| // Copyright 2016 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef NET_SPDY_HPACK_HPACK_HUFFMAN_DECODER_H_ |
| #define NET_SPDY_HPACK_HPACK_HUFFMAN_DECODER_H_ |
| |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| #include <string> |
| |
| #include "net/base/net_export.h" |
| #include "net/spdy/hpack/hpack_input_stream.h" |
| |
| namespace net { |
| namespace test { |
| class HpackHuffmanDecoderPeer; |
| } // namespace test |
| |
| // Declared as a class to simplify testing. |
| // No instances are actually allocated. |
| class NET_EXPORT_PRIVATE HpackHuffmanDecoder { |
| public: |
| typedef uint32_t HuffmanWord; |
| typedef size_t HuffmanCodeLength; |
| |
| HpackHuffmanDecoder() = delete; |
| |
| // Decodes a string that has been encoded using the HPACK Huffman Code (see |
| // https://httpwg.github.io/specs/rfc7541.html#huffman.code), reading the |
| // encoded bitstream from |*in|, appending each decoded char to |*out|. |
| // To avoid repeatedly growing the |*out| string, the caller should reserve |
| // sufficient space in |*out| to hold decoded output. |
| // DecodeString() halts when |in| runs out of input, in which case true is |
| // returned. It also halts (returning false) if an invalid Huffman code |
| // prefix is read. |
| static bool DecodeString(HpackInputStream* in, std::string* out); |
| |
| private: |
| friend class test::HpackHuffmanDecoderPeer; |
| |
| // The following private methods are declared here rather than simply |
| // inlined into DecodeString so that they can be tested directly. |
| |
| // Returns the length (in bits) of the HPACK Huffman code that starts with |
| // the high bits of |value|. |
| static HuffmanCodeLength CodeLengthOfPrefix(HuffmanWord value); |
| |
| // Decodes the code in the high |code_length| bits of |bits| to the |
| // corresponding canonical symbol. |
| // Returns a value in the range [0, 256] (257 values). 256 is the EOS symbol, |
| // which must not be explicitly encoded; the HPACK spec says that a decoder |
| // must treat EOS as a decoding error. |
| // Note that the canonical symbol is not the final value to be output because |
| // the source symbols are not in descending probability order, so another |
| // translation is required (see CanonicalToSource below). |
| static HuffmanWord DecodeToCanonical(HuffmanCodeLength code_length, |
| HuffmanWord bits); |
| |
| // Converts a canonical symbol to the source symbol (the char in the original |
| // string that was encoded). |
| static char CanonicalToSource(HuffmanWord canonical); |
| }; |
| |
| } // namespace net |
| |
| #endif // NET_SPDY_HPACK_HPACK_HUFFMAN_DECODER_H_ |