Revert of Add new HTTP/2 and HPACK decoder in net/http2/.

net/http2/hpack/huffman/http2_hpack_huffman_decoder.h

-// 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_HTTP2_HPACK_HUFFMAN_HTTP2_HPACK_HUFFMAN_DECODER_H_
-#define NET_HTTP2_HPACK_HUFFMAN_HTTP2_HPACK_HUFFMAN_DECODER_H_
-
-// HpackHuffmanDecoder is an incremental decoder of strings that have been
-// encoded using the Huffman table defined in the HPACK spec.
-// By incremental, we mean that the HpackHuffmanDecoder::Decode method does
-// not require the entire string to be provided, and can instead decode the
-// string as fragments of it become available (e.g. as HPACK block fragments
-// are received for decoding by HpackEntryDecoder).
-
-#include <stddef.h>
-
-#include <iosfwd>
-#include <string>
-
-#include "base/strings/string_piece.h"
-#include "net/base/net_export.h"
-
-namespace net {
-
-// HuffmanAccumulator is used to store bits during decoding, e.g. next N bits
-// that have not yet been decoded, but have been extracted from the encoded
-// string).  An advantage of using a uint64 for the accumulator
-// is that it has room for the bits of the longest code plus the bits of a full
-// byte; that means that when adding more bits to the accumulator, it can always
-// be done in whole bytes. For example, if we currently have 26 bits in the
-// accumulator, and need more to decode the current symbol, we can add a whole
-// byte to the accumulator, and not have to do juggling with adding 6 bits (to
-// reach 30), and then keep track of the last two bits we've not been able to
-// add to the accumulator.
-typedef uint64_t HuffmanAccumulator;
-typedef size_t HuffmanAccumulatorBitCount;
-
-// HuffmanBitBuffer stores the leading edge of bits to be decoded. The high
-// order bit of accumulator_ is the next bit to be decoded.
-class NET_EXPORT_PRIVATE HuffmanBitBuffer {
- public:
-  HuffmanBitBuffer();
-
-  // Prepare for decoding a new Huffman encoded string.
-  void Reset();
-
-  // Add as many whole bytes to the accumulator (accumulator_) as possible,
-  // returning the number of bytes added.
-  size_t AppendBytes(base::StringPiece input);
-
-  // Get the bits of the accumulator.
-  HuffmanAccumulator value() const { return accumulator_; }
-
-  // Number of bits of the encoded string that are in the accumulator
-  // (accumulator_).
-  HuffmanAccumulatorBitCount count() const { return count_; }
-
-  // Are there no bits in the accumulator?
-  bool IsEmpty() const { return count_ == 0; }
-
-  // Number of additional bits that can be added to the accumulator.
-  HuffmanAccumulatorBitCount free_count() const;
-
-  // Consume the leading |code_length| bits of the accumulator.
-  void ConsumeBits(HuffmanAccumulatorBitCount code_length);
-
-  // Are the contents valid for the end of a Huffman encoded string? The RFC
-  // states that EOS (end-of-string) symbol must not be explicitly encoded in
-  // the bit stream, but any unused bits in the final byte must be set to the
-  // prefix of the EOS symbol, which is all 1 bits. So there can be at most 7
-  // such bits.
-  // Returns true if the bit buffer is empty, or contains at most 7 bits, all
-  // of them 1. Otherwise returns false.
-  bool InputProperlyTerminated() const;
-
-  std::string DebugString() const;
-
- private:
-  HuffmanAccumulator accumulator_;
-  HuffmanAccumulatorBitCount count_;
-};
-
-inline std::ostream& operator<<(std::ostream& out, const HuffmanBitBuffer& v) {
-  return out << v.DebugString();
-}
-
-class NET_EXPORT_PRIVATE HpackHuffmanDecoder {
- public:
-  HpackHuffmanDecoder();
-  ~HpackHuffmanDecoder();
-
-  // Prepare for decoding a new Huffman encoded string.
-  void Reset() { bit_buffer_.Reset(); }
-
-  // Decode the portion of a HPACK Huffman encoded string that is in |input|,
-  // appending the decoded symbols into |*output|, stopping when more bits are
-  // needed to determine the next symbol, which/ means that the input has been
-  // drained, and also that the bit_buffer_ is empty or that the bits that are
-  // in it are not a whole symbol.
-  // If |input| is the start of a string, the caller must first call Reset.
-  // If |input| includes the end of the encoded string, the caller must call
-  // InputProperlyTerminated after Decode has returned true in order to
-  // determine if the encoded string was properly terminated.
-  // Returns false if something went wrong (e.g. the encoding contains the code
-  // EOS symbol). Otherwise returns true, in which case input has been fully
-  // decoded or buffered; in particular, if the low-order bit of the final byte
-  // of the input is not the last bit of an encoded symbol, then bit_buffer_
-  // will contain the leading bits of the code for that symbol, but not the
-  // final bits of that code.
-  // Note that output should be empty, but that it is not cleared by Decode().
-  bool Decode(base::StringPiece input, std::string* output);
-
-  // Is what remains in the bit_buffer_ valid at the end of an encoded string?
-  // Call after passing the the final portion of a Huffman string to Decode,
-  // and getting true as the result.
-  bool InputProperlyTerminated() const {
-    return bit_buffer_.InputProperlyTerminated();
-  }
-
-  bool IsEmptyForTest() const { return bit_buffer_.IsEmpty(); }
-
-  std::string DebugString() const;
-
-  //////////////////////////////////////////////////////////////////////////////
-  // Alternate implementations of Decode:
-
-  // As above, implemented using a tree of if statements to determine the code
-  // length, etc., which are returned as a tree. See PrefixToInfo. This is the
-  // original implementation, current as of 2016-8-8.
-  bool DecodeWithIfTreeAndStruct(base::StringPiece input, std::string* output);
-
-  // Based on DecodeWithIfTreeAndStruct, but adds an optimization for the common
-  // case of short codes (5, 6 or 7), which make up a large fraction of the
-  // frequency distribution on which the HPACK table was based.
-  // TODO(jamessynge): Be precise about that fraction.
-  bool DecodeShortCodesFirst(base::StringPiece input, std::string* output);
-
- private:
-  HuffmanBitBuffer bit_buffer_;
-};
-
-inline std::ostream& operator<<(std::ostream& out,
-                                const HpackHuffmanDecoder& v) {
-  return out << v.DebugString();
-}
-
-}  // namespace net
-
-#endif  // NET_HTTP2_HPACK_HUFFMAN_HTTP2_HPACK_HUFFMAN_DECODER_H_