storage/browser/blob/file_stream_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 STORAGE_BLOB_FILE_STREAM_READER_H_
#define STORAGE_BLOB_FILE_STREAM_READER_H_

#include "base/basictypes.h"
#include "base/compiler_specific.h"
#include "base/files/file.h"
#include "net/base/completion_callback.h"
#include "storage/browser/storage_browser_export.h"

namespace base {
class FilePath;
class TaskRunner;
class Time;
}

namespace net {
class IOBuffer;
}

namespace storage {
class FileSystemContext;
class FileSystemURL;
}

namespace storage {

// A generic interface for reading a file-like object.
class FileStreamReader {
 public:
  // Creates a new FileReader for a local file |file_path|.
  // |initial_offset| specifies the offset in the file where the first read
  // should start.  If the given offset is out of the file range any
  // read operation may error out with net::ERR_REQUEST_RANGE_NOT_SATISFIABLE.
  // |expected_modification_time| specifies the expected last modification
  // If the value is non-null, the reader will check the underlying file's
  // actual modification time to see if the file has been modified, and if
  // it does any succeeding read operations should fail with
  // ERR_UPLOAD_FILE_CHANGED error.
  STORAGE_EXPORT static FileStreamReader*
      CreateForLocalFile(base::TaskRunner* task_runner,
                         const base::FilePath& file_path,
                         int64 initial_offset,
                         const base::Time& expected_modification_time);

  // Creates a new reader for a filesystem URL |url| form |initial_offset|.
  // |expected_modification_time| specifies the expected last modification if
  // the value is non-null, the reader will check the underlying file's actual
  // modification time to see if the file has been modified, and if it does any
  // succeeding read operations should fail with ERR_UPLOAD_FILE_CHANGED error.
  STORAGE_EXPORT static FileStreamReader*
      CreateForFileSystemFile(storage::FileSystemContext* context,
                              const storage::FileSystemURL& url,
                              int64 initial_offset,
                              const base::Time& expected_modification_time);

  // Verify if the underlying file has not been modified.
  STORAGE_EXPORT static bool VerifySnapshotTime(
      const base::Time& expected_modification_time,
      const base::File::Info& file_info);

  // It is valid to delete the reader at any time.  If the stream is deleted
  // while it has a pending read, its callback will not be called.
  virtual ~FileStreamReader() {}

  // 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.
  //
  // If the stream is deleted while it has an in-flight Read operation
  // |callback| will not be called.
  virtual int Read(net::IOBuffer* buf, int buf_len,
                   const net::CompletionCallback& callback) = 0;

  // Returns the length of the file if it could successfully retrieve the
  // file info *and* its last modification time equals to
  // expected modification time (rv >= 0 cases).
  // Otherwise, a negative error code is returned (rv < 0 cases).
  // If the stream is deleted while it has an in-flight GetLength operation
  // |callback| will not be called.
  // Note that the return type is int64 to return a larger file's size (a file
  // larger than 2G) but an error code should fit in the int range (may be
  // smaller than int64 range).
  virtual int64 GetLength(const net::Int64CompletionCallback& callback) = 0;
};

}  // namespace storage

#endif  // STORAGE_BLOB_FILE_STREAM_READER_H_