[ON HOLD] Implement pull-based design for content decoding

net/filter/sdch_filter.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.
-
-// SdchFilter applies open_vcdiff content decoding to a datastream.
-// This decoding uses a pre-cached dictionary of text fragments to decode
-// (expand) the stream back to its original contents.
-//
-// This SdchFilter internally uses open_vcdiff/vcdec library to do decoding.
-//
-// SdchFilter is also a subclass of Filter. See the latter's header file
-// filter.h for sample usage.
-
-#ifndef NET_FILTER_SDCH_FILTER_H_
-#define NET_FILTER_SDCH_FILTER_H_
-
-#include <stddef.h>
-
-#include <memory>
-#include <string>
-
-#include "base/macros.h"
-#include "net/base/net_export.h"
-#include "net/base/sdch_dictionary.h"
-#include "net/base/sdch_manager.h"
-#include "net/filter/filter.h"
-
-namespace open_vcdiff {
-class VCDiffStreamingDecoder;
-}
-
-namespace net {
-
-class NET_EXPORT_PRIVATE SdchFilter : public Filter {
- public:
-  ~SdchFilter() override;
-
-  // Initializes filter decoding mode and internal control blocks.
-  bool InitDecoding(Filter::FilterType filter_type);
-
-  // Decode the pre-filter data and writes the output into |dest_buffer|
-  // The function returns FilterStatus. See filter.h for its description.
-  //
-  // Upon entry, *dest_len is the total size (in number of chars) of the
-  // destination buffer. Upon exit, *dest_len is the actual number of chars
-  // written into the destination buffer.
-  FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len) override;
-
- private:
-  // Internal status. Once we enter an error state, we stop processing data.
-  enum DecodingStatus {
-    DECODING_UNINITIALIZED,
-    WAITING_FOR_DICTIONARY_SELECTION,
-    DECODING_IN_PROGRESS,
-    DECODING_ERROR,
-    META_REFRESH_RECOVERY,  // Decoding error being handled by a meta-refresh.
-    PASS_THROUGH,  // Non-sdch content being passed without alteration.
-  };
-
-  // Only to be instantiated by Filter::Factory.
-  SdchFilter(FilterType type, const FilterContext& filter_context);
-  friend class Filter;
-
-  // Identify the suggested dictionary, and initialize underlying decompressor.
-  Filter::FilterStatus InitializeDictionary();
-
-  // Move data that was internally buffered (after decompression) to the
-  // specified dest_buffer.
-  int OutputBufferExcess(char* const dest_buffer, size_t available_space);
-
-  // Add SDCH Problem to net-log and record histogram.
-  void LogSdchProblem(SdchProblemCode problem);
-
-  // Context data from the owner of this filter.
-  const FilterContext& filter_context_;
-
-  // Tracks the status of decoding.
-  // This variable is initialized by InitDecoding and updated only by
-  // ReadFilteredData.
-  DecodingStatus decoding_status_;
-
-  // The underlying decoder that processes data.
-  // This data structure is initialized by InitDecoding and updated in
-  // ReadFilteredData.
-  std::unique_ptr<open_vcdiff::VCDiffStreamingDecoder>
-      vcdiff_streaming_decoder_;
-
-  // After the encoded response SDCH header is read, this variable contains
-  // the server hash with trailing null byte.
-  std::string dictionary_hash_;
-
-  // After assembling an entire dictionary hash (the first 9 bytes of the
-  // sdch payload, we check to see if it is plausible, meaning it has a null
-  // termination, and has 8 characters that are possible in a net-safe base64
-  // encoding. If the hash is not plausible, then the payload is probably not
-  // an SDCH encoded bundle, and various error recovery strategies can be
-  // attempted.
-  bool dictionary_hash_is_plausible_;
-
-  // We keep a copy of the URLRequestContext for use in the destructor, (at
-  // which point GetURLRequestContext() will likely return null because of
-  // the disassociation of the URLRequest from the URLRequestJob). This is
-  // safe because the URLRequestJob (and any filters) are guaranteed to be
-  // deleted before the URLRequestContext is destroyed.
-  const URLRequestContext* const url_request_context_;
-
-  // The decoder may demand a larger output buffer than the target of
-  // ReadFilteredData so we buffer the excess output between calls.
-  std::string dest_buffer_excess_;
-  // To avoid moving strings around too much, we save the index into
-  // dest_buffer_excess_ that has the next byte to output.
-  size_t dest_buffer_excess_index_;
-
-  // To get stats on activities, we keep track of source and target bytes.
-  // Visit about:histograms/Sdch to see histogram data.
-  size_t source_bytes_;
-  size_t output_bytes_;
-
-  // Error recovery in content type may add an sdch filter type, in which case
-  // we should gracefully perform pass through if the format is incorrect, or
-  // an applicable dictionary can't be found.
-  bool possible_pass_through_;
-
-  // The URL that is currently being filtered.
-  // This is used to restrict use of a dictionary to a specific URL or path.
-  GURL url_;
-
-  // To facilitate error recovery, allow filter to know if content is text/html
-  // by checking within this mime type (we may do a meta-refresh via html).
-  std::string mime_type_;
-
-  // If the response was encoded with a dictionary different than those
-  // advertised (e.g. a cached response using an old dictionary), this
-  // variable preserves that dictionary from deletion during decoding.
-  std::unique_ptr<SdchManager::DictionarySet> unexpected_dictionary_handle_;
-
-  DISALLOW_COPY_AND_ASSIGN(SdchFilter);
-};
-
-}  // namespace net
-
-#endif  // NET_FILTER_SDCH_FILTER_H_