net/spdy/hpack_encoder.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_encoder.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/logging.h"
  10 #include "net/spdy/hpack_header_table.h"
  11 #include "net/spdy/hpack_huffman_table.h"
  12 #include "net/spdy/hpack_output_stream.h"
  13
  14 namespace net {
  15
  16 using base::StringPiece;
  17 using std::string;
  18
  19 HpackEncoder::HpackEncoder(const HpackHuffmanTable& table)
  20     : output_stream_(),
  21       allow_huffman_compression_(true),
  22       huffman_table_(table),
  23       char_counts_(NULL),
  24       total_char_counts_(NULL) {}
  25
  26 HpackEncoder::~HpackEncoder() {}
  27
  28 bool HpackEncoder::EncodeHeaderSet(const std::map<string, string>& header_set,
  29                                    string* output) {
  30   // Separate header set into pseudo-headers and regular headers.
  31   Representations pseudo_headers;
  32   Representations regular_headers;
  33   for (std::map<string, string>::const_iterator it = header_set.begin();
  34        it != header_set.end(); ++it) {
  35     if (it->first == "cookie") {
  36       // Note that there can only be one "cookie" header, because header_set is
  37       // a map.
  38       CookieToCrumbs(*it, &regular_headers);
  39     } else if (it->first[0] == kPseudoHeaderPrefix) {
  40       DecomposeRepresentation(*it, &pseudo_headers);
  41     } else {
  42       DecomposeRepresentation(*it, &regular_headers);
  43     }
  44   }
  45
  46   // Encode pseudo-headers.
  47   for (Representations::const_iterator it = pseudo_headers.begin();
  48        it != pseudo_headers.end(); ++it) {
  49     const HpackEntry* entry =
  50         header_table_.GetByNameAndValue(it->first, it->second);
  51     if (entry != NULL) {
  52       EmitIndex(entry);
  53     } else {
  54       if (it->first == ":authority") {
  55         // :authority is always present and rarely changes, and has moderate
  56         // length, therefore it makes a lot of sense to index (insert in the
  57         // header table).
  58         EmitIndexedLiteral(*it);
  59       } else {
  60         // Most common pseudo-header fields are represented in the static table,
  61         // while uncommon ones are small, so do not index them.
  62         EmitNonIndexedLiteral(*it);
  63       }
  64     }
  65   }
  66
  67   // Encode regular headers.
  68   for (Representations::const_iterator it = regular_headers.begin();
  69        it != regular_headers.end(); ++it) {
  70     const HpackEntry* entry =
  71         header_table_.GetByNameAndValue(it->first, it->second);
  72     if (entry != NULL) {
  73       EmitIndex(entry);
  74     } else {
  75       EmitIndexedLiteral(*it);
  76     }
  77   }
  78
  79   output_stream_.TakeString(output);
  80   return true;
  81 }
  82
  83 bool HpackEncoder::EncodeHeaderSetWithoutCompression(
  84     const std::map<string, string>& header_set,
  85     string* output) {
  86
  87   allow_huffman_compression_ = false;
  88   for (std::map<string, string>::const_iterator it = header_set.begin();
  89        it != header_set.end(); ++it) {
  90     // Note that cookies are not crumbled in this case.
