root/net/quic/quic_framer.cc

DEFINITIONS

1. Delta
2. ClosestTo
3. ReadSequenceNumberLength
4. CanTruncate
5. OnWindowUpdateFrame
6. OnBlockedFrame
7. creation_time_
8. GetMinStreamFrameSize
9. GetMinAckFrameSize
10. GetStopWaitingFrameSize
11. GetMinRstStreamFrameSize
12. GetMinConnectionCloseFrameSize
13. GetMinGoAwayFrameSize
14. GetWindowUpdateFrameSize
15. GetBlockedFrameSize
16. GetStreamIdSize
17. GetStreamOffsetSize
18. GetVersionNegotiationPacketSize
19. IsSupportedVersion
20. GetSerializedFrameLength
21. GetPacketEntropyHash
22. BuildUnsizedDataPacket
23. BuildDataPacket
24. BuildFecPacket
25. BuildPublicResetPacket
26. BuildVersionNegotiationPacket
27. ProcessPacket
28. ProcessVersionNegotiationPacket
29. ProcessDataPacket
30. ProcessPublicResetPacket
31. ProcessRevivedPacket
32. AppendPacketHeader
33. CalculatePacketSequenceNumberFromWire
34. ProcessPublicHeader
35. GetMinSequenceNumberLength
36. GetSequenceNumberFlags
37. GetAckFrameInfo
38. ProcessPacketHeader
39. ProcessPacketSequenceNumber
40. ProcessFrameData
41. ProcessStreamFrame
42. ProcessAckFrame
43. ProcessReceivedInfo
44. ProcessStopWaitingFrame
45. ProcessQuicCongestionFeedbackFrame
46. ProcessRstStreamFrame
47. ProcessConnectionCloseFrame
48. ProcessGoAwayFrame
49. ProcessWindowUpdateFrame
50. ProcessBlockedFrame
51. GetAssociatedDataFromEncryptedPacket
52. SetDecrypter
53. SetAlternativeDecrypter
54. decrypter
55. alternative_decrypter
56. SetEncrypter
57. encrypter
58. SwapCryptersForTest
59. EncryptPacket
60. GetMaxPlaintextSize
61. DecryptPayload
62. GetAckFrameSize
63. ComputeFrameLength
64. AppendTypeByte
65. AppendPacketSequenceNumber
66. AppendStreamFrame
67. set_version
68. AppendAckFrameAndTypeByte
69. AppendCongestionFeedbackFrame
70. AppendStopWaitingFrame
71. AppendRstStreamFrame
72. AppendConnectionCloseFrame
73. AppendGoAwayFrame
74. AppendWindowUpdateFrame
75. AppendBlockedFrame
76. RaiseError

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/quic/quic_framer.h"

#include "base/containers/hash_tables.h"
#include "base/stl_util.h"
#include "net/quic/crypto/crypto_framer.h"
#include "net/quic/crypto/crypto_handshake_message.h"
#include "net/quic/crypto/crypto_protocol.h"
#include "net/quic/crypto/quic_decrypter.h"
#include "net/quic/crypto/quic_encrypter.h"
#include "net/quic/quic_data_reader.h"
#include "net/quic/quic_data_writer.h"
#include "net/quic/quic_flags.h"
#include "net/quic/quic_socket_address_coder.h"

using base::StringPiece;
using std::make_pair;
using std::map;
using std::max;
using std::min;
using std::numeric_limits;
using std::string;

namespace net {

namespace {

// Mask to select the lowest 48 bits of a sequence number.
const QuicPacketSequenceNumber k6ByteSequenceNumberMask =
    GG_UINT64_C(0x0000FFFFFFFFFFFF);
const QuicPacketSequenceNumber k4ByteSequenceNumberMask =
    GG_UINT64_C(0x00000000FFFFFFFF);
const QuicPacketSequenceNumber k2ByteSequenceNumberMask =
    GG_UINT64_C(0x000000000000FFFF);
const QuicPacketSequenceNumber k1ByteSequenceNumberMask =
    GG_UINT64_C(0x00000000000000FF);

const QuicConnectionId k1ByteConnectionIdMask = GG_UINT64_C(0x00000000000000FF);
const QuicConnectionId k4ByteConnectionIdMask = GG_UINT64_C(0x00000000FFFFFFFF);

// Number of bits the sequence number length bits are shifted from the right
// edge of the public header.
const uint8 kPublicHeaderSequenceNumberShift = 4;

// New Frame Types, QUIC v. >= 10:
// There are two interpretations for the Frame Type byte in the QUIC protocol,
// resulting in two Frame Types: Special Frame Types and Regular Frame Types.
//
// Regular Frame Types use the Frame Type byte simply. Currently defined
// Regular Frame Types are:
// Padding            : 0b 00000000 (0x00)
// ResetStream        : 0b 00000001 (0x01)
// ConnectionClose    : 0b 00000010 (0x02)
// GoAway             : 0b 00000011 (0x03)
// WindowUpdate       : 0b 00000100 (0x04)
// Blocked            : 0b 00000101 (0x05)
//
// Special Frame Types encode both a Frame Type and corresponding flags
// all in the Frame Type byte. Currently defined Special Frame Types are:
// Stream             : 0b 1xxxxxxx
// Ack                : 0b 01xxxxxx
// CongestionFeedback : 0b 001xxxxx
//
// Semantics of the flag bits above (the x bits) depends on the frame type.

// Masks to determine if the frame type is a special use
// and for specific special frame types.
const uint8 kQuicFrameTypeSpecialMask = 0xE0;  // 0b 11100000
const uint8 kQuicFrameTypeStreamMask = 0x80;
const uint8 kQuicFrameTypeAckMask = 0x40;
const uint8 kQuicFrameTypeCongestionFeedbackMask = 0x20;

// Stream frame relative shifts and masks for interpreting the stream flags.
// StreamID may be 1, 2, 3, or 4 bytes.
const uint8 kQuicStreamIdShift = 2;
const uint8 kQuicStreamIDLengthMask = 0x03;

// Offset may be 0, 2, 3, 4, 5, 6, 7, 8 bytes.
const uint8 kQuicStreamOffsetShift = 3;
const uint8 kQuicStreamOffsetMask = 0x07;

// Data length may be 0 or 2 bytes.
const uint8 kQuicStreamDataLengthShift = 1;
const uint8 kQuicStreamDataLengthMask = 0x01;

// Fin bit may be set or not.
const uint8 kQuicStreamFinShift = 1;
const uint8 kQuicStreamFinMask = 0x01;

// Sequence number size shift used in AckFrames.
const uint8 kQuicSequenceNumberLengthShift = 2;

// Acks may be truncated.
const uint8 kQuicAckTruncatedShift = 1;
const uint8 kQuicAckTruncatedMask = 0x01;

// Acks may not have any nacks.
const uint8 kQuicHasNacksMask = 0x01;

// Returns the absolute value of the difference between |a| and |b|.
QuicPacketSequenceNumber Delta(QuicPacketSequenceNumber a,
                               QuicPacketSequenceNumber b) {
  // Since these are unsigned numbers, we can't just return abs(a - b)
  if (a < b) {
    return b - a;
  }
  return a - b;
}

QuicPacketSequenceNumber ClosestTo(QuicPacketSequenceNumber target,
                                   QuicPacketSequenceNumber a,
                                   QuicPacketSequenceNumber b) {
  return (Delta(target, a) < Delta(target, b)) ? a : b;
}

QuicSequenceNumberLength ReadSequenceNumberLength(uint8 flags) {
  switch (flags & PACKET_FLAGS_6BYTE_SEQUENCE) {
    case PACKET_FLAGS_6BYTE_SEQUENCE:
      return PACKET_6BYTE_SEQUENCE_NUMBER;
    case PACKET_FLAGS_4BYTE_SEQUENCE:
      return PACKET_4BYTE_SEQUENCE_NUMBER;
    case PACKET_FLAGS_2BYTE_SEQUENCE:
      return PACKET_2BYTE_SEQUENCE_NUMBER;
    case PACKET_FLAGS_1BYTE_SEQUENCE:
      return PACKET_1BYTE_SEQUENCE_NUMBER;
    default:
      LOG(DFATAL) << "Unreachable case statement.";
      return PACKET_6BYTE_SEQUENCE_NUMBER;
  }
}

bool CanTruncate(
    QuicVersion version, const QuicFrame& frame, size_t free_bytes) {
  if ((frame.type == ACK_FRAME || frame.type == CONNECTION_CLOSE_FRAME) &&
      free_bytes >=
          QuicFramer::GetMinAckFrameSize(version,
                                         PACKET_6BYTE_SEQUENCE_NUMBER,
                                         PACKET_6BYTE_SEQUENCE_NUMBER)) {
    return true;
  }
  return false;
}

}  // namespace

bool QuicFramerVisitorInterface::OnWindowUpdateFrame(
    const QuicWindowUpdateFrame& frame) {
  return true;
}

bool QuicFramerVisitorInterface::OnBlockedFrame(const QuicBlockedFrame& frame) {
  return true;
}

QuicFramer::QuicFramer(const QuicVersionVector& supported_versions,
                       QuicTime creation_time,
                       bool is_server)
    : visitor_(NULL),
      fec_builder_(NULL),
      entropy_calculator_(NULL),
      error_(QUIC_NO_ERROR),
      last_sequence_number_(0),
      last_serialized_connection_id_(0),
      supported_versions_(supported_versions),
      alternative_decrypter_latch_(false),
      is_server_(is_server),
      validate_flags_(true),
      creation_time_(creation_time) {
  DCHECK(!supported_versions.empty());
  quic_version_ = supported_versions_[0];
  decrypter_.reset(QuicDecrypter::Create(kNULL));
  encrypter_[ENCRYPTION_NONE].reset(
      QuicEncrypter::Create(kNULL));
}

QuicFramer::~QuicFramer() {}

// static
size_t QuicFramer::GetMinStreamFrameSize(QuicVersion version,
                                         QuicStreamId stream_id,
                                         QuicStreamOffset offset,
                                         bool last_frame_in_packet,
                                         InFecGroup is_in_fec_group) {
  bool no_stream_frame_length = last_frame_in_packet &&
                                is_in_fec_group == NOT_IN_FEC_GROUP;
  return kQuicFrameTypeSize + GetStreamIdSize(stream_id) +
      GetStreamOffsetSize(offset) +
      (no_stream_frame_length ? 0 : kQuicStreamPayloadLengthSize);
}

// static
size_t QuicFramer::GetMinAckFrameSize(
    QuicVersion version,
    QuicSequenceNumberLength sequence_number_length,
    QuicSequenceNumberLength largest_observed_length) {
  return kQuicFrameTypeSize + kQuicEntropyHashSize +
      sequence_number_length + kQuicEntropyHashSize +
      largest_observed_length + kQuicDeltaTimeLargestObservedSize;
}

// static
size_t QuicFramer::GetStopWaitingFrameSize(
    QuicSequenceNumberLength sequence_number_length) {
  return kQuicFrameTypeSize + kQuicEntropyHashSize +
      sequence_number_length;
}

// static
size_t QuicFramer::GetMinRstStreamFrameSize(QuicVersion quic_version) {
  if (quic_version > QUIC_VERSION_13) {
    return kQuicFrameTypeSize + kQuicMaxStreamIdSize +
           kQuicMaxStreamOffsetSize + kQuicErrorCodeSize +
           kQuicErrorDetailsLengthSize;
  } else {
    return kQuicFrameTypeSize + kQuicMaxStreamIdSize + kQuicErrorCodeSize +
           kQuicErrorDetailsLengthSize;
  }
}

