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      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_NE(-1,
     67             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(version_,
    105       SpdyConstants::SerializeFrameType(version_, type)));
    106   DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
    107   DCHECK_LT(SPDY3, framer.protocol_version());
    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<int>(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_ <= SPDY3) {
    172     DCHECK_GE(SpdyConstants::GetFrameMaximumSize(version_) -
    173               framer.GetFrameMinimumSize(),
    174               length);
    175   } else {
    176     DCHECK_GE(SpdyConstants::GetFrameMaximumSize(version_), length);
    177   }
    178   bool success = false;
    179   const size_t old_length = length_;
    180 
    181   if (version_ <= SPDY3) {
    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_LT(SPDY3, framer.protocol_version());
    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
    226