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1 // Copyright 2016 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_HPACK_HUFFMAN_DECODER_H_ | |
6 #define NET_SPDY_HPACK_HPACK_HUFFMAN_DECODER_H_ | |
7 | |
8 #include <stddef.h> | |
9 #include <stdint.h> | |
10 | |
11 #include "net/base/net_export.h" | |
12 #include "net/spdy/hpack/hpack_input_stream.h" | |
13 #include "net/spdy/platform/api/spdy_string.h" | |
14 | |
15 namespace net { | |
16 namespace test { | |
17 class HpackHuffmanDecoderPeer; | |
18 } // namespace test | |
19 | |
20 // Declared as a class to simplify testing. | |
21 // No instances are actually allocated. | |
22 class NET_EXPORT_PRIVATE HpackHuffmanDecoder { | |
23 public: | |
24 typedef uint32_t HuffmanWord; | |
25 typedef size_t HuffmanCodeLength; | |
26 | |
27 HpackHuffmanDecoder() = delete; | |
28 | |
29 // Decodes a string that has been encoded using the HPACK Huffman Code (see | |
30 // https://httpwg.github.io/specs/rfc7541.html#huffman.code), reading the | |
31 // encoded bitstream from |*in|, appending each decoded char to |*out|. | |
32 // To avoid repeatedly growing the |*out| string, the caller should reserve | |
33 // sufficient space in |*out| to hold decoded output. | |
34 // DecodeString() halts when |in| runs out of input, in which case true is | |
35 // returned. It also halts (returning false) if an invalid Huffman code | |
36 // prefix is read. | |
37 static bool DecodeString(HpackInputStream* in, SpdyString* out); | |
38 | |
39 private: | |
40 friend class test::HpackHuffmanDecoderPeer; | |
41 | |
42 // The following private methods are declared here rather than simply | |
43 // inlined into DecodeString so that they can be tested directly. | |
44 | |
45 // Returns the length (in bits) of the HPACK Huffman code that starts with | |
46 // the high bits of |value|. | |
47 static HuffmanCodeLength CodeLengthOfPrefix(HuffmanWord value); | |
48 | |
49 // Decodes the code in the high |code_length| bits of |bits| to the | |
50 // corresponding canonical symbol. | |
51 // Returns a value in the range [0, 256] (257 values). 256 is the EOS symbol, | |
52 // which must not be explicitly encoded; the HPACK spec says that a decoder | |
53 // must treat EOS as a decoding error. | |
54 // Note that the canonical symbol is not the final value to be output because | |
55 // the source symbols are not in descending probability order, so another | |
56 // translation is required (see CanonicalToSource below). | |
57 static HuffmanWord DecodeToCanonical(HuffmanCodeLength code_length, | |
58 HuffmanWord bits); | |
59 | |
60 // Converts a canonical symbol to the source symbol (the char in the original | |
61 // string that was encoded). | |
62 static char CanonicalToSource(HuffmanWord canonical); | |
63 }; | |
64 | |
65 } // namespace net | |
66 | |
67 #endif // NET_SPDY_HPACK_HPACK_HUFFMAN_DECODER_H_ | |
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