BoringSSL as optional cryptobackend for ngtcp2

PR добавляет возможность использовать BoringSSL в ngtcp2 в качестве криптобиблиотеки. Для проектов в Аркадии, уже зависящих от ngtcp2, добавлена явная зависимость от слоя абстракции quictls (сейчас в транке ngtcp2 собирается с quictls).
commit_hash:3d6607abecfcff2157859acbdd18f9d0345ac485

1 files changed, 827 insertions, 0 deletions

diff --git a/contrib/restricted/google/boringssl/ssl/d1_both.cc b/contrib/restricted/google/boringssl/ssl/d1_both.cc
new file mode 100644
index 00000000000..8f141cad022
--- /dev/null
+++ b/contrib/restricted/google/boringssl/ssl/d1_both.cc
@@ -0,0 +1,827 @@
+/*
+ * DTLS implementation written by Nagendra Modadugu
+ * ([email protected]) for the OpenSSL project 2005.
+ */
+/* ====================================================================
+ * Copyright (c) 1998-2005 The OpenSSL Project.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. All advertising materials mentioning features or use of this
+ *    software must display the following acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
+ *
+ * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
+ *    endorse or promote products derived from this software without
+ *    prior written permission. For written permission, please contact
+ *    [email protected].
+ *
+ * 5. Products derived from this software may not be called "OpenSSL"
+ *    nor may "OpenSSL" appear in their names without prior written
+ *    permission of the OpenSSL Project.
+ *
+ * 6. Redistributions of any form whatsoever must retain the following
+ *    acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
+ * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This product includes cryptographic software written by Eric Young
+ * ([email protected]).  This product includes software written by Tim
+ * Hudson ([email protected]).
+ *
+ */
+/* Copyright (C) 1995-1998 Eric Young ([email protected])
+ * All rights reserved.
+ *
+ * This package is an SSL implementation written
+ * by Eric Young ([email protected]).
+ * The implementation was written so as to conform with Netscapes SSL.
+ *
+ * This library is free for commercial and non-commercial use as long as
+ * the following conditions are aheared to.  The following conditions
+ * apply to all code found in this distribution, be it the RC4, RSA,
+ * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
+ * included with this distribution is covered by the same copyright terms
+ * except that the holder is Tim Hudson ([email protected]).
+ *
+ * Copyright remains Eric Young's, and as such any Copyright notices in
+ * the code are not to be removed.
+ * If this package is used in a product, Eric Young should be given attribution
+ * as the author of the parts of the library used.
+ * This can be in the form of a textual message at program startup or
+ * in documentation (online or textual) provided with the package.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *    "This product includes cryptographic software written by
+ *     Eric Young ([email protected])"
+ *    The word 'cryptographic' can be left out if the rouines from the library
+ *    being used are not cryptographic related :-).
+ * 4. If you include any Windows specific code (or a derivative thereof) from
+ *    the apps directory (application code) you must include an acknowledgement:
+ *    "This product includes software written by Tim Hudson ([email protected])"
+ *
+ * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * The licence and distribution terms for any publically available version or
+ * derivative of this code cannot be changed.  i.e. this code cannot simply be
+ * copied and put under another distribution licence
+ * [including the GNU Public Licence.] */
+
+#include <contrib/restricted/google/boringssl/include/openssl/ssl.h>
+
+#include <assert.h>
+#include <limits.h>
+#include <string.h>
+
+#include <contrib/restricted/google/boringssl/include/openssl/err.h>
+#include <contrib/restricted/google/boringssl/include/openssl/evp.h>
+#include <contrib/restricted/google/boringssl/include/openssl/mem.h>
+#include <contrib/restricted/google/boringssl/include/openssl/rand.h>
+
+#include "../crypto/internal.h"
+#include "internal.h"
+
+
+BSSL_NAMESPACE_BEGIN
+
+// TODO(davidben): 28 comes from the size of IP + UDP header. Is this reasonable
+// for these values? Notably, why is kMinMTU a function of the transport
+// protocol's overhead rather than, say, what's needed to hold a minimally-sized
+// handshake fragment plus protocol overhead.
