICT_TRUE(n < current_chunk_.size())) {
     RemoveChunkPrefix(n);
   } else if (n != 0) {
-    btree_reader_ ? AdvanceBytesBtree(n) : AdvanceBytesSlowPath(n);
+    if (btree_reader_) {
+      AdvanceBytesBtree(n);
+    } else {
+      bytes_remaining_ = 0;
+    }
   }
 }
 
@@ -1457,7 +1579,7 @@ inline void Cord::ForEachChunk(
   }
 }
 
-// Nonmember Cord-to-Cord relational operarators.
+// Nonmember Cord-to-Cord relational operators.
 inline bool operator==(const Cord& lhs, const Cord& rhs) {
   if (lhs.contents_.IsSame(rhs.contents_)) return true;
   size_t rhs_size = rhs.size();
@@ -1508,7 +1630,6 @@ class CordTestAccess {
  public:
   static size_t FlatOverhead();
   static size_t MaxFlatLength();
-  static size_t SizeofCordRepConcat();
   static size_t SizeofCordRepExternal();
   static size_t SizeofCordRepSubstring();
   static size_t FlatTagToLength(uint8_t tag);
diff --git a/contrib/restricted/abseil-cpp/absl/strings/cord_analysis.cc b/contrib/restricted/abseil-cpp/absl/strings/cord_analysis.cc
new file mode 100644
index 0000000000..73d3c4e6ff
--- /dev/null
+++ b/contrib/restricted/abseil-cpp/absl/strings/cord_analysis.cc
@@ -0,0 +1,188 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/cord_analysis.h"
+
+#include <cstddef>
+#include <cstdint>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#include "absl/container/inlined_vector.h"
+#include "absl/strings/internal/cord_data_edge.h"
+#include "absl/strings/internal/cord_internal.h"
+#include "absl/strings/internal/cord_rep_btree.h"
+#include "absl/strings/internal/cord_rep_crc.h"
+#include "absl/strings/internal/cord_rep_flat.h"
+#include "absl/strings/internal/cord_rep_ring.h"
+//
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/functional/function_ref.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+namespace {
+
+// Accounting mode for analyzing memory usage.
+enum class Mode { kTotal, kFairShare };
+
+// CordRepRef holds a `const CordRep*` reference in rep, and depending on mode,
+// holds a 'fraction' representing a cumulative inverse refcount weight.
+template <Mode mode>
+struct CordRepRef {
+  // Instantiates a CordRepRef instance.
+  explicit CordRepRef(const CordRep* r) : rep(r) {}
+
+  // Creates a child reference holding the provided child.
+  // Overloaded to add cumulative reference count for kFairShare.
+  CordRepRef Child(const CordRep* child) const { return CordRepRef(child); }
+
+  const CordRep* rep;
+};
+
+// RawUsage holds the computed total number of bytes.
+template <Mode mode>
+struct RawUsage {
+  size_t total = 0;
+
+  // Add 'size' to total, ignoring the CordRepRef argument.
+  void Add(size_t size, CordRepRef<mode>) { total += size; }
+};
+
+// Returns n / refcount avoiding a div for the common refcount == 1.
+template <typename refcount_t>
+double MaybeDiv(double d, refcount_t refcount) {
+  return refcount == 1 ? d : d / refcount;
+}
+
+// Overloaded 'kFairShare' specialization for CordRepRef. This class holds a
+// `fraction` value which represents a cumulative inverse refcount weight.
+// For example, a top node with a reference count of 2 will have a fraction
+// value of 1/2 = 0.5, representing the 'fair share' of memory it references.
+// A node below such a node with a reference count of 5 then has a fraction of
+// 0.5 / 5 = 0.1 representing the fair share of memory below that node, etc.
+template <>
+struct CordRepRef<Mode::kFairShare> {
+  // Creates a CordRepRef with the provided rep and top (parent) fraction.
+  explicit CordRepRef(const CordRep* r, double frac = 1.0)
+      : rep(r), fraction(MaybeDiv(frac, r->refcount.Get())) {}
+
+  // Returns a CordRepRef with a fraction of `this->fraction / child.refcount`
+  CordRepRef Child(const CordRep* child) const {
+    return CordRepRef(child, fraction);
+  }
+
+  const CordRep* rep;
+  double fraction;
+};
+
+// Overloaded 'kFairShare' specialization for RawUsage
+template <>
+struct RawUsage<Mode::kFairShare> {
+  double total = 0;
+
+  // Adds `size` multiplied by `rep.fraction` to the total size.
+  void Add(size_t size, CordRepRef<Mode::kFairShare> rep) {
+    total += static_cast<double>(size) * rep.fraction;
+  }
+};
+
+// Computes the estimated memory size of the provided data edge.
+// External reps are assumed 'heap allocated at their exact size'.
+template <Mode mode>
+void AnalyzeDataEdge(CordRepRef<mode> rep, RawUsage<mode>& raw_usage) {
+  assert(IsDataEdge(rep.rep));
+
+  // Consume all substrings
+  if (rep.rep->tag == SUBSTRING) {
+    raw_usage.Add(sizeof(CordRepSubstring), rep);
+    rep = rep.Child(rep.rep->substring()->child);
+  }
+
+  // Consume FLAT / EXTERNAL
+  const size_t size =
+      rep.rep->tag >= FLAT
+          ? rep.rep->flat()->AllocatedSize()
+          : rep.rep->length + sizeof(CordRepExternalImpl<intptr_t>);
+  raw_usage.Add(size, rep);
+}
+
+// Computes the memory size of the provided Ring tree.
+template <Mode mode>
+void AnalyzeRing(CordRepRef<mode> rep, RawUsage<mode>& raw_usage) {
+  const CordRepRing* ring = rep.rep->ring();
+  raw_usage.Add(CordRepRing::AllocSize(ring->capacity()), rep);
+  ring->ForEach([&](CordRepRing::index_type pos) {
+    AnalyzeDataEdge(rep.Child(ring->entry_child(pos)), raw_usage);
+  });
+}
+
+// Computes the memory size of the provided Btree tree.
+template <Mode mode>
+void AnalyzeBtree(CordRepRef<mode> rep, RawUsage<mode>& raw_usage) {
+  raw_usage.Add(sizeof(CordRepBtree), rep);
+  const CordRepBtree* tree = rep.rep->btree();
+  if (tree->height() > 0) {
+    for (CordRep* edge : tree->Edges()) {
+      AnalyzeBtree(rep.Child(edge), raw_usage);
+    }
+  } else {
+    for (CordRep* edge : tree->Edges()) {
+      AnalyzeDataEdge(rep.Child(edge), raw_usage);
+    }
+  }
+}
+
+template <Mode mode>
+size_t GetEstimatedUsage(const CordRep* rep) {
+  // Zero initialized memory usage totals.
+  RawUsage<mode> raw_usage;
+
+  // Capture top level node and refcount into a CordRepRef.
+  CordRepRef<mode> repref(rep);
+
+  // Consume the top level CRC node if present.
+  if (repref.rep->tag == CRC) {
+    raw_usage.Add(sizeof(CordRepCrc), repref);
+    repref = repref.Child(repref.rep->crc()->child);
+  }
+
+  if (IsDataEdge(repref.rep)) {
+    AnalyzeDataEdge(repref, raw_usage);
+  } else if (repref.rep->tag == BTREE) {
+    AnalyzeBtree(repref, raw_usage);
+  } else if (repref.rep->tag == RING) {
+    AnalyzeRing(repref, raw_usage);
+  } else {
+    assert(false);
+  }
+
+  return static_cast<size_t>(raw_usage.total);
+}
+
+}  // namespace
+
+size_t GetEstimatedMemoryUsage(const CordRep* rep) {
+  return GetEstimatedUsage<Mode::kTotal>(rep);
+}
+
+size_t GetEstimatedFairShareMemoryUsage(const CordRep* rep) {
+  return GetEstimatedUsage<Mode::kFairShare>(rep);
+}
+
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/contrib/restricted/abseil-cpp/absl/strings/cord_analysis.h b/contrib/restricted/abseil-cpp/absl/strings/cord_analysis.h
new file mode 100644
index 0000000000..7041ad1aa5
--- /dev/null
+++ b/contrib/restricted/abseil-cpp/absl/strings/cord_analysis.h
@@ -0,0 +1,44 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_CORD_ANALYSIS_H_
+#define ABSL_STRINGS_CORD_ANALYSIS_H_
+
+#include <cstddef>
+#include <cstdint>
+
+#include "absl/base/config.h"
+#include "absl/strings/internal/cord_internal.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+// Returns the *approximate* number of bytes held in full or in part by this
+// Cord (which may not remain the same between invocations). Cords that share
+// memory could each be "charged" independently for the same shared memory.
+size_t GetEstimatedMemoryUsage(const CordRep* rep);
+
+// Returns the *approximate* number of bytes held in full or in part by this
+// CordRep weighted by the sharing ratio of that data. For example, if some data
+// edge is shared by 4 different Cords, then each cord is attribute 1/4th of
+// the total memory usage as a 'fair share' of the total memory usage.
+size_t GetEstimatedFairShareMemoryUsage(const CordRep* rep);
+
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+
+#endif  // ABSL_STRINGS_CORD_ANALYSIS_H_
diff --git a/contrib/restricted/abseil-cpp/absl/strings/cord_buffer.cc b/contrib/restricted/abseil-cpp/absl/strings/cord_buffer.cc
new file mode 100644
index 0000000000..fad6269cb9
--- /dev/null
+++ b/contrib/restricted/abseil-cpp/absl/strings/cord_buffer.cc
@@ -0,0 +1,30 @@
+// Copyright 2022 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/cord_buffer.h"
+
+#include <cstddef>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+constexpr size_t CordBuffer::kDefaultLimit;
+constexpr size_t CordBuffer::kCustomLimit;
+#endif
+
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/contrib/restricted/abseil-cpp/absl/strings/cord_buffer.h b/contrib/restricted/abseil-cpp/absl/strings/cord_buffer.h
new file mode 100644
index 0000000000..56a6ce6f6e
--- /dev/null
+++ b/contrib/restricted/abseil-cpp/absl/strings/cord_buffer.h
@@ -0,0 +1,572 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: cord_buffer.h
+// -----------------------------------------------------------------------------
+//
+// This file defines an `absl::CordBuffer` data structure to hold data for
+// eventual inclusion within an existing `Cord` data structure. Cord buffers are
+// useful for building large Cords that may require custom allocation of its
+// associated memory.
+//
+#ifndef ABSL_STRINGS_CORD_BUFFER_H_
+#define ABSL_STRINGS_CORD_BUFFER_H_
+
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+#include <utility>
+
+#include "absl/base/config.h"
+#include "absl/base/macros.h"
+#include "absl/numeric/bits.h"
+#include "absl/strings/internal/cord_internal.h"
+#include "absl/strings/internal/cord_rep_flat.h"
+#include "absl/types/span.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+class Cord;
+class CordBufferTestPeer;
+
+// CordBuffer
+//
+// CordBuffer manages memory buffers for purposes such as zero-copy APIs as well
+// as applications building cords with large data requiring granular control
+// over the allocation and size of cord data. For example, a function creating
+// a cord of random data could use a CordBuffer as follows:
+//
+//   absl::Cord CreateRandomCord(size_t length) {
+//     absl::Cord cord;
+//     while (length > 0) {
+//       CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(length);
+//       absl::Span<char> data = buffer.available_up_to(length);
+//       FillRandomValues(data.data(), data.size());
+//       buffer.IncreaseLengthBy(data.size());
+//       cord.Append(std::move(buffer));
+//       length -= data.size();
+//     }
+//     return cord;
+//   }
+//
+// CordBuffer instances are by default limited to a capacity of `kDefaultLimit`
+// bytes. `kDefaultLimit` is currently just under 4KiB, but this default may
+// change in the future and/or for specific architectures. The default limit is
+// aimed to provide a good trade-off between performance and memory overhead.
+// Smaller buffers typically incur more compute cost while larger buffers are
+// more CPU efficient but create significant memory overhead because of such
+// allocations being less granular. Using larger buffers may also increase the
+// risk of memory fragmentation.
+//
+// Applications create a buffer using one of the `CreateWithDefaultLimit()` or
+// `CreateWithCustomLimit()` methods. The returned instance will have a non-zero
+// capacity and a zero length. Applications use the `data()` method to set the
+// contents of the managed memory, and once done filling the buffer, use the
+// `IncreaseLengthBy()` or 'SetLength()' method to specify the length of the
+// initialized data before adding the buffer to a Cord.
+//
+// The `CreateWithCustomLimit()` method is intended for applications needing
+// larger buffers than the default memory limit, allowing the allocation of up
+// to a capacity of `kCustomLimit` bytes minus some minimum internal overhead.
+// The usage of `CreateWithCustomLimit()` should be limited to only those use
+// cases where the distribution of the input is relatively well known, and/or
+// where the trade-off between the efficiency gains outweigh the risk of memory
+// fragmentation. See the documentation for `CreateWithCustomLimit()` for more
+// information on using larger custom limits.
+//
+// The capacity of a `CordBuffer` returned by one of the `Create` methods may
+// be larger than the requested capacity due to rounding, alignment and
+// granularity of the memory allocator. Applications should use the `capacity`
+// method to obtain the effective capacity of the returned instance as
+// demonstrated in the provided example above.
+//
+// CordBuffer is a move-only class. All references into the managed memory are
+// invalidated when an instance is moved into either another CordBuffer instance
+// or a Cord. Writing to a location obtained by a previous call to `data()`
+// after an instance was moved will lead to undefined behavior.
+//
+// A `moved from` CordBuffer instance will have a valid, but empty state.
+// CordBuffer is thread compatible.
+class CordBuffer {
+ public:
+  // kDefaultLimit
+  //
+  // Default capacity limits of allocated CordBuffers.
+  // See the class comments for more information on allocation limits.
+  static constexpr size_t kDefaultLimit = cord_internal::kMaxFlatLength;
+
+  // kCustomLimit
+  //
+  // Maximum size for CreateWithCustomLimit() allocated buffers.
+  // Note that the effective capacity may be slightly less
+  // because of internal overhead of internal cord buffers.
+  static constexpr size_t kCustomLimit = 64U << 10;
+
+  // Constructors, Destructors and Assignment Operators
+
+  // Creates an empty CordBuffer.
+  CordBuffer() = default;
+
+  // Destroys this CordBuffer instance and, if not empty, releases any memory
+  // managed by this instance, invalidating previously returned references.
+  ~CordBuffer();
+
+  // CordBuffer is move-only
+  CordBuffer(CordBuffer&& rhs) noexcept;
+  CordBuffer& operator=(CordBuffer&&) noexcept;
+  CordBuffer(const CordBuffer&) = delete;
+  CordBuffer& operator=(const CordBuffer&) = delete;
+
+  // CordBuffer::MaximumPayload()
+  //
+  // Returns the guaranteed maximum payload for a CordBuffer returned by the
+  // `CreateWithDefaultLimit()` method. While small, each internal buffer inside
+  // a Cord incurs an overhead to manage the length, type and reference count
+  // for the buffer managed inside the cord tree. Applications can use this
+  // method to get approximate number of buffers required for a given byte
+  // size, etc.
+  //
+  // For example:
+  //   const size_t payload = absl::CordBuffer::MaximumPayload();
+  //   const size_t buffer_count = (total_size + payload - 1) / payload;
+  //   buffers.reserve(buffer_count);
+  static constexpr size_t MaximumPayload();
+
+  // Overload to the above `MaximumPayload()` except that it returns the
+  // maximum payload for a CordBuffer returned by the `CreateWithCustomLimit()`
+  // method given the provided `block_size`.
+  static constexpr size_t MaximumPayload(size_t block_size);
+
+  // CordBuffer::CreateWithDefaultLimit()
+  //
+  // Creates a CordBuffer instance of the desired `capacity`, capped at the
+  // default limit `kDefaultLimit`. The returned buffer has a guaranteed
+  // capacity of at least `min(kDefaultLimit, capacity)`. See the class comments
+  // for more information on buffer capacities and intended usage.
+  static CordBuffer CreateWithDefaultLimit(size_t capacity);
+
+
+  // CordBuffer::CreateWithCustomLimit()
+  //
+  // Creates a CordBuffer instance of the desired `capacity` rounded to an
+  // appropriate power of 2 size less than, or equal to `block_size`.
+  // Requires `block_size` to be a power of 2.
+  //
+  // If `capacity` is less than or equal to `kDefaultLimit`, then this method
+  // behaves identical to `CreateWithDefaultLimit`, which means that the caller
+  // is guaranteed to get a buffer of at least the requested capacity.
+  //
+  // If `capacity` is greater than or equal to `block_size`, then this method
+  // returns a buffer with an `allocated size` of `block_size` bytes. Otherwise,
+  // this methods returns a buffer with a suitable smaller power of 2 block size
+  // to satisfy the request. The actual size depends on a number of factors, and
+  // is typically (but not necessarily) the highest or second highest power of 2
+  // value less than or equal to `capacity`.
+  //
+  // The 'allocated size' includes a small amount of overhead required for
+  // internal state, which is currently 13 bytes on 64-bit platforms. For
+  // example: a buffer created with `block_size` and `capacity' set to 8KiB
+  // will have an allocated size of 8KiB, and an effective internal `capacity`
+  // of 8KiB - 13 = 8179 bytes.
+  //
+  // To demonstrate this in practice, let's assume we want to read data from
+  // somewhat larger files using approximately 64KiB buffers:
+  //
+  //   absl::Cord ReadFromFile(int fd, size_t n) {
