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, SpdyMajorVersion version)
  36     : buffer_(new char[size]),
  37       capacity_(size),
  38       length_(0),
  39       offset_(0),
  40       version_(version) {
  41 }
  42
  43 SpdyFrameBuilder::~SpdyFrameBuilder() {
  44 }
  45
  46 char* SpdyFrameBuilder::GetWritableBuffer(size_t length) {
  47   if (!CanWrite(length)) {
  48     return NULL;
  49   }
  50   return buffer_.get() + offset_ + length_;
  51 }
  52
  53 bool SpdyFrameBuilder::Seek(size_t length) {
  54   if (!CanWrite(length)) {
  55     return false;
  56   }
  57
  58   length_ += length;
  59   return true;
  60 }
  61
  62 bool SpdyFrameBuilder::WriteControlFrameHeader(const SpdyFramer& framer,
  63                                                SpdyFrameType type,
  64                                                uint8 flags) {
  65   DCHECK_GE(SPDY3, version_);
  66   DCHECK(SpdyConstants::IsValidFrameType(
  67       version_, SpdyConstants::SerializeFrameType(version_, type)));
  68   bool success = true;
  69   FlagsAndLength flags_length = CreateFlagsAndLength(
  70       flags, capacity_ - framer.GetControlFrameHeaderSize());
  71   success &= WriteUInt16(kControlFlagMask |
  72                          SpdyConstants::SerializeMajorVersion(version_));
  73   success &= WriteUInt16(
  74       SpdyConstants::SerializeFrameType(framer.protocol_version(), type));
  75   success &= WriteBytes(&flags_length, sizeof(flags_length));
  76   DCHECK_EQ(framer.GetControlFrameHeaderSize(), length());
  77   return success;
  78 }
  79
  80 bool SpdyFrameBuilder::WriteDataFrameHeader(const SpdyFramer& framer,
  81                                             SpdyStreamId stream_id,
  82                                             uint8 flags) {
  83   if (version_ > SPDY3) {
  84     return BeginNewFrame(framer, DATA, flags, stream_id);
  85   }
  86   DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
  87   bool success = true;
  88   success &= WriteUInt32(stream_id);
  89   size_t length_field = capacity_ - framer.GetDataFrameMinimumSize();
  90   DCHECK_EQ(0u, length_field & ~static_cast<size_t>(kLengthMask));
  91   FlagsAndLength flags_length;
  92   flags_length.length = htonl(length_field);
  93   DCHECK_EQ(0, flags & ~kDataFlagsMask);
  94   flags_length.flags[0] = flags;
  95   success &= WriteBytes(&flags_length, sizeof(flags_length));
  96   DCHECK_EQ(framer.GetDataFrameMinimumSize(), length());
  97   return success;
  98 }
  99
 100 bool SpdyFrameBuilder::BeginNewFrame(const SpdyFramer& framer,
 101                                      SpdyFrameType type,
 102                                      uint8 flags,
 103                                      SpdyStreamId stream_id) {
 104   DCHECK(SpdyConstants::IsValidFrameType(
 105       version_, SpdyConstants::SerializeFrameType(version_, type)));
 106   DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
 107   DCHECK_GT(framer.protocol_version(), SPDY3);
 108   bool success = true;
 109   if (length_ > 0) {
 110     // Update length field for previous frame.
 111     OverwriteLength(framer, length_ - framer.GetPrefixLength(type));
 112     DLOG_IF(DFATAL, SpdyConstants::GetFrameMaximumSize(version_) < length_)
 113         << "Frame length  " << length_
 114         << " is longer than the maximum allowed length.";
 115   }
 116
 117   offset_ += length_;
 118   length_ = 0;
 119
 120   // Assume all remaining capacity will be used for this frame. If not,
 121   // the length will get overwritten when we begin the next frame.
 122   // Don't check for length limits here because this may be larger than the
 123   // actual frame length.
 124   success &= WriteUInt24(capacity_ - offset_ - framer.GetPrefixLength(type));
 125   success &= WriteUInt8(
 126       SpdyConstants::SerializeFrameType(version_, type));
 127   success &= WriteUInt8(flags);
 128   success &= WriteUInt32(stream_id);
 129   DCHECK_EQ(framer.GetDataFrameMinimumSize(), length_);
 130   return success;
 131 }
 132
 133 bool SpdyFrameBuilder::WriteString(const std::string& value) {
 134   if (value.size() > 0xffff) {
 135     DCHECK(false) << "Tried to write string with length > 16bit.";
 136     return false;
 137   }
 138
 139   if (!WriteUInt16(static_cast<uint16>(value.size())))
 140     return false;
 141
 142   return WriteBytes(value.data(), static_cast<uint16>(value.size()));
 143 }
 144
 145 bool SpdyFrameBuilder::WriteStringPiece32(const base::StringPiece& value) {
 146   if (!WriteUInt32(value.size())) {
 147     return false;
 148   }
 149
 150   return WriteBytes(value.data(), value.size());
 151 }
 152
 153 bool SpdyFrameBuilder::WriteBytes(const void* data, uint32 data_len) {
 154   if (!CanWrite(data_len)) {
 155     return false;
 156   }
 157
 158   char* dest = GetWritableBuffer(data_len);
 159   memcpy(dest, data, data_len);
 160   Seek(data_len);
 161   return true;
 162 }
 163
 164 bool SpdyFrameBuilder::RewriteLength(const SpdyFramer& framer) {
 165   return OverwriteLength(framer,
 166                          length_ - framer.GetControlFrameHeaderSize());
 167 }
 168
 169 bool SpdyFrameBuilder::OverwriteLength(const SpdyFramer& framer,
 170                                        size_t length) {
 171   if (version_ < SPDY4) {
 172     DCHECK_LE(length,
 173               SpdyConstants::GetFrameMaximumSize(version_) -
 174                   framer.GetFrameMinimumSize());
 175   } else {
 176     DCHECK_LE(length, SpdyConstants::GetFrameMaximumSize(version_));
 177   }
 178   bool success = false;
 179   const size_t old_length = length_;
 180
 181   if (version_ < SPDY4) {
 182     FlagsAndLength flags_length = CreateFlagsAndLength(
 183         0,  // We're not writing over the flags value anyway.
 184         length);
 185
 186     // Write into the correct location by temporarily faking the offset.
 187     length_ = 5;  // Offset at which the length field occurs.
 188     success = WriteBytes(reinterpret_cast<char*>(&flags_length) + 1,
 189                          sizeof(flags_length) - 1);
 190   } else {
 191     length_ = 0;
 192     success = WriteUInt24(length);
 193   }
 194
 195   length_ = old_length;
 196   return success;
 197 }
 198
 199 bool SpdyFrameBuilder::OverwriteFlags(const SpdyFramer& framer,
 200                                       uint8 flags) {
 201   DCHECK_GT(framer.protocol_version(), SPDY3);
 202   bool success = false;
 203   const size_t old_length = length_;
 204   // Flags are the fifth octet in the frame prefix.
 205   length_ = 4;
 206   success = WriteUInt8(flags);
 207   length_ = old_length;
 208   return success;
 209 }
 210
 211 bool SpdyFrameBuilder::CanWrite(size_t length) const {
 212   if (length > kLengthMask) {
 213     DCHECK(false);
 214     return false;
 215   }
 216
 217   if (offset_ + length_ + length > capacity_) {
 218     DCHECK(false);
 219     return false;
 220   }
 221
 222   return true;
 223 }
 224
 225 }  // namespace net