+
+// kMinMTU is the minimum acceptable MTU value.
+static const unsigned int kMinMTU = 256 - 28;
+
+// kDefaultMTU is the default MTU value to use if neither the user nor
+// the underlying BIO supplies one.
+static const unsigned int kDefaultMTU = 1500 - 28;
+
+
+// Receiving handshake messages.
+
+hm_fragment::~hm_fragment() {
+  OPENSSL_free(data);
+  OPENSSL_free(reassembly);
+}
+
+static UniquePtr<hm_fragment> dtls1_hm_fragment_new(
+    const struct hm_header_st *msg_hdr) {
+  ScopedCBB cbb;
+  UniquePtr<hm_fragment> frag = MakeUnique<hm_fragment>();
+  if (!frag) {
+    return nullptr;
+  }
+  frag->type = msg_hdr->type;
+  frag->seq = msg_hdr->seq;
+  frag->msg_len = msg_hdr->msg_len;
+
+  // Allocate space for the reassembled message and fill in the header.
+  frag->data =
+      (uint8_t *)OPENSSL_malloc(DTLS1_HM_HEADER_LENGTH + msg_hdr->msg_len);
+  if (frag->data == NULL) {
+    return nullptr;
+  }
+
+  if (!CBB_init_fixed(cbb.get(), frag->data, DTLS1_HM_HEADER_LENGTH) ||
+      !CBB_add_u8(cbb.get(), msg_hdr->type) ||
+      !CBB_add_u24(cbb.get(), msg_hdr->msg_len) ||
+      !CBB_add_u16(cbb.get(), msg_hdr->seq) ||
+      !CBB_add_u24(cbb.get(), 0 /* frag_off */) ||
+      !CBB_add_u24(cbb.get(), msg_hdr->msg_len) ||
+      !CBB_finish(cbb.get(), NULL, NULL)) {
+    return nullptr;
+  }
+
+  // If the handshake message is empty, |frag->reassembly| is NULL.
+  if (msg_hdr->msg_len > 0) {
+    // Initialize reassembly bitmask.
+    if (msg_hdr->msg_len + 7 < msg_hdr->msg_len) {
+      OPENSSL_PUT_ERROR(SSL, ERR_R_OVERFLOW);
+      return nullptr;
+    }
+    size_t bitmask_len = (msg_hdr->msg_len + 7) / 8;
+    frag->reassembly = (uint8_t *)OPENSSL_zalloc(bitmask_len);
+    if (frag->reassembly == NULL) {
+      return nullptr;
+    }
+  }
+
+  return frag;
+}
+
+// bit_range returns a |uint8_t| with bits |start|, inclusive, to |end|,
+// exclusive, set.
+static uint8_t bit_range(size_t start, size_t end) {
+  return (uint8_t)(~((1u << start) - 1) & ((1u << end) - 1));
+}
+
+// dtls1_hm_fragment_mark marks bytes |start|, inclusive, to |end|, exclusive,
+// as received in |frag|. If |frag| becomes complete, it clears
+// |frag->reassembly|. The range must be within the bounds of |frag|'s message
+// and |frag->reassembly| must not be NULL.
+static void dtls1_hm_fragment_mark(hm_fragment *frag, size_t start,
+                                   size_t end) {
+  size_t msg_len = frag->msg_len;
+
+  if (frag->reassembly == NULL || start > end || end > msg_len) {
+    assert(0);
+    return;
+  }
+  // A zero-length message will never have a pending reassembly.
+  assert(msg_len > 0);
+
+  if (start == end) {
+    return;
+  }
+
+  if ((start >> 3) == (end >> 3)) {
+    frag->reassembly[start >> 3] |= bit_range(start & 7, end & 7);
+  } else {
+    frag->reassembly[start >> 3] |= bit_range(start & 7, 8);
+    for (size_t i = (start >> 3) + 1; i < (end >> 3); i++) {
+      frag->reassembly[i] = 0xff;
+    }
+    if ((end & 7) != 0) {
+      frag->reassembly[end >> 3] |= bit_range(0, end & 7);
+    }
+  }
+
+  // Check if the fragment is complete.