+  //     absl::Cord cord;
+  //     while (n > 0) {
+  //       CordBuffer buffer = CordBuffer::CreateWithCustomLimit(64 << 10, n);
+  //       absl::Span<char> data = buffer.available_up_to(n);
+  //       ReadFileDataOrDie(fd, data.data(), data.size());
+  //       buffer.IncreaseLengthBy(data.size());
+  //       cord.Append(std::move(buffer));
+  //       n -= data.size();
+  //     }
+  //     return cord;
+  //   }
+  //
+  // If we'd use this function to read a file of 659KiB, we may get the
+  // following pattern of allocated cord buffer sizes:
+  //
+  //   CreateWithCustomLimit(64KiB, 674816) --> ~64KiB (65523)
+  //   CreateWithCustomLimit(64KiB, 674816) --> ~64KiB (65523)
+  //   ...
+  //   CreateWithCustomLimit(64KiB,  19586) --> ~16KiB (16371)
+  //   CreateWithCustomLimit(64KiB,   3215) -->   3215 (at least 3215)
+  //
+  // The reason the method returns a 16K buffer instead of a roughly 19K buffer
+  // is to reduce memory overhead and fragmentation risks. Using carefully
+  // chosen power of 2 values reduces the entropy of allocated memory sizes.
+  //
+  // Additionally, let's assume we'd use the above function on files that are
+  // generally smaller than 64K. If we'd use 'precise' sized buffers for such
+  // files, than we'd get a very wide distribution of allocated memory sizes
+  // rounded to 4K page sizes, and we'd end up with a lot of unused capacity.
+  //
+  // In general, application should only use custom sizes if the data they are
+  // consuming or storing is expected to be many times the chosen block size,
+  // and be based on objective data and performance metrics. For example, a
+  // compress function may work faster and consume less CPU when using larger
+  // buffers. Such an application should pick a size offering a reasonable
+  // trade-off between expected data size, compute savings with larger buffers,
+  // and the cost or fragmentation effect of larger buffers.
+  // Applications must pick a reasonable spot on that curve, and make sure their
+  // data meets their expectations in size distributions such as "mostly large".
+  static CordBuffer CreateWithCustomLimit(size_t block_size, size_t capacity);
+
+  // CordBuffer::available()
+  //
+  // Returns the span delineating the available capacity in this buffer
+  // which is defined as `{ data() + length(), capacity() - length() }`.
+  absl::Span<char> available();
+
+  // CordBuffer::available_up_to()
+  //
+  // Returns the span delineating the available capacity in this buffer limited
+  // to `size` bytes. This is equivalent to `available().subspan(0, size)`.
+  absl::Span<char> available_up_to(size_t size);
+
+  // CordBuffer::data()
+  //
+  // Returns a non-null reference to the data managed by this instance.
+  // Applications are allowed to write up to `capacity` bytes of instance data.
+  // CordBuffer data is uninitialized by default. Reading data from an instance
+  // that has not yet been initialized will lead to undefined behavior.
+  char* data();
+  const char* data() const;
+
+  // CordBuffer::length()
+  //
+  // Returns the length of this instance. The default length of a CordBuffer is
+  // 0, indicating an 'empty' CordBuffer. Applications must specify the length
+  // of the data in a CordBuffer before adding it to a Cord.
+  size_t length() const;
+
+  // CordBuffer::capacity()
+  //
+  // Returns the capacity of this instance. All instances have a non-zero
+  // capacity: default and `moved from` instances have a small internal buffer.
+  size_t capacity() const;
+
+  // CordBuffer::IncreaseLengthBy()
+  //
+  // Increases the length of this buffer by the specified 'n' bytes.
+  // Applications must make sure all data in this buffer up to the new length
+  // has been initialized before adding a CordBuffer to a Cord: failure to do so
+  // will lead to undefined behavior.  Requires `length() + n <= capacity()`.
+  // Typically, applications will use 'available_up_to()` to get a span of the
+  // desired capacity, and use `span.size()` to increase the length as in:
+  //   absl::Span<char> span = buffer.available_up_to(desired);
+  //   buffer.IncreaseLengthBy(span.size());
+  //   memcpy(span.data(), src, span.size());
+  //   etc...
+  void IncreaseLengthBy(size_t n);
+
+  // CordBuffer::SetLength()
+  //
+  // Sets the data length of this instance. Applications must make sure all data
+  // of the specified length has been initialized before adding a CordBuffer to
+  // a Cord: failure to do so will lead to undefined behavior.
+  // Setting the length to a small value or zero does not release any memory
+  // held by this CordBuffer instance. Requires `length <= capacity()`.
+  // Applications should preferably use the `IncreaseLengthBy()` method above
+  // in combination with the 'available()` or `available_up_to()` methods.
+  void SetLength(size_t length);
+
+ private:
+  // Make sure we don't accidentally over promise.
+  static_assert(kCustomLimit <= cord_internal::kMaxLargeFlatSize, "");
+
+  // Assume the cost of an 'uprounded' allocation to CeilPow2(size) versus
+  // the cost of allocating at least 1 extra flat <= 4KB:
+  // - Flat overhead = 13 bytes
+  // - Btree amortized cost / node =~ 13 bytes
+  // - 64 byte granularity of tcmalloc at 4K =~ 32 byte average
+  // CPU cost and efficiency requires we should at least 'save' something by
+  // splitting, as a poor man's measure, we say the slop needs to be
+  // at least double the cost offset to make it worth splitting: ~128 bytes.
+  static constexpr size_t kMaxPageSlop = 128;
+
+  // Overhead for allocation a flat.
+  static constexpr size_t kOverhead = cord_internal::kFlatOverhead;
+
+  using CordRepFlat = cord_internal::CordRepFlat;
+
+  // `Rep` is the internal data representation of a CordBuffer. The internal
+  // representation has an internal small size optimization similar to
+  // std::string (SSO).
+  struct Rep {
+    // Inline SSO size of a CordBuffer
+    static constexpr size_t kInlineCapacity = sizeof(intptr_t) * 2 - 1;
+
+    // Creates a default instance with kInlineCapacity.
+    Rep() : short_rep{} {}
+
+    // Creates an instance managing an allocated non zero CordRep.
+    explicit Rep(cord_internal::CordRepFlat* rep) : long_rep{rep} {
+      assert(rep != nullptr);
+    }
+
+    // Returns true if this instance manages the SSO internal buffer.
+    bool is_short() const {
+      constexpr size_t offset = offsetof(Short, raw_size);
+      return (reinterpret_cast<const char*>(this)[offset] & 1) != 0;
+    }
+
+    // Returns the available area of the internal SSO data
+    absl::Span<char> short_available() {
+      assert(is_short());
+      const size_t length = (short_rep.raw_size >> 1);
+      return absl::Span<char>(short_rep.data + length,
+                              kInlineCapacity - length);
+    }
+
+    // Returns the available area of the internal SSO data
+    absl::Span<char> long_available() {
+      assert(!is_short());
+      const size_t length = long_rep.rep->length;
+      return absl::Span<char>(long_rep.rep->Data() + length,
+                              long_rep.rep->Capacity() - length);
+    }
+
+    // Returns the length of the internal SSO data.
+    size_t short_length() const {
+      assert(is_short());
+      return short_rep.raw_size >> 1;
+    }
+
+    // Sets the length of the internal SSO data.
+    // Disregards any previously set CordRep instance.
+    void set_short_length(size_t length) {
+      short_rep.raw_size = static_cast<char>((length << 1) + 1);
+    }
+
+    // Adds `n` to the current short length.
+    void add_short_length(size_t n) {
+      assert(is_short());
+      short_rep.raw_size += static_cast<char>(n << 1);
+    }
+
+    // Returns reference to the internal SSO data buffer.
+    char* data() {
+      assert(is_short());
+      return short_rep.data;
+    }
+    const char* data() const {
+      assert(is_short());
+      return short_rep.data;
+    }
+
+    // Returns a pointer the external CordRep managed by this instance.
+    cord_internal::CordRepFlat* rep() const {
+      assert(!is_short());
+      return long_rep.rep;
+    }
+
+    // The internal representation takes advantage of the fact that allocated
+    // memory is always on an even address, and uses the least significant bit
+    // of the first or last byte (depending on endianness) as the inline size
+    // indicator overlapping with the least significant byte of the CordRep*.
+#if defined(ABSL_IS_BIG_ENDIAN)
+    struct Long {
+      explicit Long(cord_internal::CordRepFlat* rep_arg) : rep(rep_arg) {}
+      void* padding;
+      cord_internal::CordRepFlat* rep;
+    };
+    struct Short {
+      char data[sizeof(Long) - 1];
+      char raw_size = 1;
+    };
+#else
+    struct Long {
+      explicit Long(cord_internal::CordRepFlat* rep_arg) : rep(rep_arg) {}
+      cord_internal::CordRepFlat* rep;
+      void* padding;
+    };
+    struct Short {
+      char raw_size = 1;
+      char data[sizeof(Long) - 1];
+    };
+#endif
+
+    union {
+      Long long_rep;
+      Short short_rep;
+    };
+  };
+
+  // Power2 functions
+  static bool IsPow2(size_t size) { return absl::has_single_bit(size); }
+  static size_t Log2Floor(size_t size) { return absl::bit_width(size) - 1; }
+  static size_t Log2Ceil(size_t size) { return absl::bit_width(size - 1); }
+
+  // Implementation of `CreateWithCustomLimit()`.
+  // This implementation allows for future memory allocation hints to
+  // be passed down into the CordRepFlat allocation function.
+  template <typename... AllocationHints>
+  static CordBuffer CreateWithCustomLimitImpl(size_t block_size,
+                                              size_t capacity,
+                                              AllocationHints... hints);
+
+  // Consumes the value contained in this instance and resets the instance.
+  // This method returns a non-null Cordrep* if the current instances manages a
+  // CordRep*, and resets the instance to an empty SSO instance. If the current
+  // instance is an SSO instance, then this method returns nullptr and sets
+  // `short_value` to the inlined data value. In either case, the current
+  // instance length is reset to zero.
+  // This method is intended to be used by Cord internal functions only.
+  cord_internal::CordRep* ConsumeValue(absl::string_view& short_value) {
+    cord_internal::CordRep* rep = nullptr;
+    if (rep_.is_short()) {
+      short_value = absl::string_view(rep_.data(), rep_.short_length());
+    } else {
+      rep = rep_.rep();
+    }
+    rep_.set_short_length(0);
+    return rep;
+  }
+
+  // Internal constructor.
+  explicit CordBuffer(cord_internal::CordRepFlat* rep) : rep_(rep) {
+    assert(rep != nullptr);
+  }
+
+  Rep rep_;
+
+  friend class Cord;
+  friend class CordBufferTestPeer;
+};
+
+inline constexpr size_t CordBuffer::MaximumPayload() {
+  return cord_internal::kMaxFlatLength;
+}
+
+inline constexpr size_t CordBuffer::MaximumPayload(size_t block_size) {
+  // TODO(absl-team): Use std::min when C++11 support is dropped.
+  return (kCustomLimit < block_size ? kCustomLimit : block_size) -
+         cord_internal::kFlatOverhead;
+}
+
+inline CordBuffer CordBuffer::CreateWithDefaultLimit(size_t capacity) {
+  if (capacity > Rep::kInlineCapacity) {
+    auto* rep = cord_internal::CordRepFlat::New(capacity);
+    rep->length = 0;
+    return CordBuffer(rep);
+  }
+  return CordBuffer();
+}
+
+template <typename... AllocationHints>
+inline CordBuffer CordBuffer::CreateWithCustomLimitImpl(
+    size_t block_size, size_t capacity, AllocationHints... hints) {
+  assert(IsPow2(block_size));
+  capacity = (std::min)(capacity, kCustomLimit);
+  block_size = (std::min)(block_size, kCustomLimit);
+  if (capacity + kOverhead >= block_size) {
+    capacity = block_size;
+  } else if (capacity <= kDefaultLimit) {
+    capacity = capacity + kOverhead;
+  } else if (!IsPow2(capacity)) {
+    // Check if rounded up to next power 2 is a good enough fit
+    // with limited waste making it an acceptable direct fit.
+    const size_t rounded_up = size_t{1} << Log2Ceil(capacity);
+    const size_t slop = rounded_up - capacity;
+    if (slop >= kOverhead && slop <= kMaxPageSlop + kOverhead) {
+      capacity = rounded_up;
+    } else {
+      // Round down to highest power of 2 <= capacity.
+      // Consider a more aggressive step down if that may reduce the
+      // risk of fragmentation where 'people are holding it wrong'.
+      const size_t rounded_down = size_t{1} << Log2Floor(capacity);
+      capacity = rounded_down;
+    }
+  }
+  const size_t length = capacity - kOverhead;
+  auto* rep = CordRepFlat::New(CordRepFlat::Large(), length, hints...);
+  rep->length = 0;
+  return CordBuffer(rep);
+}
+
+inline CordBuffer CordBuffer::CreateWithCustomLimit(size_t block_size,
+                                                    size_t capacity) {
+  return CreateWithCustomLimitImpl(block_size, capacity);
+}
+
+inline CordBuffer::~CordBuffer() {
+  if (!rep_.is_short()) {
+    cord_internal::CordRepFlat::Delete(rep_.rep());
+  }
+}
+
+inline CordBuffer::CordBuffer(CordBuffer&& rhs) noexcept : rep_(rhs.rep_) {
+  rhs.rep_.set_short_length(0);
+}
+
+inline CordBuffer& CordBuffer::operator=(CordBuffer&& rhs) noexcept {
+  if (!rep_.is_short()) cord_internal::CordRepFlat::Delete(rep_.rep());
+  rep_ = rhs.rep_;
+  rhs.rep_.set_short_length(0);
+  return *this;
+}
+
+inline absl::Span<char> CordBuffer::available() {
+  return rep_.is_short() ? rep_.short_available() : rep_.long_available();
+}
+
+inline absl::Span<char> CordBuffer::available_up_to(size_t size) {
+  return available().subspan(0, size);
+}
+
+inline char* CordBuffer::data() {
+  return rep_.is_short() ? rep_.data() : rep_.rep()->Data();
+}
+
+inline const char* CordBuffer::data() const {
+  return rep_.is_short() ? rep_.data() : rep_.rep()->Data();
+}
+
+inline size_t CordBuffer::capacity() const {
+  return rep_.is_short() ? Rep::kInlineCapacity : rep_.rep()->Capacity();
+}
+
+inline size_t CordBuffer::length() const {
+  return rep_.is_short() ? rep_.short_length() : rep_.rep()->length;
+}
+
+inline void CordBuffer::SetLength(size_t length) {
+  ABSL_HARDENING_ASSERT(length <= capacity());
+  if (rep_.is_short()) {
+    rep_.set_short_length(length);
+  } else {
+    rep_.rep()->length = length;
+  }
+}
+
+inline void CordBuffer::IncreaseLengthBy(size_t n) {
+  ABSL_HARDENING_ASSERT(n <= capacity() && length() + n <= capacity());
+  if (rep_.is_short()) {
+    rep_.add_short_length(n);
+  } else {
+    rep_.rep()->length += n;
+  }
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_CORD_BUFFER_H_
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_data_edge.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_data_edge.h
new file mode 100644
index 0000000000..e18b33e1b0
--- /dev/null
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_data_edge.h
@@ -0,0 +1,63 @@
+// Copyright 2022 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_INTERNAL_CORD_DATA_EDGE_H_
+#define ABSL_STRINGS_INTERNAL_CORD_DATA_EDGE_H_
+
+#include <cassert>
+#include <cstddef>
+
+#include "absl/base/config.h"
+#include "absl/strings/internal/cord_internal.h"
+#include "absl/strings/internal/cord_rep_flat.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+// Returns true if the provided rep is a FLAT, EXTERNAL or a SUBSTRING node
+// holding a FLAT or EXTERNAL child rep. Requires `rep != nullptr`.
+inline bool IsDataEdge(const CordRep* edge) {
+  assert(edge != nullptr);
+
+  // The fast path is that `edge` is an EXTERNAL or FLAT node, making the below
+  // if a single, well predicted branch. We then repeat the FLAT or EXTERNAL
+  // check in the slow path of the SUBSTRING check to optimize for the hot path.
+  if (edge->tag == EXTERNAL || edge->tag >= FLAT) return true;
+  if (edge->tag == SUBSTRING) edge = edge->substring()->child;
+  return edge->tag == EXTERNAL || edge->tag >= FLAT;
+}
+
+// Returns the `absl::string_view` data reference for the provided data edge.
+// Requires 'IsDataEdge(edge) == true`.
+inline absl::string_view EdgeData(const CordRep* edge) {
+  assert(IsDataEdge(edge));
+
+  size_t offset = 0;
+  const size_t length = edge->length;
+  if (edge->IsSubstring()) {
+    offset = edge->substring()->start;
+    edge = edge->substring()->child;
+  }
+  return edge->tag >= FLAT
+             ? absl::string_view{edge->flat()->Data() + offset, length}
+             : absl::string_view{edge->external()->base + offset, length};
+}
+
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_CORD_DATA_EDGE_H_
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_internal.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_internal.cc
index 1767e6fcc5..b6b06cfa2a 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_internal.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_internal.cc
@@ -17,69 +17,57 @@
 #include <cassert>
 #include <memory>
 