// static
size_t QuicFramer::GetMinConnectionCloseFrameSize() {
  return kQuicFrameTypeSize + kQuicErrorCodeSize + kQuicErrorDetailsLengthSize;
}

// static
size_t QuicFramer::GetMinGoAwayFrameSize() {
  return kQuicFrameTypeSize + kQuicErrorCodeSize + kQuicErrorDetailsLengthSize +
      kQuicMaxStreamIdSize;
}

// static
size_t QuicFramer::GetWindowUpdateFrameSize() {
  return kQuicFrameTypeSize + kQuicMaxStreamIdSize + kQuicMaxStreamOffsetSize;
}

// static
size_t QuicFramer::GetBlockedFrameSize() {
  return kQuicFrameTypeSize + kQuicMaxStreamIdSize;
}

// static
size_t QuicFramer::GetStreamIdSize(QuicStreamId stream_id) {
  // Sizes are 1 through 4 bytes.
  for (int i = 1; i <= 4; ++i) {
    stream_id >>= 8;
    if (stream_id == 0) {
      return i;
    }
  }
  LOG(DFATAL) << "Failed to determine StreamIDSize.";
  return 4;
}

// static
size_t QuicFramer::GetStreamOffsetSize(QuicStreamOffset offset) {
  // 0 is a special case.
  if (offset == 0) {
    return 0;
  }
  // 2 through 8 are the remaining sizes.
  offset >>= 8;
  for (int i = 2; i <= 8; ++i) {
    offset >>= 8;
    if (offset == 0) {
      return i;
    }
  }
  LOG(DFATAL) << "Failed to determine StreamOffsetSize.";
  return 8;
}

// static
size_t QuicFramer::GetVersionNegotiationPacketSize(size_t number_versions) {
  return kPublicFlagsSize + PACKET_8BYTE_CONNECTION_ID +
      number_versions * kQuicVersionSize;
}

bool QuicFramer::IsSupportedVersion(const QuicVersion version) const {
  for (size_t i = 0; i < supported_versions_.size(); ++i) {
    if (version == supported_versions_[i]) {
      return true;
    }
  }
  return false;
}

size_t QuicFramer::GetSerializedFrameLength(
    const QuicFrame& frame,
    size_t free_bytes,
    bool first_frame,
    bool last_frame,
    InFecGroup is_in_fec_group,
    QuicSequenceNumberLength sequence_number_length) {
  if (frame.type == PADDING_FRAME) {
    // PADDING implies end of packet.
    return free_bytes;
  }
  size_t frame_len =
      ComputeFrameLength(frame, last_frame, is_in_fec_group,
                         sequence_number_length);
  if (frame_len > free_bytes) {
    // Only truncate the first frame in a packet, so if subsequent ones go
    // over, stop including more frames.
    if (!first_frame) {
      return 0;
    }
    if (CanTruncate(quic_version_, frame, free_bytes)) {
      // Truncate the frame so the packet will not exceed kMaxPacketSize.
      // Note that we may not use every byte of the writer in this case.
      DVLOG(1) << "Truncating large frame";
      return free_bytes;
    } else if (!FLAGS_quic_allow_oversized_packets_for_test) {
      return 0;
    }
  }
  return frame_len;
}

QuicFramer::AckFrameInfo::AckFrameInfo() : max_delta(0) { }

QuicFramer::AckFrameInfo::~AckFrameInfo() { }

QuicPacketEntropyHash QuicFramer::GetPacketEntropyHash(
    const QuicPacketHeader& header) const {
  return header.entropy_flag << (header.packet_sequence_number % 8);
}

// Test only.
SerializedPacket QuicFramer::BuildUnsizedDataPacket(
    const QuicPacketHeader& header,
    const QuicFrames& frames) {
  const size_t max_plaintext_size = GetMaxPlaintextSize(kMaxPacketSize);
  size_t packet_size = GetPacketHeaderSize(header);
  for (size_t i = 0; i < frames.size(); ++i) {
    DCHECK_LE(packet_size, max_plaintext_size);
    bool first_frame = i == 0;
    bool last_frame = i == frames.size() - 1;
    const size_t frame_size = GetSerializedFrameLength(
        frames[i], max_plaintext_size - packet_size, first_frame, last_frame,
        header.is_in_fec_group,
        header.public_header.sequence_number_length);
    DCHECK(frame_size);
    packet_size += frame_size;
  }
  return BuildDataPacket(header, frames, packet_size);
}

SerializedPacket QuicFramer::BuildDataPacket(
    const QuicPacketHeader& header,
    const QuicFrames& frames,
    size_t packet_size) {
  QuicDataWriter writer(packet_size);
  const SerializedPacket kNoPacket(
      0, PACKET_1BYTE_SEQUENCE_NUMBER, NULL, 0, NULL);
  if (!AppendPacketHeader(header, &writer)) {
    LOG(DFATAL) << "AppendPacketHeader failed";
    return kNoPacket;
  }

  for (size_t i = 0; i < frames.size(); ++i) {
    const QuicFrame& frame = frames[i];

    // Determine if we should write stream frame length in header.
    const bool no_stream_frame_length =
        (header.is_in_fec_group == NOT_IN_FEC_GROUP) &&
        (i == frames.size() - 1);
    if (!AppendTypeByte(frame, no_stream_frame_length, &writer)) {
      LOG(DFATAL) << "AppendTypeByte failed";
      return kNoPacket;
    }

    switch (frame.type) {
      case PADDING_FRAME:
        writer.WritePadding();
        break;
      case STREAM_FRAME:
        if (!AppendStreamFrame(
            *frame.stream_frame, no_stream_frame_length, &writer)) {
          LOG(DFATAL) << "AppendStreamFrame failed";
          return kNoPacket;
        }
        break;
      case ACK_FRAME:
        if (!AppendAckFrameAndTypeByte(
                header, *frame.ack_frame, &writer)) {
          LOG(DFATAL) << "AppendAckFrameAndTypeByte failed";
          return kNoPacket;
        }
        break;
      case CONGESTION_FEEDBACK_FRAME:
        if (!AppendCongestionFeedbackFrame(
                *frame.congestion_feedback_frame, &writer)) {
          LOG(DFATAL) << "AppendCongestionFeedbackFrame failed";
          return kNoPacket;
        }
        break;
      case STOP_WAITING_FRAME:
        if (quic_version_ <= QUIC_VERSION_15) {
          LOG(DFATAL) << "Attempt to add a StopWaitingFrame in "
                      << QuicVersionToString(quic_version_);
          return kNoPacket;
        }
        if (!AppendStopWaitingFrame(
                header, *frame.stop_waiting_frame, &writer)) {
          LOG(DFATAL) << "AppendStopWaitingFrame failed";
          return kNoPacket;
        }
        break;
      case RST_STREAM_FRAME:
        if (!AppendRstStreamFrame(*frame.rst_stream_frame, &writer)) {
          LOG(DFATAL) << "AppendRstStreamFrame failed";
          return kNoPacket;
        }
        break;
      case CONNECTION_CLOSE_FRAME:
        if (!AppendConnectionCloseFrame(
                *frame.connection_close_frame, &writer)) {
          LOG(DFATAL) << "AppendConnectionCloseFrame failed";
          return kNoPacket;
        }
        break;
      case GOAWAY_FRAME:
        if (!AppendGoAwayFrame(*frame.goaway_frame, &writer)) {
          LOG(DFATAL) << "AppendGoAwayFrame failed";
          return kNoPacket;
        }
        break;
      case WINDOW_UPDATE_FRAME:
        if (quic_version_ > QUIC_VERSION_13) {
          if (!AppendWindowUpdateFrame(*frame.window_update_frame, &writer)) {
            LOG(DFATAL) << "AppendWindowUpdateFrame failed";
            return kNoPacket;
          }
        } else {
          LOG(DFATAL) << "Attempt to add a WindowUpdateFrame in "
                      << QuicVersionToString(quic_version_);
          return kNoPacket;
        }
        break;
      case BLOCKED_FRAME:
        if (quic_version_ > QUIC_VERSION_13) {
          if (!AppendBlockedFrame(*frame.blocked_frame, &writer)) {
            LOG(DFATAL) << "AppendBlockedFrame failed";
            return kNoPacket;
          }
        } else {
          LOG(DFATAL) << "Attempt to add a BlockedFrame in "
                      << QuicVersionToString(quic_version_);
          return kNoPacket;
        }
        break;
      default:
        RaiseError(QUIC_INVALID_FRAME_DATA);
        LOG(DFATAL) << "QUIC_INVALID_FRAME_DATA";
        return kNoPacket;
    }
  }

  // Save the length before writing, because take clears it.
  const size_t len = writer.length();
  // Less than or equal because truncated acks end up with max_plaintex_size
  // length, even though they're typically slightly shorter.
  DCHECK_LE(len, packet_size);
  QuicPacket* packet = QuicPacket::NewDataPacket(
      writer.take(), len, true, header.public_header.connection_id_length,
      header.public_header.version_flag,
      header.public_header.sequence_number_length);

  if (fec_builder_) {
    fec_builder_->OnBuiltFecProtectedPayload(header,
                                             packet->FecProtectedData());
  }

  return SerializedPacket(header.packet_sequence_number,
                          header.public_header.sequence_number_length, packet,
                          GetPacketEntropyHash(header), NULL);
}

SerializedPacket QuicFramer::BuildFecPacket(const QuicPacketHeader& header,
                                            const QuicFecData& fec) {
  DCHECK_EQ(IN_FEC_GROUP, header.is_in_fec_group);
  DCHECK_NE(0u, header.fec_group);
  size_t len = GetPacketHeaderSize(header);
  len += fec.redundancy.length();

  QuicDataWriter writer(len);
  const SerializedPacket kNoPacket(
      0, PACKET_1BYTE_SEQUENCE_NUMBER, NULL, 0, NULL);
  if (!AppendPacketHeader(header, &writer)) {
    LOG(DFATAL) << "AppendPacketHeader failed";
    return kNoPacket;
  }

  if (!writer.WriteBytes(fec.redundancy.data(), fec.redundancy.length())) {
    LOG(DFATAL) << "Failed to add FEC";
    return kNoPacket;
  }

  return SerializedPacket(
      header.packet_sequence_number,
      header.public_header.sequence_number_length,
      QuicPacket::NewFecPacket(writer.take(), len, true,
                               header.public_header.connection_id_length,
                               header.public_header.version_flag,
                               header.public_header.sequence_number_length),
      GetPacketEntropyHash(header), NULL);
}

// static
QuicEncryptedPacket* QuicFramer::BuildPublicResetPacket(
    const QuicPublicResetPacket& packet) {
  DCHECK(packet.public_header.reset_flag);