+  for (size_t i = 0; i < (msg_len >> 3); i++) {
+    if (frag->reassembly[i] != 0xff) {
+      return;
+    }
+  }
+  if ((msg_len & 7) != 0 &&
+      frag->reassembly[msg_len >> 3] != bit_range(0, msg_len & 7)) {
+    return;
+  }
+
+  OPENSSL_free(frag->reassembly);
+  frag->reassembly = NULL;
+}
+
+// dtls1_is_current_message_complete returns whether the current handshake
+// message is complete.
+static bool dtls1_is_current_message_complete(const SSL *ssl) {
+  size_t idx = ssl->d1->handshake_read_seq % SSL_MAX_HANDSHAKE_FLIGHT;
+  hm_fragment *frag = ssl->d1->incoming_messages[idx].get();
+  return frag != NULL && frag->reassembly == NULL;
+}
+
+// dtls1_get_incoming_message returns the incoming message corresponding to
+// |msg_hdr|. If none exists, it creates a new one and inserts it in the
+// queue. Otherwise, it checks |msg_hdr| is consistent with the existing one. It
+// returns NULL on failure. The caller does not take ownership of the result.
+static hm_fragment *dtls1_get_incoming_message(
+    SSL *ssl, uint8_t *out_alert, const struct hm_header_st *msg_hdr) {
+  if (msg_hdr->seq < ssl->d1->handshake_read_seq ||
+      msg_hdr->seq - ssl->d1->handshake_read_seq >= SSL_MAX_HANDSHAKE_FLIGHT) {
+    *out_alert = SSL_AD_INTERNAL_ERROR;
+    return NULL;
+  }
+
+  size_t idx = msg_hdr->seq % SSL_MAX_HANDSHAKE_FLIGHT;
+  hm_fragment *frag = ssl->d1->incoming_messages[idx].get();
+  if (frag != NULL) {
+    assert(frag->seq == msg_hdr->seq);
+    // The new fragment must be compatible with the previous fragments from this
+    // message.
+    if (frag->type != msg_hdr->type ||
+        frag->msg_len != msg_hdr->msg_len) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_FRAGMENT_MISMATCH);
+      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
+      return NULL;
+    }
+    return frag;
+  }
+
+  // This is the first fragment from this message.
+  ssl->d1->incoming_messages[idx] = dtls1_hm_fragment_new(msg_hdr);
+  if (!ssl->d1->incoming_messages[idx]) {
+    *out_alert = SSL_AD_INTERNAL_ERROR;
+    return NULL;
+  }
+  return ssl->d1->incoming_messages[idx].get();
+}
+
+ssl_open_record_t dtls1_open_handshake(SSL *ssl, size_t *out_consumed,
+                                       uint8_t *out_alert, Span<uint8_t> in) {
+  uint8_t type;
+  Span<uint8_t> record;
+  auto ret = dtls_open_record(ssl, &type, &record, out_consumed, out_alert, in);
+  if (ret != ssl_open_record_success) {
+    return ret;
+  }
+
+  switch (type) {
+    case SSL3_RT_APPLICATION_DATA:
+      // Unencrypted application data records are always illegal.
+      if (ssl->s3->aead_read_ctx->is_null_cipher()) {
+        OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_RECORD);
+        *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
+        return ssl_open_record_error;
+      }
+
+      // Out-of-order application data may be received between ChangeCipherSpec
+      // and finished. Discard it.
+      return ssl_open_record_discard;
+
+    case SSL3_RT_CHANGE_CIPHER_SPEC:
+      // We do not support renegotiation, so encrypted ChangeCipherSpec records
+      // are illegal.
+      if (!ssl->s3->aead_read_ctx->is_null_cipher()) {
+        OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_RECORD);
+        *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
+        return ssl_open_record_error;
+      }
+
+      if (record.size() != 1u || record[0] != SSL3_MT_CCS) {
+        OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_CHANGE_CIPHER_SPEC);
+        *out_alert = SSL_AD_ILLEGAL_PARAMETER;
+        return ssl_open_record_error;
+      }
+
+      // Flag the ChangeCipherSpec for later.
