text: // 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 QUICHE_HTTP2_HPACK_DECODER_HPACK_DECODER_STRING_BUFFER_H_
  #define QUICHE_HTTP2_HPACK_DECODER_HPACK_DECODER_STRING_BUFFER_H_
  
  // HpackDecoderStringBuffer helps an HPACK decoder to avoid copies of a string
  // literal (name or value) except when necessary (e.g. when split across two
  // or more HPACK block fragments).
  
  #include <stddef.h>
  
  #include <ostream>
  #include <string>
  
  #include "absl/strings/string_view.h"
  #include "gquiche/http2/hpack/huffman/hpack_huffman_decoder.h"
  #include "gquiche/common/platform/api/quiche_export.h"
  
  namespace http2 {
  
  class QUICHE_EXPORT_PRIVATE HpackDecoderStringBuffer {
   public:
    enum class State : uint8_t { RESET, COLLECTING, COMPLETE };
    enum class Backing : uint8_t { RESET, UNBUFFERED, BUFFERED, STATIC };
  
    HpackDecoderStringBuffer();
    ~HpackDecoderStringBuffer();
  
    HpackDecoderStringBuffer(const HpackDecoderStringBuffer&) = delete;
    HpackDecoderStringBuffer& operator=(const HpackDecoderStringBuffer&) = delete;
  
    void Reset();
    void Set(absl::string_view value, bool is_static);
  
    // Note that for Huffman encoded strings the length of the string after
    // decoding may be larger (expected), the same or even smaller; the latter
    // are unlikely, but possible if the encoder makes odd choices.
    void OnStart(bool huffman_encoded, size_t len);
    bool OnData(const char* data, size_t len);
    bool OnEnd();
    void BufferStringIfUnbuffered();
    bool IsBuffered() const;
    size_t BufferedLength() const;
  
    // Accessors for the completely collected string (i.e. Set or OnEnd has just
    // been called, and no reset of the state has occurred).
  
    // Returns a string_view pointing to the backing store for the string,
    // either the internal buffer or the original transport buffer (e.g. for a
    // literal value that wasn't Huffman encoded, and that wasn't split across
    // transport buffers).
    absl::string_view str() const;
  
    // Same as str() if state_ is COMPLETE. Otherwise, returns empty string piece.
    absl::string_view GetStringIfComplete() const;
  
    // Returns the completely collected string by value, using std::move in an
    // effort to avoid unnecessary copies. ReleaseString() must not be called
    // unless the string has been buffered (to avoid forcing a potentially
    // unnecessary copy). ReleaseString() also resets the instance so that it can
    // be used to collect another string.
    std::string ReleaseString();
  
    State state_for_testing() const { return state_; }
    Backing backing_for_testing() const { return backing_; }
    void OutputDebugStringTo(std::ostream& out) const;
  
    // Returns the estimate of dynamically allocated memory in bytes.
    size_t EstimateMemoryUsage() const;
  
   private:
    // Storage for the string being buffered, if buffering is necessary
    // (e.g. if Huffman encoded, buffer_ is storage for the decoded string).
    std::string buffer_;
  
    // The string_view to be returned by HpackDecoderStringBuffer::str(). If
    // a string has been collected, but not buffered, value_ points to that
    // string.
    absl::string_view value_;
  
    // The decoder to use if the string is Huffman encoded.
    HpackHuffmanDecoder decoder_;
  
    // Count of bytes not yet passed to OnData.
    size_t remaining_len_;
  
    // Is the HPACK string Huffman encoded?
    bool is_huffman_encoded_;
  
    // State of the string decoding process.
    State state_;
  
    // Where is the string stored?
    Backing backing_;
  };
  
  QUICHE_EXPORT_PRIVATE std::ostream& operator<<(
      std::ostream& out,
      const HpackDecoderStringBuffer& v);
  
  }  // namespace http2
  
  #endif  // QUICHE_HTTP2_HPACK_DECODER_HPACK_DECODER_STRING_BUFFER_H_
  