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

net/filter/sdch_source_stream.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_FILTER_SDCH_SOURCE_STREAM_H_
+#define NET_FILTER_SDCH_SOURCE_STREAM_H_
+
+#include <memory>
+
+#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_source_stream.h"
+
+namespace open_vcdiff {
+
+class VCDiffStreamingDecoder;
+
+}  // namespace open_vcdiff
+
+namespace net {
+
+class IOBuffer;
+
+// SdchSourceStream 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 SdchSourceStream internally uses open_vcdiff/vcdec library to do
+// decoding.
+class NET_EXPORT_PRIVATE SdchSourceStream : public FilterSourceStream {
+ public:
+  // The Delegate interface is responsible for error recovery and stats
+  // gathering. See the methods below for descriptions of which errors the
+  // delegate is expected to handle and what it can do to repair them.
+  class NET_EXPORT_PRIVATE Delegate {
+   public:
+    virtual ~Delegate(){};
+
+    // Called by the SdchSourceStream if an error occurs while parsing the
+    // server-sent dictionary ID, or if the specified dictionary can't be loaded
+    // (i.e., GetDictionary returned false). This method is expected to correct
+    // the error condition by either:
+    //   a) returning true and calling ReplaceOutput or Passthrough, or
+    //   b) returning false, in which case the SourceStream will return an error
+    //      to its caller
+    // Conceptually, the return value is true if the error has been
+    // handled/recovered from and false if not.
+    // This method must not retain a reference to |source| after returning.
+    virtual bool OnDictionaryError(SdchSourceStream* source) = 0;
+
+    // Called by the SdchSourceStream if an error occurs while decoding the
+    // vcdiff-compressed data stream. Semantics are similar to
+    // OnDictionaryError above. This method must not retain a reference to
+    // |source| after returning.
+    virtual bool OnDecodingError(SdchSourceStream* source) = 0;
+
+    // Called by the SdchSourceStream to request the text of the specified
+    // dictionary. This method must either:
+    //   * Fill in |*text| and return true, or
+    //   * Leave |*text| untouched and return false.
+    // The return value is true if the named dictionary could be found and false
+    // otherwise.
+    //
+    // The |server_id| string is guaranteed to be a syntactically valid SDCH
+    // server-id.
+    virtual bool OnGetDictionary(const std::string& server_id,
+                                 const std::string** text) = 0;
+  };
+
+  SdchSourceStream(std::unique_ptr<SourceStream> previous, Delegate* delegate);
+  ~SdchSourceStream() override;
+
+  // For use by SdchSourceStreamDelegate. Switches this stream source into
+  // "passthrough" mode, where it will not decode any further output with
+  // vcdiff. This method can only be called during an invocation of the
+  // delegate's OnDictionaryError or OnDecodingError functions.
+  virtual void StopDecoding();
+
+  // For use by SdchSourceStreamDelegate. Replaces the entire output of this
+  // stream with the supplied |data|, which is of length |size|. Note that
+  // calling this method also stops vcdiff decoding as a side-effect - |data|
+  // should not point to vcdiff-encoded data. This method can only be called
+  // during an invocation of the delegate's OnDictionaryError or
+  // OnDecodingError functions.
+  virtual void ReplaceOutput(const char* data, size_t size);
+
+ private:
+  enum SdchStreamState {
+    SDCH_STREAM_ERROR,
+    SDCH_STREAM_MORE_INPUT,
+    SDCH_STREAM_MORE_OUTPUT_SPACE,
+  };
+
+  // SourceStream implementation:
+  std::string GetTypeAsString() const override;
+  int FilterData(IOBuffer* output_buffer,
+                 size_t output_buffer_size,
+                 DrainableIOBuffer* input_buffer) override;
+
+  SdchStreamState Decompress(IOBuffer* output_buffer,
+                             size_t output_buffer_size,
+                             DrainableIOBuffer* input_buffer,
+                             size_t* bytes_read);
+  // Pass any remaining input through without alteration.
+  SdchStreamState PassThrough(IOBuffer* output_buffer,
+                              size_t output_buffer_size,
+                              DrainableIOBuffer* input_buffer,
+                              size_t* bytes_read);
+
+  // Flushes data in |buffered_output_| to |output_buffer|.
+  SdchStreamState Flush(IOBuffer* output_buffer,
+                        size_t output_buffer_size,
+                        size_t* bytes_read);
+
+  bool LoadDictionary(DrainableIOBuffer* input_buffer);
+
+  // Returns whether |id| looks like a dictionary ID, meaning 8 characters of
+  // base64url followed by a null character.
+  bool CouldBeDictionaryId(const std::string& id) const;
+
+  bool AskDelegateToHandleDictionaryError();
+  bool AskDelegateToHandleDecodingError();
+
+  std::unique_ptr<open_vcdiff::VCDiffStreamingDecoder> decoder_;
+  Delegate* delegate_;
+
+  // After the encoded response SDCH header is read, this variable contains
+  // the server hash with trailing null byte.
+  std::string dictionary_id_;
+
+  // Since vcdiff may generate quite a bit of output at once, SdchSourceStream
+  // has to buffer excess output (more than requested by the caller) here to
+  // return later. This could maybe become quite large.
+  std::string buffered_output_;
+
+  bool output_replaced_;
+  bool passthrough_;
+  bool dictionary_tried_load_;
+
+  bool in_delegate_handler_;
+
+  DISALLOW_COPY_AND_ASSIGN(SdchSourceStream);
+};
+
+}  // namespace net
+
+#endif  // NET_FILTER_SDCH_SOURCE_STREAM_H_