+#include "absl/base/internal/raw_logging.h"
 #include "absl/container/inlined_vector.h"
 #include "absl/strings/internal/cord_rep_btree.h"
+#include "absl/strings/internal/cord_rep_crc.h"
 #include "absl/strings/internal/cord_rep_flat.h"
 #include "absl/strings/internal/cord_rep_ring.h"
+#include "absl/strings/str_cat.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace cord_internal {
 
-ABSL_CONST_INIT std::atomic<bool> cord_btree_enabled(kCordEnableBtreeDefault);
 ABSL_CONST_INIT std::atomic<bool> cord_ring_buffer_enabled(
     kCordEnableRingBufferDefault);
 ABSL_CONST_INIT std::atomic<bool> shallow_subcords_enabled(
     kCordShallowSubcordsDefault);
 ABSL_CONST_INIT std::atomic<bool> cord_btree_exhaustive_validation(false);
 
+void LogFatalNodeType(CordRep* rep) {
+  ABSL_INTERNAL_LOG(FATAL, absl::StrCat("Unexpected node type: ",
+                                        static_cast<int>(rep->tag)));
+}
+
 void CordRep::Destroy(CordRep* rep) {
   assert(rep != nullptr);
 
-  absl::InlinedVector<CordRep*, Constants::kInlinedVectorSize> pending;
   while (true) {
     assert(!rep->refcount.IsImmortal());
-    if (rep->tag == CONCAT) {
-      CordRepConcat* rep_concat = rep->concat();
-      CordRep* right = rep_concat->right;
-      if (!right->refcount.Decrement()) {
-        pending.push_back(right);
-      }
-      CordRep* left = rep_concat->left;
-      delete rep_concat;
-      rep = nullptr;
-      if (!left->refcount.Decrement()) {
-        rep = left;
-        continue;
-      }
-    } else if (rep->tag == BTREE) {
+    if (rep->tag == BTREE) {
       CordRepBtree::Destroy(rep->btree());
-      rep = nullptr;
+      return;
     } else if (rep->tag == RING) {
       CordRepRing::Destroy(rep->ring());
-      rep = nullptr;
+      return;
     } else if (rep->tag == EXTERNAL) {
       CordRepExternal::Delete(rep);
-      rep = nullptr;
+      return;
     } else if (rep->tag == SUBSTRING) {
       CordRepSubstring* rep_substring = rep->substring();
-      CordRep* child = rep_substring->child;
+      rep = rep_substring->child;
       delete rep_substring;
-      rep = nullptr;
-      if (!child->refcount.Decrement()) {
-        rep = child;
-        continue;
+      if (rep->refcount.Decrement()) {
+        return;
       }
+    } else if (rep->tag == CRC) {
+      CordRepCrc::Destroy(rep->crc());
+      return;
     } else {
+      assert(rep->IsFlat());
       CordRepFlat::Delete(rep);
-      rep = nullptr;
-    }
-
-    if (!pending.empty()) {
-      rep = pending.back();
-      pending.pop_back();
-    } else {
-      break;
+      return;
     }
   }
 }
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_internal.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_internal.h
index bfe5564e46..b50fb79a55 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_internal.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_internal.h
@@ -21,6 +21,7 @@
 #include <cstdint>
 #include <type_traits>
 
+#include "absl/base/attributes.h"
 #include "absl/base/config.h"
 #include "absl/base/internal/endian.h"
 #include "absl/base/internal/invoke.h"
@@ -33,16 +34,27 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace cord_internal {
 
+// The overhead of a vtable is too much for Cord, so we roll our own subclasses
+// using only a single byte to differentiate classes from each other - the "tag"
+// byte.  Define the subclasses first so we can provide downcasting helper
+// functions in the base class.
+struct CordRep;
+struct CordRepConcat;
+struct CordRepExternal;
+struct CordRepFlat;
+struct CordRepSubstring;
+struct CordRepCrc;
+class CordRepRing;
+class CordRepBtree;
+
 class CordzInfo;
 
 // Default feature enable states for cord ring buffers
 enum CordFeatureDefaults {
-  kCordEnableBtreeDefault = true,
   kCordEnableRingBufferDefault = false,
   kCordShallowSubcordsDefault = false
 };
 
-extern std::atomic<bool> cord_btree_enabled;
 extern std::atomic<bool> cord_ring_buffer_enabled;
 extern std::atomic<bool> shallow_subcords_enabled;
 
@@ -52,10 +64,6 @@ extern std::atomic<bool> shallow_subcords_enabled;
 // O(n^2) complexity as recursive / full tree validation is O(n).
 extern std::atomic<bool> cord_btree_exhaustive_validation;
 
-inline void enable_cord_btree(bool enable) {
-  cord_btree_enabled.store(enable, std::memory_order_relaxed);
-}
-
 inline void enable_cord_ring_buffer(bool enable) {
   cord_ring_buffer_enabled.store(enable, std::memory_order_relaxed);
 }
@@ -80,6 +88,9 @@ enum Constants {
   kMaxBytesToCopy = 511
 };
 
+// Emits a fatal error "Unexpected node type: xyz" and aborts the program.
+ABSL_ATTRIBUTE_NORETURN void LogFatalNodeType(CordRep* rep);
+
 // Compact class for tracking the reference count and state flags for CordRep
 // instances.  Data is stored in an atomic int32_t for compactness and speed.
 class RefcountAndFlags {
@@ -87,9 +98,6 @@ class RefcountAndFlags {
   constexpr RefcountAndFlags() : count_{kRefIncrement} {}
   struct Immortal {};
   explicit constexpr RefcountAndFlags(Immortal) : count_(kImmortalFlag) {}
-  struct WithCrc {};
-  explicit constexpr RefcountAndFlags(WithCrc)
-      : count_(kCrcFlag | kRefIncrement) {}
 
   // Increments the reference count. Imposes no memory ordering.
   inline void Increment() {
@@ -125,32 +133,14 @@ class RefcountAndFlags {
     return count_.load(std::memory_order_acquire) >> kNumFlags;
   }
 
-  // Returns true if the referenced object carries a CRC value.
-  bool HasCrc() const {
-    return (count_.load(std::memory_order_relaxed) & kCrcFlag) != 0;
-  }
-
-  // Returns true iff the atomic integer is 1 and this node does not store
-  // a CRC.  When both these conditions are met, the current thread owns
-  // the reference and no other thread shares it, so its contents may be
-  // safely mutated.
-  //
-  // If the referenced item is shared, carries a CRC, or is immortal,
-  // it should not be modified in-place, and this function returns false.
-  //
-  // This call performs the memory barrier needed for the owning thread
-  // to act on the object, so that if it returns true, it may safely
-  // assume exclusive access to the object.
-  inline bool IsMutable() {
-    return (count_.load(std::memory_order_acquire)) == kRefIncrement;
-  }
-
-  // Returns whether the atomic integer is 1.  Similar to IsMutable(),
-  // but does not check for a stored CRC.  (An unshared node with a CRC is not
-  // mutable, because changing its data would invalidate the CRC.)
-  //
-  // When this returns true, there are no other references, and data sinks
-  // may safely adopt the children of the CordRep.
+  // Returns whether the atomic integer is 1.
+  // If the reference count is used in the conventional way, a
+  // reference count of 1 implies that the current thread owns the
+  // reference and no other thread shares it.
+  // This call performs the test for a reference count of one, and
+  // performs the memory barrier needed for the owning thread
+  // to act on the object, knowing that it has exclusive access to the
+  // object.  Always returns false when the immortal bit is set.
   inline bool IsOne() {
     return (count_.load(std::memory_order_acquire) & kRefcountMask) ==
            kRefIncrement;
@@ -166,51 +156,43 @@ class RefcountAndFlags {
   // used for the StringConstant constructor to avoid collecting immutable
   // constant cords.
   // kReservedFlag is reserved for future use.
-  enum {
+  enum Flags {
     kNumFlags = 2,
 
     kImmortalFlag = 0x1,
-    kCrcFlag = 0x2,
+    kReservedFlag = 0x2,
     kRefIncrement = (1 << kNumFlags),
 
     // Bitmask to use when checking refcount by equality.  This masks out
     // all flags except kImmortalFlag, which is part of the refcount for
     // purposes of equality.  (A refcount of 0 or 1 does not count as 0 or 1
     // if the immortal bit is set.)
-    kRefcountMask = ~kCrcFlag,
+    kRefcountMask = ~kReservedFlag,
   };
 
   std::atomic<int32_t> count_;
 };
 
-// The overhead of a vtable is too much for Cord, so we roll our own subclasses
-// using only a single byte to differentiate classes from each other - the "tag"
-// byte.  Define the subclasses first so we can provide downcasting helper
-// functions in the base class.
-
-struct CordRepConcat;
-struct CordRepExternal;
-struct CordRepFlat;
-struct CordRepSubstring;
-class CordRepRing;
-class CordRepBtree;
-
 // Various representations that we allow
 enum CordRepKind {
-  CONCAT = 0,
+  UNUSED_0 = 0,
   SUBSTRING = 1,
-  BTREE = 2,
-  RING = 3,
-  EXTERNAL = 4,
+  CRC = 2,
+  BTREE = 3,
+  RING = 4,
+  EXTERNAL = 5,
 
   // We have different tags for different sized flat arrays,
-  // starting with FLAT, and limited to MAX_FLAT_TAG. The 225 value is based on
-  // the current 'size to tag' encoding of 8 / 32 bytes. If a new tag is needed
-  // in the future, then 'FLAT' and 'MAX_FLAT_TAG' should be adjusted as well
-  // as the Tag <---> Size logic so that FLAT stil represents the minimum flat
-  // allocation size. (32 bytes as of now).
-  FLAT = 5,
-  MAX_FLAT_TAG = 225
+  // starting with FLAT, and limited to MAX_FLAT_TAG. The below values map to an
+  // allocated range of 32 bytes to 256 KB. The current granularity is:
+  // - 8 byte granularity for flat sizes in [32 - 512]
+  // - 64 byte granularity for flat sizes in (512 - 8KiB]
+  // - 4KiB byte granularity for flat sizes in (8KiB, 256 KiB]
+  // If a new tag is needed in the future, then 'FLAT' and 'MAX_FLAT_TAG' should
+  // be adjusted as well as the Tag <---> Size mapping logic so that FLAT still
+  // represents the minimum flat allocation size. (32 bytes as of now).
+  FLAT = 6,
+  MAX_FLAT_TAG = 248
 };
 
 // There are various locations where we want to check if some rep is a 'plain'
@@ -225,6 +207,18 @@ static_assert(EXTERNAL == RING + 1, "BTREE and EXTERNAL not consecutive");
 static_assert(FLAT == EXTERNAL + 1, "EXTERNAL and FLAT not consecutive");
 
 struct CordRep {
+  // Result from an `extract edge` operation. Contains the (possibly changed)
+  // tree node as well as the extracted edge, or {tree, nullptr} if no edge
+  // could be extracted.
+  // On success, the returned `tree` value is null if `extracted` was the only
+  // data edge inside the tree, a data edge if there were only two data edges in
+  // the tree, or the (possibly new / smaller) remaining tree with the extracted
+  // data edge removed.
+  struct ExtractResult {
+    CordRep* tree;
+    CordRep* extracted;
+  };
+
   CordRep() = default;
   constexpr CordRep(RefcountAndFlags::Immortal immortal, size_t l)
       : length(l), refcount(immortal), tag(EXTERNAL), storage{} {}
@@ -249,18 +243,18 @@ struct CordRep {
 
   // Returns true if this instance's tag matches the requested type.
   constexpr bool IsRing() const { return tag == RING; }
-  constexpr bool IsConcat() const { return tag == CONCAT; }
   constexpr bool IsSubstring() const { return tag == SUBSTRING; }
+  constexpr bool IsCrc() const { return tag == CRC; }
   constexpr bool IsExternal() const { return tag == EXTERNAL; }
   constexpr bool IsFlat() const { return tag >= FLAT; }
   constexpr bool IsBtree() const { return tag == BTREE; }
 
   inline CordRepRing* ring();
   inline const CordRepRing* ring() const;
-  inline CordRepConcat* concat();
-  inline const CordRepConcat* concat() const;
   inline CordRepSubstring* substring();
   inline const CordRepSubstring* substring() const;
+  inline CordRepCrc* crc();
+  inline const CordRepCrc* crc() const;
   inline CordRepExternal* external();
   inline const CordRepExternal* external() const;
   inline CordRepFlat* flat();
@@ -283,17 +277,23 @@ struct CordRep {
   static inline void Unref(CordRep* rep);
 };
 
-struct CordRepConcat : public CordRep {
-  CordRep* left;
-  CordRep* right;
-
-  uint8_t depth() const { return storage[0]; }
-  void set_depth(uint8_t depth) { storage[0] = depth; }
-};
-
 struct CordRepSubstring : public CordRep {
   size_t start;  // Starting offset of substring in child
   CordRep* child;
+
+  // Creates a substring on `child`, adopting a reference on `child`.
+  // Requires `child` to be either a flat or external node, and `pos` and `n` to
+  // form a non-empty partial sub range of `'child`, i.e.:
+  // `n > 0 && n < length && n + pos <= length`
+  static inline CordRepSubstring* Create(CordRep* child, size_t pos, size_t n);
+
+  // Creates a substring of `rep`. Does not adopt a reference on `rep`.
+  // Requires `IsDataEdge(rep) && n > 0 && pos + n <= rep->length`.
+  // If `n == rep->length` then this method returns `CordRep::Ref(rep)`
+  // If `rep` is a substring of a flat or external node, then this method will
+  // return a new substring of that flat or external node with `pos` adjusted
+  // with the original `start` position.
+  static inline CordRep* Substring(CordRep* rep, size_t pos, size_t n);
 };
 
 // Type for function pointer that will invoke the releaser function and also
@@ -357,6 +357,47 @@ struct CordRepExternalImpl
   }
 };
 
+inline CordRepSubstring* CordRepSubstring::Create(CordRep* child, size_t pos,
+                                                  size_t n) {
+  assert(child != nullptr);
+  assert(n > 0);
+  assert(n < child->length);
+  assert(pos < child->length);
+  assert(n <= child->length - pos);
+
+  // TODO(b/217376272): Harden internal logic.
+  // Move to strategical places inside the Cord logic and make this an assert.
+  if (ABSL_PREDICT_FALSE(!(child->IsExternal() || child->IsFlat()))) {
+    LogFatalNodeType(child);
+  }
+
+  CordRepSubstring* rep = new CordRepSubstring();
+  rep->length = n;
+  rep->tag = SUBSTRING;
+  rep->start = pos;
+  rep->child = child;
+  return rep;
+}
+
+inline CordRep* CordRepSubstring::Substring(CordRep* rep, size_t pos,
+                                            size_t n) {
+  assert(rep != nullptr);
+  assert(n != 0);
+  assert(pos < rep->length);
+  assert(n <= rep->length - pos);
+  if (n == rep->length) return CordRep::Ref(rep);
+  if (rep->IsSubstring()) {
+    pos += rep->substring()->start;
+    rep = rep->substring()->child;
+  }
+  CordRepSubstring* substr = new CordRepSubstring();
+  substr->length = n;
+  substr->tag = SUBSTRING;
+  substr->start = pos;
+  substr->child = CordRep::Ref(rep);
+  return substr;
+}
+
 inline void CordRepExternal::Delete(CordRep* rep) {
   assert(rep != nullptr && rep->IsExternal());
   auto* rep_external = static_cast<CordRepExternal*>(rep);
@@ -370,7 +411,8 @@ struct ConstInitExternalStorage {
 };
 
 template <typename Str>
-CordRepExternal ConstInitExternalStorage<Str>::value(Str::value);
+ABSL_CONST_INIT CordRepExternal
+    ConstInitExternalStorage<Str>::value(Str::value);
 
 enum {
   kMaxInline = 15,
@@ -456,8 +498,8 @@ class InlineData {
   // Requires the current instance to hold a tree value.
   CordzInfo* cordz_info() const {
     assert(is_tree());
-    intptr_t info =
-        static_cast<intptr_t>(absl::big_endian::ToHost64(as_tree_.cordz_info));
+    intptr_t info = static_cast<intptr_t>(
+        absl::big_endian::ToHost64(static_cast<uint64_t>(as_tree_.cordz_info)));
     assert(info & 1);
     return reinterpret_cast<CordzInfo*>(info - 1);
   }
@@ -467,8 +509,9 @@ class InlineData {
   // Requires the current instance to hold a tree value.
   void set_cordz_info(CordzInfo* cordz_info) {
     assert(is_tree());
-    intptr_t info = reinterpret_cast<intptr_t>(cordz_info) | 1;
-    as_tree_.cordz_info = absl::big_endian::FromHost64(info);
+    uintptr_t info = reinterpret_cast<uintptr_t>(cordz_info) | 1;
+    as_tree_.cordz_info =
+        static_cast<cordz_info_t>(absl::big_endian::FromHost64(info));
   }
 