  CryptoHandshakeMessage reset;
  reset.set_tag(kPRST);
  reset.SetValue(kRNON, packet.nonce_proof);
  reset.SetValue(kRSEQ, packet.rejected_sequence_number);
  if (!packet.client_address.address().empty()) {
    // packet.client_address is non-empty.
    QuicSocketAddressCoder address_coder(packet.client_address);
    string serialized_address = address_coder.Encode();
    if (serialized_address.empty()) {
      return NULL;
    }
    reset.SetStringPiece(kCADR, serialized_address);
  }
  const QuicData& reset_serialized = reset.GetSerialized();

  size_t len =
      kPublicFlagsSize + PACKET_8BYTE_CONNECTION_ID + reset_serialized.length();
  QuicDataWriter writer(len);

  uint8 flags = static_cast<uint8>(PACKET_PUBLIC_FLAGS_RST |
                                   PACKET_PUBLIC_FLAGS_8BYTE_CONNECTION_ID);
  if (!writer.WriteUInt8(flags)) {
    return NULL;
  }

  if (!writer.WriteUInt64(packet.public_header.connection_id)) {
    return NULL;
  }

  if (!writer.WriteBytes(reset_serialized.data(), reset_serialized.length())) {
    return NULL;
  }

  return new QuicEncryptedPacket(writer.take(), len, true);
}

QuicEncryptedPacket* QuicFramer::BuildVersionNegotiationPacket(
    const QuicPacketPublicHeader& header,
    const QuicVersionVector& supported_versions) {
  DCHECK(header.version_flag);
  size_t len = GetVersionNegotiationPacketSize(supported_versions.size());
  QuicDataWriter writer(len);

  uint8 flags = static_cast<uint8>(PACKET_PUBLIC_FLAGS_VERSION |
                                   PACKET_PUBLIC_FLAGS_8BYTE_CONNECTION_ID);
  if (!writer.WriteUInt8(flags)) {
    return NULL;
  }

  if (!writer.WriteUInt64(header.connection_id)) {
    return NULL;
  }

  for (size_t i = 0; i < supported_versions.size(); ++i) {
    if (!writer.WriteUInt32(QuicVersionToQuicTag(supported_versions[i]))) {
      return NULL;
    }
  }

  return new QuicEncryptedPacket(writer.take(), len, true);
}

bool QuicFramer::ProcessPacket(const QuicEncryptedPacket& packet) {
  DCHECK(!reader_.get());
  reader_.reset(new QuicDataReader(packet.data(), packet.length()));

  visitor_->OnPacket();

  // First parse the public header.
  QuicPacketPublicHeader public_header;
  if (!ProcessPublicHeader(&public_header)) {
    DLOG(WARNING) << "Unable to process public header.";
    DCHECK_NE("", detailed_error_);
    return RaiseError(QUIC_INVALID_PACKET_HEADER);
  }

  if (!visitor_->OnUnauthenticatedPublicHeader(public_header)) {
    // The visitor suppresses further processing of the packet.
    reader_.reset(NULL);
    return true;
  }

  if (is_server_ && public_header.version_flag &&
      public_header.versions[0] != quic_version_) {
    if (!visitor_->OnProtocolVersionMismatch(public_header.versions[0])) {
      reader_.reset(NULL);
      return true;
    }
  }

  bool rv;
  if (!is_server_ && public_header.version_flag) {
    rv = ProcessVersionNegotiationPacket(&public_header);
  } else if (public_header.reset_flag) {
    rv = ProcessPublicResetPacket(public_header);
  } else {
    rv = ProcessDataPacket(public_header, packet);
  }

  reader_.reset(NULL);
  return rv;
}

bool QuicFramer::ProcessVersionNegotiationPacket(
    QuicPacketPublicHeader* public_header) {
  DCHECK(!is_server_);
  // Try reading at least once to raise error if the packet is invalid.
  do {
    QuicTag version;
    if (!reader_->ReadBytes(&version, kQuicVersionSize)) {
      set_detailed_error("Unable to read supported version in negotiation.");
      return RaiseError(QUIC_INVALID_VERSION_NEGOTIATION_PACKET);
    }
    public_header->versions.push_back(QuicTagToQuicVersion(version));
  } while (!reader_->IsDoneReading());

  visitor_->OnVersionNegotiationPacket(*public_header);
  return true;
}

bool QuicFramer::ProcessDataPacket(
    const QuicPacketPublicHeader& public_header,
    const QuicEncryptedPacket& packet) {
  QuicPacketHeader header(public_header);
  if (!ProcessPacketHeader(&header, packet)) {
    DLOG(WARNING) << "Unable to process data packet header.";
    return false;
  }

  if (!visitor_->OnPacketHeader(header)) {
    // The visitor suppresses further processing of the packet.
    return true;
  }

  if (packet.length() > kMaxPacketSize) {
    DLOG(WARNING) << "Packet too large: " << packet.length();
    return RaiseError(QUIC_PACKET_TOO_LARGE);
  }

  // Handle the payload.
  if (!header.fec_flag) {
    if (header.is_in_fec_group == IN_FEC_GROUP) {
      StringPiece payload = reader_->PeekRemainingPayload();
      visitor_->OnFecProtectedPayload(payload);
    }
    if (!ProcessFrameData(header)) {
      DCHECK_NE(QUIC_NO_ERROR, error_);  // ProcessFrameData sets the error.
      DLOG(WARNING) << "Unable to process frame data.";
      return false;
    }
  } else {
    QuicFecData fec_data;
    fec_data.fec_group = header.fec_group;
    fec_data.redundancy = reader_->ReadRemainingPayload();
    visitor_->OnFecData(fec_data);
  }

  visitor_->OnPacketComplete();
  return true;
}

bool QuicFramer::ProcessPublicResetPacket(
    const QuicPacketPublicHeader& public_header) {
  QuicPublicResetPacket packet(public_header);

  if (public_header.sequence_number_length == PACKET_6BYTE_SEQUENCE_NUMBER) {
    // An old-style public reset packet has the
    // PACKET_PUBLIC_FLAGS_6BYTE_SEQUENCE bits set in the public flags.
    // TODO(wtc): remove this when we drop support for QUIC_VERSION_13.
    if (!reader_->ReadUInt64(&packet.nonce_proof)) {
      set_detailed_error("Unable to read nonce proof.");
      return RaiseError(QUIC_INVALID_PUBLIC_RST_PACKET);
    }

    if (!reader_->ReadUInt48(&packet.rejected_sequence_number)) {
      set_detailed_error("Unable to read rejected sequence number.");
      return RaiseError(QUIC_INVALID_PUBLIC_RST_PACKET);
    }

    visitor_->OnPublicResetPacket(packet);
    return true;
  }

  scoped_ptr<CryptoHandshakeMessage> reset(
      CryptoFramer::ParseMessage(reader_->ReadRemainingPayload()));
  if (!reset.get()) {
    set_detailed_error("Unable to read reset message.");
    return RaiseError(QUIC_INVALID_PUBLIC_RST_PACKET);
  }
  if (reset->tag() != kPRST) {
    set_detailed_error("Incorrect message tag.");
    return RaiseError(QUIC_INVALID_PUBLIC_RST_PACKET);
  }

  if (reset->GetUint64(kRNON, &packet.nonce_proof) != QUIC_NO_ERROR) {
    set_detailed_error("Unable to read nonce proof.");
    return RaiseError(QUIC_INVALID_PUBLIC_RST_PACKET);
  }
  // TODO(satyamshekhar): validate nonce to protect against DoS.

  if (reset->GetUint64(kRSEQ, &packet.rejected_sequence_number) !=
      QUIC_NO_ERROR) {
    set_detailed_error("Unable to read rejected sequence number.");
    return RaiseError(QUIC_INVALID_PUBLIC_RST_PACKET);
  }

  StringPiece address;
  if (reset->GetStringPiece(kCADR, &address)) {
    QuicSocketAddressCoder address_coder;
    if (address_coder.Decode(address.data(), address.length())) {
      packet.client_address = IPEndPoint(address_coder.ip(),
                                         address_coder.port());
    }
  }

  visitor_->OnPublicResetPacket(packet);
  return true;
}

bool QuicFramer::ProcessRevivedPacket(QuicPacketHeader* header,
                                      StringPiece payload) {
  DCHECK(!reader_.get());

  visitor_->OnRevivedPacket();

  header->entropy_hash = GetPacketEntropyHash(*header);

  if (!visitor_->OnPacketHeader(*header)) {
    return true;
  }

  if (payload.length() > kMaxPacketSize) {
    set_detailed_error("Revived packet too large.");
    return RaiseError(QUIC_PACKET_TOO_LARGE);
  }

  reader_.reset(new QuicDataReader(payload.data(), payload.length()));
  if (!ProcessFrameData(*header)) {
    DCHECK_NE(QUIC_NO_ERROR, error_);  // ProcessFrameData sets the error.
    DLOG(WARNING) << "Unable to process frame data.";
    return false;
  }

  visitor_->OnPacketComplete();
  reader_.reset(NULL);
  return true;
}

bool QuicFramer::AppendPacketHeader(const QuicPacketHeader& header,
                                    QuicDataWriter* writer) {
  DVLOG(1) << "Appending header: " << header;
  DCHECK(header.fec_group > 0 || header.is_in_fec_group == NOT_IN_FEC_GROUP);
  uint8 public_flags = 0;
  if (header.public_header.reset_flag) {
    public_flags |= PACKET_PUBLIC_FLAGS_RST;
  }
  if (header.public_header.version_flag) {
    public_flags |= PACKET_PUBLIC_FLAGS_VERSION;
  }

  public_flags |=
      GetSequenceNumberFlags(header.public_header.sequence_number_length)
          << kPublicHeaderSequenceNumberShift;

  switch (header.public_header.connection_id_length) {
    case PACKET_0BYTE_CONNECTION_ID:
      if (!writer->WriteUInt8(
              public_flags | PACKET_PUBLIC_FLAGS_0BYTE_CONNECTION_ID)) {
        return false;
      }
      break;
    case PACKET_1BYTE_CONNECTION_ID:
      if (!writer->WriteUInt8(
              public_flags | PACKET_PUBLIC_FLAGS_1BYTE_CONNECTION_ID)) {
         return false;
      }
      if (!writer->WriteUInt8(
              header.public_header.connection_id & k1ByteConnectionIdMask)) {
        return false;
      }
      break;
    case PACKET_4BYTE_CONNECTION_ID:
      if (!writer->WriteUInt8(
              public_flags | PACKET_PUBLIC_FLAGS_4BYTE_CONNECTION_ID)) {
         return false;
      }
      if (!writer->WriteUInt32(
              header.public_header.connection_id & k4ByteConnectionIdMask)) {
        return false;
      }
      break;
    case PACKET_8BYTE_CONNECTION_ID:
      if (!writer->WriteUInt8(
              public_flags | PACKET_PUBLIC_FLAGS_8BYTE_CONNECTION_ID)) {
        return false;
      }
      if (!writer->WriteUInt64(header.public_header.connection_id)) {
        return false;
      }
      break;
  }
  last_serialized_connection_id_ = header.public_header.connection_id;

  if (header.public_header.version_flag) {
    DCHECK(!is_server_);
    writer->WriteUInt32(QuicVersionToQuicTag(quic_version_));
  }

  if (!AppendPacketSequenceNumber(header.public_header.sequence_number_length,
                                  header.packet_sequence_number, writer)) {
    return false;
  }

  uint8 private_flags = 0;
  if (header.entropy_flag) {
    private_flags |= PACKET_PRIVATE_FLAGS_ENTROPY;
  }
  if (header.is_in_fec_group == IN_FEC_GROUP) {
    private_flags |= PACKET_PRIVATE_FLAGS_FEC_GROUP;
  }
  if (header.fec_flag) {
    private_flags |= PACKET_PRIVATE_FLAGS_FEC;
  }
  if (!writer->WriteUInt8(private_flags)) {
    return false;
  }

  // The FEC group number is the sequence number of the first fec
  // protected packet, or 0 if this packet is not protected.
  if (header.is_in_fec_group == IN_FEC_GROUP) {
    DCHECK_GE(header.packet_sequence_number, header.fec_group);
    DCHECK_GT(255u, header.packet_sequence_number - header.fec_group);
    // Offset from the current packet sequence number to the first fec
    // protected packet.
    uint8 first_fec_protected_packet_offset =
        header.packet_sequence_number - header.fec_group;
    if (!writer->WriteBytes(&first_fec_protected_packet_offset, 1)) {
      return false;
    }
  }

  return true;
}

QuicPacketSequenceNumber QuicFramer::CalculatePacketSequenceNumberFromWire(
    QuicSequenceNumberLength sequence_number_length,
    QuicPacketSequenceNumber packet_sequence_number) const {
  // The new sequence number might have wrapped to the next epoch, or
  // it might have reverse wrapped to the previous epoch, or it might
  // remain in the same epoch.  Select the sequence number closest to the
  // next expected sequence number, the previous sequence number plus 1.

