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Side by Side Diff: net/spdy/hpack_huffman_table.h

Issue 992733002: Remove //net (except for Android test stuff) and sdch (Closed) Base URL: git@github.com:domokit/mojo.git@master
Patch Set: Created 5 years, 9 months ago
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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_HUFFMAN_TABLE_H_
6 #define NET_SPDY_HPACK_HUFFMAN_TABLE_H_
7
8 #include <cstddef>
9 #include <string>
10 #include <vector>
11
12 #include "base/basictypes.h"
13 #include "base/strings/string_piece.h"
14 #include "net/base/net_export.h"
15 #include "net/spdy/hpack_constants.h"
16
17 namespace net {
18
19 namespace test {
20 class HpackHuffmanTablePeer;
21 } // namespace test
22
23 class HpackInputStream;
24 class HpackOutputStream;
25
26 // HpackHuffmanTable encodes and decodes string literals using a constructed
27 // canonical Huffman code. Once initialized, an instance is read only and
28 // may be accessed only through its const interface.
29 class NET_EXPORT_PRIVATE HpackHuffmanTable {
30 public:
31 friend class test::HpackHuffmanTablePeer;
32
33 typedef HpackHuffmanSymbol Symbol;
34
35 // DecodeTables are multilevel indexes on code prefixes. Each table indexes
36 // a portion of the prefix mapped to DecodeEntry, which in turn either
37 // captures a terminal symbol, or points to the next DecodeTable to consult
38 // with successive portions of the prefix.
39 struct NET_EXPORT_PRIVATE DecodeEntry {
40 DecodeEntry();
41 DecodeEntry(uint8 next_table_index, uint8 length, uint16 symbol_id);
42
43 // The next table to consult. If this is a terminal,
44 // |next_table_index| will be self-referential.
45 uint8 next_table_index;
46 // Bit-length of terminal code, if this is a terminal. Length of the
47 // longest code having this prefix, if non-terminal.
48 uint8 length;
49 // Set only for terminal entries.
50 uint16 symbol_id;
51 };
52 struct NET_EXPORT_PRIVATE DecodeTable {
53 // Number of bits indexed by the chain leading to this table.
54 uint8 prefix_length;
55 // Number of additional prefix bits this table indexes.
56 uint8 indexed_length;
57 // Entries are represented as a length |size()| slice into
58 // |decode_entries_| beginning at |entries_offset|.
59 size_t entries_offset;
60 // Returns |1 << indexed_length|.
61 size_t size() const;
62 };
63
64 HpackHuffmanTable();
65 ~HpackHuffmanTable();
66
67 // Prepares HpackHuffmanTable to encode & decode the canonical Huffman
68 // code as determined by the given symbols. Must be called exactly once.
69 // Returns false if the input symbols define an invalid coding, and true
70 // otherwise. Symbols must be presented in ascending ID order with no gaps,
71 // and |symbol_count| must fit in a uint16.
72 bool Initialize(const Symbol* input_symbols, size_t symbol_count);
73
74 // Returns whether Initialize() has been successfully called.
75 bool IsInitialized() const;
76
77 // Encodes the input string to the output stream using the table's Huffman
78 // context.
79 void EncodeString(base::StringPiece in, HpackOutputStream* out) const;
80
81 // Returns the encoded size of the input string.
82 size_t EncodedSize(base::StringPiece in) const;
83
84 // Decodes symbols from |in| into |out|. It is the caller's responsibility
85 // to ensure |out| has a reserved a sufficient buffer to hold decoded output.
86 // DecodeString() halts when |in| runs out of input, in which case true is
87 // returned. It also halts (returning false) if an invalid Huffman code
88 // prefix is read, or if |out_capacity| would otherwise be overflowed.
89 bool DecodeString(HpackInputStream* in,
90 size_t out_capacity,
91 std::string* out) const;
92
93 private:
94 // Expects symbols ordered on length & ID ascending.
95 void BuildDecodeTables(const std::vector<Symbol>& symbols);
96
97 // Expects symbols ordered on ID ascending.
98 void BuildEncodeTable(const std::vector<Symbol>& symbols);
99
100 // Adds a new DecodeTable with the argument prefix & indexed length.
101 // Returns the new table index.
102 uint8 AddDecodeTable(uint8 prefix, uint8 indexed);
103
104 const DecodeEntry& Entry(const DecodeTable& table, uint32 index) const;
105
106 void SetEntry(const DecodeTable& table, uint32 index,
107 const DecodeEntry& entry);
108
109 std::vector<DecodeTable> decode_tables_;
110 std::vector<DecodeEntry> decode_entries_;
111
112 // Symbol code and code length, in ascending symbol ID order.
113 // Codes are stored in the most-significant bits of the word.
114 std::vector<uint32> code_by_id_;
115 std::vector<uint8> length_by_id_;
116
117 // The first 8 bits of the longest code. Applied when generating padding bits.
118 uint8 pad_bits_;
119
120 // If initialization fails, preserve the symbol ID which failed validation
121 // for examination in tests.
122 uint16 failed_symbol_id_;
123 };
124
125 } // namespace net
126
127 #endif // NET_SPDY_HPACK_HUFFMAN_TABLE_H_
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