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

net/filter/filter_stream_source.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_FILTER_STREAM_SOURCE_H_
+#define NET_FILTER_FILTER_STREAM_SOURCE_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "net/base/completion_callback.h"
+#include "net/base/io_buffer.h"
+#include "net/base/net_errors.h"
+#include "net/base/net_export.h"
+#include "net/filter/stream_source.h"
+
+namespace net {
+
+class IOBuffer;
+
+// FilterStreamSource represents StreamSources that always have a previous
+// source from which undecoded input can be read. Except the first source in
+// the filter chain, all other sources should implement FilterStreamSource
+// instead of StreamSource.
+class NET_EXPORT_PRIVATE FilterStreamSource : public StreamSource {
+ public:
+  // |previous| is the previous StreamSource in the chain. |previous| cannot be
+  // null.
+  FilterStreamSource(SourceType type, std::unique_ptr<StreamSource> previous);
+
+  ~FilterStreamSource() override;
+
+  int Read(IOBuffer* read_buffer,
+           size_t read_buffer_size,
+           const CompletionCallback& callback) override;
+
+  std::string OrderedTypeStringList() const override;
+
+ private:
+  enum State {
+    STATE_NONE,
+    // Reading data from |previous|.
+    STATE_READ_DATA,
+    // Reading data from |previous| completed.
+    STATE_READ_DATA_COMPLETE,
+    // Filtering data contained in |buffer_|.
+    STATE_FILTER_DATA,
+    // Filtering data contained in |buffer_| completed.
+    STATE_FILTER_DATA_COMPLETE,
+    STATE_DONE,
+  };
+
+  int DoLoop(int result);
+  int DoReadData();
+  int DoReadDataComplete(int result);
+  int DoFilterData(int result);
+  int DoFilterDataComplete(int result);
+
+  void DoCallback(int result);
+
+  void OnPreviousReadCompleted(int result);
+  // Subclasses should implement this method to filter data from
+  // |input_buffer_| and write to |output_buffer|.
+  // This method must complete synchronously (i.e. It cannot return
+  // ERR_IO_PENDING).
+  virtual int FilterData(IOBuffer* output_buffer,
+                         size_t output_buffer_size,
+                         DrainableIOBuffer* input_buffer) = 0;
+
+  // Returns a string representation of the type of this FilterStreamSource.
+  // This is for UMA logging.
+  virtual std::string GetTypeAsString() const = 0;
+
+  // Previous StreamSource in the chain.
+  std::unique_ptr<StreamSource> previous_;
+
+  State next_state_;
+
+  // Buffer for reading data out of |previous_| and then for use by |this|
+  // before the filtered data is returned through Read().
+  scoped_refptr<IOBuffer> input_buffer_;
+  // Keep this as a member because subclass might not drain everything in a
+  // single FilterData().
+  scoped_refptr<DrainableIOBuffer> drainable_input_buffer_;
+
+  // Not null if there is a pending Read.
+  scoped_refptr<IOBuffer> output_buffer_;
+  size_t output_buffer_size_;
+  CompletionCallback callback_;
+
+  // Reading from |previous_| has returned 0 byte or an error code.
+  bool previous_eof_reached_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilterStreamSource);
+};
+
+}  // namespace net
+
+#endif  // NET_FILTER_FILTER_STREAM_SOURCE_H_