  // epoch_delta is the delta between epochs the sequence number was serialized
  // with, so the correct value is likely the same epoch as the last sequence
  // number or an adjacent epoch.
  const QuicPacketSequenceNumber epoch_delta =
      GG_UINT64_C(1) << (8 * sequence_number_length);
  QuicPacketSequenceNumber next_sequence_number = last_sequence_number_ + 1;
  QuicPacketSequenceNumber epoch = last_sequence_number_ & ~(epoch_delta - 1);
  QuicPacketSequenceNumber prev_epoch = epoch - epoch_delta;
  QuicPacketSequenceNumber next_epoch = epoch + epoch_delta;

  return ClosestTo(next_sequence_number,
                   epoch + packet_sequence_number,
                   ClosestTo(next_sequence_number,
                             prev_epoch + packet_sequence_number,
                             next_epoch + packet_sequence_number));
}

bool QuicFramer::ProcessPublicHeader(
    QuicPacketPublicHeader* public_header) {
  uint8 public_flags;
  if (!reader_->ReadBytes(&public_flags, 1)) {
    set_detailed_error("Unable to read public flags.");
    return false;
  }

  public_header->reset_flag = (public_flags & PACKET_PUBLIC_FLAGS_RST) != 0;
  public_header->version_flag =
      (public_flags & PACKET_PUBLIC_FLAGS_VERSION) != 0;

  if (validate_flags_ &&
      !public_header->version_flag && public_flags > PACKET_PUBLIC_FLAGS_MAX) {
    set_detailed_error("Illegal public flags value.");
    return false;
  }

  if (public_header->reset_flag && public_header->version_flag) {
    set_detailed_error("Got version flag in reset packet");
    return false;
  }

  switch (public_flags & PACKET_PUBLIC_FLAGS_8BYTE_CONNECTION_ID) {
    case PACKET_PUBLIC_FLAGS_8BYTE_CONNECTION_ID:
      if (!reader_->ReadUInt64(&public_header->connection_id)) {
        set_detailed_error("Unable to read ConnectionId.");
        return false;
      }
      public_header->connection_id_length = PACKET_8BYTE_CONNECTION_ID;
      break;
    case PACKET_PUBLIC_FLAGS_4BYTE_CONNECTION_ID:
      // If the connection_id is truncated, expect to read the last serialized
      // connection_id.
      if (!reader_->ReadBytes(&public_header->connection_id,
                              PACKET_4BYTE_CONNECTION_ID)) {
        set_detailed_error("Unable to read ConnectionId.");
        return false;
      }
      if ((public_header->connection_id & k4ByteConnectionIdMask) !=
          (last_serialized_connection_id_ & k4ByteConnectionIdMask)) {
        set_detailed_error("Truncated 4 byte ConnectionId does not match "
                           "previous connection_id.");
        return false;
      }
      public_header->connection_id_length = PACKET_4BYTE_CONNECTION_ID;
      public_header->connection_id = last_serialized_connection_id_;
      break;
    case PACKET_PUBLIC_FLAGS_1BYTE_CONNECTION_ID:
      if (!reader_->ReadBytes(&public_header->connection_id,
                              PACKET_1BYTE_CONNECTION_ID)) {
        set_detailed_error("Unable to read ConnectionId.");
        return false;
      }
      if ((public_header->connection_id & k1ByteConnectionIdMask) !=
          (last_serialized_connection_id_ & k1ByteConnectionIdMask)) {
        set_detailed_error("Truncated 1 byte ConnectionId does not match "
                           "previous connection_id.");
        return false;
      }
      public_header->connection_id_length = PACKET_1BYTE_CONNECTION_ID;
      public_header->connection_id = last_serialized_connection_id_;
      break;
    case PACKET_PUBLIC_FLAGS_0BYTE_CONNECTION_ID:
      public_header->connection_id_length = PACKET_0BYTE_CONNECTION_ID;
      public_header->connection_id = last_serialized_connection_id_;
      break;
  }

  public_header->sequence_number_length =
      ReadSequenceNumberLength(
          public_flags >> kPublicHeaderSequenceNumberShift);

  // Read the version only if the packet is from the client.
  // version flag from the server means version negotiation packet.
  if (public_header->version_flag && is_server_) {
    QuicTag version_tag;
    if (!reader_->ReadUInt32(&version_tag)) {
      set_detailed_error("Unable to read protocol version.");
      return false;
    }

    // If the version from the new packet is the same as the version of this
    // framer, then the public flags should be set to something we understand.
    // If not, this raises an error.
    QuicVersion version = QuicTagToQuicVersion(version_tag);
    if (version == quic_version_ && public_flags > PACKET_PUBLIC_FLAGS_MAX) {
      set_detailed_error("Illegal public flags value.");
      return false;
    }
    public_header->versions.push_back(version);
  }
  return true;
}

// static
QuicSequenceNumberLength QuicFramer::GetMinSequenceNumberLength(
    QuicPacketSequenceNumber sequence_number) {
  if (sequence_number < 1 << (PACKET_1BYTE_SEQUENCE_NUMBER * 8)) {
    return PACKET_1BYTE_SEQUENCE_NUMBER;
  } else if (sequence_number < 1 << (PACKET_2BYTE_SEQUENCE_NUMBER * 8)) {
    return PACKET_2BYTE_SEQUENCE_NUMBER;
  } else if (sequence_number <
             GG_UINT64_C(1) << (PACKET_4BYTE_SEQUENCE_NUMBER * 8)) {
    return PACKET_4BYTE_SEQUENCE_NUMBER;
  } else {
    return PACKET_6BYTE_SEQUENCE_NUMBER;
  }
}

// static
uint8 QuicFramer::GetSequenceNumberFlags(
    QuicSequenceNumberLength sequence_number_length) {
  switch (sequence_number_length) {
    case PACKET_1BYTE_SEQUENCE_NUMBER:
      return PACKET_FLAGS_1BYTE_SEQUENCE;
    case PACKET_2BYTE_SEQUENCE_NUMBER:
      return PACKET_FLAGS_2BYTE_SEQUENCE;
    case PACKET_4BYTE_SEQUENCE_NUMBER:
      return PACKET_FLAGS_4BYTE_SEQUENCE;
    case PACKET_6BYTE_SEQUENCE_NUMBER:
      return PACKET_FLAGS_6BYTE_SEQUENCE;
    default:
      LOG(DFATAL) << "Unreachable case statement.";
      return PACKET_FLAGS_6BYTE_SEQUENCE;
  }
}

// static
QuicFramer::AckFrameInfo QuicFramer::GetAckFrameInfo(
    const QuicAckFrame& frame) {
  const ReceivedPacketInfo& received_info = frame.received_info;

  AckFrameInfo ack_info;
  if (!received_info.missing_packets.empty()) {
    DCHECK_GE(received_info.largest_observed,
              *received_info.missing_packets.rbegin());
    size_t cur_range_length = 0;
    SequenceNumberSet::const_iterator iter =
        received_info.missing_packets.begin();
    QuicPacketSequenceNumber last_missing = *iter;
    ++iter;
    for (; iter != received_info.missing_packets.end(); ++iter) {
      if (cur_range_length != numeric_limits<uint8>::max() &&
          *iter == (last_missing + 1)) {
        ++cur_range_length;
      } else {
        ack_info.nack_ranges[last_missing - cur_range_length]
            = cur_range_length;
        cur_range_length = 0;
      }
      ack_info.max_delta = max(ack_info.max_delta, *iter - last_missing);
      last_missing = *iter;
    }
    // Include the last nack range.
    ack_info.nack_ranges[last_missing - cur_range_length] = cur_range_length;
    // Include the range to the largest observed.
    ack_info.max_delta = max(ack_info.max_delta,
                             received_info.largest_observed - last_missing);
  }
  return ack_info;
}

bool QuicFramer::ProcessPacketHeader(
    QuicPacketHeader* header,
    const QuicEncryptedPacket& packet) {
  if (!ProcessPacketSequenceNumber(header->public_header.sequence_number_length,
                                   &header->packet_sequence_number)) {
    set_detailed_error("Unable to read sequence number.");
    return RaiseError(QUIC_INVALID_PACKET_HEADER);
  }

  if (header->packet_sequence_number == 0u) {
    set_detailed_error("Packet sequence numbers cannot be 0.");
    return RaiseError(QUIC_INVALID_PACKET_HEADER);
  }

  if (!visitor_->OnUnauthenticatedHeader(*header)) {
    return false;
  }

  if (!DecryptPayload(*header, packet)) {
    set_detailed_error("Unable to decrypt payload.");
    return RaiseError(QUIC_DECRYPTION_FAILURE);
  }

  uint8 private_flags;
  if (!reader_->ReadBytes(&private_flags, 1)) {
    set_detailed_error("Unable to read private flags.");
    return RaiseError(QUIC_INVALID_PACKET_HEADER);
  }

  if (private_flags > PACKET_PRIVATE_FLAGS_MAX) {
    set_detailed_error("Illegal private flags value.");
    return RaiseError(QUIC_INVALID_PACKET_HEADER);
  }

  header->entropy_flag = (private_flags & PACKET_PRIVATE_FLAGS_ENTROPY) != 0;
  header->fec_flag = (private_flags & PACKET_PRIVATE_FLAGS_FEC) != 0;

  if ((private_flags & PACKET_PRIVATE_FLAGS_FEC_GROUP) != 0) {
    header->is_in_fec_group = IN_FEC_GROUP;
    uint8 first_fec_protected_packet_offset;
    if (!reader_->ReadBytes(&first_fec_protected_packet_offset, 1)) {
      set_detailed_error("Unable to read first fec protected packet offset.");
      return RaiseError(QUIC_INVALID_PACKET_HEADER);
    }
    if (first_fec_protected_packet_offset >= header->packet_sequence_number) {
      set_detailed_error("First fec protected packet offset must be less "
                         "than the sequence number.");
      return RaiseError(QUIC_INVALID_PACKET_HEADER);
    }
    header->fec_group =
        header->packet_sequence_number - first_fec_protected_packet_offset;
  }

  header->entropy_hash = GetPacketEntropyHash(*header);
  // Set the last sequence number after we have decrypted the packet
  // so we are confident is not attacker controlled.
  last_sequence_number_ = header->packet_sequence_number;
  return true;
}

bool QuicFramer::ProcessPacketSequenceNumber(
    QuicSequenceNumberLength sequence_number_length,
    QuicPacketSequenceNumber* sequence_number) {
  QuicPacketSequenceNumber wire_sequence_number = 0u;
  if (!reader_->ReadBytes(&wire_sequence_number, sequence_number_length)) {
    return false;
  }

