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diff --git a/net/base/file_stream.h b/net/base/file_stream.h
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+++ b/net/base/file_stream.h
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+// Copyright (c) 2008 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.
+
+// This file defines FileStream, a basic interface for reading and writing files
+// synchronously or asynchronously with support for seeking to an offset.
+// Note that even when used asynchronously, only one operation is supported at
+// a time.
+
+#ifndef NET_BASE_FILE_STREAM_H_
+#define NET_BASE_FILE_STREAM_H_
+
+#include "base/platform_file.h"
+#include "net/base/completion_callback.h"
+
+namespace net {
+
+// TODO(darin): Move this to a more generic location.
+// This explicit mapping matches both FILE_ on Windows and SEEK_ on Linux.
+enum Whence {
+  FROM_BEGIN   = 0,
+  FROM_CURRENT = 1,
+  FROM_END     = 2
+};
+
+class FileStream {
+ public:
+  FileStream();
+  ~FileStream();
+
+  // Call this method to close the FileStream.  It is OK to call Close
+  // multiple times.  Redundant calls are ignored.
+  // Note that if there are any pending async operations, they'll be aborted.
+  void Close();
+
+  // Call this method to open the FileStream.  The remaining methods
+  // cannot be used unless this method returns OK.  If the file cannot be
+  // opened then an error code is returned.
+  // open_flags is a bitfield of base::PlatformFileFlags
+  int Open(const std::wstring& path, int open_flags);
+
+  // Returns true if Open succeeded and Close has not been called.
+  bool IsOpen() const;
+
+  // Adjust the position from where data is read.  Upon success, the stream
+  // position relative to the start of the file is returned.  Otherwise, an
+  // error code is returned.  It is not valid to call Seek while a Read call
+  // has a pending completion.
+  int64 Seek(Whence whence, int64 offset);
+
+  // Returns the number of bytes available to read from the current stream
+  // position until the end of the file.  Otherwise, an error code is returned.
+  int64 Available();
+
+  // Call this method to read data from the current stream position.  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 opened with PLATFORM_FILE_ASYNC, then a non-null callback
+  // must be passed to this method.  In asynchronous mode, if the read could
+  // not complete synchronously, then ERR_IO_PENDING is returned, and the
+  // callback will be notified on the current thread (via the MessageLoop) when
+  // the read has completed.
+  // 
+  // In the case of an asychronous read, the memory pointed to by |buf| must
+  // remain valid until the callback is notified.  However, it is valid to
+  // destroy or close the file stream while there is an asynchronous read in
+  // progress.  That will cancel the read and allow the buffer to be freed.
+  // 
+  // This method should not be called if the stream was opened WRITE_ONLY.
+  int Read(char* buf, int buf_len, CompletionCallback* callback);
+
+  // Call this method to write data at the current stream position.  Up to
+  // buf_len bytes will be written from buf. (In other words, partial writes are
+  // allowed.)  Returns the number of bytes written, or an error code if the 
+  // operation could not be performed.
+  //
+  // If opened with PLATFORM_FILE_ASYNC, then a non-null callback
+  // must be passed to this method.  In asynchronous mode, if the write could
+  // not complete synchronously, then ERR_IO_PENDING is returned, and the
+  // callback will be notified on the current thread (via the MessageLoop) when
+  // the write has completed.
+  // 
+  // In the case of an asychronous write, the memory pointed to by |buf| must
+  // remain valid until the callback is notified.  However, it is valid to
+  // destroy or close the file stream while there is an asynchronous write in
+  // progress.  That will cancel the write and allow the buffer to be freed.
+  // 
+  // This method should not be called if the stream was opened READ_ONLY.
+  int Write(const char* buf, int buf_len, CompletionCallback* callback);
+
+ private:
+  class AsyncContext;
+  friend class AsyncContext;
+
+  // This member is used to support asynchronous reads.  It is non-null when
+  // the FileStream was opened with PLATFORM_FILE_ASYNC.
+  scoped_ptr<AsyncContext> async_context_;
+
+  base::PlatformFile file_;
+  int open_flags_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileStream);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_FILE_STREAM_H_