Use ByteStream in downloads system to decouple source and sink.

content/browser/download/byte_stream.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_DOWNLOAD_BYTE_STREAM_H_
 #define CONTENT_BROWSER_DOWNLOAD_BYTE_STREAM_H_
 #pragma once
 
 #include <set>
 #include <utility>
@@ skipping 64 matching lines @@
 
   // Register a callback to be called when the stream transitions from
   // full to having space available.  The callback will always be
   // called on the task runner associated with the ByteStreamInput.
   // This callback will only be called if a call to Write has previously
   // returned false (i.e. the ByteStream has been filled).
   // Multiple calls to this function are supported, though note that it
   // is the callers responsibility to handle races with space becoming
   // available (i.e. in the case of that race either of the before
   // or after callbacks may be called).
+  // The callback will not be called after ByteStreamInput destruction.
   virtual void RegisterCallback(const base::Closure& source_callback) = 0;
 };
 
 class CONTENT_EXPORT ByteStreamOutput {
  public:
   enum StreamState { STREAM_EMPTY, STREAM_HAS_DATA, STREAM_COMPLETE };
 
   virtual ~ByteStreamOutput() = 0;
 
   // Returns STREAM_EMPTY if there is no data on the ByteStream and
   // Close() has not been called, and STREAM_COMPLETE if there
   // is no data on the ByteStream and Close() has been called.
   // If there is data on the ByteStream, returns STREAM_HAS_DATA
   // and fills in |*data| with a pointer to the data, and |*length|
   // with its length.
   virtual StreamState Read(scoped_refptr<net::IOBuffer>* data,
                            size_t* length) = 0;
 
   // Only valid to call if Read() has returned STREAM_COMPLETE.
   virtual DownloadInterruptReason GetStatus() const = 0;
 
   // Register a callback to be called when data is added or the source
   // completes.  The callback will be always be called on the owning
   // task runner.  Multiple calls to this function are supported,
   // though note that it is the callers responsibility to handle races
   // with data becoming available (i.e. in the case of that race
   // either of the before or after callbacks may be called).
+  // The callback will not be called after ByteStreamOutput destruction.
   virtual void RegisterCallback(const base::Closure& sink_callback) = 0;
 };
 
 CONTENT_EXPORT void CreateByteStream(
     scoped_refptr<base::SequencedTaskRunner> input_task_runner,
     scoped_refptr<base::SequencedTaskRunner> output_task_runner,
     size_t buffer_size,
     scoped_ptr<ByteStreamInput>* input,
     scoped_ptr<ByteStreamOutput>* output);
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_BYTE_STREAM_H_