  // TODO(ianswett): Explore the usefulness of trying multiple sequence numbers
  // in case the first guess is incorrect.
  *sequence_number =
      CalculatePacketSequenceNumberFromWire(sequence_number_length,
                                            wire_sequence_number);
  return true;
}

bool QuicFramer::ProcessFrameData(const QuicPacketHeader& header) {
  if (reader_->IsDoneReading()) {
    set_detailed_error("Packet has no frames.");
    return RaiseError(QUIC_MISSING_PAYLOAD);
  }
  while (!reader_->IsDoneReading()) {
    uint8 frame_type;
    if (!reader_->ReadBytes(&frame_type, 1)) {
      set_detailed_error("Unable to read frame type.");
      return RaiseError(QUIC_INVALID_FRAME_DATA);
    }

    if (frame_type & kQuicFrameTypeSpecialMask) {
      // Stream Frame
      if (frame_type & kQuicFrameTypeStreamMask) {
        QuicStreamFrame frame;
        if (!ProcessStreamFrame(frame_type, &frame)) {
          return RaiseError(QUIC_INVALID_STREAM_DATA);
        }
        if (!visitor_->OnStreamFrame(frame)) {
          DVLOG(1) << "Visitor asked to stop further processing.";
          // Returning true since there was no parsing error.
          return true;
        }
        continue;
      }

      // Ack Frame
      if (frame_type & kQuicFrameTypeAckMask) {
        QuicAckFrame frame;
        if (!ProcessAckFrame(header, frame_type, &frame)) {
          return RaiseError(QUIC_INVALID_ACK_DATA);
        }
        if (!visitor_->OnAckFrame(frame)) {
          DVLOG(1) << "Visitor asked to stop further processing.";
          // Returning true since there was no parsing error.
          return true;
        }
        continue;
      }

      // Congestion Feedback Frame
      if (frame_type & kQuicFrameTypeCongestionFeedbackMask) {
        QuicCongestionFeedbackFrame frame;
        if (!ProcessQuicCongestionFeedbackFrame(&frame)) {
          return RaiseError(QUIC_INVALID_CONGESTION_FEEDBACK_DATA);
        }
        if (!visitor_->OnCongestionFeedbackFrame(frame)) {
          DVLOG(1) << "Visitor asked to stop further processing.";
          // Returning true since there was no parsing error.
          return true;
        }
        continue;
      }

      // This was a special frame type that did not match any
      // of the known ones. Error.
      set_detailed_error("Illegal frame type.");
      DLOG(WARNING) << "Illegal frame type: "
                    << static_cast<int>(frame_type);
      return RaiseError(QUIC_INVALID_FRAME_DATA);
    }

    switch (frame_type) {
      case PADDING_FRAME:
        // We're done with the packet.
        return true;

      case RST_STREAM_FRAME: {
        QuicRstStreamFrame frame;
        if (!ProcessRstStreamFrame(&frame)) {
          return RaiseError(QUIC_INVALID_RST_STREAM_DATA);
        }
        if (!visitor_->OnRstStreamFrame(frame)) {
          DVLOG(1) << "Visitor asked to stop further processing.";
          // Returning true since there was no parsing error.
          return true;
        }
        continue;
      }

      case CONNECTION_CLOSE_FRAME: {
        QuicConnectionCloseFrame frame;
        if (!ProcessConnectionCloseFrame(&frame)) {
          return RaiseError(QUIC_INVALID_CONNECTION_CLOSE_DATA);
        }

        if (!visitor_->OnConnectionCloseFrame(frame)) {
          DVLOG(1) << "Visitor asked to stop further processing.";
          // Returning true since there was no parsing error.
          return true;
        }
        continue;
      }

      case GOAWAY_FRAME: {
        QuicGoAwayFrame goaway_frame;
        if (!ProcessGoAwayFrame(&goaway_frame)) {
          return RaiseError(QUIC_INVALID_GOAWAY_DATA);
        }
        if (!visitor_->OnGoAwayFrame(goaway_frame)) {
          DVLOG(1) << "Visitor asked to stop further processing.";
          // Returning true since there was no parsing error.
          return true;
        }
        continue;
      }

      case WINDOW_UPDATE_FRAME: {
        if (quic_version_ > QUIC_VERSION_13) {
          QuicWindowUpdateFrame window_update_frame;
          if (!ProcessWindowUpdateFrame(&window_update_frame)) {
            return RaiseError(QUIC_INVALID_WINDOW_UPDATE_DATA);
          }
          if (!visitor_->OnWindowUpdateFrame(window_update_frame)) {
            DVLOG(1) << "Visitor asked to stop further processing.";
            // Returning true since there was no parsing error.
            return true;
          }
        } else {
          LOG(DFATAL) << "Trying to read a WindowUpdateFrame in "
                      << QuicVersionToString(quic_version_);
          return RaiseError(QUIC_INTERNAL_ERROR);
        }
        continue;
      }

      case BLOCKED_FRAME: {
        if (quic_version_ > QUIC_VERSION_13) {
          QuicBlockedFrame blocked_frame;
          if (!ProcessBlockedFrame(&blocked_frame)) {
            return RaiseError(QUIC_INVALID_BLOCKED_DATA);
          }
          if (!visitor_->OnBlockedFrame(blocked_frame)) {
            DVLOG(1) << "Visitor asked to stop further processing.";
            // Returning true since there was no parsing error.
            return true;
          }
        } else {
          LOG(DFATAL) << "Trying to read a BlockedFrame in "
                      << QuicVersionToString(quic_version_);
          return RaiseError(QUIC_INTERNAL_ERROR);
        }
        continue;
      }

      case STOP_WAITING_FRAME: {
        if (quic_version_ <= QUIC_VERSION_15) {
          LOG(DFATAL) << "Trying to read a StopWaiting in "
                      << QuicVersionToString(quic_version_);
          return RaiseError(QUIC_INTERNAL_ERROR);
        }
        QuicStopWaitingFrame stop_waiting_frame;
        if (!ProcessStopWaitingFrame(header, &stop_waiting_frame)) {
          return RaiseError(QUIC_INVALID_STOP_WAITING_DATA);
        }
        if (!visitor_->OnStopWaitingFrame(stop_waiting_frame)) {
          DVLOG(1) << "Visitor asked to stop further processing.";
          // Returning true since there was no parsing error.
          return true;
        }
        continue;
      }

      default:
        set_detailed_error("Illegal frame type.");
        DLOG(WARNING) << "Illegal frame type: "
                      << static_cast<int>(frame_type);
        return RaiseError(QUIC_INVALID_FRAME_DATA);
    }
  }

  return true;
}

bool QuicFramer::ProcessStreamFrame(uint8 frame_type,
                                    QuicStreamFrame* frame) {
  uint8 stream_flags = frame_type;

  stream_flags &= ~kQuicFrameTypeStreamMask;

  // Read from right to left: StreamID, Offset, Data Length, Fin.
  const uint8 stream_id_length = (stream_flags & kQuicStreamIDLengthMask) + 1;
  stream_flags >>= kQuicStreamIdShift;

  uint8 offset_length = (stream_flags & kQuicStreamOffsetMask);
  // There is no encoding for 1 byte, only 0 and 2 through 8.
  if (offset_length > 0) {
    offset_length += 1;
  }
  stream_flags >>= kQuicStreamOffsetShift;

  bool has_data_length =
      (stream_flags & kQuicStreamDataLengthMask) == kQuicStreamDataLengthMask;
  stream_flags >>= kQuicStreamDataLengthShift;

  frame->fin = (stream_flags & kQuicStreamFinMask) == kQuicStreamFinShift;

  frame->stream_id = 0;
  if (!reader_->ReadBytes(&frame->stream_id, stream_id_length)) {
    set_detailed_error("Unable to read stream_id.");
    return false;
  }

  frame->offset = 0;
  if (!reader_->ReadBytes(&frame->offset, offset_length)) {
    set_detailed_error("Unable to read offset.");
    return false;
  }

  StringPiece frame_data;
  if (has_data_length) {
    if (!reader_->ReadStringPiece16(&frame_data)) {
      set_detailed_error("Unable to read frame data.");
      return false;
    }
  } else {
    if (!reader_->ReadStringPiece(&frame_data, reader_->BytesRemaining())) {
      set_detailed_error("Unable to read frame data.");
      return false;
    }
  }
  // Point frame to the right data.
  frame->data.Clear();
  if (!frame_data.empty()) {
    frame->data.Append(const_cast<char*>(frame_data.data()), frame_data.size());
  }

  return true;
}

bool QuicFramer::ProcessAckFrame(const QuicPacketHeader& header,
                                 uint8 frame_type,
                                 QuicAckFrame* frame) {
  if (quic_version_ <= QUIC_VERSION_15) {
    if (!ProcessStopWaitingFrame(header, &frame->sent_info)) {
      return false;
    }
  }
  if (!ProcessReceivedInfo(frame_type, &frame->received_info)) {
    return false;
  }
  return true;
}

bool QuicFramer::ProcessReceivedInfo(uint8 frame_type,
                                     ReceivedPacketInfo* received_info) {
  // Determine the three lengths from the frame type: largest observed length,
  // missing sequence number length, and missing range length.
  const QuicSequenceNumberLength missing_sequence_number_length =
      ReadSequenceNumberLength(frame_type);
  frame_type >>= kQuicSequenceNumberLengthShift;
  const QuicSequenceNumberLength largest_observed_sequence_number_length =
      ReadSequenceNumberLength(frame_type);
  frame_type >>= kQuicSequenceNumberLengthShift;
  received_info->is_truncated = frame_type & kQuicAckTruncatedMask;
  frame_type >>= kQuicAckTruncatedShift;
  bool has_nacks = frame_type & kQuicHasNacksMask;

  if (!reader_->ReadBytes(&received_info->entropy_hash, 1)) {
    set_detailed_error("Unable to read entropy hash for received packets.");
    return false;
  }

  if (!reader_->ReadBytes(&received_info->largest_observed,
                          largest_observed_sequence_number_length)) {
    set_detailed_error("Unable to read largest observed.");
    return false;
  }

  uint64 delta_time_largest_observed_us;
  if (!reader_->ReadUFloat16(&delta_time_largest_observed_us)) {
    set_detailed_error("Unable to read delta time largest observed.");
    return false;
  }

  if (delta_time_largest_observed_us == kUFloat16MaxValue) {
    received_info->delta_time_largest_observed = QuicTime::Delta::Infinite();
  } else {
    received_info->delta_time_largest_observed =
        QuicTime::Delta::FromMicroseconds(delta_time_largest_observed_us);
  }

  if (!has_nacks) {
    return true;
  }

  uint8 num_missing_ranges;
  if (!reader_->ReadBytes(&num_missing_ranges, 1)) {
    set_detailed_error("Unable to read num missing packet ranges.");
    return false;
  }

  QuicPacketSequenceNumber last_sequence_number =
      received_info->largest_observed;
  for (size_t i = 0; i < num_missing_ranges; ++i) {
    QuicPacketSequenceNumber missing_delta = 0;
    if (!reader_->ReadBytes(&missing_delta, missing_sequence_number_length)) {
      set_detailed_error("Unable to read missing sequence number delta.");
      return false;
    }
    last_sequence_number -= missing_delta;
    QuicPacketSequenceNumber range_length = 0;
    if (!reader_->ReadBytes(&range_length, PACKET_1BYTE_SEQUENCE_NUMBER)) {
      set_detailed_error("Unable to read missing sequence number range.");
      return false;
    }
    for (size_t i = 0; i <= range_length; ++i) {
      received_info->missing_packets.insert(last_sequence_number - i);
    }
    // Subtract an extra 1 to ensure ranges are represented efficiently and
    // can't overlap by 1 sequence number.  This allows a missing_delta of 0
    // to represent an adjacent nack range.
    last_sequence_number -= (range_length + 1);
  }

  if (quic_version_ != QUIC_VERSION_13) {
    // Parse the revived packets list.
    uint8 num_revived_packets;
    if (!reader_->ReadBytes(&num_revived_packets, 1)) {
      set_detailed_error("Unable to read num revived packets.");
      return false;
    }

    for (size_t i = 0; i < num_revived_packets; ++i) {
      QuicPacketSequenceNumber revived_packet = 0;
      if (!reader_->ReadBytes(&revived_packet,
                              largest_observed_sequence_number_length)) {
        set_detailed_error("Unable to read revived packet.");
        return false;
      }

      received_info->revived_packets.insert(revived_packet);
    }
  }

  return true;
}

bool QuicFramer::ProcessStopWaitingFrame(const QuicPacketHeader& header,
                                         QuicStopWaitingFrame* stop_waiting) {
  if (!reader_->ReadBytes(&stop_waiting->entropy_hash, 1)) {
    set_detailed_error("Unable to read entropy hash for sent packets.");
    return false;
  }