  91     EmitNonIndexedLiteral(*it);
  92   }
  93   allow_huffman_compression_ = true;
  94   output_stream_.TakeString(output);
  95   return true;
  96 }
  97
  98 void HpackEncoder::EmitIndex(const HpackEntry* entry) {
  99   output_stream_.AppendPrefix(kIndexedOpcode);
 100   output_stream_.AppendUint32(header_table_.IndexOf(entry));
 101 }
 102
 103 void HpackEncoder::EmitIndexedLiteral(const Representation& representation) {
 104   output_stream_.AppendPrefix(kLiteralIncrementalIndexOpcode);
 105   EmitLiteral(representation);
 106   header_table_.TryAddEntry(representation.first, representation.second);
 107 }
 108
 109 void HpackEncoder::EmitNonIndexedLiteral(
 110     const Representation& representation) {
 111   output_stream_.AppendPrefix(kLiteralNoIndexOpcode);
 112   output_stream_.AppendUint32(0);
 113   EmitString(representation.first);
 114   EmitString(representation.second);
 115 }
 116
 117 void HpackEncoder::EmitLiteral(const Representation& representation) {
 118   const HpackEntry* name_entry = header_table_.GetByName(representation.first);
 119   if (name_entry != NULL) {
 120     output_stream_.AppendUint32(header_table_.IndexOf(name_entry));
 121   } else {
 122     output_stream_.AppendUint32(0);
 123     EmitString(representation.first);
 124   }
 125   EmitString(representation.second);
 126 }
 127
 128 void HpackEncoder::EmitString(StringPiece str) {
 129   size_t encoded_size = (!allow_huffman_compression_ ? str.size()
 130                          : huffman_table_.EncodedSize(str));
 131   if (encoded_size < str.size()) {
 132     output_stream_.AppendPrefix(kStringLiteralHuffmanEncoded);
 133     output_stream_.AppendUint32(encoded_size);
 134     huffman_table_.EncodeString(str, &output_stream_);
 135   } else {
 136     output_stream_.AppendPrefix(kStringLiteralIdentityEncoded);
 137     output_stream_.AppendUint32(str.size());
 138     output_stream_.AppendBytes(str);
 139   }
 140   UpdateCharacterCounts(str);
 141 }
 142
 143 void HpackEncoder::SetCharCountsStorage(std::vector<size_t>* char_counts,
 144                                         size_t* total_char_counts) {
 145   CHECK_LE(256u, char_counts->size());
 146   char_counts_ = char_counts;
 147   total_char_counts_ = total_char_counts;
 148 }
 149
 150 void HpackEncoder::UpdateCharacterCounts(base::StringPiece str) {
 151   if (char_counts_ == NULL || total_char_counts_ == NULL) {
 152     return;
 153   }
 154   for (StringPiece::const_iterator it = str.begin(); it != str.end(); ++it) {
 155     ++(*char_counts_)[static_cast<uint8>(*it)];
 156   }
 157   (*total_char_counts_) += str.size();
 158 }
 159
 160 // static
 161 void HpackEncoder::CookieToCrumbs(const Representation& cookie,
 162                                   Representations* out) {
 163   size_t prior_size = out->size();
 164
 165   // See Section 8.1.2.5. "Compressing the Cookie Header Field" in the HTTP/2
 166   // specification at https://tools.ietf.org/html/draft-ietf-httpbis-http2-14.
 167   // Cookie values are split into individually-encoded HPACK representations.
 168   for (size_t pos = 0;;) {
 169     size_t end = cookie.second.find(";", pos);
 170
 171     if (end == StringPiece::npos) {
 172       out->push_back(make_pair(
 173           cookie.first,
 174           cookie.second.substr(pos)));
 175       break;
 176     }
 177     out->push_back(make_pair(
 178         cookie.first,
 179         cookie.second.substr(pos, end - pos)));
 180
 181     // Consume next space if present.
 182     pos = end + 1;
 183     if (pos != cookie.second.size() && cookie.second[pos] == ' ') {
 184       pos++;
 185     }
 186   }
 187   // Sort crumbs and remove duplicates.
 188   std::sort(out->begin() + prior_size, out->end());
 189   out->erase(std::unique(out->begin() + prior_size, out->end()),
 190              out->end());
 191 }
 192
 193 // static
 194 void HpackEncoder::DecomposeRepresentation(const Representation& header_field,
 195                                            Representations* out) {
 196   size_t pos = 0;
 197   size_t end = 0;
 198   while (end != StringPiece::npos) {
 199     end = header_field.second.find('\0', pos);
 200     out->push_back(make_pair(header_field.first,
 201                              header_field.second.substr(pos, end - pos)));
 202     pos = end + 1;
 203   }
 204 }
 205
 206 }  // namespace net