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

net/filter/gzip_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.
-
-// GZipFilter applies gzip and deflate content encoding/decoding to a data
-// stream. As specified by HTTP 1.1, with gzip encoding the content is
-// wrapped with a gzip header, and with deflate encoding the content is in
-// a raw, headerless DEFLATE stream.
-//
-// Internally GZipFilter uses zlib inflate to do decoding.
-//
-// GZipFilter is a subclass of Filter. See the latter's header file filter.h
-// for sample usage.
-
-#ifndef NET_FILTER_GZIP_FILTER_H_
-#define NET_FILTER_GZIP_FILTER_H_
-
-#include <memory>
-
-#include "base/macros.h"
-#include "net/filter/filter.h"
-
-typedef struct z_stream_s z_stream;
-
-namespace net {
-
-class GZipHeader;
-
-class GZipFilter : public Filter {
- public:
-  ~GZipFilter() override;
-
-  // Initializes filter decoding mode and internal control blocks.
-  // Parameter filter_type specifies the type of filter, which corresponds to
-  // either gzip or deflate decoding. The function returns true if success and
-  // false otherwise.
-  // The filter can only be initialized once.
-  bool InitDecoding(Filter::FilterType filter_type);
-
-  // Decodes the pre-filter data and writes the output into the dest_buffer
-  // passed in.
-  // 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.
-  //
-  // This function will fail if there is no pre-filter data in the
-  // stream_buffer_. On the other hand, *dest_len can be 0 upon successful
-  // return. For example, the internal zlib may process some pre-filter data
-  // but not produce output yet.
-  FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len) override;
-
- private:
-  enum DecodingStatus {
-    DECODING_UNINITIALIZED,
-    DECODING_IN_PROGRESS,
-    DECODING_DONE,
-    DECODING_ERROR
-  };
-
-  enum DecodingMode {
-    DECODE_MODE_GZIP,
-    DECODE_MODE_DEFLATE,
-    DECODE_MODE_UNKNOWN
-  };
-
-  enum GZipCheckHeaderState {
-    GZIP_CHECK_HEADER_IN_PROGRESS,
-    GZIP_GET_COMPLETE_HEADER,
-    GZIP_GET_INVALID_HEADER
-  };
-
-  static const int kGZipFooterSize = 8;
-
-  // Only to be instantiated by Filter::Factory.
-  explicit GZipFilter(FilterType type);
-  friend class Filter;
-
-  // Parses and verifies the GZip header.
-  // Upon exit, the function updates gzip_header_status_ accordingly.
-  //
-  // The function returns Filter::FILTER_OK if it gets a complete header and
-  // there are more data in the pre-filter buffer.
-  // The function returns Filter::FILTER_NEED_MORE_DATA if it parses all data
-  // in the pre-filter buffer, either getting a complete header or a partial
-  // header. The caller needs to check gzip_header_status_ and call this
-  // function again for partial header.
-  // The function returns Filter::FILTER_ERROR if error occurs.
-  FilterStatus CheckGZipHeader();
-
-  // Internal function to decode the pre-filter data and writes the output into
-  // the dest_buffer passed in.
-  //
-  // This is the internal version of ReadFilteredData. See the latter's
-  // comments for the use of function.
-  FilterStatus DoInflate(char* dest_buffer, int* dest_len);
-
-  // Inserts a zlib header to the data stream before calling zlib inflate.
-  // This is used to work around server bugs. See more comments at the place
-  // it is called in gzip_filter.cc.
-  // The function returns true on success and false otherwise.
-  bool InsertZlibHeader();
-
-  // Skip the 8 byte GZip footer after z_stream_end
-  void SkipGZipFooter();
-
-  // Tracks the status of decoding.
-  // This variable is initialized by InitDecoding and updated only by
-  // ReadFilteredData.
-  DecodingStatus decoding_status_;
-
-  // Indicates the type of content decoding the GZipFilter is performing.
-  // This variable is set only once by InitDecoding.
-  DecodingMode decoding_mode_;
-
-  // Used to parse the gzip header in gzip stream.
-  // It is used when the decoding_mode_ is DECODE_MODE_GZIP.
-  std::unique_ptr<GZipHeader> gzip_header_;
-
-  // Tracks the progress of parsing gzip header.
-  // This variable is maintained by gzip_header_.
-  GZipCheckHeaderState gzip_header_status_;
-
-  // A flag used by InsertZlibHeader to record whether we've successfully added
-  // a zlib header to this stream.
-  bool zlib_header_added_;
-
-  // Tracks how many bytes of gzip footer have been received.
-  int gzip_footer_bytes_;
-
-  // The control block of zlib which actually does the decoding.
-  // This data structure is initialized by InitDecoding and updated only by
-  // DoInflate, with InsertZlibHeader being the exception as a workaround.
-  std::unique_ptr<z_stream> zlib_stream_;
-
-  // For robustness, when we see the solo sdch filter, we chain in a gzip filter
-  // in front of it, with this flag to indicate that the gzip decoding might not
-  // be needed.  This handles a strange case where "Content-Encoding: sdch,gzip"
-  // is reduced by an errant proxy to "Content-Encoding: sdch", while the
-  // content is indeed really gzipped result of sdch :-/.
-  // If this flag is set, then we will revert to being a pass through filter if
-  // we don't get a valid gzip header.
-  bool possible_sdch_pass_through_;
-
-  DISALLOW_COPY_AND_ASSIGN(GZipFilter);
-};
-
-}  // namespace net
-
-#endif  // NET_FILTER_GZIP_FILTER_H__