net/spdy/hpack/hpack_input_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_input_stream.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/basictypes.h"
  10 #include "base/logging.h"
  11
  12 namespace net {
  13
  14 using base::StringPiece;
  15 using std::string;
  16
  17 HpackInputStream::HpackInputStream(uint32 max_string_literal_size,
  18                                    StringPiece buffer)
  19     : max_string_literal_size_(max_string_literal_size),
  20       buffer_(buffer),
  21       bit_offset_(0) {}
  22
  23 HpackInputStream::~HpackInputStream() {}
  24
  25 bool HpackInputStream::HasMoreData() const {
  26   return !buffer_.empty();
  27 }
  28
  29 bool HpackInputStream::MatchPrefixAndConsume(HpackPrefix prefix) {
  30   DCHECK_GT(prefix.bit_size, 0u);
  31   DCHECK_LE(prefix.bit_size, 8u);
  32
  33   uint32 peeked = 0;
  34   size_t peeked_count = 0;
  35
  36   if (!PeekBits(&peeked_count, &peeked))
  37     return false;
  38
  39   if ((peeked >> (32 - prefix.bit_size)) == prefix.bits) {
  40     ConsumeBits(prefix.bit_size);
  41     return true;
  42   }
  43   return false;
  44 }
  45
  46 bool HpackInputStream::PeekNextOctet(uint8* next_octet) {
  47   if ((bit_offset_ > 0) || buffer_.empty())
  48     return false;
  49
  50   *next_octet = buffer_[0];
  51   return true;
  52 }
  53
  54 bool HpackInputStream::DecodeNextOctet(uint8* next_octet) {
  55   if (!PeekNextOctet(next_octet))
  56     return false;
  57
  58   buffer_.remove_prefix(1);
  59   return true;
  60 }
  61
  62 bool HpackInputStream::DecodeNextUint32(uint32* I) {
  63   size_t N = 8 - bit_offset_;
  64   DCHECK_GT(N, 0u);
  65   DCHECK_LE(N, 8u);
  66
  67   bit_offset_ = 0;
  68
  69   *I = 0;
  70
  71   uint8 next_marker = (1 << N) - 1;
  72   uint8 next_octet = 0;
  73   if (!DecodeNextOctet(&next_octet))
  74     return false;
  75   *I = next_octet & next_marker;
  76
  77   bool has_more = (*I == next_marker);
  78   size_t shift = 0;
  79   while (has_more && (shift < 32)) {
  80     uint8 next_octet = 0;
  81     if (!DecodeNextOctet(&next_octet))
  82       return false;
  83     has_more = (next_octet & 0x80) != 0;
  84     next_octet &= 0x7f;
  85     uint32 addend = next_octet << shift;
  86     // Check for overflow.
  87     if ((addend >> shift) != next_octet) {
  88       return false;
  89     }
  90     *I += addend;
  91     shift += 7;
  92   }
  93
  94   return !has_more;
  95 }
  96
  97 bool HpackInputStream::DecodeNextIdentityString(StringPiece* str) {
  98   uint32 size = 0;
  99   if (!DecodeNextUint32(&size))
 100     return false;
 101
 102   if (size > max_string_literal_size_)
 103     return false;
 104
 105   if (size > buffer_.size())
 106     return false;
 107
 108   *str = StringPiece(buffer_.data(), size);
 109   buffer_.remove_prefix(size);
 110   return true;
 111 }
 112
 113 bool HpackInputStream::DecodeNextHuffmanString(const HpackHuffmanTable& table,
 114                                                string* str) {
 115   uint32 encoded_size = 0;
 116   if (!DecodeNextUint32(&encoded_size))
 117     return false;
 118
 119   if (encoded_size > buffer_.size())
 120     return false;
 121
 122   HpackInputStream bounded_reader(max_string_literal_size_,
 123                                   StringPiece(buffer_.data(), encoded_size));
 124   buffer_.remove_prefix(encoded_size);
 125
 126   // HpackHuffmanTable will not decode beyond |max_string_literal_size_|.
 127   return table.DecodeString(&bounded_reader, max_string_literal_size_, str);
 128 }
 129
 130 bool HpackInputStream::PeekBits(size_t* peeked_count, uint32* out) {
 131   size_t byte_offset = (bit_offset_ + *peeked_count) / 8;
 132   size_t bit_offset = (bit_offset_ + *peeked_count) % 8;
 133
 134   if (*peeked_count >= 32 || byte_offset >= buffer_.size()) {
 135     return false;
 136   }
 137   // We'll read the minimum of the current byte remainder,
 138   // and the remaining unfilled bits of |out|.
 139   size_t bits_to_read = std::min(32 - *peeked_count, 8 - bit_offset);
 140
 141   uint32 new_bits = static_cast<uint32>(buffer_[byte_offset]);
 142   // Shift byte remainder to most-signifcant bits of |new_bits|.
 143   // This drops the leading |bit_offset| bits of the byte.
 144   new_bits = new_bits << (24 + bit_offset);
 145   // Shift bits to the most-significant open bits of |out|.
 146   new_bits = new_bits >> *peeked_count;
 147
 148   CHECK_EQ(*out & new_bits, 0u);
 149   *out |= new_bits;
 150
 151   *peeked_count += bits_to_read;
 152   return true;
 153 }
 154
 155 void HpackInputStream::ConsumeBits(size_t bit_count) {
 156   size_t byte_count = (bit_offset_ + bit_count) / 8;
 157   bit_offset_ = (bit_offset_ + bit_count) % 8;
 158   CHECK_GE(buffer_.size(), byte_count);
 159   if (bit_offset_ != 0) {
 160     CHECK_GT(buffer_.size(), 0u);
 161   }
 162   buffer_.remove_prefix(byte_count);
 163 }
 164
 165 void HpackInputStream::ConsumeByteRemainder() {
 166   if (bit_offset_ != 0) {
 167     ConsumeBits(8 - bit_offset_);
 168   }
 169 }
 170
 171 }  // namespace net