   // Resets the current cordz_info to null / empty.
@@ -568,16 +611,6 @@ class InlineData {
 
 static_assert(sizeof(InlineData) == kMaxInline + 1, "");
 
-inline CordRepConcat* CordRep::concat() {
-  assert(IsConcat());
-  return static_cast<CordRepConcat*>(this);
-}
-
-inline const CordRepConcat* CordRep::concat() const {
-  assert(IsConcat());
-  return static_cast<const CordRepConcat*>(this);
-}
-
 inline CordRepSubstring* CordRep::substring() {
   assert(IsSubstring());
   return static_cast<CordRepSubstring*>(this);
@@ -599,7 +632,9 @@ inline const CordRepExternal* CordRep::external() const {
 }
 
 inline CordRep* CordRep::Ref(CordRep* rep) {
-  assert(rep != nullptr);
+  // ABSL_ASSUME is a workaround for
+  // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585
+  ABSL_ASSUME(rep != nullptr);
   rep->refcount.Increment();
   return rep;
 }
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree.cc
index 4404f33a12..cacbf3da30 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree.cc
@@ -22,6 +22,7 @@
 #include "absl/base/attributes.h"
 #include "absl/base/config.h"
 #include "absl/base/internal/raw_logging.h"
+#include "absl/strings/internal/cord_data_edge.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_consume.h"
 #include "absl/strings/internal/cord_rep_flat.h"
@@ -32,7 +33,9 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace cord_internal {
 
-constexpr size_t CordRepBtree::kMaxCapacity;  // NOLINT: needed for c++ < c++17
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+constexpr size_t CordRepBtree::kMaxCapacity;
+#endif
 
 namespace {
 
@@ -69,7 +72,7 @@ void DumpAll(const CordRep* rep, bool include_contents, std::ostream& stream,
       // indentation and prefix / labels keeps us within roughly 80-100 wide.
       constexpr size_t kMaxDataLength = 60;
       stream << ", data = \""
-             << CordRepBtree::EdgeData(r).substr(0, kMaxDataLength)
+             << EdgeData(r).substr(0, kMaxDataLength)
              << (r->length > kMaxDataLength ? "\"..." : "\"");
     }
     stream << '\n';
@@ -119,6 +122,7 @@ CordRepSubstring* CreateSubstring(CordRep* rep, size_t offset, size_t n) {
     rep = CordRep::Ref(substring->child);
     CordRep::Unref(substring);
   }
+  assert(rep->IsExternal() || rep->IsFlat());
   CordRepSubstring* substring = new CordRepSubstring();
   substring->length = n;
   substring->tag = SUBSTRING;
@@ -149,7 +153,7 @@ inline CordRep* MakeSubstring(CordRep* rep, size_t offset) {
 CordRep* ResizeEdge(CordRep* edge, size_t length, bool is_mutable) {
   assert(length > 0);
   assert(length <= edge->length);
-  assert(CordRepBtree::IsDataEdge(edge));
+  assert(IsDataEdge(edge));
   if (length >= edge->length) return edge;
 
   if (is_mutable && (edge->tag >= FLAT || edge->tag == SUBSTRING)) {
@@ -190,24 +194,29 @@ inline void FastUnref(R* r, Fn&& fn) {
   }
 }
 
-// Deletes a leaf node data edge. Requires `rep` to be an EXTERNAL or FLAT
-// node, or a SUBSTRING of an EXTERNAL or FLAT node.
-void DeleteLeafEdge(CordRep* rep) {
-  for (;;) {
+
+void DeleteSubstring(CordRepSubstring* substring) {
+  CordRep* rep = substring->child;
+  if (!rep->refcount.Decrement()) {
     if (rep->tag >= FLAT) {
       CordRepFlat::Delete(rep->flat());
-      return;
-    }
-    if (rep->tag == EXTERNAL) {
+    } else {
+      assert(rep->tag == EXTERNAL);
       CordRepExternal::Delete(rep->external());
-      return;
     }
-    assert(rep->tag == SUBSTRING);
-    CordRepSubstring* substring = rep->substring();
-    rep = substring->child;
-    assert(rep->tag == EXTERNAL || rep->tag >= FLAT);
-    delete substring;
-    if (rep->refcount.Decrement()) return;
+  }
+  delete substring;
+}
+
+// Deletes a leaf node data edge. Requires `IsDataEdge(rep)`.
+void DeleteLeafEdge(CordRep* rep) {
+  assert(IsDataEdge(rep));
+  if (rep->tag >= FLAT) {
+    CordRepFlat::Delete(rep->flat());
+  } else if (rep->tag == EXTERNAL) {
+    CordRepExternal::Delete(rep->external());
+  } else {
+    DeleteSubstring(rep->substring());
   }
 }
 
@@ -216,8 +225,8 @@ void DeleteLeafEdge(CordRep* rep) {
 // propagate node changes up the stack.
 template <EdgeType edge_type>
 struct StackOperations {
-  // Returns true if the node at 'depth' is mutable, i.e. has a refcount
-  // of one, carries no CRC, and all of its parent nodes have a refcount of one.
+  // Returns true if the node at 'depth' is not shared, i.e. has a refcount
+  // of one and all of its parent nodes have a refcount of one.
   inline bool owned(int depth) const { return depth < share_depth; }
 
   // Returns the node at 'depth'.
@@ -228,11 +237,11 @@ struct StackOperations {
   inline CordRepBtree* BuildStack(CordRepBtree* tree, int depth) {
     assert(depth <= tree->height());
     int current_depth = 0;
-    while (current_depth < depth && tree->refcount.IsMutable()) {
+    while (current_depth < depth && tree->refcount.IsOne()) {
       stack[current_depth++] = tree;
       tree = tree->Edge(edge_type)->btree();
     }
-    share_depth = current_depth + (tree->refcount.IsMutable() ? 1 : 0);
+    share_depth = current_depth + (tree->refcount.IsOne() ? 1 : 0);
     while (current_depth < depth) {
       stack[current_depth++] = tree;
       tree = tree->Edge(edge_type)->btree();
@@ -241,17 +250,17 @@ struct StackOperations {
   }
 
   // Builds a stack with the invariant that all nodes are private owned / not
-  // shared and carry no CRC data. This is used in iterative updates where a
-  // previous propagation guaranteed all nodes have this property.
+  // shared. This is used in iterative updates where a previous propagation
+  // guaranteed all nodes are owned / private.
   inline void BuildOwnedStack(CordRepBtree* tree, int height) {
     assert(height <= CordRepBtree::kMaxHeight);
     int depth = 0;
     while (depth < height) {
-      assert(tree->refcount.IsMutable());
+      assert(tree->refcount.IsOne());
       stack[depth++] = tree;
       tree = tree->Edge(edge_type)->btree();
     }
-    assert(tree->refcount.IsMutable());
+    assert(tree->refcount.IsOne());
     share_depth = depth + 1;
   }
 
@@ -336,12 +345,12 @@ struct StackOperations {
     return Unwind</*propagate=*/true>(tree, depth, length, result);
   }
 
-  // `share_depth` contains the depth at which the nodes in the stack cannot
-  // be mutated. I.e., if the top most level is shared (i.e.:
-  // `!refcount.IsMutable()`), then `share_depth` is 0. If the 2nd node
-  // is shared (and implicitly all nodes below that) then `share_depth` is 1,
-  // etc. A `share_depth` greater than the depth of the stack indicates that
-  // none of the nodes in the stack are shared.
+  // `share_depth` contains the depth at which the nodes in the stack become
+  // shared. I.e., if the top most level is shared (i.e.: `!refcount.IsOne()`),
+  // then `share_depth` is 0. If the 2nd node is shared (and implicitly all
+  // nodes below that) then `share_depth` is 1, etc. A `share_depth` greater
+  // than the depth of the stack indicates that none of the nodes in the stack
+  // are shared.
   int share_depth;
 
   NodeStack stack;
@@ -372,19 +381,37 @@ void CordRepBtree::Dump(const CordRep* rep, std::ostream& stream) {
   Dump(rep, absl::string_view(), false, stream);
 }
 
-void CordRepBtree::DestroyLeaf(CordRepBtree* tree, size_t begin, size_t end) {
-  for (CordRep* edge : tree->Edges(begin, end)) {
-    FastUnref(edge, DeleteLeafEdge);
+template <size_t size>
+static void DestroyTree(CordRepBtree* tree) {
+  for (CordRep* node : tree->Edges()) {
+    if (node->refcount.Decrement()) continue;
+    for (CordRep* edge : node->btree()->Edges()) {
+      if (edge->refcount.Decrement()) continue;
+      if (size == 1) {
+        DeleteLeafEdge(edge);
+      } else {
+        CordRepBtree::Destroy(edge->btree());
+      }
+    }
+    CordRepBtree::Delete(node->btree());
   }
-  Delete(tree);
+  CordRepBtree::Delete(tree);
 }
 
-void CordRepBtree::DestroyNonLeaf(CordRepBtree* tree, size_t begin,
-                                  size_t end) {
-  for (CordRep* edge : tree->Edges(begin, end)) {
-    FastUnref(edge->btree(), Destroy);
+void CordRepBtree::Destroy(CordRepBtree* tree) {
+  switch (tree->height()) {
+    case 0:
+      for (CordRep* edge : tree->Edges()) {
+        if (!edge->refcount.Decrement()) {
+          DeleteLeafEdge(edge);
+        }
+      }
+      return CordRepBtree::Delete(tree);
+    case 1:
+      return DestroyTree<1>(tree);
+    default:
+      return DestroyTree<2>(tree);
   }
-  Delete(tree);
 }
 
 bool CordRepBtree::IsValid(const CordRepBtree* tree, bool shallow) {
@@ -773,7 +800,7 @@ CopyResult CordRepBtree::CopyPrefix(size_t n, bool allow_folding) {
 
 CordRep* CordRepBtree::ExtractFront(CordRepBtree* tree) {
   CordRep* front = tree->Edge(tree->begin());
-  if (tree->refcount.IsMutable()) {
+  if (tree->refcount.IsOne()) {
     Unref(tree->Edges(tree->begin() + 1, tree->end()));
     CordRepBtree::Delete(tree);
   } else {
@@ -786,7 +813,7 @@ CordRep* CordRepBtree::ExtractFront(CordRepBtree* tree) {
 CordRepBtree* CordRepBtree::ConsumeBeginTo(CordRepBtree* tree, size_t end,
                                            size_t new_length) {
   assert(end <= tree->end());
-  if (tree->refcount.IsMutable()) {
+  if (tree->refcount.IsOne()) {
     Unref(tree->Edges(end, tree->end()));
     tree->set_end(end);
     tree->length = new_length;
@@ -813,13 +840,13 @@ CordRep* CordRepBtree::RemoveSuffix(CordRepBtree* tree, size_t n) {
 
   size_t length = len - n;
   int height = tree->height();
-  bool is_mutable = tree->refcount.IsMutable();
+  bool is_mutable = tree->refcount.IsOne();
 
   // Extract all top nodes which are reduced to size = 1
   Position pos = tree->IndexOfLength(length);
   while (pos.index == tree->begin()) {
     CordRep* edge = ExtractFront(tree);
-    is_mutable &= edge->refcount.IsMutable();
+    is_mutable &= edge->refcount.IsOne();
     if (height-- == 0) return ResizeEdge(edge, length, is_mutable);
     tree = edge->btree();
     pos = tree->IndexOfLength(length);
@@ -835,8 +862,8 @@ CordRep* CordRepBtree::RemoveSuffix(CordRepBtree* tree, size_t n) {
   length = pos.n;
   while (length != edge->length) {
     // ConsumeBeginTo guarantees `tree` is a clean, privately owned copy.
-    assert(tree->refcount.IsMutable());
-    const bool edge_is_mutable = edge->refcount.IsMutable();
+    assert(tree->refcount.IsOne());
+    const bool edge_is_mutable = edge->refcount.IsOne();
 
     if (height-- == 0) {
       tree->edges_[pos.index] = ResizeEdge(edge, length, edge_is_mutable);
@@ -973,7 +1000,7 @@ char CordRepBtree::GetCharacter(size_t offset) const {
 Span<char> CordRepBtree::GetAppendBufferSlow(size_t size) {
   // The inlined version in `GetAppendBuffer()` deals with all heights <= 3.
   assert(height() >= 4);
-  assert(refcount.IsMutable());
+  assert(refcount.IsOne());
 
   // Build a stack of nodes we may potentially need to update if we find a
   // non-shared FLAT with capacity at the leaf level.
@@ -982,13 +1009,13 @@ Span<char> CordRepBtree::GetAppendBufferSlow(size_t size) {
   CordRepBtree* stack[kMaxDepth];
   for (int i = 0; i < depth; ++i) {
     node = node->Edge(kBack)->btree();
-    if (!node->refcount.IsMutable()) return {};
+    if (!node->refcount.IsOne()) return {};
     stack[i] = node;
   }
 
   // Must be a privately owned, mutable flat.
   CordRep* const edge = node->Edge(kBack);
-  if (!edge->refcount.IsMutable() || edge->tag < FLAT) return {};
+  if (!edge->refcount.IsOne() || edge->tag < FLAT) return {};
 
   // Must have capacity.
   const size_t avail = edge->flat()->Capacity() - edge->length;
@@ -1123,6 +1150,79 @@ CordRepBtree* CordRepBtree::Rebuild(CordRepBtree* tree) {
   return nullptr;
 }
 
+CordRepBtree::ExtractResult CordRepBtree::ExtractAppendBuffer(
+    CordRepBtree* tree, size_t extra_capacity) {
+  int depth = 0;
+  NodeStack stack;
+
+  // Set up default 'no success' result which is {tree, nullptr}.
+  ExtractResult result;
+  result.tree = tree;
+  result.extracted = nullptr;
+
+  // Dive down the right side of the tree, making sure no edges are shared.
+  while (tree->height() > 0) {
+    if (!tree->refcount.IsOne()) return result;
+    stack[depth++] = tree;
+    tree = tree->Edge(kBack)->btree();
+  }
+  if (!tree->refcount.IsOne()) return result;
+
+  // Validate we ended on a non shared flat.
+  CordRep* rep = tree->Edge(kBack);
+  if (!(rep->IsFlat() && rep->refcount.IsOne())) return result;
+
+  // Verify it has at least the requested extra capacity.
+  CordRepFlat* flat = rep->flat();
+  const size_t length = flat->length;
+  const size_t avail = flat->Capacity() - flat->length;
+  if (extra_capacity > avail) return result;
+
+  // Set the extracted flat in the result.
+  result.extracted = flat;
+
+  // Cascading delete all nodes that become empty.
+  while (tree->size() == 1) {
+    CordRepBtree::Delete(tree);
+    if (--depth < 0) {
+      // We consumed the entire tree: return nullptr for new tree.
+      result.tree = nullptr;
+      return result;
+    }
+    rep = tree;
+    tree = stack[depth];
+  }
+
+  // Remove the edge or cascaded up parent node.
+  tree->set_end(tree->end() - 1);
+  tree->length -= length;
+
+  // Adjust lengths up the tree.
+  while (depth > 0) {
+    tree = stack[--depth];
+    tree->length -= length;
+  }
+
+  // Remove unnecessary top nodes with size = 1. This may iterate all the way
+  // down to the leaf node in which case we simply return the remaining last
+  // edge in that node and the extracted flat.
+  while (tree->size() == 1) {
+    int height = tree->height();
+    rep = tree->Edge(kBack);
+    Delete(tree);
+    if (height == 0) {
+      // We consumed the leaf: return the sole data edge as the new tree.
+      result.tree = rep;
+      return result;
+    }
+    tree = rep->btree();
+  }
+
+  // Done: return the (new) top level node and extracted flat.
+  result.tree = tree;
+  return result;
+}
+
 }  // namespace cord_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree.h
index bb38f0c3fe..2cbc09eca1 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree.h
@@ -22,6 +22,7 @@
 #include "absl/base/config.h"
 #include "absl/base/internal/raw_logging.h"
 #include "absl/base/optimization.h"
+#include "absl/strings/internal/cord_data_edge.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_flat.h"
 #include "absl/strings/string_view.h"
@@ -163,6 +164,9 @@ class CordRepBtree : public CordRep {
   // typically after a ref_count.Decrement() on the last reference count.
   static void Destroy(CordRepBtree* tree);
 
+  // Destruction
+  static void Delete(CordRepBtree* tree) { delete tree; }
+
   // Use CordRep::Unref() as we overload for absl::Span<CordRep* const>.
   using CordRep::Unref;
 
@@ -240,11 +244,41 @@ class CordRepBtree : public CordRep {
   // length of the flat node and involved tree nodes have been increased by
   // `span.length()`. The caller is responsible for immediately assigning values
   // to all uninitialized data reference by the returned span.
-  // Requires `this->refcount.IsMutable()`: this function forces the
-  // caller to do this fast path check on the top level node, as this is the
-  // most commonly shared node of a cord tree.
+  // Requires `this->refcount.IsOne()`: this function forces the caller to do
+  // this fast path check on the top level node, as this is the most commonly
+  // shared node of a cord tree.
   Span<char> GetAppendBuffer(size_t size);
 