+      ssl->d1->has_change_cipher_spec = true;
+      ssl_do_msg_callback(ssl, 0 /* read */, SSL3_RT_CHANGE_CIPHER_SPEC,
+                          record);
+      return ssl_open_record_success;
+
+    case SSL3_RT_HANDSHAKE:
+      // Break out to main processing.
+      break;
+
+    default:
+      OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_RECORD);
+      *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
+      return ssl_open_record_error;
+  }
+
+  CBS cbs;
+  CBS_init(&cbs, record.data(), record.size());
+  while (CBS_len(&cbs) > 0) {
+    // Read a handshake fragment.
+    struct hm_header_st msg_hdr;
+    CBS body;
+    if (!dtls1_parse_fragment(&cbs, &msg_hdr, &body)) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_HANDSHAKE_RECORD);
+      *out_alert = SSL_AD_DECODE_ERROR;
+      return ssl_open_record_error;
+    }
+
+    const size_t frag_off = msg_hdr.frag_off;
+    const size_t frag_len = msg_hdr.frag_len;
+    const size_t msg_len = msg_hdr.msg_len;
+    if (frag_off > msg_len || frag_off + frag_len < frag_off ||
+        frag_off + frag_len > msg_len ||
+        msg_len > ssl_max_handshake_message_len(ssl)) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_EXCESSIVE_MESSAGE_SIZE);
+      *out_alert = SSL_AD_ILLEGAL_PARAMETER;
+      return ssl_open_record_error;
+    }
+
+    // The encrypted epoch in DTLS has only one handshake message.
+    if (ssl->d1->r_epoch == 1 && msg_hdr.seq != ssl->d1->handshake_read_seq) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_RECORD);
+      *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
+      return ssl_open_record_error;
+    }
+
+    if (msg_hdr.seq < ssl->d1->handshake_read_seq ||
+        msg_hdr.seq >
+            (unsigned)ssl->d1->handshake_read_seq + SSL_MAX_HANDSHAKE_FLIGHT) {
+      // Ignore fragments from the past, or ones too far in the future.
+      continue;
+    }
+
+    hm_fragment *frag = dtls1_get_incoming_message(ssl, out_alert, &msg_hdr);
+    if (frag == NULL) {
+      return ssl_open_record_error;
+    }
+    assert(frag->msg_len == msg_len);
+
+    if (frag->reassembly == NULL) {
+      // The message is already assembled.
+      continue;
+    }
+    assert(msg_len > 0);
+
+    // Copy the body into the fragment.
+    OPENSSL_memcpy(frag->data + DTLS1_HM_HEADER_LENGTH + frag_off,
+                   CBS_data(&body), CBS_len(&body));
+    dtls1_hm_fragment_mark(frag, frag_off, frag_off + frag_len);
+  }
+
+  return ssl_open_record_success;
+}
+
+bool dtls1_get_message(const SSL *ssl, SSLMessage *out) {
+  if (!dtls1_is_current_message_complete(ssl)) {
+    return false;
+  }
+
+  size_t idx = ssl->d1->handshake_read_seq % SSL_MAX_HANDSHAKE_FLIGHT;
+  hm_fragment *frag = ssl->d1->incoming_messages[idx].get();
+  out->type = frag->type;
+  CBS_init(&out->body, frag->data + DTLS1_HM_HEADER_LENGTH, frag->msg_len);
+  CBS_init(&out->raw, frag->data, DTLS1_HM_HEADER_LENGTH + frag->msg_len);
+  out->is_v2_hello = false;
+  if (!ssl->s3->has_message) {
+    ssl_do_msg_callback(ssl, 0 /* read */, SSL3_RT_HANDSHAKE, out->raw);
+    ssl->s3->has_message = true;
+  }
+  return true;
+}
+
+void dtls1_next_message(SSL *ssl) {
+  assert(ssl->s3->has_message);
+  assert(dtls1_is_current_message_complete(ssl));
+  size_t index = ssl->d1->handshake_read_seq % SSL_MAX_HANDSHAKE_FLIGHT;
+  ssl->d1->incoming_messages[index].reset();
+  ssl->d1->handshake_read_seq++;
+  ssl->s3->has_message = false;
+  // If we previously sent a flight, mark it as having a reply, so
+  // |on_handshake_complete| can manage post-handshake retransmission.