  QuicPacketSequenceNumber least_unacked_delta = 0;
  if (!reader_->ReadBytes(&least_unacked_delta,
                          header.public_header.sequence_number_length)) {
    set_detailed_error("Unable to read least unacked delta.");
    return false;
  }
  DCHECK_GE(header.packet_sequence_number, least_unacked_delta);
  stop_waiting->least_unacked =
      header.packet_sequence_number - least_unacked_delta;

  return true;
}

bool QuicFramer::ProcessQuicCongestionFeedbackFrame(
    QuicCongestionFeedbackFrame* frame) {
  uint8 feedback_type;
  if (!reader_->ReadBytes(&feedback_type, 1)) {
    set_detailed_error("Unable to read congestion feedback type.");
    return false;
  }
  frame->type =
      static_cast<CongestionFeedbackType>(feedback_type);

  switch (frame->type) {
    case kInterArrival: {
      CongestionFeedbackMessageInterArrival* inter_arrival =
          &frame->inter_arrival;
      if (quic_version_ == QUIC_VERSION_13) {
        uint16 unused_accumulated_number_of_lost_packets;
        if (!reader_->ReadUInt16(
                &unused_accumulated_number_of_lost_packets)) {
          set_detailed_error(
              "Unable to read accumulated number of lost packets.");
          return false;
        }
      }
      uint8 num_received_packets;
      if (!reader_->ReadBytes(&num_received_packets, 1)) {
        set_detailed_error("Unable to read num received packets.");
        return false;
      }

      if (num_received_packets > 0u) {
        uint64 smallest_received;
        if (!ProcessPacketSequenceNumber(PACKET_6BYTE_SEQUENCE_NUMBER,
                                         &smallest_received)) {
          set_detailed_error("Unable to read smallest received.");
          return false;
        }

        uint64 time_received_us;
        if (!reader_->ReadUInt64(&time_received_us)) {
          set_detailed_error("Unable to read time received.");
          return false;
        }
        QuicTime time_received = creation_time_.Add(
            QuicTime::Delta::FromMicroseconds(time_received_us));

        inter_arrival->received_packet_times.insert(
            make_pair(smallest_received, time_received));

        for (uint8 i = 0; i < num_received_packets - 1; ++i) {
          uint16 sequence_delta;
          if (!reader_->ReadUInt16(&sequence_delta)) {
            set_detailed_error(
                "Unable to read sequence delta in received packets.");
            return false;
          }

          int32 time_delta_us;
          if (!reader_->ReadBytes(&time_delta_us, sizeof(time_delta_us))) {
            set_detailed_error(
                "Unable to read time delta in received packets.");
            return false;
          }
          QuicPacketSequenceNumber packet = smallest_received + sequence_delta;
          inter_arrival->received_packet_times.insert(
              make_pair(packet, time_received.Add(
                  QuicTime::Delta::FromMicroseconds(time_delta_us))));
        }
      }
      break;
    }
    case kFixRate: {
      uint32 bitrate = 0;
      if (!reader_->ReadUInt32(&bitrate)) {
        set_detailed_error("Unable to read bitrate.");
        return false;
      }
      frame->fix_rate.bitrate = QuicBandwidth::FromBytesPerSecond(bitrate);
      break;
    }
    case kTCP: {
      CongestionFeedbackMessageTCP* tcp = &frame->tcp;
      if (quic_version_ == QUIC_VERSION_13) {
        uint16 unused_accumulated_number_of_lost_packets;
        if (!reader_->ReadUInt16(&unused_accumulated_number_of_lost_packets)) {
          set_detailed_error(
              "Unable to read accumulated number of lost packets.");
          return false;
        }
      }
      // TODO(ianswett): Remove receive window, since it's constant.
      uint16 receive_window = 0;
      if (!reader_->ReadUInt16(&receive_window)) {
        set_detailed_error("Unable to read receive window.");
        return false;
      }
      // Simple bit packing, don't send the 4 least significant bits.
      tcp->receive_window = static_cast<QuicByteCount>(receive_window) << 4;
      break;
    }
    default:
      set_detailed_error("Illegal congestion feedback type.");
      DLOG(WARNING) << "Illegal congestion feedback type: "
                    << frame->type;
      return RaiseError(QUIC_INVALID_FRAME_DATA);
  }

  return true;
}

bool QuicFramer::ProcessRstStreamFrame(QuicRstStreamFrame* frame) {
  if (!reader_->ReadUInt32(&frame->stream_id)) {
    set_detailed_error("Unable to read stream_id.");
    return false;
  }

  if (quic_version_ > QUIC_VERSION_13) {
    if (!reader_->ReadUInt64(&frame->byte_offset)) {
      set_detailed_error("Unable to read rst stream sent byte offset.");
      return false;
    }
  }

  uint32 error_code;
  if (!reader_->ReadUInt32(&error_code)) {
    set_detailed_error("Unable to read rst stream error code.");
    return false;
  }

  if (error_code >= QUIC_STREAM_LAST_ERROR ||
      error_code < QUIC_STREAM_NO_ERROR) {
    set_detailed_error("Invalid rst stream error code.");
    return false;
  }

  frame->error_code = static_cast<QuicRstStreamErrorCode>(error_code);

  StringPiece error_details;
  if (!reader_->ReadStringPiece16(&error_details)) {
    set_detailed_error("Unable to read rst stream error details.");
    return false;
  }
  frame->error_details = error_details.as_string();

  return true;
}

bool QuicFramer::ProcessConnectionCloseFrame(QuicConnectionCloseFrame* frame) {
  uint32 error_code;
  if (!reader_->ReadUInt32(&error_code)) {
    set_detailed_error("Unable to read connection close error code.");
    return false;
  }

  if (error_code >= QUIC_LAST_ERROR ||
         error_code < QUIC_NO_ERROR) {
    set_detailed_error("Invalid error code.");
    return false;
  }

  frame->error_code = static_cast<QuicErrorCode>(error_code);

  StringPiece error_details;
  if (!reader_->ReadStringPiece16(&error_details)) {
    set_detailed_error("Unable to read connection close error details.");
    return false;
  }
  frame->error_details = error_details.as_string();

  return true;
}

bool QuicFramer::ProcessGoAwayFrame(QuicGoAwayFrame* frame) {
  uint32 error_code;
  if (!reader_->ReadUInt32(&error_code)) {
    set_detailed_error("Unable to read go away error code.");
    return false;
  }
  frame->error_code = static_cast<QuicErrorCode>(error_code);

  if (error_code >= QUIC_LAST_ERROR ||
      error_code < QUIC_NO_ERROR) {
    set_detailed_error("Invalid error code.");
    return false;
  }

  uint32 stream_id;
  if (!reader_->ReadUInt32(&stream_id)) {
    set_detailed_error("Unable to read last good stream id.");
    return false;
  }
  frame->last_good_stream_id = static_cast<QuicStreamId>(stream_id);

  StringPiece reason_phrase;
  if (!reader_->ReadStringPiece16(&reason_phrase)) {
    set_detailed_error("Unable to read goaway reason.");
    return false;
  }
  frame->reason_phrase = reason_phrase.as_string();

  return true;
}

bool QuicFramer::ProcessWindowUpdateFrame(QuicWindowUpdateFrame* frame) {
  if (!reader_->ReadUInt32(&frame->stream_id)) {
    set_detailed_error("Unable to read stream_id.");
    return false;
  }

  if (!reader_->ReadUInt64(&frame->byte_offset)) {
    set_detailed_error("Unable to read window byte_offset.");
    return false;
  }

  return true;
}

bool QuicFramer::ProcessBlockedFrame(QuicBlockedFrame* frame) {
  if (!reader_->ReadUInt32(&frame->stream_id)) {
    set_detailed_error("Unable to read stream_id.");
    return false;
  }

  return true;
}

// static
StringPiece QuicFramer::GetAssociatedDataFromEncryptedPacket(
    const QuicEncryptedPacket& encrypted,
    QuicConnectionIdLength connection_id_length,
    bool includes_version,
    QuicSequenceNumberLength sequence_number_length) {
  return StringPiece(
      encrypted.data() + kStartOfHashData, GetStartOfEncryptedData(
          connection_id_length, includes_version, sequence_number_length)
      - kStartOfHashData);
}

void QuicFramer::SetDecrypter(QuicDecrypter* decrypter) {
  DCHECK(alternative_decrypter_.get() == NULL);
  decrypter_.reset(decrypter);
}

void QuicFramer::SetAlternativeDecrypter(QuicDecrypter* decrypter,
                                         bool latch_once_used) {
  alternative_decrypter_.reset(decrypter);
  alternative_decrypter_latch_ = latch_once_used;
}

const QuicDecrypter* QuicFramer::decrypter() const {
  return decrypter_.get();
}

const QuicDecrypter* QuicFramer::alternative_decrypter() const {
  return alternative_decrypter_.get();
}

void QuicFramer::SetEncrypter(EncryptionLevel level,
                              QuicEncrypter* encrypter) {
  DCHECK_GE(level, 0);
  DCHECK_LT(level, NUM_ENCRYPTION_LEVELS);
  encrypter_[level].reset(encrypter);
}

const QuicEncrypter* QuicFramer::encrypter(EncryptionLevel level) const {
  DCHECK_GE(level, 0);
  DCHECK_LT(level, NUM_ENCRYPTION_LEVELS);
  DCHECK(encrypter_[level].get() != NULL);
  return encrypter_[level].get();
}

void QuicFramer::SwapCryptersForTest(QuicFramer* other) {
  for (int i = ENCRYPTION_NONE; i < NUM_ENCRYPTION_LEVELS; i++) {
    encrypter_[i].swap(other->encrypter_[i]);
  }
  decrypter_.swap(other->decrypter_);
  alternative_decrypter_.swap(other->alternative_decrypter_);

  const bool other_latch = other->alternative_decrypter_latch_;
  other->alternative_decrypter_latch_ = alternative_decrypter_latch_;
  alternative_decrypter_latch_ = other_latch;
}