+  // Extracts the right-most data edge from this tree iff:
+  // - the tree and all internal edges to the right-most node are not shared.
+  // - the right-most node is a FLAT node and not shared.
+  // - the right-most node has at least the desired extra capacity.
+  //
+  // Returns {tree, nullptr} if any of the above conditions are not met.
+  // This method effectively removes data from the tree. The intent of this
+  // method is to allow applications appending small string data to use
+  // pre-existing capacity, and add the modified rep back to the tree.
+  //
+  // Simplified such code would look similar to this:
+  //   void MyTreeBuilder::Append(string_view data) {
+  //     ExtractResult result = CordRepBtree::ExtractAppendBuffer(tree_, 1);
+  //     if (CordRep* rep = result.extracted) {
+  //       size_t available = rep->Capacity() - rep->length;
+  //       size_t n = std::min(data.size(), n);
+  //       memcpy(rep->Data(), data.data(), n);
+  //       rep->length += n;
+  //       data.remove_prefix(n);
+  //       if (!result.tree->IsBtree()) {
+  //         tree_ = CordRepBtree::Create(result.tree);
+  //       }
+  //       tree_ = CordRepBtree::Append(tree_, rep);
+  //     }
+  //     ...
+  //     // Remaining edge in `result.tree`.
+  //   }
+  static ExtractResult ExtractAppendBuffer(CordRepBtree* tree,
+                                           size_t extra_capacity = 1);
+
   // Returns the `height` of the tree. The height of a tree is limited to
   // kMaxHeight. `height` is implemented as an `int` as in some places we
   // use negative (-1) values for 'data edges'.
@@ -277,13 +311,6 @@ class CordRepBtree : public CordRep {
   // Requires this instance to be a leaf node, and `index` to be valid index.
   inline absl::string_view Data(size_t index) const;
 
-  static const char* EdgeDataPtr(const CordRep* r);
-  static absl::string_view EdgeData(const CordRep* r);
-
-  // Returns true if the provided rep is a FLAT, EXTERNAL or a SUBSTRING node
-  // holding a FLAT or EXTERNAL child rep.
-  static bool IsDataEdge(const CordRep* rep);
-
   // Diagnostics: returns true if `tree` is valid and internally consistent.
   // If `shallow` is false, then the provided top level node and all child nodes
   // below it are recursively checked. If `shallow` is true, only the provided
@@ -410,12 +437,6 @@ class CordRepBtree : public CordRep {
   // Requires `offset` < length.
   Position IndexBeyond(size_t offset) const;
 
-  // Destruction
-  static void DestroyLeaf(CordRepBtree* tree, size_t begin, size_t end);
-  static void DestroyNonLeaf(CordRepBtree* tree, size_t begin, size_t end);
-  static void DestroyTree(CordRepBtree* tree, size_t begin, size_t end);
-  static void Delete(CordRepBtree* tree) { delete tree; }
-
   // Creates a new leaf node containing as much data as possible from `data`.
   // The data is added either forwards or reversed depending on `edge_type`.
   // Callers must check the length of the returned node to determine if all data
@@ -604,34 +625,11 @@ inline absl::Span<CordRep* const> CordRepBtree::Edges(size_t begin,
   return {edges_ + begin, static_cast<size_t>(end - begin)};
 }
 
-inline const char* CordRepBtree::EdgeDataPtr(const CordRep* r) {
-  assert(IsDataEdge(r));
-  size_t offset = 0;
-  if (r->tag == SUBSTRING) {
-    offset = r->substring()->start;
-    r = r->substring()->child;
-  }
-  return (r->tag >= FLAT ? r->flat()->Data() : r->external()->base) + offset;
-}
-
-inline absl::string_view CordRepBtree::EdgeData(const CordRep* r) {
-  return absl::string_view(EdgeDataPtr(r), r->length);
-}
-
 inline absl::string_view CordRepBtree::Data(size_t index) const {
   assert(height() == 0);
   return EdgeData(Edge(index));
 }
 
-inline bool CordRepBtree::IsDataEdge(const CordRep* rep) {
-  // The fast path is that `rep` is an EXTERNAL or FLAT node, making the below
-  // if a single, well predicted branch. We then repeat the FLAT or EXTERNAL
-  // check in the slow path the SUBSTRING check to optimize for the hot path.
-  if (rep->tag == EXTERNAL || rep->tag >= FLAT) return true;
-  if (rep->tag == SUBSTRING) rep = rep->substring()->child;
-  return rep->tag == EXTERNAL || rep->tag >= FLAT;
-}
-
 inline CordRepBtree* CordRepBtree::New(int height) {
   CordRepBtree* tree = new CordRepBtree;
   tree->length = 0;
@@ -659,19 +657,6 @@ inline CordRepBtree* CordRepBtree::New(CordRepBtree* front,
   return tree;
 }
 
-inline void CordRepBtree::DestroyTree(CordRepBtree* tree, size_t begin,
-                                      size_t end) {
-  if (tree->height() == 0) {
-    DestroyLeaf(tree, begin, end);
-  } else {
-    DestroyNonLeaf(tree, begin, end);
-  }
-}
-
-inline void CordRepBtree::Destroy(CordRepBtree* tree) {
-  DestroyTree(tree, tree->begin(), tree->end());
-}
-
 inline void CordRepBtree::Unref(absl::Span<CordRep* const> edges) {
   for (CordRep* edge : edges) {
     if (ABSL_PREDICT_FALSE(!edge->refcount.Decrement())) {
@@ -731,7 +716,7 @@ inline void CordRepBtree::AlignBegin() {
     // size, and then do overlapping load/store of up to 4 pointers (inlined as
     // XMM, YMM or ZMM load/store) and up to 2 pointers (XMM / YMM), which is a)
     // compact and b) not clobbering any registers.
-    ABSL_INTERNAL_ASSUME(new_end <= kMaxCapacity);
+    ABSL_ASSUME(new_end <= kMaxCapacity);
 #ifdef __clang__
 #pragma unroll 1
 #endif
@@ -749,7 +734,7 @@ inline void CordRepBtree::AlignEnd() {
     const size_t new_end = end() + delta;
     set_begin(new_begin);
     set_end(new_end);
-    ABSL_INTERNAL_ASSUME(new_end <= kMaxCapacity);
+    ABSL_ASSUME(new_end <= kMaxCapacity);
 #ifdef __clang__
 #pragma unroll 1
 #endif
@@ -849,7 +834,7 @@ inline CordRepBtree* CordRepBtree::Create(CordRep* rep) {
 }
 
 inline Span<char> CordRepBtree::GetAppendBuffer(size_t size) {
-  assert(refcount.IsMutable());
+  assert(refcount.IsOne());
   CordRepBtree* tree = this;
   const int height = this->height();
   CordRepBtree* n1 = tree;
@@ -858,21 +843,21 @@ inline Span<char> CordRepBtree::GetAppendBuffer(size_t size) {
   switch (height) {
     case 3:
       tree = tree->Edge(kBack)->btree();
-      if (!tree->refcount.IsMutable()) return {};
+      if (!tree->refcount.IsOne()) return {};
       n2 = tree;
       ABSL_FALLTHROUGH_INTENDED;
     case 2:
       tree = tree->Edge(kBack)->btree();
-      if (!tree->refcount.IsMutable()) return {};
+      if (!tree->refcount.IsOne()) return {};
       n1 = tree;
       ABSL_FALLTHROUGH_INTENDED;
     case 1:
       tree = tree->Edge(kBack)->btree();
-      if (!tree->refcount.IsMutable()) return {};
+      if (!tree->refcount.IsOne()) return {};
       ABSL_FALLTHROUGH_INTENDED;
     case 0:
       CordRep* edge = tree->Edge(kBack);
-      if (!edge->refcount.IsMutable()) return {};
+      if (!edge->refcount.IsOne()) return {};
       if (edge->tag < FLAT) return {};
       size_t avail = edge->flat()->Capacity() - edge->length;
       if (avail == 0) return {};
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.cc
index d1f9995d00..9b896a3d09 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.cc
@@ -16,6 +16,7 @@
 
 #include <cassert>
 
+#include "absl/strings/internal/cord_data_edge.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_btree.h"
 
@@ -39,7 +40,7 @@ inline CordRep* Substring(CordRep* rep, size_t offset, size_t n) {
   assert(n <= rep->length);
   assert(offset < rep->length);
   assert(offset <= rep->length - n);
-  assert(CordRepBtree::IsDataEdge(rep));
+  assert(IsDataEdge(rep));
 
   if (n == 0) return nullptr;
   if (n == rep->length) return CordRep::Ref(rep);
@@ -49,6 +50,7 @@ inline CordRep* Substring(CordRep* rep, size_t offset, size_t n) {
     rep = rep->substring()->child;
   }
 
+  assert(rep->IsExternal() || rep->IsFlat());
   CordRepSubstring* substring = new CordRepSubstring();
   substring->length = n;
   substring->tag = SUBSTRING;
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.h
index 971b92eda6..3d581c877e 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_navigator.h
@@ -143,8 +143,8 @@ class CordRepBtreeNavigator {
   // `index_` and `node_` contain the navigation state as the 'path' to the
   // current data edge which is at `node_[0]->Edge(index_[0])`. The contents
   // of these are undefined until the instance is initialized (`height_ >= 0`).
-  uint8_t index_[CordRepBtree::kMaxHeight];
-  CordRepBtree* node_[CordRepBtree::kMaxHeight];
+  uint8_t index_[CordRepBtree::kMaxDepth];
+  CordRepBtree* node_[CordRepBtree::kMaxDepth];
 };
 
 // Returns true if this instance is not empty.
@@ -173,6 +173,7 @@ template <CordRepBtree::EdgeType edge_type>
 inline CordRep* CordRepBtreeNavigator::Init(CordRepBtree* tree) {
   assert(tree != nullptr);
   assert(tree->size() > 0);
+  assert(tree->height() <= CordRepBtree::kMaxHeight);
   int height = height_ = tree->height();
   size_t index = tree->index(edge_type);
   node_[height] = tree;
@@ -206,6 +207,7 @@ inline CordRepBtreeNavigator::Position CordRepBtreeNavigator::Seek(
 inline CordRepBtreeNavigator::Position CordRepBtreeNavigator::InitOffset(
     CordRepBtree* tree, size_t offset) {
   assert(tree != nullptr);
+  assert(tree->height() <= CordRepBtree::kMaxHeight);
   if (ABSL_PREDICT_FALSE(offset >= tree->length)) return {nullptr, 0};
   height_ = tree->height();
   node_[height_] = tree;
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.cc
index 5dc76966d2..0d0e860139 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.cc
@@ -17,6 +17,7 @@
 #include <cassert>
 
 #include "absl/base/config.h"
+#include "absl/strings/internal/cord_data_edge.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_btree.h"
 #include "absl/strings/internal/cord_rep_btree_navigator.h"
@@ -44,7 +45,7 @@ absl::string_view CordRepBtreeReader::Read(size_t n, size_t chunk_size,
   // can directly return the substring into the current data edge as the next
   // chunk. We can easily establish from the above code that `navigator_.Next()`
   // has not been called as that requires `chunk_size` to be zero.
-  if (n < chunk_size) return CordRepBtree::EdgeData(edge).substr(result.n);
+  if (n < chunk_size) return EdgeData(edge).substr(result.n);
 
   // The amount of data taken from the last edge is `chunk_size` and `result.n`
   // contains the offset into the current edge trailing the read data (which can
@@ -60,7 +61,7 @@ absl::string_view CordRepBtreeReader::Read(size_t n, size_t chunk_size,
   // We did not read all data, return remaining data from current edge.
   edge = navigator_.Current();
   remaining_ -= consumed_by_read + edge->length;
-  return CordRepBtree::EdgeData(edge).substr(result.n);
+  return EdgeData(edge).substr(result.n);
 }
 
 }  // namespace cord_internal
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.h
index 7aa79dbf10..8db8f8dd17 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.h
@@ -18,6 +18,7 @@
 #include <cassert>
 
 #include "absl/base/config.h"
+#include "absl/strings/internal/cord_data_edge.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_btree.h"
 #include "absl/strings/internal/cord_rep_btree_navigator.h"
@@ -167,7 +168,7 @@ inline absl::string_view CordRepBtreeReader::Init(CordRepBtree* tree) {
   assert(tree != nullptr);
   const CordRep* edge = navigator_.InitFirst(tree);
   remaining_ = tree->length - edge->length;
-  return CordRepBtree::EdgeData(edge);
+  return EdgeData(edge);
 }
 
 inline absl::string_view CordRepBtreeReader::Next() {
@@ -175,7 +176,7 @@ inline absl::string_view CordRepBtreeReader::Next() {
   const CordRep* edge = navigator_.Next();
   assert(edge != nullptr);
   remaining_ -= edge->length;
-  return CordRepBtree::EdgeData(edge);
+  return EdgeData(edge);
 }
 
 inline absl::string_view CordRepBtreeReader::Skip(size_t skip) {
@@ -190,7 +191,7 @@ inline absl::string_view CordRepBtreeReader::Skip(size_t skip) {
   // The combined length of all edges skipped before `pos.edge` is `skip -
   // pos.offset`, all of which are 'consumed', as well as the current edge.
   remaining_ -= skip - pos.offset + pos.edge->length;
-  return CordRepBtree::EdgeData(pos.edge).substr(pos.offset);
+  return EdgeData(pos.edge).substr(pos.offset);
 }
 
 inline absl::string_view CordRepBtreeReader::Seek(size_t offset) {
@@ -199,7 +200,7 @@ inline absl::string_view CordRepBtreeReader::Seek(size_t offset) {
     remaining_ = 0;
     return {};
   }
-  absl::string_view chunk = CordRepBtree::EdgeData(pos.edge).substr(pos.offset);
+  absl::string_view chunk = EdgeData(pos.edge).substr(pos.offset);
   remaining_ = length() - offset - chunk.length();
   return chunk;
 }
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_consume.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_consume.cc
index 81514543db..20a5579767 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_consume.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_consume.cc
@@ -40,88 +40,21 @@ CordRep* ClipSubstring(CordRepSubstring* substring) {
   return child;
 }
 
-// Unrefs the provided `concat`, and returns `{concat->left, concat->right}`
-// Adds or assumes a reference on `concat->left` and `concat->right`.
-// Returns an array of 2 elements containing the left and right nodes.
-std::array<CordRep*, 2> ClipConcat(CordRepConcat* concat) {
-  std::array<CordRep*, 2> result{concat->left, concat->right};
-  if (concat->refcount.IsOne()) {
-    delete concat;
-  } else {
-    CordRep::Ref(result[0]);
-    CordRep::Ref(result[1]);
-    CordRep::Unref(concat);
-  }
-  return result;
-}
+}  // namespace
 
-void Consume(bool forward, CordRep* rep, ConsumeFn consume_fn) {
+void Consume(CordRep* rep, ConsumeFn consume_fn) {
   size_t offset = 0;
   size_t length = rep->length;
-  struct Entry {
-    CordRep* rep;
-    size_t offset;
-    size_t length;
-  };
-  absl::InlinedVector<Entry, 40> stack;
-
-  for (;;) {
-    if (rep->tag == CONCAT) {
-      std::array<CordRep*, 2> res = ClipConcat(rep->concat());
-      CordRep* left = res[0];
-      CordRep* right = res[1];
-
-      if (left->length <= offset) {
-        // Don't need left node
-        offset -= left->length;
-        CordRep::Unref(left);
-        rep = right;
-        continue;
-      }
 
-      size_t length_left = left->length - offset;
-      if (length_left >= length) {
-        // Don't need right node
-        CordRep::Unref(right);
-        rep = left;
-        continue;
-      }
-
-      // Need both nodes
-      size_t length_right = length - length_left;
-      if (forward) {
-        stack.push_back({right, 0, length_right});
-        rep = left;
-        length = length_left;
-      } else {
-        stack.push_back({left, offset, length_left});
-        rep = right;
-        offset = 0;
-        length = length_right;
-      }
-    } else if (rep->tag == SUBSTRING) {
-      offset += rep->substring()->start;
-      rep = ClipSubstring(rep->substring());
-    } else {
-      consume_fn(rep, offset, length);
-      if (stack.empty()) return;
-
-      rep = stack.back().rep;
-      offset = stack.back().offset;
-      length = stack.back().length;
-      stack.pop_back();
-    }
+  if (rep->tag == SUBSTRING) {
+    offset += rep->substring()->start;
+    rep = ClipSubstring(rep->substring());
   }
-}
-
-}  // namespace
-
-void Consume(CordRep* rep, ConsumeFn consume_fn) {
-  return Consume(true, rep, std::move(consume_fn));
+  consume_fn(rep, offset, length);
 }
 
 void ReverseConsume(CordRep* rep, ConsumeFn consume_fn) {
-  return Consume(false, rep, std::move(consume_fn));
+  return Consume(rep, std::move(consume_fn));
 }
 
