hpack_constants.h revision 03b57e008b61dfcb1fbad3aea950ae0e001748b0 
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
16namespace net {
17
18// An HpackPrefix signifies |bits| stored in the top |bit_size| bits
19// of an octet.
20struct HpackPrefix {
21  uint8 bits;
22  size_t bit_size;
23};
24
25// Represents a symbol and its Huffman code (stored in most-significant bits).
26struct HpackHuffmanSymbol {
27  uint32 code;
28  uint8 length;
29  uint16 id;
30};
31
32class HpackHuffmanTable;
33
34const uint32 kDefaultHeaderTableSizeSetting = 4096;
35
36// Largest string literal an HpackDecoder/HpackEncoder will attempt to process
37// before returning an error.
38const 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.
43const uint32 kMaxDecodeBufferSize = 32 * 1024;
44
45// 6.2: Flag for a string literal that is stored unmodified (i.e.,
46// without Huffman encoding).
47const HpackPrefix kStringLiteralIdentityEncoded = { 0x0, 1 };
48
49// 6.2: Flag for a Huffman-coded string literal.
50const HpackPrefix kStringLiteralHuffmanEncoded = { 0x1, 1 };
51
52// 7.1: Opcode for an indexed header field.
53const HpackPrefix kIndexedOpcode = { 0x1, 1 };
54
55// 7.2.1: Opcode for a literal header field with incremental indexing.
56const HpackPrefix kLiteralIncrementalIndexOpcode = { 0x1, 2 };
57
58// 7.2.2: Opcode for a literal header field without indexing.
59const HpackPrefix kLiteralNoIndexOpcode = { 0x0, 4 };
60
61// 7.2.3: Opcode for a literal header field which is never indexed.
62const 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.
66const HpackPrefix kHeaderTableSizeUpdateOpcode = { 0x1, 3 };
67
68// Returns symbol code table from "Appendix C. Huffman Codes".
69NET_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.
74NET_EXPORT_PRIVATE const HpackHuffmanTable& ObtainHpackHuffmanTable();
75
76}  // namespace net
77
78#endif  // NET_SPDY_HPACK_CONSTANTS_H_
79