QuicEncryptedPacket* QuicFramer::EncryptPacket(
    EncryptionLevel level,
    QuicPacketSequenceNumber packet_sequence_number,
    const QuicPacket& packet) {
  DCHECK(encrypter_[level].get() != NULL);

  scoped_ptr<QuicData> out(encrypter_[level]->EncryptPacket(
      packet_sequence_number, packet.AssociatedData(), packet.Plaintext()));
  if (out.get() == NULL) {
    RaiseError(QUIC_ENCRYPTION_FAILURE);
    return NULL;
  }
  StringPiece header_data = packet.BeforePlaintext();
  size_t len =  header_data.length() + out->length();
  char* buffer = new char[len];
  // TODO(rch): eliminate this buffer copy by passing in a buffer to Encrypt().
  memcpy(buffer, header_data.data(), header_data.length());
  memcpy(buffer + header_data.length(), out->data(), out->length());
  return new QuicEncryptedPacket(buffer, len, true);
}

size_t QuicFramer::GetMaxPlaintextSize(size_t ciphertext_size) {
  // In order to keep the code simple, we don't have the current encryption
  // level to hand. Both the NullEncrypter and AES-GCM have a tag length of 12.
  size_t min_plaintext_size = ciphertext_size;

  for (int i = ENCRYPTION_NONE; i < NUM_ENCRYPTION_LEVELS; i++) {
    if (encrypter_[i].get() != NULL) {
      size_t size = encrypter_[i]->GetMaxPlaintextSize(ciphertext_size);
      if (size < min_plaintext_size) {
        min_plaintext_size = size;
      }
    }
  }

  return min_plaintext_size;
}

bool QuicFramer::DecryptPayload(const QuicPacketHeader& header,
                                const QuicEncryptedPacket& packet) {
  StringPiece encrypted;
  if (!reader_->ReadStringPiece(&encrypted, reader_->BytesRemaining())) {
    return false;
  }
  DCHECK(decrypter_.get() != NULL);
  decrypted_.reset(decrypter_->DecryptPacket(
      header.packet_sequence_number,
      GetAssociatedDataFromEncryptedPacket(
          packet,
          header.public_header.connection_id_length,
          header.public_header.version_flag,
          header.public_header.sequence_number_length),
      encrypted));
  if  (decrypted_.get() == NULL && alternative_decrypter_.get() != NULL) {
    decrypted_.reset(alternative_decrypter_->DecryptPacket(
        header.packet_sequence_number,
        GetAssociatedDataFromEncryptedPacket(
            packet,
            header.public_header.connection_id_length,
            header.public_header.version_flag,
            header.public_header.sequence_number_length),
        encrypted));
    if (decrypted_.get() != NULL) {
      if (alternative_decrypter_latch_) {
        // Switch to the alternative decrypter and latch so that we cannot
        // switch back.
        decrypter_.reset(alternative_decrypter_.release());
      } else {
        // Switch the alternative decrypter so that we use it first next time.
        decrypter_.swap(alternative_decrypter_);
      }
    }
  }

  if  (decrypted_.get() == NULL) {
    DLOG(WARNING) << "DecryptPacket failed";
    return false;
  }

  reader_.reset(new QuicDataReader(decrypted_->data(), decrypted_->length()));
  return true;
}

size_t QuicFramer::GetAckFrameSize(
    const QuicAckFrame& ack,
    QuicSequenceNumberLength sequence_number_length) {
  AckFrameInfo ack_info = GetAckFrameInfo(ack);
  QuicSequenceNumberLength largest_observed_length =
      GetMinSequenceNumberLength(ack.received_info.largest_observed);
  QuicSequenceNumberLength missing_sequence_number_length =
      GetMinSequenceNumberLength(ack_info.max_delta);

  size_t ack_size = GetMinAckFrameSize(quic_version_,
                                       sequence_number_length,
                                       largest_observed_length);
  if (!ack_info.nack_ranges.empty()) {
    ack_size += kNumberOfMissingPacketsSize  +
        (quic_version_ == QUIC_VERSION_13 ? 0 : kNumberOfRevivedPacketsSize);
    ack_size += ack_info.nack_ranges.size() *
      (missing_sequence_number_length + PACKET_1BYTE_SEQUENCE_NUMBER);
    ack_size +=
        ack.received_info.revived_packets.size() * largest_observed_length;
  }
  return ack_size;
}

size_t QuicFramer::ComputeFrameLength(
    const QuicFrame& frame,
    bool last_frame_in_packet,
    InFecGroup is_in_fec_group,
    QuicSequenceNumberLength sequence_number_length) {
  switch (frame.type) {
    case STREAM_FRAME:
      return GetMinStreamFrameSize(quic_version_,
                                   frame.stream_frame->stream_id,
                                   frame.stream_frame->offset,
                                   last_frame_in_packet,
                                   is_in_fec_group) +
          frame.stream_frame->data.TotalBufferSize();
    case ACK_FRAME: {
      return GetAckFrameSize(*frame.ack_frame, sequence_number_length);
    }
    case CONGESTION_FEEDBACK_FRAME: {
      size_t len = kQuicFrameTypeSize;
      const QuicCongestionFeedbackFrame& congestion_feedback =
          *frame.congestion_feedback_frame;
      len += 1;  // Congestion feedback type.

      switch (congestion_feedback.type) {
        case kInterArrival: {
          const CongestionFeedbackMessageInterArrival& inter_arrival =
              congestion_feedback.inter_arrival;
          if (quic_version_ == QUIC_VERSION_13) {
            len += 2;  // Accumulated number of lost packets.
          }
          len += 1;  // Number received packets.
          if (inter_arrival.received_packet_times.size() > 0) {
            len += PACKET_6BYTE_SEQUENCE_NUMBER;  // Smallest received.
            len += 8;  // Time.
            // 2 bytes per sequence number delta plus 4 bytes per delta time.
            len += PACKET_6BYTE_SEQUENCE_NUMBER *
                (inter_arrival.received_packet_times.size() - 1);
          }
          break;
        }
        case kFixRate:
          len += 4;  // Bitrate.
          break;
        case kTCP:
          if (quic_version_ == QUIC_VERSION_13) {
            len += 2;  // Accumulated number of lost packets.
          }
          len += 2;  // Receive window.
          break;
        default:
          set_detailed_error("Illegal feedback type.");
          DVLOG(1) << "Illegal feedback type: " << congestion_feedback.type;
          break;
      }
      return len;
    }
    case STOP_WAITING_FRAME:
      return GetStopWaitingFrameSize(sequence_number_length);
    case RST_STREAM_FRAME:
      return GetMinRstStreamFrameSize(quic_version_) +
          frame.rst_stream_frame->error_details.size();
    case CONNECTION_CLOSE_FRAME:
      return GetMinConnectionCloseFrameSize() +
          frame.connection_close_frame->error_details.size();
    case GOAWAY_FRAME:
      return GetMinGoAwayFrameSize() + frame.goaway_frame->reason_phrase.size();
    case WINDOW_UPDATE_FRAME:
      return GetWindowUpdateFrameSize();
    case BLOCKED_FRAME:
      return GetBlockedFrameSize();
    case PADDING_FRAME:
      DCHECK(false);
      return 0;
    case NUM_FRAME_TYPES:
      DCHECK(false);
      return 0;
  }

  // Not reachable, but some Chrome compilers can't figure that out.  *sigh*
  DCHECK(false);
  return 0;
}

bool QuicFramer::AppendTypeByte(const QuicFrame& frame,
                                bool no_stream_frame_length,
                                QuicDataWriter* writer) {
  uint8 type_byte = 0;
  switch (frame.type) {
    case STREAM_FRAME: {
      if (frame.stream_frame == NULL) {
        LOG(DFATAL) << "Failed to append STREAM frame with no stream_frame.";
      }
      // Fin bit.
      type_byte |= frame.stream_frame->fin ? kQuicStreamFinMask : 0;

      // Data Length bit.
      type_byte <<= kQuicStreamDataLengthShift;
      type_byte |= no_stream_frame_length ? 0: kQuicStreamDataLengthMask;

      // Offset 3 bits.
      type_byte <<= kQuicStreamOffsetShift;
      const size_t offset_len = GetStreamOffsetSize(frame.stream_frame->offset);
      if (offset_len > 0) {
        type_byte |= offset_len - 1;
      }

      // stream id 2 bits.
      type_byte <<= kQuicStreamIdShift;
      type_byte |= GetStreamIdSize(frame.stream_frame->stream_id) - 1;
      type_byte |= kQuicFrameTypeStreamMask;  // Set Stream Frame Type to 1.
      break;
    }
    case ACK_FRAME:
      return true;
    case CONGESTION_FEEDBACK_FRAME: {
      // TODO(ianswett): Use extra 5 bits in the congestion feedback framing.
      type_byte = kQuicFrameTypeCongestionFeedbackMask;
      break;
    }
    default:
      type_byte = frame.type;
      break;
  }

  return writer->WriteUInt8(type_byte);
}

// static
bool QuicFramer::AppendPacketSequenceNumber(
    QuicSequenceNumberLength sequence_number_length,
    QuicPacketSequenceNumber packet_sequence_number,
    QuicDataWriter* writer) {
  // Ensure the entire sequence number can be written.
  if (writer->capacity() - writer->length() <
      static_cast<size_t>(sequence_number_length)) {
    return false;
  }
  switch (sequence_number_length) {
    case PACKET_1BYTE_SEQUENCE_NUMBER:
      return writer->WriteUInt8(
          packet_sequence_number & k1ByteSequenceNumberMask);
      break;
    case PACKET_2BYTE_SEQUENCE_NUMBER:
      return writer->WriteUInt16(
          packet_sequence_number & k2ByteSequenceNumberMask);
      break;
    case PACKET_4BYTE_SEQUENCE_NUMBER:
      return writer->WriteUInt32(
          packet_sequence_number & k4ByteSequenceNumberMask);
      break;
    case PACKET_6BYTE_SEQUENCE_NUMBER:
      return writer->WriteUInt48(
          packet_sequence_number & k6ByteSequenceNumberMask);
      break;
    default:
      DCHECK(false) << "sequence_number_length: " << sequence_number_length;
      return false;
  }
}

bool QuicFramer::AppendStreamFrame(
    const QuicStreamFrame& frame,
    bool no_stream_frame_length,
    QuicDataWriter* writer) {
  if (!writer->WriteBytes(&frame.stream_id, GetStreamIdSize(frame.stream_id))) {
    LOG(DFATAL) << "Writing stream id size failed.";
    return false;
  }
  if (!writer->WriteBytes(&frame.offset, GetStreamOffsetSize(frame.offset))) {
    LOG(DFATAL) << "Writing offset size failed.";
    return false;
  }
  if (!no_stream_frame_length) {
    if (!writer->WriteUInt16(frame.data.TotalBufferSize())) {
      LOG(DFATAL) << "Writing stream frame length failed";
      return false;
    }
  }

  if (!writer->WriteIOVector(frame.data)) {
    LOG(DFATAL) << "Writing frame data failed.";
    return false;
  }
  return true;
}

// static
void QuicFramer::set_version(const QuicVersion version) {
  DCHECK(IsSupportedVersion(version)) << QuicVersionToString(version);
  quic_version_ = version;
}

bool QuicFramer::AppendAckFrameAndTypeByte(
    const QuicPacketHeader& header,
    const QuicAckFrame& frame,
    QuicDataWriter* writer) {
  AckFrameInfo ack_info = GetAckFrameInfo(frame);
  QuicPacketSequenceNumber ack_largest_observed =
      frame.received_info.largest_observed;
  QuicSequenceNumberLength largest_observed_length =
      GetMinSequenceNumberLength(ack_largest_observed);
  QuicSequenceNumberLength missing_sequence_number_length =
      GetMinSequenceNumberLength(ack_info.max_delta);
  // Determine whether we need to truncate ranges.
  size_t available_range_bytes = writer->capacity() - writer->length() -
      GetMinAckFrameSize(quic_version_,
                         header.public_header.sequence_number_length,
                         largest_observed_length) -
      (quic_version_ == QUIC_VERSION_13 ? 0 : kNumberOfRevivedPacketsSize);
  size_t max_num_ranges = available_range_bytes /
      (missing_sequence_number_length + PACKET_1BYTE_SEQUENCE_NUMBER);
  max_num_ranges =
      min(static_cast<size_t>(numeric_limits<uint8>::max()), max_num_ranges);
  bool truncated = ack_info.nack_ranges.size() > max_num_ranges;
  DVLOG_IF(1, truncated) << "Truncating ack from "
                         << ack_info.nack_ranges.size() << " ranges to "
                         << max_num_ranges;