 }  // namespace cord_internal
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_crc.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_crc.cc
new file mode 100644
index 0000000000..ee14035410
--- /dev/null
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_crc.cc
@@ -0,0 +1,54 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/cord_rep_crc.h"
+
+#include <cassert>
+#include <cstdint>
+
+#include "absl/base/config.h"
+#include "absl/strings/internal/cord_internal.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+CordRepCrc* CordRepCrc::New(CordRep* child, uint32_t crc) {
+  assert(child != nullptr);
+  if (child->IsCrc()) {
+    if (child->refcount.IsOne()) {
+      child->crc()->crc = crc;
+      return child->crc();
+    }
+    CordRep* old = child;
+    child = old->crc()->child;
+    CordRep::Ref(child);
+    CordRep::Unref(old);
+  }
+  auto* new_cordrep = new CordRepCrc;
+  new_cordrep->length = child->length;
+  new_cordrep->tag = cord_internal::CRC;
+  new_cordrep->child = child;
+  new_cordrep->crc = crc;
+  return new_cordrep;
+}
+
+void CordRepCrc::Destroy(CordRepCrc* node) {
+  CordRep::Unref(node->child);
+  delete node;
+}
+
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_crc.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_crc.h
new file mode 100644
index 0000000000..5294b0d133
--- /dev/null
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_crc.h
@@ -0,0 +1,102 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
+#define ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
+
+#include <cassert>
+#include <cstdint>
+
+#include "absl/base/config.h"
+#include "absl/base/optimization.h"
+#include "absl/strings/internal/cord_internal.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+// CordRepCrc is a CordRep node intended only to appear at the top level of a
+// cord tree.  It associates an "expected CRC" with the contained data, to allow
+// for easy passage of checksum data in Cord data flows.
+//
+// From Cord's perspective, the crc value has no semantics; any validation of
+// the contained checksum is the user's responsibility.
+struct CordRepCrc : public CordRep {
+  CordRep* child;
+  uint32_t crc;
+
+  // Consumes `child` and returns a CordRepCrc prefixed tree containing `child`.
+  // If the specified `child` is itself a CordRepCrc node, then this method
+  // either replaces the existing node, or directly updates the crc value in it
+  // depending on the node being shared or not, i.e.: refcount.IsOne().
+  // `child` must not be null. Never returns null.
+  static CordRepCrc* New(CordRep* child, uint32_t crc);
+
+  // Destroys (deletes) the provided node. `node` must not be null.
+  static void Destroy(CordRepCrc* node);
+};
+
+// Consumes `rep` and returns a CordRep* with any outer CordRepCrc wrapper
+// removed.  This is usually a no-op (returning `rep`), but this will remove and
+// unref an outer CordRepCrc node.
+inline CordRep* RemoveCrcNode(CordRep* rep) {
+  assert(rep != nullptr);
+  if (ABSL_PREDICT_FALSE(rep->IsCrc())) {
+    CordRep* child = rep->crc()->child;
+    if (rep->refcount.IsOne()) {
+      delete rep->crc();
+    } else {
+      CordRep::Ref(child);
+      CordRep::Unref(rep);
+    }
+    return child;
+  }
+  return rep;
+}
+
+// Returns `rep` if it is not a CordRepCrc node, or its child if it is.
+// Does not consume or create a reference on `rep` or the returned value.
+inline CordRep* SkipCrcNode(CordRep* rep) {
+  assert(rep != nullptr);
+  if (ABSL_PREDICT_FALSE(rep->IsCrc())) {
+    return rep->crc()->child;
+  } else {
+    return rep;
+  }
+}
+
+inline const CordRep* SkipCrcNode(const CordRep* rep) {
+  assert(rep != nullptr);
+  if (ABSL_PREDICT_FALSE(rep->IsCrc())) {
+    return rep->crc()->child;
+  } else {
+    return rep;
+  }
+}
+
+inline CordRepCrc* CordRep::crc() {
+  assert(IsCrc());
+  return static_cast<CordRepCrc*>(this);
+}
+
+inline const CordRepCrc* CordRep::crc() const {
+  assert(IsCrc());
+  return static_cast<const CordRepCrc*>(this);
+}
+
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_flat.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_flat.h
index 4d0f988697..e3e27fcd7c 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_flat.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_flat.h
@@ -20,6 +20,8 @@
 #include <cstdint>
 #include <memory>
 
+#include "absl/base/config.h"
+#include "absl/base/macros.h"
 #include "absl/strings/internal/cord_internal.h"
 
 namespace absl {
@@ -42,23 +44,45 @@ static constexpr size_t kMinFlatSize = 32;
 static constexpr size_t kMaxFlatSize = 4096;
 static constexpr size_t kMaxFlatLength = kMaxFlatSize - kFlatOverhead;
 static constexpr size_t kMinFlatLength = kMinFlatSize - kFlatOverhead;
+static constexpr size_t kMaxLargeFlatSize = 256 * 1024;
+static constexpr size_t kMaxLargeFlatLength = kMaxLargeFlatSize - kFlatOverhead;
 
+// kTagBase should make the Size <--> Tag computation resilient
+// against changes to the value of FLAT when we add a new tag..
+static constexpr uint8_t kTagBase = FLAT - 4;
+
+// Converts the provided rounded size to the corresponding tag
 constexpr uint8_t AllocatedSizeToTagUnchecked(size_t size) {
-  return static_cast<uint8_t>((size <= 1024) ? size / 8 + 1
-                                             : 129 + size / 32 - 1024 / 32);
+  return static_cast<uint8_t>(size <= 512 ? kTagBase + size / 8
+                              : size <= 8192
+                                  ? kTagBase + 512 / 8 + size / 64 - 512 / 64
+                                  : kTagBase + 512 / 8 + ((8192 - 512) / 64) +
+                                        size / 4096 - 8192 / 4096);
+}
+
+// Converts the provided tag to the corresponding allocated size
+constexpr size_t TagToAllocatedSize(uint8_t tag) {
+  return (tag <= kTagBase + 512 / 8) ? tag * 8 - kTagBase * 8
+         : (tag <= kTagBase + (512 / 8) + ((8192 - 512) / 64))
+             ? 512 + tag * 64 - kTagBase * 64 - 512 / 8 * 64
+             : 8192 + tag * 4096 - kTagBase * 4096 -
+                   ((512 / 8) + ((8192 - 512) / 64)) * 4096;
 }
 
-static_assert(kMinFlatSize / 8 + 1 >= FLAT, "");
-static_assert(AllocatedSizeToTagUnchecked(kMaxFlatSize) <= MAX_FLAT_TAG, "");
+static_assert(AllocatedSizeToTagUnchecked(kMinFlatSize) == FLAT, "");
+static_assert(AllocatedSizeToTagUnchecked(kMaxLargeFlatSize) == MAX_FLAT_TAG,
+              "");
 
-// Helper functions for rounded div, and rounding to exact sizes.
-constexpr size_t DivUp(size_t n, size_t m) { return (n + m - 1) / m; }
-constexpr size_t RoundUp(size_t n, size_t m) { return DivUp(n, m) * m; }
+// RoundUp logically performs `((n + m - 1) / m) * m` to round up to the nearest
+// multiple of `m`, optimized for the invariant that `m` is a power of 2.
+constexpr size_t RoundUp(size_t n, size_t m) {
+  return (n + m - 1) & (0 - m);
+}
 
 // Returns the size to the nearest equal or larger value that can be
 // expressed exactly as a tag value.
 inline size_t RoundUpForTag(size_t size) {
-  return RoundUp(size, (size <= 1024) ? 8 : 32);
+  return RoundUp(size, (size <= 512) ? 8 : (size <= 8192 ? 64 : 4096));
 }
 
 // Converts the allocated size to a tag, rounding down if the size
@@ -71,26 +95,26 @@ inline uint8_t AllocatedSizeToTag(size_t size) {
   return tag;
 }
 
-// Converts the provided tag to the corresponding allocated size
-constexpr size_t TagToAllocatedSize(uint8_t tag) {
-  return (tag <= 129) ? ((tag - 1) * 8) : (1024 + (tag - 129) * 32);
-}
-
 // Converts the provided tag to the corresponding available data length
 constexpr size_t TagToLength(uint8_t tag) {
   return TagToAllocatedSize(tag) - kFlatOverhead;
 }
 
 // Enforce that kMaxFlatSize maps to a well-known exact tag value.
-static_assert(TagToAllocatedSize(225) == kMaxFlatSize, "Bad tag logic");
+static_assert(TagToAllocatedSize(MAX_FLAT_TAG) == kMaxLargeFlatSize,
+              "Bad tag logic");
 
 struct CordRepFlat : public CordRep {
+  // Tag for explicit 'large flat' allocation
+  struct Large {};
+
   // Creates a new flat node.
-  static CordRepFlat* New(size_t len) {
+  template <size_t max_flat_size, typename... Args>
+  static CordRepFlat* NewImpl(size_t len, Args... args ABSL_ATTRIBUTE_UNUSED) {
     if (len <= kMinFlatLength) {
       len = kMinFlatLength;
-    } else if (len > kMaxFlatLength) {
-      len = kMaxFlatLength;
+    } else if (len > max_flat_size - kFlatOverhead) {
+      len = max_flat_size - kFlatOverhead;
     }
 
     // Round size up so it matches a size we can exactly express in a tag.
@@ -101,6 +125,12 @@ struct CordRepFlat : public CordRep {
     return rep;
   }
 
+  static CordRepFlat* New(size_t len) { return NewImpl<kMaxFlatSize>(len); }
+
+  static CordRepFlat* New(Large, size_t len) {
+    return NewImpl<kMaxLargeFlatSize>(len);
+  }
+
   // Deletes a CordRepFlat instance created previously through a call to New().
   // Flat CordReps are allocated and constructed with raw ::operator new and
   // placement new, and must be destructed and deallocated accordingly.
@@ -117,6 +147,17 @@ struct CordRepFlat : public CordRep {
 #endif
   }
 
+  // Create a CordRepFlat containing `data`, with an optional additional
+  // extra capacity of up to `extra` bytes. Requires that `data.size()`
+  // is less than kMaxFlatLength.
+  static CordRepFlat* Create(absl::string_view data, size_t extra = 0) {
+    assert(data.size() <= kMaxFlatLength);
+    CordRepFlat* flat = New(data.size() + (std::min)(extra, kMaxFlatLength));
+    memcpy(flat->Data(), data.data(), data.size());
+    flat->length = data.size();
+    return flat;
+  }
+
   // Returns a pointer to the data inside this flat rep.
   char* Data() { return reinterpret_cast<char*>(storage); }
   const char* Data() const { return reinterpret_cast<const char*>(storage); }
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_ring.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_ring.cc
index 07c77eb3e5..af2fc7683d 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_ring.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cord_rep_ring.cc
@@ -129,7 +129,9 @@ class CordRepRing::Filler {
   index_type pos_;
 };
 
-constexpr size_t CordRepRing::kMaxCapacity; // NOLINT: needed for c++11
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+constexpr size_t CordRepRing::kMaxCapacity;
+#endif
 
 bool CordRepRing::IsValid(std::ostream& output) const {
   if (capacity_ == 0) {
@@ -277,7 +279,7 @@ CordRepRing* CordRepRing::Mutable(CordRepRing* rep, size_t extra) {
   // Get current number of entries, and check for max capacity.
   size_t entries = rep->entries();
 
-  if (!rep->refcount.IsMutable()) {
+  if (!rep->refcount.IsOne()) {
     return Copy(rep, rep->head(), rep->tail(), extra);
   } else if (entries + extra > rep->capacity()) {
     const size_t min_grow = rep->capacity() + rep->capacity() / 2;
@@ -292,10 +294,10 @@ CordRepRing* CordRepRing::Mutable(CordRepRing* rep, size_t extra) {
 }
 
 Span<char> CordRepRing::GetAppendBuffer(size_t size) {
-  assert(refcount.IsMutable());
+  assert(refcount.IsOne());
   index_type back = retreat(tail_);
   CordRep* child = entry_child(back);
-  if (child->tag >= FLAT && child->refcount.IsMutable()) {
+  if (child->tag >= FLAT && child->refcount.IsOne()) {
     size_t capacity = child->flat()->Capacity();
     pos_type end_pos = entry_end_pos(back);
     size_t data_offset = entry_data_offset(back);
@@ -312,10 +314,10 @@ Span<char> CordRepRing::GetAppendBuffer(size_t size) {
 }
 
 Span<char> CordRepRing::GetPrependBuffer(size_t size) {
-  assert(refcount.IsMutable());
+  assert(refcount.IsOne());
   CordRep* child = entry_child(head_);
   size_t data_offset = entry_data_offset(head_);
-  if (data_offset && child->refcount.IsMutable() && child->tag >= FLAT) {
+  if (data_offset && child->refcount.IsOne() && child->tag >= FLAT) {
     size_t n = (std::min)(data_offset, size);
     this->length += n;
     begin_pos_ -= n;
@@ -504,7 +506,7 @@ CordRepRing* CordRepRing::Prepend(CordRepRing* rep, CordRep* child) {
 
 CordRepRing* CordRepRing::Append(CordRepRing* rep, absl::string_view data,
                                  size_t extra) {
-  if (rep->refcount.IsMutable()) {
+  if (rep->refcount.IsOne()) {
     Span<char> avail = rep->GetAppendBuffer(data.length());
     if (!avail.empty()) {
       memcpy(avail.data(), data.data(), avail.length());
@@ -538,7 +540,7 @@ CordRepRing* CordRepRing::Append(CordRepRing* rep, absl::string_view data,
 
 CordRepRing* CordRepRing::Prepend(CordRepRing* rep, absl::string_view data,
                                   size_t extra) {
-  if (rep->refcount.IsMutable()) {
+  if (rep->refcount.IsOne()) {
     Span<char> avail = rep->GetPrependBuffer(data.length());
     if (!avail.empty()) {
       const char* tail = data.data() + data.length() - avail.length();
@@ -678,7 +680,7 @@ CordRepRing* CordRepRing::SubRing(CordRepRing* rep, size_t offset,
   Position tail = rep->FindTail(head.index, offset + len);
   const size_t new_entries = rep->entries(head.index, tail.index);
 
-  if (rep->refcount.IsMutable() && extra <= (rep->capacity() - new_entries)) {
+  if (rep->refcount.IsOne() && extra <= (rep->capacity() - new_entries)) {
     // We adopt a privately owned rep and no extra entries needed.
     if (head.index != rep->head_) UnrefEntries(rep, rep->head_, head.index);
     if (tail.index != rep->tail_) UnrefEntries(rep, tail.index, rep->tail_);
@@ -715,7 +717,7 @@ CordRepRing* CordRepRing::RemovePrefix(CordRepRing* rep, size_t len,
   }
 
   Position head = rep->Find(len);
-  if (rep->refcount.IsMutable()) {
+  if (rep->refcount.IsOne()) {
     if (head.index != rep->head_) UnrefEntries(rep, rep->head_, head.index);
     rep->head_ = head.index;
   } else {
@@ -745,7 +747,7 @@ CordRepRing* CordRepRing::RemoveSuffix(CordRepRing* rep, size_t len,
   }
 
   Position tail = rep->FindTail(rep->length - len);
-  if (rep->refcount.IsMutable()) {
+  if (rep->refcount.IsOne()) {
     // We adopt a privately owned rep, scrub.
     if (tail.index != rep->tail_) UnrefEntries(rep, tail.index, rep->tail_);
     rep->tail_ = tail.index;
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_info.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_info.cc
index 5c18bbc566..dac3fd8b1b 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_info.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_info.cc
@@ -20,6 +20,7 @@
 #include "absl/debugging/stacktrace.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_btree.h"
+#include "absl/strings/internal/cord_rep_crc.h"
 #include "absl/strings/internal/cord_rep_ring.h"
 #include "absl/strings/internal/cordz_handle.h"
 #include "absl/strings/internal/cordz_statistics.h"
@@ -33,7 +34,9 @@ namespace cord_internal {
 
 using ::absl::base_internal::SpinLockHolder;
 
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr int CordzInfo::kMaxStackDepth;
+#endif
 
 ABSL_CONST_INIT CordzInfo::List CordzInfo::global_list_{absl::kConstInit};
 
@@ -81,6 +84,14 @@ class CordRepAnalyzer {
     size_t refcount = rep->refcount.Get();
     RepRef repref{rep, (refcount > 1) ? refcount - 1 : 1};
 
+    // Process the top level CRC node, if present.
+    if (repref.rep->tag == CRC) {
+      statistics_.node_count++;
+      statistics_.node_counts.crc++;
+      memory_usage_.Add(sizeof(CordRepCrc), repref.refcount);
+      repref = repref.Child(repref.rep->crc()->child);
+    }
+
     // Process all top level linear nodes (substrings and flats).
     repref = CountLinearReps(repref, memory_usage_);
 
@@ -89,8 +100,6 @@ class CordRepAnalyzer {
         AnalyzeRing(repref);
       } else if (repref.rep->tag == BTREE) {
         AnalyzeBtree(repref);
-      } else if (repref.rep->tag == CONCAT) {
-        AnalyzeConcat(repref);
       } else {
         // We should have either a concat, btree, or ring node if not null.
         assert(false);
@@ -132,14 +141,6 @@ class CordRepAnalyzer {
     }
   };
 