+  if (ssl->d1->outgoing_messages_complete) {
+    ssl->d1->flight_has_reply = true;
+  }
+}
+
+bool dtls_has_unprocessed_handshake_data(const SSL *ssl) {
+  size_t current = ssl->d1->handshake_read_seq % SSL_MAX_HANDSHAKE_FLIGHT;
+  for (size_t i = 0; i < SSL_MAX_HANDSHAKE_FLIGHT; i++) {
+    // Skip the current message.
+    if (ssl->s3->has_message && i == current) {
+      assert(dtls1_is_current_message_complete(ssl));
+      continue;
+    }
+    if (ssl->d1->incoming_messages[i] != nullptr) {
+      return true;
+    }
+  }
+  return false;
+}
+
+bool dtls1_parse_fragment(CBS *cbs, struct hm_header_st *out_hdr,
+                          CBS *out_body) {
+  OPENSSL_memset(out_hdr, 0x00, sizeof(struct hm_header_st));
+
+  if (!CBS_get_u8(cbs, &out_hdr->type) ||
+      !CBS_get_u24(cbs, &out_hdr->msg_len) ||
+      !CBS_get_u16(cbs, &out_hdr->seq) ||
+      !CBS_get_u24(cbs, &out_hdr->frag_off) ||
+      !CBS_get_u24(cbs, &out_hdr->frag_len) ||
+      !CBS_get_bytes(cbs, out_body, out_hdr->frag_len)) {
+    return false;
+  }
+
+  return true;
+}
+
+ssl_open_record_t dtls1_open_change_cipher_spec(SSL *ssl, size_t *out_consumed,
+                                                uint8_t *out_alert,
+                                                Span<uint8_t> in) {
+  if (!ssl->d1->has_change_cipher_spec) {
+    // dtls1_open_handshake processes both handshake and ChangeCipherSpec.
+    auto ret = dtls1_open_handshake(ssl, out_consumed, out_alert, in);
+    if (ret != ssl_open_record_success) {
+      return ret;
+    }
+  }
+  if (ssl->d1->has_change_cipher_spec) {
+    ssl->d1->has_change_cipher_spec = false;
+    return ssl_open_record_success;
+  }
+  return ssl_open_record_discard;
+}
+
+
+// Sending handshake messages.
+
+void DTLS_OUTGOING_MESSAGE::Clear() { data.Reset(); }
+
+void dtls_clear_outgoing_messages(SSL *ssl) {
+  for (size_t i = 0; i < ssl->d1->outgoing_messages_len; i++) {
+    ssl->d1->outgoing_messages[i].Clear();
+  }
+  ssl->d1->outgoing_messages_len = 0;
+  ssl->d1->outgoing_written = 0;
+  ssl->d1->outgoing_offset = 0;
+  ssl->d1->outgoing_messages_complete = false;
+  ssl->d1->flight_has_reply = false;
+}
+
+bool dtls1_init_message(const SSL *ssl, CBB *cbb, CBB *body, uint8_t type) {
+  // Pick a modest size hint to save most of the |realloc| calls.
+  if (!CBB_init(cbb, 64) ||
+      !CBB_add_u8(cbb, type) ||
+      !CBB_add_u24(cbb, 0 /* length (filled in later) */) ||
+      !CBB_add_u16(cbb, ssl->d1->handshake_write_seq) ||
+      !CBB_add_u24(cbb, 0 /* offset */) ||
+      !CBB_add_u24_length_prefixed(cbb, body)) {
+    return false;
+  }
+
+  return true;
+}
+
+bool dtls1_finish_message(const SSL *ssl, CBB *cbb, Array<uint8_t> *out_msg) {
+  if (!CBBFinishArray(cbb, out_msg) ||
+      out_msg->size() < DTLS1_HM_HEADER_LENGTH) {
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return false;
+  }
+
+  // Fix up the header. Copy the fragment length into the total message
+  // length.
