MTP Streaming: Readahead Buffer

chrome/browser/media_galleries/fileapi/readahead_file_stream_reader.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.
+
+#ifndef CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_
+#define CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_
+
+#include <queue>
+
+#include "base/memory/weak_ptr.h"
+#include "net/base/io_buffer.h"
+#include "webkit/browser/blob/file_stream_reader.h"
+
+// Wraps a source FileStreamReader with a readahead buffer.
+class ReadaheadFileStreamReader
+    : public NON_EXPORTED_BASE(webkit_blob::FileStreamReader) {
+ public:
+  // Takes ownership of |source|.
+  explicit ReadaheadFileStreamReader(webkit_blob::FileStreamReader* source);
+
+  virtual ~ReadaheadFileStreamReader();
+
+  // FileStreamReader overrides.
+  virtual int Read(net::IOBuffer* buf, int buf_len,
+                   const net::CompletionCallback& callback) OVERRIDE;
+  virtual int64 GetLength(
+      const net::Int64CompletionCallback& callback) OVERRIDE;
+
+ private:
+  struct Request;
+
+  // Returns the number of bytes consumed from the interal buffer into |buf|.
+  int ConsumeFromBuffer(net::IOBuffer* buf, int buf_len);

[vandebo (ex-Chrome), 2014/03/04 18:51:32]

Out of the context of this comment, this name is confusing, it's easy to thing
that you're consuming from |buf|...

FillFromCache ?

[tommycli, 2014/03/04 21:14:58]

Done.

+
+  // Reads into a new buffer from the source reader. This calls
+  // OnFinishReadFromUnderlying when it completes (either synchronously or

[vandebo (ex-Chrome), 2014/03/04 18:51:32]

nit: ...FromSource

[tommycli, 2014/03/04 21:14:58]

Done.

+  // asynchronously).
+  void ReadFromSource();
+  void OnFinishReadFromSource(net::IOBuffer* buffer, int result);
+
+  // This is reset to NULL upon encountering a read error or EOF.
+  scoped_ptr<webkit_blob::FileStreamReader> source_;
+
+  // This stores the error or EOF from the source FileStreamReader. Its
+  // value is undefined if |source_| is non-NULL.
+  int source_error_;
+
+  int64 current_offset_;
+
+  // This contains a queue of buffers filled from |source_|, waiting to be
+  // consumed.
+  std::queue<scoped_refptr<net::DrainableIOBuffer>> buffers_;
+
+  // The read request waiting for the source FileStreamReader to finish
+  // reading and fill a buffer.
+  scoped_ptr<Request> pending_read_;
+
+  bool source_has_pending_read_;
+
+  base::WeakPtrFactory<ReadaheadFileStreamReader> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ReadaheadFileStreamReader);
+};
+
+#endif  // CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_