-  // Returns `rr` if `rr.rep` is not null and a CONCAT type.
-  // Asserts that `rr.rep` is a concat node or null.
-  static RepRef AssertConcat(RepRef repref) {
-    const CordRep* rep = repref.rep;
-    assert(rep == nullptr || rep->tag == CONCAT);
-    return (rep != nullptr && rep->tag == CONCAT) ? repref : RepRef{nullptr, 0};
-  }
-
   // Counts a flat of the provide allocated size
   void CountFlat(size_t size) {
     statistics_.node_count++;
@@ -192,34 +193,6 @@ class CordRepAnalyzer {
     return rep;
   }
 
-  // Analyzes the provided concat node in a flattened recursive way.
-  void AnalyzeConcat(RepRef rep) {
-    absl::InlinedVector<RepRef, 47> pending;
-
-    while (rep.rep != nullptr) {
-      const CordRepConcat* concat = rep.rep->concat();
-      RepRef left = rep.Child(concat->left);
-      RepRef right = rep.Child(concat->right);
-
-      statistics_.node_count++;
-      statistics_.node_counts.concat++;
-      memory_usage_.Add(sizeof(CordRepConcat), rep.refcount);
-
-      right = AssertConcat(CountLinearReps(right, memory_usage_));
-      rep = AssertConcat(CountLinearReps(left, memory_usage_));
-      if (rep.rep != nullptr) {
-        if (right.rep != nullptr) {
-          pending.push_back(right);
-        }
-      } else if (right.rep != nullptr) {
-        rep = right;
-      } else if (!pending.empty()) {
-        rep = pending.back();
-        pending.pop_back();
-      }
-    }
-  }
-
   // Analyzes the provided ring.
   void AnalyzeRing(RepRef rep) {
     statistics_.node_count++;
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_statistics.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_statistics.h
index da4c7dbb8c..5707190577 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_statistics.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_statistics.h
@@ -41,6 +41,7 @@ struct CordzStatistics {
     size_t concat = 0;     // #concat reps
     size_t ring = 0;       // #ring buffer reps
     size_t btree = 0;      // #btree reps
+    size_t crc = 0;        // #crc reps
   };
 
   // The size of the cord in bytes. This matches the result of Cord::size().
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_update_tracker.h b/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_update_tracker.h
index 1f764486eb..c5170662bf 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_update_tracker.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/cordz_update_tracker.h
@@ -39,8 +39,8 @@ class CordzUpdateTracker {
   // Tracked update methods.
   enum MethodIdentifier {
     kUnknown,
-    kAppendBuffer,
     kAppendCord,
+    kAppendCordBuffer,
     kAppendExternalMemory,
     kAppendString,
     kAssignCord,
@@ -50,16 +50,18 @@ class CordzUpdateTracker {
     kConstructorString,
     kCordReader,
     kFlatten,
+    kGetAppendBuffer,
     kGetAppendRegion,
     kMakeCordFromExternal,
     kMoveAppendCord,
     kMoveAssignCord,
     kMovePrependCord,
-    kPrependBuffer,
     kPrependCord,
+    kPrependCordBuffer,
     kPrependString,
     kRemovePrefix,
     kRemoveSuffix,
+    kSetExpectedChecksum,
     kSubCord,
 
     // kNumMethods defines the number of entries: must be the last entry.
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/escaping.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/escaping.cc
index c5271286ad..cfea096111 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/escaping.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/escaping.cc
@@ -21,7 +21,7 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace strings_internal {
 
-const char kBase64Chars[] =
+ABSL_CONST_INIT const char kBase64Chars[] =
     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
 size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding) {
@@ -102,8 +102,8 @@ size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
     }
   }
   // To save time, we didn't update szdest or szsrc in the loop.  So do it now.
-  szdest = limit_dest - cur_dest;
-  szsrc = limit_src - cur_src;
+  szdest = static_cast<size_t>(limit_dest - cur_dest);
+  szsrc = static_cast<size_t>(limit_src - cur_src);
 
   /* now deal with the tail (<=3 bytes) */
   switch (szsrc) {
@@ -154,7 +154,8 @@ size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
       // the loop because the loop above always reads 4 bytes, and the fourth
       // byte is past the end of the input.
       if (szdest < 4) return 0;
-      uint32_t in = (cur_src[0] << 16) + absl::big_endian::Load16(cur_src + 1);
+      uint32_t in =
+          (uint32_t{cur_src[0]} << 16) + absl::big_endian::Load16(cur_src + 1);
       cur_dest[0] = base64[in >> 18];
       in &= 0x3FFFF;
       cur_dest[1] = base64[in >> 12];
@@ -172,7 +173,7 @@ size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
       ABSL_RAW_LOG(FATAL, "Logic problem? szsrc = %zu", szsrc);
       break;
   }
-  return (cur_dest - dest);
+  return static_cast<size_t>(cur_dest - dest);
 }
 
 }  // namespace strings_internal
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/ostringstream.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/ostringstream.cc
index 05324c780c..dc6cfe1686 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/ostringstream.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/ostringstream.cc
@@ -27,7 +27,7 @@ OStringStream::Buf::int_type OStringStream::overflow(int c) {
 
 std::streamsize OStringStream::xsputn(const char* s, std::streamsize n) {
   assert(s_);
-  s_->append(s, n);
+  s_->append(s, static_cast<size_t>(n));
   return n;
 }
 
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/arg.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/arg.cc
index e28a29b171..02aeeebec7 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/arg.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/arg.cc
@@ -320,7 +320,7 @@ bool ConvertIntArg(T v, const FormatConversionSpecImpl conv,
       return ConvertFloatImpl(static_cast<double>(v), conv, sink);
 
     default:
-       ABSL_INTERNAL_ASSUME(false);
+       ABSL_ASSUME(false);
   }
 
   if (conv.is_basic()) {
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/arg.h b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/arg.h
index 3c91be701f..b9dda90901 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/arg.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/arg.h
@@ -144,7 +144,7 @@ StringConvertResult FormatConvertImpl(const AbslCord& value,
   size_t space_remaining = 0;
 
   int width = conv.width();
-  if (width >= 0) space_remaining = width;
+  if (width >= 0) space_remaining = static_cast<size_t>(width);
 
   size_t to_write = value.size();
 
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/bind.h b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/bind.h
index b26cff6648..80f29654b3 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/bind.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/bind.h
@@ -25,6 +25,7 @@
 #include "absl/strings/internal/str_format/checker.h"
 #include "absl/strings/internal/str_format/parser.h"
 #include "absl/types/span.h"
+#include "absl/utility/utility.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
@@ -87,6 +88,36 @@ class FormatSpecTemplate
     : public MakeDependent<UntypedFormatSpec, Args...>::type {
   using Base = typename MakeDependent<UntypedFormatSpec, Args...>::type;
 
+  template <bool res>
+  struct ErrorMaker {
+    constexpr bool operator()(int) const { return res; }
+  };
+
+  template <int i, int j>
+  static constexpr bool CheckArity(ErrorMaker<true> SpecifierCount = {},
+                                   ErrorMaker<i == j> ParametersPassed = {}) {
+    static_assert(SpecifierCount(i) == ParametersPassed(j),
+                  "Number of arguments passed must match the number of "
+                  "conversion specifiers.");
+    return true;
+  }
+
+  template <FormatConversionCharSet specified, FormatConversionCharSet passed,
+            int arg>
+  static constexpr bool CheckMatch(
+      ErrorMaker<Contains(specified, passed)> MismatchedArgumentNumber = {}) {
+    static_assert(MismatchedArgumentNumber(arg),
+                  "Passed argument must match specified format.");
+    return true;
+  }
+
+  template <FormatConversionCharSet... C, size_t... I>
+  static bool CheckMatches(absl::index_sequence<I...>) {
+    bool res[] = {true, CheckMatch<Args, C, I + 1>()...};
+    (void)res;
+    return true;
+  }
+
  public:
 #ifdef ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
 
@@ -112,7 +143,8 @@ class FormatSpecTemplate
   template <typename T = void>
   FormatSpecTemplate(string_view s)  // NOLINT
       __attribute__((enable_if(str_format_internal::EnsureConstexpr(s),
-                               "constexpr trap"))) {
+                               "constexpr trap")))
+      : Base("to avoid noise in the compiler error") {
     static_assert(sizeof(T*) == 0,
                   "Format specified does not match the arguments passed.");
   }
@@ -133,13 +165,12 @@ class FormatSpecTemplate
 
 #endif  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
 
-  template <
-      FormatConversionCharSet... C,
-      typename = typename std::enable_if<sizeof...(C) == sizeof...(Args)>::type,
-      typename = typename std::enable_if<AllOf(Contains(Args,
-                                                        C)...)>::type>
+  template <FormatConversionCharSet... C>
   FormatSpecTemplate(const ExtendedParsedFormat<C...>& pc)  // NOLINT
-      : Base(&pc) {}
+      : Base(&pc) {
+    CheckArity<sizeof...(C), sizeof...(Args)>();
+    CheckMatches<C...>(absl::make_index_sequence<sizeof...(C)>{});
+  }
 };
 
 class Streamable {
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/checker.h b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/checker.h
index 2a2601eccf..4fd19d13ae 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/checker.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/checker.h
@@ -22,9 +22,14 @@
 // Compile time check support for entry points.
 
 #ifndef ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
-#if ABSL_HAVE_ATTRIBUTE(enable_if) && !defined(__native_client__)
+// We disable format checker under vscode intellisense compilation.
+// See https://github.com/microsoft/vscode-cpptools/issues/3683 for
+// more details.
+#if ABSL_HAVE_ATTRIBUTE(enable_if) && !defined(__native_client__) && \
+    !defined(__INTELLISENSE__)
 #define ABSL_INTERNAL_ENABLE_FORMAT_CHECKER 1
-#endif  // ABSL_HAVE_ATTRIBUTE(enable_if) && !defined(__native_client__)
+#endif  // ABSL_HAVE_ATTRIBUTE(enable_if) && !defined(__native_client__) &&
+        // !defined(__INTELLISENSE__)
 #endif  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
 
 namespace absl {
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/extension.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/extension.cc
index 484f6ebfc1..f93153d5c0 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/extension.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/extension.cc
@@ -33,6 +33,8 @@ std::string FlagsToString(Flags v) {
   return s;
 }
 
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+
 #define ABSL_INTERNAL_X_VAL(id) \
   constexpr absl::FormatConversionChar FormatConversionCharInternal::id;
 ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL, )
@@ -45,17 +47,14 @@ constexpr absl::FormatConversionChar FormatConversionCharInternal::kNone;
 ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_CHAR_SET_CASE, )
 #undef ABSL_INTERNAL_CHAR_SET_CASE
 
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kStar;
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kIntegral;
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kFloating;
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kNumeric;
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kPointer;
 
+#endif  // ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+
 bool FormatSinkImpl::PutPaddedString(string_view value, int width,
                                      int precision, bool left) {
   size_t space_remaining = 0;
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/extension.h b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/extension.h
index 55cbb56d0a..55e8ac882d 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/extension.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/extension.h
@@ -19,6 +19,7 @@
 #include <limits.h>
 
 #include <cstddef>
+#include <cstdint>
 #include <cstring>
 #include <ostream>
 
@@ -70,7 +71,7 @@ class FormatSinkImpl {
   ~FormatSinkImpl() { Flush(); }
 
   void Flush() {
-    raw_.Write(string_view(buf_, pos_ - buf_));
+    raw_.Write(string_view(buf_, static_cast<size_t>(pos_ - buf_)));
     pos_ = buf_;
   }
 
@@ -120,7 +121,9 @@ class FormatSinkImpl {
   }
 
  private:
-  size_t Avail() const { return buf_ + sizeof(buf_) - pos_; }
+  size_t Avail() const {
+    return static_cast<size_t>(buf_ + sizeof(buf_) - pos_);
+  }
 
   FormatRawSinkImpl raw_;
   size_t size_ = 0;
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/output.h b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/output.h
index 8030dae00f..15e751ab6f 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/output.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/output.h
@@ -22,6 +22,7 @@
 #define ABSL_STRINGS_INTERNAL_STR_FORMAT_OUTPUT_H_
 
 #include <cstdio>
+#include <ios>
 #include <ostream>
 #include <string>
 
@@ -71,7 +72,7 @@ inline void AbslFormatFlush(std::string* out, string_view s) {
   out->append(s.data(), s.size());
 }
 inline void AbslFormatFlush(std::ostream* out, string_view s) {
-  out->write(s.data(), s.size());
+  out->write(s.data(), static_cast<std::streamsize>(s.size()));
 }
 
 inline void AbslFormatFlush(FILERawSink* sink, string_view v) {
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/parser.h b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/parser.h
index ad8646edff..32b91d034d 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/parser.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_format/parser.h
@@ -151,7 +151,8 @@ bool ParseFormatString(string_view src, Consumer consumer) {
   const char* p = src.data();
   const char* const end = p + src.size();
   while (p != end) {
-    const char* percent = static_cast<const char*>(memchr(p, '%', end - p));
+    const char* percent =
+        static_cast<const char*>(memchr(p, '%', static_cast<size_t>(end - p)));
     if (!percent) {
       // We found the last substring.
       return consumer.Append(string_view(p, end - p));
@@ -242,7 +243,8 @@ class ParsedFormatBase {
     string_view text(base, 0);
     for (const auto& item : items_) {
       const char* const end = text.data() + text.size();
-      text = string_view(end, (base + item.text_end) - end);
+      text =
+          string_view(end, static_cast<size_t>((base + item.text_end) - end));
       if (item.is_conversion) {
         if (!consumer.ConvertOne(item.conv, text)) return false;
       } else {
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/str_join_internal.h b/contrib/restricted/abseil-cpp/absl/strings/internal/str_join_internal.h
index 31dbf672f0..d97d5033d8 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/str_join_internal.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/str_join_internal.h
@@ -229,10 +229,11 @@ std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s,
   std::string result;
   if (start != end) {
     // Sums size
-    size_t result_size = start->size();
+    auto&& start_value = *start;
+    size_t result_size = start_value.size();
     for (Iterator it = start; ++it != end;) {
       result_size += s.size();
-      result_size += it->size();
+      result_size += (*it).size();
     }
 
     if (result_size > 0) {
@@ -240,13 +241,15 @@ std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s,
 
       // Joins strings
       char* result_buf = &*result.begin();
-      memcpy(result_buf, start->data(), start->size());
-      result_buf += start->size();
+
+      memcpy(result_buf, start_value.data(), start_value.size());
+      result_buf += start_value.size();
       for (Iterator it = start; ++it != end;) {
         memcpy(result_buf, s.data(), s.size());
         result_buf += s.size();
-        memcpy(result_buf, it->data(), it->size());
-        result_buf += it->size();
+        auto&& value = *it;
+        memcpy(result_buf, value.data(), value.size());
+        result_buf += value.size();
       }
     }
   }
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/string_constant.h b/contrib/restricted/abseil-cpp/absl/strings/internal/string_constant.h
index a11336b7f0..f68b17d75e 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/string_constant.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/string_constant.h
@@ -35,17 +35,25 @@ namespace strings_internal {
 // below.
 template <typename T>
 struct StringConstant {
+ private:
+  static constexpr bool TryConstexprEval(absl::string_view view) {
+    return view.empty() || 2 * view[0] != 1;
+  }
+
+ public:
   static constexpr absl::string_view value = T{}();
   constexpr absl::string_view operator()() const { return value; }
 
   // Check to be sure `view` points to constant data.
   // Otherwise, it can't be constant evaluated.
-  static_assert(value.empty() || 2 * value[0] != 1,
+  static_assert(TryConstexprEval(value),
                 "The input string_view must point to constant data.");
 };
 
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 template <typename T>
-constexpr absl::string_view StringConstant<T>::value;  // NOLINT
+constexpr absl::string_view StringConstant<T>::value;
+#endif
 
