net/spdy/hpack_constants.h

   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 #ifndef NET_SPDY_HPACK_CONSTANTS_H_
   6 #define NET_SPDY_HPACK_CONSTANTS_H_
   7
   8 #include <vector>
   9
  10 #include "base/basictypes.h"
  11 #include "net/base/net_export.h"
  12
  13 // All section references below are to
  14 // http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-08
  15
  16 namespace net {
  17
  18 // An HpackPrefix signifies |bits| stored in the top |bit_size| bits
  19 // of an octet.
  20 struct HpackPrefix {
  21   uint8 bits;
  22   size_t bit_size;
  23 };
  24
  25 // Represents a symbol and its Huffman code (stored in most-significant bits).
  26 struct HpackHuffmanSymbol {
  27   uint32 code;
  28   uint8 length;
  29   uint16 id;
  30 };
  31
  32 class HpackHuffmanTable;
  33
  34 const uint32 kDefaultHeaderTableSizeSetting = 4096;
  35
  36 // Largest string literal an HpackDecoder/HpackEncoder will attempt to process
  37 // before returning an error.
  38 const uint32 kDefaultMaxStringLiteralSize = 16 * 1024;
  39
  40 // Maximum amount of encoded header buffer HpackDecoder will retain before
  41 // returning an error.
  42 // TODO(jgraettinger): Remove with SpdyHeadersHandlerInterface switch.
  43 const uint32 kMaxDecodeBufferSize = 32 * 1024;
  44
  45 // 6.2: Flag for a string literal that is stored unmodified (i.e.,
  46 // without Huffman encoding).
  47 const HpackPrefix kStringLiteralIdentityEncoded = { 0x0, 1 };
  48
  49 // 6.2: Flag for a Huffman-coded string literal.
  50 const HpackPrefix kStringLiteralHuffmanEncoded = { 0x1, 1 };
  51
  52 // 7.1: Opcode for an indexed header field.
  53 const HpackPrefix kIndexedOpcode = { 0x1, 1 };
  54
  55 // 7.2.1: Opcode for a literal header field with incremental indexing.
  56 const HpackPrefix kLiteralIncrementalIndexOpcode = { 0x1, 2 };
  57
  58 // 7.2.2: Opcode for a literal header field without indexing.
  59 const HpackPrefix kLiteralNoIndexOpcode = { 0x0, 4 };
  60
  61 // 7.2.3: Opcode for a literal header field which is never indexed.
  62 const HpackPrefix kLiteralNeverIndexOpcode = { 0x1, 4 };
  63
  64 // 7.3: Opcode for maximum header table size update. Begins a varint-encoded
  65 // table size with a 5-bit prefix.
  66 const HpackPrefix kHeaderTableSizeUpdateOpcode = { 0x1, 3 };
  67
  68 // Returns symbol code table from "Appendix C. Huffman Codes".
  69 NET_EXPORT_PRIVATE std::vector<HpackHuffmanSymbol> HpackHuffmanCode();
  70
  71 // Returns a HpackHuffmanTable instance initialized with |kHpackHuffmanCode|.
  72 // The instance is read-only, has static lifetime, and is safe to share amoung
  73 // threads. This function is thread-safe.
  74 NET_EXPORT_PRIVATE const HpackHuffmanTable& ObtainHpackHuffmanTable();
  75
  76 }  // namespace net
  77
  78 #endif  // NET_SPDY_HPACK_CONSTANTS_H_