  // Write out the type byte by setting the low order bits and doing shifts
  // to make room for the next bit flags to be set.
  // Whether there are any nacks.
  uint8 type_byte = ack_info.nack_ranges.empty() ? 0 : kQuicHasNacksMask;

  // truncating bit.
  type_byte <<= kQuicAckTruncatedShift;
  type_byte |= truncated ? kQuicAckTruncatedMask : 0;

  // Largest observed sequence number length.
  type_byte <<= kQuicSequenceNumberLengthShift;
  type_byte |= GetSequenceNumberFlags(largest_observed_length);

  // Missing sequence number length.
  type_byte <<= kQuicSequenceNumberLengthShift;
  type_byte |= GetSequenceNumberFlags(missing_sequence_number_length);

  type_byte |= kQuicFrameTypeAckMask;

  if (!writer->WriteUInt8(type_byte)) {
    return false;
  }

  if (quic_version_ <= QUIC_VERSION_15) {
    if (!AppendStopWaitingFrame(header, frame.sent_info, writer)) {
      return false;
    }
  }

  const ReceivedPacketInfo& received_info = frame.received_info;
  QuicPacketEntropyHash ack_entropy_hash = received_info.entropy_hash;
  NackRangeMap::reverse_iterator ack_iter = ack_info.nack_ranges.rbegin();
  if (truncated) {
    // Skip the nack ranges which the truncated ack won't include and set
    // a correct largest observed for the truncated ack.
    for (size_t i = 1; i < (ack_info.nack_ranges.size() - max_num_ranges);
         ++i) {
      ++ack_iter;
    }
    // If the last range is followed by acks, include them.
    // If the last range is followed by another range, specify the end of the
    // range as the largest_observed.
    ack_largest_observed = ack_iter->first - 1;
    // Also update the entropy so it matches the largest observed.
    ack_entropy_hash = entropy_calculator_->EntropyHash(ack_largest_observed);
    ++ack_iter;
  }

  if (!writer->WriteUInt8(ack_entropy_hash)) {
    return false;
  }

  if (!AppendPacketSequenceNumber(largest_observed_length,
                                  ack_largest_observed, writer)) {
    return false;
  }

  uint64 delta_time_largest_observed_us = kUFloat16MaxValue;
  if (!received_info.delta_time_largest_observed.IsInfinite()) {
    DCHECK_LE(0u,
              frame.received_info.delta_time_largest_observed.ToMicroseconds());
    delta_time_largest_observed_us =
        received_info.delta_time_largest_observed.ToMicroseconds();
  }

  if (!writer->WriteUFloat16(delta_time_largest_observed_us)) {
    return false;
  }

  if (ack_info.nack_ranges.empty()) {
    return true;
  }

  const uint8 num_missing_ranges =
      min(ack_info.nack_ranges.size(), max_num_ranges);
  if (!writer->WriteBytes(&num_missing_ranges, 1)) {
    return false;
  }

  int num_ranges_written = 0;
  QuicPacketSequenceNumber last_sequence_written = ack_largest_observed;
  for (; ack_iter != ack_info.nack_ranges.rend(); ++ack_iter) {
    // Calculate the delta to the last number in the range.
    QuicPacketSequenceNumber missing_delta =
        last_sequence_written - (ack_iter->first + ack_iter->second);
    if (!AppendPacketSequenceNumber(missing_sequence_number_length,
                                    missing_delta, writer)) {
      return false;
    }
    if (!AppendPacketSequenceNumber(PACKET_1BYTE_SEQUENCE_NUMBER,
                                    ack_iter->second, writer)) {
      return false;
    }
    // Subtract 1 so a missing_delta of 0 means an adjacent range.
    last_sequence_written = ack_iter->first - 1;
    ++num_ranges_written;
  }
  DCHECK_EQ(num_missing_ranges, num_ranges_written);

  if (quic_version_ != QUIC_VERSION_13) {
    // Append revived packets.
    // If not all the revived packets fit, only mention the ones that do.
    uint8 num_revived_packets =
        min(received_info.revived_packets.size(),
            static_cast<size_t>(numeric_limits<uint8>::max()));
    num_revived_packets = min(
        static_cast<size_t>(num_revived_packets),
        (writer->capacity() - writer->length()) / largest_observed_length);
    if (!writer->WriteBytes(&num_revived_packets, 1)) {
      return false;
    }

    SequenceNumberSet::const_iterator iter =
        received_info.revived_packets.begin();
    for (int i = 0; i < num_revived_packets; ++i, ++iter) {
      LOG_IF(DFATAL, !ContainsKey(received_info.missing_packets, *iter));
      if (!AppendPacketSequenceNumber(largest_observed_length,
                                      *iter, writer)) {
        return false;
      }
    }
  }

  return true;
}

bool QuicFramer::AppendCongestionFeedbackFrame(
    const QuicCongestionFeedbackFrame& frame,
    QuicDataWriter* writer) {
  if (!writer->WriteBytes(&frame.type, 1)) {
    return false;
  }

  switch (frame.type) {
    case kInterArrival: {
      const CongestionFeedbackMessageInterArrival& inter_arrival =
          frame.inter_arrival;
      if (quic_version_ == QUIC_VERSION_13) {
        // accumulated_number_of_lost_packets is removed.  Always write 0.
        if (!writer->WriteUInt16(0)) {
          return false;
        }
      }
      DCHECK_GE(numeric_limits<uint8>::max(),
                inter_arrival.received_packet_times.size());
      if (inter_arrival.received_packet_times.size() >
          numeric_limits<uint8>::max()) {
        return false;
      }
      // TODO(ianswett): Make num_received_packets a varint.
      uint8 num_received_packets =
          inter_arrival.received_packet_times.size();
      if (!writer->WriteBytes(&num_received_packets, 1)) {
        return false;
      }
      if (num_received_packets > 0) {
        TimeMap::const_iterator it =
            inter_arrival.received_packet_times.begin();

        QuicPacketSequenceNumber lowest_sequence = it->first;
        if (!AppendPacketSequenceNumber(PACKET_6BYTE_SEQUENCE_NUMBER,
                                        lowest_sequence, writer)) {
          return false;
        }

        QuicTime lowest_time = it->second;
        if (!writer->WriteUInt64(
                lowest_time.Subtract(creation_time_).ToMicroseconds())) {
          return false;
        }

        for (++it; it != inter_arrival.received_packet_times.end(); ++it) {
          QuicPacketSequenceNumber sequence_delta = it->first - lowest_sequence;
          DCHECK_GE(numeric_limits<uint16>::max(), sequence_delta);
          if (sequence_delta > numeric_limits<uint16>::max()) {
            return false;
          }
          if (!writer->WriteUInt16(static_cast<uint16>(sequence_delta))) {
            return false;
          }

          int32 time_delta_us =
              it->second.Subtract(lowest_time).ToMicroseconds();
          if (!writer->WriteBytes(&time_delta_us, sizeof(time_delta_us))) {
            return false;
          }
        }
      }
      break;
    }
    case kFixRate: {
      const CongestionFeedbackMessageFixRate& fix_rate =
          frame.fix_rate;
      if (!writer->WriteUInt32(fix_rate.bitrate.ToBytesPerSecond())) {
        return false;
      }
      break;
    }
    case kTCP: {
      const CongestionFeedbackMessageTCP& tcp = frame.tcp;
      DCHECK_LE(tcp.receive_window, 1u << 20);
      // Simple bit packing, don't send the 4 least significant bits.
      uint16 receive_window = static_cast<uint16>(tcp.receive_window >> 4);
      if (quic_version_ == QUIC_VERSION_13) {
        // accumulated_number_of_lost_packets is removed.  Always write 0.
        if (!writer->WriteUInt16(0)) {
          return false;
        }
      }
      if (!writer->WriteUInt16(receive_window)) {
        return false;
      }
      break;
    }
    default:
      return false;
  }

  return true;
}

bool QuicFramer::AppendStopWaitingFrame(
    const QuicPacketHeader& header,
    const QuicStopWaitingFrame& frame,
    QuicDataWriter* writer) {
  DCHECK_GE(header.packet_sequence_number, frame.least_unacked);
  const QuicPacketSequenceNumber least_unacked_delta =
      header.packet_sequence_number - frame.least_unacked;
  const QuicPacketSequenceNumber length_shift =
      header.public_header.sequence_number_length * 8;
  if (!writer->WriteUInt8(frame.entropy_hash)) {
    LOG(DFATAL) << " hash failed";
    return false;
  }

  if (least_unacked_delta >> length_shift > 0) {
    LOG(DFATAL) << "sequence_number_length "
                << header.public_header.sequence_number_length
                << " is too small for least_unacked_delta: "
                << least_unacked_delta;
    return false;
  }
  if (!AppendPacketSequenceNumber(header.public_header.sequence_number_length,
                                  least_unacked_delta, writer)) {
    LOG(DFATAL) << " seq failed: "
                << header.public_header.sequence_number_length;
    return false;
  }

  return true;
}

bool QuicFramer::AppendRstStreamFrame(
        const QuicRstStreamFrame& frame,
        QuicDataWriter* writer) {
  if (!writer->WriteUInt32(frame.stream_id)) {
    return false;
  }

  if (quic_version_ > QUIC_VERSION_13) {
    if (!writer->WriteUInt64(frame.byte_offset)) {
      return false;
    }
  }

  uint32 error_code = static_cast<uint32>(frame.error_code);
  if (!writer->WriteUInt32(error_code)) {
    return false;
  }

  if (!writer->WriteStringPiece16(frame.error_details)) {
    return false;
  }
  return true;
}

bool QuicFramer::AppendConnectionCloseFrame(
    const QuicConnectionCloseFrame& frame,
    QuicDataWriter* writer) {
  uint32 error_code = static_cast<uint32>(frame.error_code);
  if (!writer->WriteUInt32(error_code)) {
    return false;
  }
  if (!writer->WriteStringPiece16(frame.error_details)) {
    return false;
  }
  return true;
}

bool QuicFramer::AppendGoAwayFrame(const QuicGoAwayFrame& frame,
                                   QuicDataWriter* writer) {
  uint32 error_code = static_cast<uint32>(frame.error_code);
  if (!writer->WriteUInt32(error_code)) {
    return false;
  }
  uint32 stream_id = static_cast<uint32>(frame.last_good_stream_id);
  if (!writer->WriteUInt32(stream_id)) {
    return false;
  }
  if (!writer->WriteStringPiece16(frame.reason_phrase)) {
    return false;
  }
  return true;
}

bool QuicFramer::AppendWindowUpdateFrame(const QuicWindowUpdateFrame& frame,
                                         QuicDataWriter* writer) {
  uint32 stream_id = static_cast<uint32>(frame.stream_id);
  if (!writer->WriteUInt32(stream_id)) {
    return false;
  }
  if (!writer->WriteUInt64(frame.byte_offset)) {
    return false;
  }
  return true;
}

bool QuicFramer::AppendBlockedFrame(const QuicBlockedFrame& frame,
                                    QuicDataWriter* writer) {
  uint32 stream_id = static_cast<uint32>(frame.stream_id);
  if (!writer->WriteUInt32(stream_id)) {
    return false;
  }
  return true;
}

bool QuicFramer::RaiseError(QuicErrorCode error) {
  DVLOG(1) << "Error detail: " << detailed_error_;
  set_error(error);
  visitor_->OnError(this);
  reader_.reset(NULL);
  return false;
}

}  // namespace net