+  OPENSSL_memcpy(out_msg->data() + 1,
+                 out_msg->data() + DTLS1_HM_HEADER_LENGTH - 3, 3);
+  return true;
+}
+
+// ssl_size_t_greater_than_32_bits returns whether |v| exceeds the bounds of a
+// 32-bit value. The obvious thing doesn't work because, in some 32-bit build
+// configurations, the compiler warns that the test is always false and breaks
+// the build.
+static bool ssl_size_t_greater_than_32_bits(size_t v) {
+#if defined(OPENSSL_64_BIT)
+  return v > 0xffffffff;
+#elif defined(OPENSSL_32_BIT)
+  return false;
+#else
+#error "Building for neither 32- nor 64-bits."
+#endif
+}
+
+// add_outgoing adds a new handshake message or ChangeCipherSpec to the current
+// outgoing flight. It returns true on success and false on error.
+static bool add_outgoing(SSL *ssl, bool is_ccs, Array<uint8_t> data) {
+  if (ssl->d1->outgoing_messages_complete) {
+    // If we've begun writing a new flight, we received the peer flight. Discard
+    // the timer and the our flight.
+    dtls1_stop_timer(ssl);
+    dtls_clear_outgoing_messages(ssl);
+  }
+
+  static_assert(SSL_MAX_HANDSHAKE_FLIGHT <
+                    (1 << 8 * sizeof(ssl->d1->outgoing_messages_len)),
+                "outgoing_messages_len is too small");
+  if (ssl->d1->outgoing_messages_len >= SSL_MAX_HANDSHAKE_FLIGHT ||
+      ssl_size_t_greater_than_32_bits(data.size())) {
+    assert(false);
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return false;
+  }
+
+  if (!is_ccs) {
+    // TODO(svaldez): Move this up a layer to fix abstraction for SSLTranscript
+    // on hs.
+    if (ssl->s3->hs != NULL &&
+        !ssl->s3->hs->transcript.Update(data)) {
+      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+      return false;
+    }
+    ssl->d1->handshake_write_seq++;
+  }
+
+  DTLS_OUTGOING_MESSAGE *msg =
+      &ssl->d1->outgoing_messages[ssl->d1->outgoing_messages_len];
+  msg->data = std::move(data);
+  msg->epoch = ssl->d1->w_epoch;
+  msg->is_ccs = is_ccs;
+
+  ssl->d1->outgoing_messages_len++;
+  return true;
+}
+
+bool dtls1_add_message(SSL *ssl, Array<uint8_t> data) {
+  return add_outgoing(ssl, false /* handshake */, std::move(data));
+}
+
+bool dtls1_add_change_cipher_spec(SSL *ssl) {
+  return add_outgoing(ssl, true /* ChangeCipherSpec */, Array<uint8_t>());
+}
+
+// dtls1_update_mtu updates the current MTU from the BIO, ensuring it is above
+// the minimum.
+static void dtls1_update_mtu(SSL *ssl) {
+  // TODO(davidben): No consumer implements |BIO_CTRL_DGRAM_SET_MTU| and the
+  // only |BIO_CTRL_DGRAM_QUERY_MTU| implementation could use
+  // |SSL_set_mtu|. Does this need to be so complex?
+  if (ssl->d1->mtu < dtls1_min_mtu() &&
+      !(SSL_get_options(ssl) & SSL_OP_NO_QUERY_MTU)) {
+    long mtu = BIO_ctrl(ssl->wbio.get(), BIO_CTRL_DGRAM_QUERY_MTU, 0, NULL);
+    if (mtu >= 0 && mtu <= (1 << 30) && (unsigned)mtu >= dtls1_min_mtu()) {
+      ssl->d1->mtu = (unsigned)mtu;
+    } else {
+      ssl->d1->mtu = kDefaultMTU;
+      BIO_ctrl(ssl->wbio.get(), BIO_CTRL_DGRAM_SET_MTU, ssl->d1->mtu, NULL);
+    }
+  }
+
+  // The MTU should be above the minimum now.
+  assert(ssl->d1->mtu >= dtls1_min_mtu());
+}
+
+enum seal_result_t {
+  seal_error,
+  seal_no_progress,
+  seal_partial,
+  seal_success,
+};
+
+// seal_next_message seals |msg|, which must be the next message, to |out|. If
+// progress was made, it returns |seal_partial| or |seal_success| and sets
+// |*out_len| to the number of bytes written.
