Add FileReader interface and implement FileSystemFileReader

webkit/blob/file_reader.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 WEBKIT_BLOB_FILE_READER_H_
+#define WEBKIT_BLOB_FILE_READER_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "net/base/completion_callback.h"
+#include "webkit/blob/blob_export.h"
+
+namespace net {
+class FileStream;
+class IOBuffer;
+}
+
+namespace webkit_blob {
+
+// A generic interface for reading a file-like object.
+class BLOB_EXPORT FileReader {
+ public:
+  virtual ~FileReader() {}
+
+  // Reads from the current cursor position asynchronously.
+  //
+  // Up to buf_len bytes will be copied into buf.  (In other words, partial
+  // reads are allowed.)  Returns the number of bytes copied, 0 if at
+  // end-of-file, or an error code if the operation could not be performed.
+  // If the read could not complete synchronously, then ERR_IO_PENDING is
+  // returned, and the callback will be run on the thread where Read()
+  // was called, when the read has completed.
+  //
+  // It is invalid to call Read while there is an in-flight Read operation.
+  virtual int Read(net::IOBuffer* buf, int buf_len,
+                   const net::CompletionCallback& callback) = 0;
+};
+
+}  // namespace webkit_blob
+
+#endif  // WEBKIT_BLOB_FILE_READER_H_