Add FileReaderInterface. Move StringFileWriter to StringFile and

util/file/file_reader.h

+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_UTIL_FILE_FILE_READER_H_
+#define CRASHPAD_UTIL_FILE_FILE_READER_H_
+
+#include <sys/types.h>
+
+#include "base/basictypes.h"
+#include "base/files/file_path.h"
+#include "util/file/file_io.h"
+#include "util/file/file_seeker.h"
+
+namespace crashpad {
+
+//! \brief An interface to read to files and other file-like objects with
+//!     semantics matching the underlying platform (POSIX or Windows).
+class FileReaderInterface : public FileSeekerInterface {
+ public:
+  //! \brief Wraps ReadFile(), or provides an implementation with identical
+  //!     semantics.
+  //!
+  //! \return The number of bytes actually read if the operation succeeded,
+  //!     which may be `0` or any positive value less than or equal to \a size.
+  //!     `-1` if the operation failed, with an error message logged.
+  virtual ssize_t Read(void* data, size_t size) = 0;
+
+ protected:
+  ~FileReaderInterface() {}
+};
+
+//! \brief A file reader backed by a FileHandle.
+//!
+//! FileReader requires users to provide a FilePath to open, but this class
+//! accepts an already-open FileHandle instead. Like FileReader, this class may
+//! read from a filesystem-based file, but unlike FileReader, this class is not
+//! responsible for opening or closing the file. Users of this class must ensure
+//! that the file handle is closed appropriately elsewhere. Objects of this
+//! class may be used to read from file handles not associated with
+//! filesystem-based files, although special attention should be paid to the
+//! Seek() method, which may not function on file handles that do not refer to
+//! disk-based files.
+//!
+//! This class is expected to be used when other code is responsible for
+//! opening files and already provides file handles.
+class WeakFileHandleFileReader : public FileReaderInterface {
+ public:
+  explicit WeakFileHandleFileReader(FileHandle file_handle);
+  ~WeakFileHandleFileReader();
+
+  // FileReaderInterface:
+  ssize_t Read(void* data, size_t size) override;
+
+  // FileSeekerInterface:
+
+  //! \copydoc FileReaderInterface::Seek()
+  //!
+  //! \note This method is only guaranteed to function on file handles referring
+  //!     to disk-based files.
+  FileOffset Seek(FileOffset offset, int whence) override;
+
+ private:
+  void set_file_handle(FileHandle file_handle) { file_handle_ = file_handle; }
+
+  FileHandle file_handle_;  // weak
+
+  // FileReader uses this class as its internal implementation, and it needs to
+  // be able to call set_file_handle(). FileReader cannot initialize a
+  // WeakFileHandleFileReader with a correct file descriptor at the time of
+  // construction because no file descriptor will be available until
+  // FileReader::Open() is called.
+  friend class FileReader;
+
+  DISALLOW_COPY_AND_ASSIGN(WeakFileHandleFileReader);
+};
+
+//! \brief A file reader implementation that wraps traditional system file
+//!     operations on files accessed through the filesystem.
+class FileReader : public FileReaderInterface {
+ public:
+  FileReader();
+  ~FileReader();
+
+  // FileReaderInterface:
+
+  //! \brief Wraps LoggingOpenFileForRead().
+  //!
+  //! \return `true` if the operation succeeded, `false` if it failed, with an
+  //!     error message logged.
+  //!
+  //! \note After a successful call, this method cannot be called again until
+  //!     after Close().
+  bool Open(const base::FilePath& path,
+            FileWriteMode write_mode,
+            FilePermissions permissions);
+
+  //! \brief Wraps CheckedCloseHandle().
+  //!
+  //! \note It is only valid to call this method on an object that has had a
+  //!     successful Open() that has not yet been matched by a subsequent call
+  //!     to this method.
+  void Close();
+
+  // FileReaderInterface:
+
+  //! \copydoc FileReaderInterface::Read()
+  //!
+  //! \note It is only valid to call this method between a successful Open() and
+  //!     a Close().
+  ssize_t Read(void* data, size_t size) override;
+
+  // FileSeekerInterface:
+
+  //! \copydoc FileReaderInterface::Seek()
+  //!
+  //! \note It is only valid to call this method between a successful Open() and
+  //!     a Close().
+  FileOffset Seek(FileOffset offset, int whence) override;
+
+ private:
+  ScopedFileHandle file_;
+  WeakFileHandleFileReader weak_file_handle_file_reader_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileReader);
+};
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_FILE_FILE_READER_H_