+static enum seal_result_t seal_next_message(SSL *ssl, uint8_t *out,
+                                            size_t *out_len, size_t max_out,
+                                            const DTLS_OUTGOING_MESSAGE *msg) {
+  assert(ssl->d1->outgoing_written < ssl->d1->outgoing_messages_len);
+  assert(msg == &ssl->d1->outgoing_messages[ssl->d1->outgoing_written]);
+
+  enum dtls1_use_epoch_t use_epoch = dtls1_use_current_epoch;
+  if (ssl->d1->w_epoch >= 1 && msg->epoch == ssl->d1->w_epoch - 1) {
+    use_epoch = dtls1_use_previous_epoch;
+  } else if (msg->epoch != ssl->d1->w_epoch) {
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return seal_error;
+  }
+
+  size_t overhead = dtls_max_seal_overhead(ssl, use_epoch);
+  size_t prefix = dtls_seal_prefix_len(ssl, use_epoch);
+
+  if (msg->is_ccs) {
+    // Check there is room for the ChangeCipherSpec.
+    static const uint8_t kChangeCipherSpec[1] = {SSL3_MT_CCS};
+    if (max_out < sizeof(kChangeCipherSpec) + overhead) {
+      return seal_no_progress;
+    }
+
+    if (!dtls_seal_record(ssl, out, out_len, max_out,
+                          SSL3_RT_CHANGE_CIPHER_SPEC, kChangeCipherSpec,
+                          sizeof(kChangeCipherSpec), use_epoch)) {
+      return seal_error;
+    }
+
+    ssl_do_msg_callback(ssl, 1 /* write */, SSL3_RT_CHANGE_CIPHER_SPEC,
+                        kChangeCipherSpec);
+    return seal_success;
+  }
+
+  // DTLS messages are serialized as a single fragment in |msg|.
+  CBS cbs, body;
+  struct hm_header_st hdr;
+  CBS_init(&cbs, msg->data.data(), msg->data.size());
+  if (!dtls1_parse_fragment(&cbs, &hdr, &body) ||
+      hdr.frag_off != 0 ||
+      hdr.frag_len != CBS_len(&body) ||
+      hdr.msg_len != CBS_len(&body) ||
+      !CBS_skip(&body, ssl->d1->outgoing_offset) ||
+      CBS_len(&cbs) != 0) {
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return seal_error;
+  }
+
+  // Determine how much progress can be made.
+  if (max_out < DTLS1_HM_HEADER_LENGTH + 1 + overhead || max_out < prefix) {
+    return seal_no_progress;
+  }
+  size_t todo = CBS_len(&body);
+  if (todo > max_out - DTLS1_HM_HEADER_LENGTH - overhead) {
+    todo = max_out - DTLS1_HM_HEADER_LENGTH - overhead;
+  }
+
+  // Assemble a fragment, to be sealed in-place.
+  ScopedCBB cbb;
+  CBB child;
+  uint8_t *frag = out + prefix;
+  size_t max_frag = max_out - prefix, frag_len;
+  if (!CBB_init_fixed(cbb.get(), frag, max_frag) ||
+      !CBB_add_u8(cbb.get(), hdr.type) ||
+      !CBB_add_u24(cbb.get(), hdr.msg_len) ||
+      !CBB_add_u16(cbb.get(), hdr.seq) ||
+      !CBB_add_u24(cbb.get(), ssl->d1->outgoing_offset) ||
+      !CBB_add_u24_length_prefixed(cbb.get(), &child) ||
+      !CBB_add_bytes(&child, CBS_data(&body), todo) ||
+      !CBB_finish(cbb.get(), NULL, &frag_len)) {
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return seal_error;
+  }
+
+  ssl_do_msg_callback(ssl, 1 /* write */, SSL3_RT_HANDSHAKE,
+                      MakeSpan(frag, frag_len));
+
+  if (!dtls_seal_record(ssl, out, out_len, max_out, SSL3_RT_HANDSHAKE,
+                        out + prefix, frag_len, use_epoch)) {
+    return seal_error;
+  }
+
+  if (todo == CBS_len(&body)) {
+    // The next message is complete.
