net/spdy/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_output_stream.h"
   6
   7 #include "base/logging.h"
   8
   9
  10 namespace net {
  11
  12 using base::StringPiece;
  13 using std::string;
  14
  15 HpackOutputStream::HpackOutputStream()
  16     : bit_offset_(0) {}
  17
  18 HpackOutputStream::~HpackOutputStream() {}
  19
  20 void HpackOutputStream::AppendBits(uint8 bits, size_t bit_size) {
  21   DCHECK_GT(bit_size, 0u);
  22   DCHECK_LE(bit_size, 8u);
  23   DCHECK_EQ(bits >> bit_size, 0);
  24   size_t new_bit_offset = bit_offset_ + bit_size;
  25   if (bit_offset_ == 0) {
  26     // Buffer ends on a byte boundary.
  27     DCHECK_LE(bit_size, 8u);
  28     buffer_.append(1, bits << (8 - bit_size));
  29   } else if (new_bit_offset <= 8) {
  30     // Buffer does not end on a byte boundary but the given bits fit
  31     // in the remainder of the last byte.
  32     *buffer_.rbegin() |= bits << (8 - new_bit_offset);
  33   } else {
  34     // Buffer does not end on a byte boundary and the given bits do
  35     // not fit in the remainder of the last byte.
  36     *buffer_.rbegin() |= bits >> (new_bit_offset - 8);
  37     buffer_.append(1, bits << (16 - new_bit_offset));
  38   }
  39   bit_offset_ = new_bit_offset % 8;
  40 }
  41
  42 void HpackOutputStream::AppendPrefix(HpackPrefix prefix) {
  43   AppendBits(prefix.bits, prefix.bit_size);
  44 }
  45
  46 void HpackOutputStream::AppendBytes(StringPiece buffer) {
  47   DCHECK_EQ(bit_offset_, 0u);
  48   buffer_.append(buffer.data(), buffer.size());
  49 }
  50
  51 void HpackOutputStream::AppendUint32(uint32 I) {
  52   // The algorithm below is adapted from the pseudocode in 4.1.1.
  53   size_t N = 8 - bit_offset_;
  54   uint8 max_first_byte = static_cast<uint8>((1 << N) - 1);
  55   if (I < max_first_byte) {
  56     AppendBits(static_cast<uint8>(I), N);
  57   } else {
  58     AppendBits(max_first_byte, N);
  59     I -= max_first_byte;
  60     while ((I & ~0x7f) != 0) {
  61       buffer_.append(1, (I & 0x7f) | 0x80);
  62       I >>= 7;
  63     }
  64     AppendBits(static_cast<uint8>(I), 8);
  65   }
  66 }
  67
  68 void HpackOutputStream::TakeString(string* output) {
  69   // This must hold, since all public functions cause the buffer to
  70   // end on a byte boundary.
  71   DCHECK_EQ(bit_offset_, 0u);
  72   buffer_.swap(*output);
  73   buffer_.clear();
  74   bit_offset_ = 0;
  75 }
  76
  77 }  // namespace net