 // Factory function for `StringConstant` instances.
 // It supports callables that have a constexpr default constructor and a
diff --git a/contrib/restricted/abseil-cpp/absl/strings/internal/utf8.cc b/contrib/restricted/abseil-cpp/absl/strings/internal/utf8.cc
index 8fd8edc1ec..7ecb93dfbe 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/internal/utf8.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/internal/utf8.cc
@@ -25,25 +25,25 @@ size_t EncodeUTF8Char(char *buffer, char32_t utf8_char) {
     *buffer = static_cast<char>(utf8_char);
     return 1;
   } else if (utf8_char <= 0x7FF) {
-    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    buffer[1] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[0] = 0xC0 | utf8_char;
+    buffer[0] = static_cast<char>(0xC0 | utf8_char);
     return 2;
   } else if (utf8_char <= 0xFFFF) {
-    buffer[2] = 0x80 | (utf8_char & 0x3F);
+    buffer[2] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    buffer[1] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[0] = 0xE0 | utf8_char;
+    buffer[0] = static_cast<char>(0xE0 | utf8_char);
     return 3;
   } else {
-    buffer[3] = 0x80 | (utf8_char & 0x3F);
+    buffer[3] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[2] = 0x80 | (utf8_char & 0x3F);
+    buffer[2] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    buffer[1] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[0] = 0xF0 | utf8_char;
+    buffer[0] = static_cast<char>(0xF0 | utf8_char);
     return 4;
   }
 }
diff --git a/contrib/restricted/abseil-cpp/absl/strings/numbers.cc b/contrib/restricted/abseil-cpp/absl/strings/numbers.cc
index cbd84c918b..e798fc69f7 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/numbers.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/numbers.cc
@@ -757,8 +757,8 @@ struct LookupTables {
 //
 // uint128& operator/=(uint128) is not constexpr, so hardcode the resulting
 // array to avoid a static initializer.
-template<>
-const uint128 LookupTables<uint128>::kVmaxOverBase[] = {
+template <>
+ABSL_CONST_INIT const uint128 LookupTables<uint128>::kVmaxOverBase[] = {
     0,
     0,
     MakeUint128(9223372036854775807u, 18446744073709551615u),
@@ -809,8 +809,8 @@ const uint128 LookupTables<uint128>::kVmaxOverBase[] = {
 //
 // int128& operator/=(int128) is not constexpr, so hardcode the resulting array
 // to avoid a static initializer.
-template<>
-const int128 LookupTables<int128>::kVmaxOverBase[] = {
+template <>
+ABSL_CONST_INIT const int128 LookupTables<int128>::kVmaxOverBase[] = {
     0,
     0,
     MakeInt128(4611686018427387903, 18446744073709551615u),
@@ -862,8 +862,8 @@ const int128 LookupTables<int128>::kVmaxOverBase[] = {
 //
 // int128& operator/=(int128) is not constexpr, so hardcode the resulting array
 // to avoid a static initializer.
-template<>
-const int128 LookupTables<int128>::kVminOverBase[] = {
+template <>
+ABSL_CONST_INIT const int128 LookupTables<int128>::kVminOverBase[] = {
     0,
     0,
     MakeInt128(-4611686018427387904, 0u),
@@ -904,11 +904,11 @@ const int128 LookupTables<int128>::kVminOverBase[] = {
 };
 
 template <typename IntType>
-const IntType LookupTables<IntType>::kVmaxOverBase[] =
+ABSL_CONST_INIT const IntType LookupTables<IntType>::kVmaxOverBase[] =
     X_OVER_BASE_INITIALIZER(std::numeric_limits<IntType>::max());
 
 template <typename IntType>
-const IntType LookupTables<IntType>::kVminOverBase[] =
+ABSL_CONST_INIT const IntType LookupTables<IntType>::kVminOverBase[] =
     X_OVER_BASE_INITIALIZER(std::numeric_limits<IntType>::min());
 
 #undef X_OVER_BASE_INITIALIZER
diff --git a/contrib/restricted/abseil-cpp/absl/strings/numbers.h b/contrib/restricted/abseil-cpp/absl/strings/numbers.h
index 899e623c8c..86c84ed39b 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/numbers.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/numbers.h
@@ -23,12 +23,12 @@
 #ifndef ABSL_STRINGS_NUMBERS_H_
 #define ABSL_STRINGS_NUMBERS_H_
 
-#ifdef __SSE4_2__
+#ifdef __SSSE3__
+#include <tmmintrin.h>
+#endif
+
 #ifdef _MSC_VER
 #include <intrin.h>
-#else
-#include <x86intrin.h>
-#endif
 #endif
 
 #include <cstddef>
@@ -40,14 +40,7 @@
 #include <type_traits>
 
 #include "absl/base/config.h"
-#ifdef __SSE4_2__
-// TODO(jorg): Remove this when we figure out the right way
-// to swap bytes on SSE 4.2 that works with the compilers
-// we claim to support.  Also, add tests for the compiler
-// that doesn't support the Intel _bswap64 intrinsic but
-// does support all the SSE 4.2 intrinsics
 #include "absl/base/internal/endian.h"
-#endif
 #include "absl/base/macros.h"
 #include "absl/base/port.h"
 #include "absl/numeric/bits.h"
@@ -185,16 +178,19 @@ char* FastIntToBuffer(int_type i, char* buffer) {
   // TODO(jorg): This signed-ness check is used because it works correctly
   // with enums, and it also serves to check that int_type is not a pointer.
   // If one day something like std::is_signed<enum E> works, switch to it.
-  if (static_cast<int_type>(1) - 2 < 0) {  // Signed
-    if (sizeof(i) > 32 / 8) {           // 33-bit to 64-bit
+  // These conditions are constexpr bools to suppress MSVC warning C4127.
+  constexpr bool kIsSigned = static_cast<int_type>(1) - 2 < 0;
+  constexpr bool kUse64Bit = sizeof(i) > 32 / 8;
+  if (kIsSigned) {
+    if (kUse64Bit) {
       return FastIntToBuffer(static_cast<int64_t>(i), buffer);
-    } else {  // 32-bit or less
+    } else {
       return FastIntToBuffer(static_cast<int32_t>(i), buffer);
     }
-  } else {                     // Unsigned
-    if (sizeof(i) > 32 / 8) {  // 33-bit to 64-bit
+  } else {
+    if (kUse64Bit) {
       return FastIntToBuffer(static_cast<uint64_t>(i), buffer);
-    } else {  // 32-bit or less
+    } else {
       return FastIntToBuffer(static_cast<uint32_t>(i), buffer);
     }
   }
@@ -213,22 +209,25 @@ ABSL_MUST_USE_RESULT bool safe_strtoi_base(absl::string_view s, int_type* out,
   // TODO(jorg): This signed-ness check is used because it works correctly
   // with enums, and it also serves to check that int_type is not a pointer.
   // If one day something like std::is_signed<enum E> works, switch to it.
-  if (static_cast<int_type>(1) - 2 < 0) {  // Signed
-    if (sizeof(*out) == 64 / 8) {       // 64-bit
+  // These conditions are constexpr bools to suppress MSVC warning C4127.
+  constexpr bool kIsSigned = static_cast<int_type>(1) - 2 < 0;
+  constexpr bool kUse64Bit = sizeof(*out) == 64 / 8;
+  if (kIsSigned) {
+    if (kUse64Bit) {
       int64_t val;
       parsed = numbers_internal::safe_strto64_base(s, &val, base);
       *out = static_cast<int_type>(val);
-    } else {  // 32-bit
+    } else {
       int32_t val;
       parsed = numbers_internal::safe_strto32_base(s, &val, base);
       *out = static_cast<int_type>(val);
     }
-  } else {                         // Unsigned
-    if (sizeof(*out) == 64 / 8) {  // 64-bit
+  } else {
+    if (kUse64Bit) {
       uint64_t val;
       parsed = numbers_internal::safe_strtou64_base(s, &val, base);
       *out = static_cast<int_type>(val);
-    } else {  // 32-bit
+    } else {
       uint32_t val;
       parsed = numbers_internal::safe_strtou32_base(s, &val, base);
       *out = static_cast<int_type>(val);
@@ -244,7 +243,7 @@ ABSL_MUST_USE_RESULT bool safe_strtoi_base(absl::string_view s, int_type* out,
 // Returns the number of non-pad digits of the output (it can never be zero
 // since 0 has one digit).
 inline size_t FastHexToBufferZeroPad16(uint64_t val, char* out) {
-#ifdef __SSE4_2__
+#ifdef ABSL_INTERNAL_HAVE_SSSE3
   uint64_t be = absl::big_endian::FromHost64(val);
   const auto kNibbleMask = _mm_set1_epi8(0xf);
   const auto kHexDigits = _mm_setr_epi8('0', '1', '2', '3', '4', '5', '6', '7',
@@ -263,7 +262,7 @@ inline size_t FastHexToBufferZeroPad16(uint64_t val, char* out) {
   }
 #endif
   // | 0x1 so that even 0 has 1 digit.
-  return 16 - countl_zero(val | 0x1) / 4;
+  return 16 - static_cast<size_t>(countl_zero(val | 0x1) / 4);
 }
 
 }  // namespace numbers_internal
diff --git a/contrib/restricted/abseil-cpp/absl/strings/str_cat.h b/contrib/restricted/abseil-cpp/absl/strings/str_cat.h
index a8a85c7322..a94bc5df69 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/str_cat.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/str_cat.h
@@ -214,23 +214,29 @@ class AlphaNum {
   // A bool ctor would also convert incoming pointers (bletch).
 
   AlphaNum(int x)  // NOLINT(runtime/explicit)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(unsigned int x)  // NOLINT(runtime/explicit)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(long x)  // NOLINT(*)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(unsigned long x)  // NOLINT(*)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(long long x)  // NOLINT(*)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(unsigned long long x)  // NOLINT(*)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
 
   AlphaNum(float f)  // NOLINT(runtime/explicit)
       : piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {}
@@ -245,7 +251,8 @@ class AlphaNum {
       const strings_internal::AlphaNumBuffer<size>& buf)
       : piece_(&buf.data[0], buf.size) {}
 
-  AlphaNum(const char* c_str) : piece_(c_str) {}  // NOLINT(runtime/explicit)
+  AlphaNum(const char* c_str)                     // NOLINT(runtime/explicit)
+      : piece_(NullSafeStringView(c_str)) {}      // NOLINT(runtime/explicit)
   AlphaNum(absl::string_view pc) : piece_(pc) {}  // NOLINT(runtime/explicit)
 
   template <typename Allocator>
diff --git a/contrib/restricted/abseil-cpp/absl/strings/str_join.h b/contrib/restricted/abseil-cpp/absl/strings/str_join.h
index 33534536cf..ee5ae7efdf 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/str_join.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/str_join.h
@@ -72,21 +72,15 @@ ABSL_NAMESPACE_BEGIN
 // functions. You may provide your own Formatter to enable `absl::StrJoin()` to
 // work with arbitrary types.
 //
-// The following is an example of a custom Formatter that simply uses
-// `std::to_string()` to format an integer as a std::string.
-//
-//   struct MyFormatter {
-//     void operator()(std::string* out, int i) const {
-//       out->append(std::to_string(i));
-//     }
-//   };
-//
-// You would use the above formatter by passing an instance of it as the final
-// argument to `absl::StrJoin()`:
-//
-//   std::vector<int> v = {1, 2, 3, 4};
-//   std::string s = absl::StrJoin(v, "-", MyFormatter());
-//   EXPECT_EQ("1-2-3-4", s);
+// The following is an example of a custom Formatter that uses
+// `absl::FormatDuration` to join a list of `absl::Duration`s.
+//
+//   std::vector<absl::Duration> v = {absl::Seconds(1), absl::Milliseconds(10)};
+//   std::string s =
+//       absl::StrJoin(v, ", ", [](std::string* out, absl::Duration dur) {
+//         absl::StrAppend(out, absl::FormatDuration(dur));
+//       });
+//   EXPECT_EQ("1s, 10ms", s);
 //
 // The following standard formatters are provided within this file:
 //
diff --git a/contrib/restricted/abseil-cpp/absl/strings/str_split.h b/contrib/restricted/abseil-cpp/absl/strings/str_split.h
index bfbca422a8..7bbb68a343 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/str_split.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/str_split.h
@@ -461,8 +461,7 @@ using EnableSplitIfString =
 // first two split strings become the `std::pair` `.first` and `.second`
 // members, respectively. The remaining split substrings are discarded. If there
 // are less than two split substrings, the empty string is used for the
-// corresponding
-// `std::pair` member.
+// corresponding `std::pair` member.
 //
 // Example:
 //
diff --git a/contrib/restricted/abseil-cpp/absl/strings/string_view.cc b/contrib/restricted/abseil-cpp/absl/strings/string_view.cc
index d596e08cde..adce3be94e 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/string_view.cc
+++ b/contrib/restricted/abseil-cpp/absl/strings/string_view.cc
@@ -207,22 +207,11 @@ string_view::size_type string_view::find_last_not_of(
   return npos;
 }
 
-// MSVC has non-standard behavior that implicitly creates definitions for static
-// const members. These implicit definitions conflict with explicit out-of-class
-// member definitions that are required by the C++ standard, resulting in
-// LNK1169 "multiply defined" errors at link time. __declspec(selectany) asks
-// MSVC to choose only one definition for the symbol it decorates. See details
-// at https://msdn.microsoft.com/en-us/library/34h23df8(v=vs.100).aspx
-#ifdef _MSC_VER
-#define ABSL_STRING_VIEW_SELECTANY __declspec(selectany)
-#else
-#define ABSL_STRING_VIEW_SELECTANY
-#endif
 
-ABSL_STRING_VIEW_SELECTANY
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr string_view::size_type string_view::npos;
-ABSL_STRING_VIEW_SELECTANY
 constexpr string_view::size_type string_view::kMaxSize;
+#endif
 
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/contrib/restricted/abseil-cpp/absl/strings/string_view.h b/contrib/restricted/abseil-cpp/absl/strings/string_view.h
index 65e74ccb1d..d0c870696c 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/string_view.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/string_view.h
@@ -57,8 +57,9 @@ ABSL_NAMESPACE_END
 
 #error "std::string_view should be used in all configurations"
 
-#if ABSL_HAVE_BUILTIN(__builtin_memcmp) || \
-    (defined(__GNUC__) && !defined(__clang__))
+#if ABSL_HAVE_BUILTIN(__builtin_memcmp) ||        \
+    (defined(__GNUC__) && !defined(__clang__)) || \
+    (defined(_MSC_VER) && _MSC_VER >= 1928)
 #define ABSL_INTERNAL_STRING_VIEW_MEMCMP __builtin_memcmp
 #else  // ABSL_HAVE_BUILTIN(__builtin_memcmp)
 #define ABSL_INTERNAL_STRING_VIEW_MEMCMP memcmp
diff --git a/contrib/restricted/abseil-cpp/absl/strings/strip.h b/contrib/restricted/abseil-cpp/absl/strings/strip.h
index 111872ca54..341e66fc92 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/strip.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/strip.h
@@ -34,8 +34,9 @@ ABSL_NAMESPACE_BEGIN
 
 // ConsumePrefix()
 //
-// Strips the `expected` prefix from the start of the given string, returning
-// `true` if the strip operation succeeded or false otherwise.
+// Strips the `expected` prefix, if found, from the start of `str`.
+// If the operation succeeded, `true` is returned.  If not, `false`
+// is returned and `str` is not modified.
 //
 // Example:
 //
@@ -49,8 +50,9 @@ inline bool ConsumePrefix(absl::string_view* str, absl::string_view expected) {
 }
 // ConsumeSuffix()
 //
-// Strips the `expected` suffix from the end of the given string, returning
-// `true` if the strip operation succeeded or false otherwise.
+// Strips the `expected` suffix, if found, from the end of `str`.
+// If the operation succeeded, `true` is returned.  If not, `false`
+// is returned and `str` is not modified.
 //
 // Example:
 //
@@ -65,7 +67,7 @@ inline bool ConsumeSuffix(absl::string_view* str, absl::string_view expected) {
 
 // StripPrefix()
 //
-// Returns a view into the input string 'str' with the given 'prefix' removed,
+// Returns a view into the input string `str` with the given `prefix` removed,
 // but leaving the original string intact. If the prefix does not match at the
 // start of the string, returns the original string instead.
 ABSL_MUST_USE_RESULT inline absl::string_view StripPrefix(
@@ -76,7 +78,7 @@ ABSL_MUST_USE_RESULT inline absl::string_view StripPrefix(
 
 // StripSuffix()
 //
-// Returns a view into the input string 'str' with the given 'suffix' removed,
+// Returns a view into the input string `str` with the given `suffix` removed,
 // but leaving the original string intact. If the suffix does not match at the
 // end of the string, returns the original string instead.
 ABSL_MUST_USE_RESULT inline absl::string_view StripSuffix(
diff --git a/contrib/restricted/abseil-cpp/absl/strings/substitute.h b/contrib/restricted/abseil-cpp/absl/strings/substitute.h
index 151c56f543..6d2b08abb9 100644
--- a/contrib/restricted/abseil-cpp/absl/strings/substitute.h
+++ b/contrib/restricted/abseil-cpp/absl/strings/substitute.h
@@ -159,8 +159,8 @@ class Arg {
   Arg(Hex hex);  // NOLINT(runtime/explicit)
   Arg(Dec dec);  // NOLINT(runtime/explicit)
 
-  // vector<bool>::reference and const_reference require special help to
-  // convert to `AlphaNum` because it requires two user defined conversions.
+  // vector<bool>::reference and const_reference require special help to convert
+  // to `Arg` because it requires two user defined conversions.
   template <typename T,
             absl::enable_if_t<
                 std::is_class<T>::value &&
@@ -174,6 +174,14 @@ class Arg {
   // "0x<hex value>". However, in the case of `nullptr`, "NULL" is printed.
   Arg(const void* value);  // NOLINT(runtime/explicit)
 
+  // Normal enums are already handled by the integer formatters.
+  // This overload matches only scoped enums.
+  template <typename T,
+            typename = typename std::enable_if<
+                std::is_enum<T>{} && !std::is_convertible<T, int>{}>::type>
+  Arg(T value)  // NOLINT(google-explicit-constructor)
+      : Arg(static_cast<typename std::underlying_type<T>::type>(value)) {}
+
   Arg(const Arg&) = delete;
   Arg& operator=(const Arg&) = delete;