net/spdy/spdy_frame_builder.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/spdy/spdy_frame_builder.h"
   6
   7 #include <limits>
   8
   9 #include "base/logging.h"
  10 #include "net/spdy/spdy_framer.h"
  11 #include "net/spdy/spdy_protocol.h"
  12
  13 namespace net {
  14
  15 namespace {
  16
  17 // A special structure for the 8 bit flags and 24 bit length fields.
  18 union FlagsAndLength {
  19   uint8 flags_[4];  // 8 bits
  20   uint32 length_;   // 24 bits
  21 };
  22
  23 // Creates a FlagsAndLength.
  24 FlagsAndLength CreateFlagsAndLength(uint8 flags, size_t length) {
  25   DCHECK_EQ(0u, length & ~static_cast<size_t>(kLengthMask));
  26   FlagsAndLength flags_length;
  27   flags_length.length_ = htonl(static_cast<uint32>(length));
  28   DCHECK_EQ(0, flags & ~kControlFlagsMask);
  29   flags_length.flags_[0] = flags;
  30   return flags_length;
  31 }
  32
  33 }  // namespace
  34
  35 SpdyFrameBuilder::SpdyFrameBuilder(size_t size)
  36     : buffer_(new char[size]),
  37       capacity_(size),
  38       length_(0) {
  39 }
  40
  41 SpdyFrameBuilder::~SpdyFrameBuilder() {
  42 }
  43
  44 char* SpdyFrameBuilder::GetWritableBuffer(size_t length) {
  45   if (!CanWrite(length)) {
  46     return NULL;
  47   }
  48   return buffer_.get() + length_;
  49 }
  50
  51 bool SpdyFrameBuilder::Seek(size_t length) {
  52   if (!CanWrite(length)) {
  53     return false;
  54   }
  55
  56   length_ += length;
  57   return true;
  58 }
  59
  60 bool SpdyFrameBuilder::WriteControlFrameHeader(const SpdyFramer& framer,
  61                                                SpdyFrameType type,
  62                                                uint8 flags) {
  63   DCHECK_GE(type, FIRST_CONTROL_TYPE);
  64   DCHECK_LE(type, LAST_CONTROL_TYPE);
  65   DCHECK_GT(4, framer.protocol_version());
  66   bool success = true;
  67   FlagsAndLength flags_length = CreateFlagsAndLength(
  68       flags, capacity_ - framer.GetControlFrameHeaderSize());
  69   success &= WriteUInt16(kControlFlagMask | framer.protocol_version());
  70   success &= WriteUInt16(type);
  71   success &= WriteBytes(&flags_length, sizeof(flags_length));
  72   DCHECK_EQ(framer.GetControlFrameHeaderSize(), length());
  73   return success;
  74 }
  75
  76 bool SpdyFrameBuilder::WriteDataFrameHeader(const SpdyFramer& framer,
  77                                             SpdyStreamId stream_id,
  78                                             SpdyDataFlags flags) {
  79   if (framer.protocol_version() >= 4) {
  80     return WriteFramePrefix(framer, DATA, flags, stream_id);
  81   }
  82   DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
  83   bool success = true;
  84   success &= WriteUInt32(stream_id);
  85   size_t length_field = capacity_ - framer.GetDataFrameMinimumSize();
  86   DCHECK_EQ(0u, length_field & ~static_cast<size_t>(kLengthMask));
  87   FlagsAndLength flags_length;
  88   flags_length.length_ = htonl(length_field);
  89   DCHECK_EQ(0, flags & ~kDataFlagsMask);
  90   flags_length.flags_[0] = flags;
  91   success &= WriteBytes(&flags_length, sizeof(flags_length));
  92   DCHECK_EQ(framer.GetDataFrameMinimumSize(), length());
  93   return success;
  94 }
  95
  96 bool SpdyFrameBuilder::WriteFramePrefix(const SpdyFramer& framer,
  97                                         SpdyFrameType type,
  98                                         uint8 flags,
  99                                         SpdyStreamId stream_id) {
 100   DCHECK_LE(DATA, type);
 101   DCHECK_GE(LAST_CONTROL_TYPE, type);
 102   DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
 103   DCHECK_LE(4, framer.protocol_version());
 104   bool success = true;
 105   // Upstream DCHECK's that capacity_ is under the maximum frame size at this
 106   // point. Chromium does not, because of the large additional zlib inflation
 107   // factor we use. (Frame size is is still checked by OverwriteLength() below).
 108   success &= WriteUInt16(capacity_);
 109   success &= WriteUInt8(type);
 110   success &= WriteUInt8(flags);
 111   success &= WriteUInt32(stream_id);
 112   DCHECK_EQ(framer.GetDataFrameMinimumSize(), length());
 113   return success;
 114 }
 115
 116 bool SpdyFrameBuilder::WriteString(const std::string& value) {
 117   if (value.size() > 0xffff) {
 118     DCHECK(false) << "Tried to write string with length > 16bit.";
 119     return false;
 120   }
 121
 122   if (!WriteUInt16(static_cast<int>(value.size())))
 123     return false;
 124
 125   return WriteBytes(value.data(), static_cast<uint16>(value.size()));
 126 }
 127
 128 bool SpdyFrameBuilder::WriteStringPiece32(const base::StringPiece& value) {
 129   if (!WriteUInt32(value.size())) {
 130     return false;
 131   }
 132
 133   return WriteBytes(value.data(), value.size());
 134 }
 135
 136 bool SpdyFrameBuilder::WriteBytes(const void* data, uint32 data_len) {
 137   if (!CanWrite(data_len)) {
 138     return false;
 139   }
 140
 141   char* dest = GetWritableBuffer(data_len);
 142   memcpy(dest, data, data_len);
 143   Seek(data_len);
 144   return true;
 145 }
 146
 147 bool SpdyFrameBuilder::RewriteLength(const SpdyFramer& framer) {
 148   if (framer.protocol_version() < 4) {
 149     return OverwriteLength(framer,
 150                            length_ - framer.GetControlFrameHeaderSize());
 151   } else {
 152     return OverwriteLength(framer, length_);
 153   }
 154 }
 155
 156 bool SpdyFrameBuilder::OverwriteLength(const SpdyFramer& framer,
 157                                        size_t length) {
 158   if (framer.protocol_version() < 4) {
 159     DCHECK_GT(framer.GetFrameMaximumSize() - framer.GetFrameMinimumSize(),
 160               length);
 161   } else {
 162     DCHECK_GE(framer.GetFrameMaximumSize(), length);
 163   }
 164   bool success = false;
 165   const size_t old_length = length_;
 166
 167   if (framer.protocol_version() < 4) {
 168     FlagsAndLength flags_length = CreateFlagsAndLength(
 169         0,  // We're not writing over the flags value anyway.
 170         length);
 171
 172     // Write into the correct location by temporarily faking the offset.
 173     length_ = 5;  // Offset at which the length field occurs.
 174     success = WriteBytes(reinterpret_cast<char*>(&flags_length) + 1,
 175                          sizeof(flags_length) - 1);
 176   } else {
 177     length_ = 0;
 178     success = WriteUInt16(length);
 179   }
 180
 181   length_ = old_length;
 182   return success;
 183 }
 184
 185 bool SpdyFrameBuilder::CanWrite(size_t length) const {
 186   if (length > kLengthMask) {
 187     DCHECK(false);
 188     return false;
 189   }
 190
 191   if (length_ + length > capacity_) {
 192     DCHECK(false);
 193     return false;
 194   }
 195
 196   return true;
 197 }
 198
 199 }  // namespace net