net/spdy/hpack/hpack_output_stream.cc

   1 // Copyright 2014 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/hpack/hpack_output_stream.h"
   6
   7 #include "base/logging.h"
   8
   9 namespace net {
  10
  11 using base::StringPiece;
  12 using std::string;
  13
  14 HpackOutputStream::HpackOutputStream() : bit_offset_(0) {}
  15
  16 HpackOutputStream::~HpackOutputStream() {}
  17
  18 void HpackOutputStream::AppendBits(uint8 bits, size_t bit_size) {
  19   DCHECK_GT(bit_size, 0u);
  20   DCHECK_LE(bit_size, 8u);
  21   DCHECK_EQ(bits >> bit_size, 0);
  22   size_t new_bit_offset = bit_offset_ + bit_size;
  23   if (bit_offset_ == 0) {
  24     // Buffer ends on a byte boundary.
  25     DCHECK_LE(bit_size, 8u);
  26     buffer_.append(1, bits << (8 - bit_size));
  27   } else if (new_bit_offset <= 8) {
  28     // Buffer does not end on a byte boundary but the given bits fit
  29     // in the remainder of the last byte.
  30     *buffer_.rbegin() |= bits << (8 - new_bit_offset);
  31   } else {
  32     // Buffer does not end on a byte boundary and the given bits do
  33     // not fit in the remainder of the last byte.
  34     *buffer_.rbegin() |= bits >> (new_bit_offset - 8);
  35     buffer_.append(1, bits << (16 - new_bit_offset));
  36   }
  37   bit_offset_ = new_bit_offset % 8;
  38 }
  39
  40 void HpackOutputStream::AppendPrefix(HpackPrefix prefix) {
  41   AppendBits(prefix.bits, prefix.bit_size);
  42 }
  43
  44 void HpackOutputStream::AppendBytes(StringPiece buffer) {
  45   DCHECK_EQ(bit_offset_, 0u);
  46   buffer_.append(buffer.data(), buffer.size());
  47 }
  48
  49 void HpackOutputStream::AppendUint32(uint32 I) {
  50   // The algorithm below is adapted from the pseudocode in 6.1.
  51   size_t N = 8 - bit_offset_;
  52   uint8 max_first_byte = static_cast<uint8>((1 << N) - 1);
  53   if (I < max_first_byte) {
  54     AppendBits(static_cast<uint8>(I), N);
  55   } else {
  56     AppendBits(max_first_byte, N);
  57     I -= max_first_byte;
  58     while ((I & ~0x7f) != 0) {
  59       buffer_.append(1, (I & 0x7f) | 0x80);
  60       I >>= 7;
  61     }
  62     AppendBits(static_cast<uint8>(I), 8);
  63   }
  64 }
  65
  66 void HpackOutputStream::TakeString(string* output) {
  67   // This must hold, since all public functions cause the buffer to
  68   // end on a byte boundary.
  69   DCHECK_EQ(bit_offset_, 0u);
  70   buffer_.swap(*output);
  71   buffer_.clear();
  72   bit_offset_ = 0;
  73 }
  74
  75 }  // namespace net