intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

1 files changed, 57 insertions, 0 deletions

diff --git a/library/cpp/on_disk/chunks/reader.h b/library/cpp/on_disk/chunks/reader.h
new file mode 100644
index 0000000000..c5fe783319
--- /dev/null
+++ b/library/cpp/on_disk/chunks/reader.h
@@ -0,0 +1,57 @@
+#pragma once
+
+#include <util/generic/array_ref.h>
+#include <util/generic/vector.h>
+#include <util/generic/yexception.h>
+
+class TBlob;
+
+class TChunkedDataReader {
+public:
+    TChunkedDataReader(const TBlob& blob);
+
+    inline const void* GetBlock(size_t index) const {
+        CheckIndex(index);
+        return Offsets[index];
+    }
+
+    inline size_t GetBlockLen(size_t index) const {
+        CheckIndex(index);
+
+        if (Version == 0) {
+            if (index + 1 < Offsets.size()) {
+                return Offsets[index + 1] - Offsets[index];
+            }
+
+            return Size - (Offsets.back() - Offsets.front());
+        }
+
+        return Lengths[index];
+    }
+
+    TBlob GetBlob(size_t index) const;
+
+    template <typename T>
+    TArrayRef<const T> GetRegion(size_t index) const {
+        size_t len = GetBlockLen(index);
+        Y_ENSURE(len % sizeof(T) == 0, "wrong data padding");
+        return TArrayRef<const T>(reinterpret_cast<const T*>(GetBlock(index)), len / sizeof(T));
+    }
+
+    inline size_t GetBlocksCount() const {
+        return Offsets.size();
+    }
+
+private:
+    inline void CheckIndex(size_t index) const {
+        if (index >= GetBlocksCount()) {
+            ythrow yexception() << "requested block " << index << " of " << GetBlocksCount() << " blocks";
+        }
+    }
+
+private:
+    ui64 Version = 0;
+    TVector<const char*> Offsets;
+    TVector<size_t> Lengths;
+    size_t Size = 0;
+};