+    ssl->d1->outgoing_offset = 0;
+    return seal_success;
+  }
+
+  ssl->d1->outgoing_offset += todo;
+  return seal_partial;
+}
+
+// seal_next_packet writes as much of the next flight as possible to |out| and
+// advances |ssl->d1->outgoing_written| and |ssl->d1->outgoing_offset| as
+// appropriate.
+static bool seal_next_packet(SSL *ssl, uint8_t *out, size_t *out_len,
+                             size_t max_out) {
+  bool made_progress = false;
+  size_t total = 0;
+  assert(ssl->d1->outgoing_written < ssl->d1->outgoing_messages_len);
+  for (; ssl->d1->outgoing_written < ssl->d1->outgoing_messages_len;
+       ssl->d1->outgoing_written++) {
+    const DTLS_OUTGOING_MESSAGE *msg =
+        &ssl->d1->outgoing_messages[ssl->d1->outgoing_written];
+    size_t len;
+    enum seal_result_t ret = seal_next_message(ssl, out, &len, max_out, msg);
+    switch (ret) {
+      case seal_error:
+        return false;
+
+      case seal_no_progress:
+        goto packet_full;
+
+      case seal_partial:
+      case seal_success:
+        out += len;
+        max_out -= len;
+        total += len;
+        made_progress = true;
+
+        if (ret == seal_partial) {
+          goto packet_full;
+        }
+        break;
+    }
+  }
+
+packet_full:
+  // The MTU was too small to make any progress.
+  if (!made_progress) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_MTU_TOO_SMALL);
+    return false;
+  }
+
+  *out_len = total;
+  return true;
+}
+
+static int send_flight(SSL *ssl) {
+  if (ssl->s3->write_shutdown != ssl_shutdown_none) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_PROTOCOL_IS_SHUTDOWN);
+    return -1;
+  }
+
+  if (ssl->wbio == nullptr) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_BIO_NOT_SET);
+    return -1;
+  }
+
+  dtls1_update_mtu(ssl);
+
+  Array<uint8_t> packet;
+  if (!packet.Init(ssl->d1->mtu)) {
+    return -1;
+  }
+
+  while (ssl->d1->outgoing_written < ssl->d1->outgoing_messages_len) {
+    uint8_t old_written = ssl->d1->outgoing_written;
+    uint32_t old_offset = ssl->d1->outgoing_offset;
+
+    size_t packet_len;
+    if (!seal_next_packet(ssl, packet.data(), &packet_len, packet.size())) {
+      return -1;
+    }
+
+    int bio_ret = BIO_write(ssl->wbio.get(), packet.data(), packet_len);
+    if (bio_ret <= 0) {
+      // Retry this packet the next time around.
+      ssl->d1->outgoing_written = old_written;
+      ssl->d1->outgoing_offset = old_offset;
+      ssl->s3->rwstate = SSL_ERROR_WANT_WRITE;
+      return bio_ret;
+    }
+  }
+
+  if (BIO_flush(ssl->wbio.get()) <= 0) {
+    ssl->s3->rwstate = SSL_ERROR_WANT_WRITE;
+    return -1;
+  }
+
+  return 1;
+}
+
+int dtls1_flush_flight(SSL *ssl) {
+  ssl->d1->outgoing_messages_complete = true;
+  // Start the retransmission timer for the next flight (if any).
+  dtls1_start_timer(ssl);
+  return send_flight(ssl);
+}
+
+int dtls1_retransmit_outgoing_messages(SSL *ssl) {
+  // Rewind to the start of the flight and write it again.
+  //
+  // TODO(davidben): This does not allow retransmits to be resumed on
+  // non-blocking write.
+  ssl->d1->outgoing_written = 0;
+  ssl->d1->outgoing_offset = 0;
+
+  return send_flight(ssl);
+}
+
+unsigned int dtls1_min_mtu(void) {
+  return kMinMTU;
+}
+
+BSSL_NAMESPACE_END