net/spdy/hpack_encoder.h

// Copyright 2014 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_ENCODER_H_
#define NET_SPDY_HPACK_ENCODER_H_

#include <map>
#include <string>
#include <vector>

#include "base/basictypes.h"
#include "base/macros.h"
#include "base/strings/string_piece.h"
#include "net/base/net_export.h"
#include "net/spdy/hpack_header_table.h"
#include "net/spdy/hpack_output_stream.h"

// An HpackEncoder encodes header sets as outlined in
// http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-07

namespace net {

class HpackHuffmanTable;

namespace test {
class HpackEncoderPeer;
}  // namespace test

class NET_EXPORT_PRIVATE HpackEncoder {
 public:
  friend class test::HpackEncoderPeer;

  // |table| is an initialized HPACK Huffman table, having an
  // externally-managed lifetime which spans beyond HpackEncoder.
  explicit HpackEncoder(const HpackHuffmanTable& table);
  ~HpackEncoder();

  // Encodes the given header set into the given string. Returns
  // whether or not the encoding was successful.
  bool EncodeHeaderSet(const std::map<std::string, std::string>& header_set,
                       std::string* output);

  // Encodes the given header set into the given string. Only non-indexed
  // literal representations are emitted, bypassing the header table. Huffman
  // coding is also not used. Returns whether the encoding was successful.
  // TODO(jgraettinger): Enable Huffman coding once the table as stablized.
  bool EncodeHeaderSetWithoutCompression(
      const std::map<std::string, std::string>& header_set,
      std::string* output);

  // Called upon a change to SETTINGS_HEADER_TABLE_SIZE. Specifically, this
  // is to be called after receiving (and sending an acknowledgement for) a
  // SETTINGS_HEADER_TABLE_SIZE update from the remote decoding endpoint.
  void ApplyHeaderTableSizeSetting(size_t size_setting) {
    header_table_.SetSettingsHeaderTableSize(size_setting);
  }

  // Sets externally-owned storage for aggregating character counts of emitted
  // literal representations.
  void SetCharCountsStorage(std::vector<size_t>* char_counts,
                            size_t* total_char_counts);

 private:
  typedef std::pair<base::StringPiece, base::StringPiece> Representation;
  typedef std::vector<Representation> Representations;

  // Emits a static/dynamic indexed representation (Section 4.2).
  void EmitDynamicIndex(HpackEntry* entry);
  void EmitStaticIndex(HpackEntry* entry);

  // Emits a literal representation (Section 4.3).
  void EmitIndexedLiteral(const Representation& representation);
  void EmitNonIndexedLiteral(const Representation& representation);
  void EmitLiteral(const Representation& representation);

  // Emits a Huffman or identity string (whichever is smaller).
  void EmitString(base::StringPiece str);

  void UpdateCharacterCounts(base::StringPiece str);

  // Determines the representation delta required to encode |header_set| in
  // the current header table context. Entries in the reference set are
  // enumerated and marked with membership in the current |header_set|.
  // Representations which must be explicitly emitted are returned.
  Representations DetermineEncodingDelta(
      const std::map<std::string, std::string>& header_set);

  // Crumbles a cookie header into sorted, de-duplicated crumbs.
  static void CookieToCrumbs(const Representation& cookie,
                             Representations* crumbs_out);

  HpackHeaderTable header_table_;
  HpackOutputStream output_stream_;

  bool allow_huffman_compression_;
  const HpackHuffmanTable& huffman_table_;

  // Externally-owned, nullable storage for character counts of literals.
  std::vector<size_t>* char_counts_;
  size_t* total_char_counts_;

  DISALLOW_COPY_AND_ASSIGN(HpackEncoder);
};

}  // namespace net

#endif  // NET_SPDY_HPACK_ENCODER_H_