crashpad/util/file/file_writer.h

// Copyright 2014 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_WRITER_H_
#define CRASHPAD_UTIL_FILE_FILE_WRITER_H_

#include <fcntl.h>
#include <stddef.h>
#include <sys/uio.h>
#include <unistd.h>

#include <string>
#include <vector>

#include "base/basictypes.h"
#include "base/files/file_path.h"
#include "base/files/scoped_file.h"

namespace crashpad {

//! \brief A version of `iovec` with a `const` #iov_base field.
//!
//! This structure is intended to be used for write operations.
//
// Type compatibility with iovec is tested with static assertions in the
// implementation file.
struct WritableIoVec {
  //! \brief The base address of a memory region for output.
  const void* iov_base;

  //! \brief The size of the memory pointed to by #iov_base.
  size_t iov_len;
};

//! \brief An interface to write to files and other file-like objects with POSIX
//!     semantics.
class FileWriterInterface {
 public:
  //! \brief Wraps `write()` or provides an alternate implementation with
  //!     identical semantics. This method will write the entire buffer,
  //!     continuing after a short write or after being interrupted.
  //!
  //! \return `true` if the operation succeeded, `false` if it failed, with an
  //!     error message logged.
  virtual bool Write(const void* data, size_t size) = 0;

  //! \brief Wraps `writev()` or provides an alternate implementation with
  //!     identical semantics. This method will write the entire buffer,
  //!     continuing after a short write or after being interrupted.
  //!
  //! \return `true` if the operation succeeded, `false` if it failed, with an
  //!     error message logged.
  //!
  //! \note The contents of \a iovecs are undefined when this method returns.
  virtual bool WriteIoVec(std::vector<WritableIoVec>* iovecs) = 0;

  //! \brief Wraps `lseek()` or provides an alternate implementation with
  //!     identical semantics.
  //!
  //! \return The return value of `lseek()`. `-1` on failure, with an error
  //!     message logged.
  virtual off_t Seek(off_t offset, int whence) = 0;

 protected:
  ~FileWriterInterface() {}
};

//! \brief A file writer implementation that wraps traditional POSIX file
//!     operations on files accessed through the filesystem.
class FileWriter : public FileWriterInterface {
 public:
  FileWriter();
  ~FileWriter();

  //! \brief Wraps `open()`.
  //!
  //! \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, int oflag, mode_t mode);

  //! \brief Wraps `close().`
  //!
  //! \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();

  // FileWriterInterface:

  //! \copydoc FileWriterInterface::Write()
  //!
  //! \note It is only valid to call this method between a successful Open() and
  //!     a Close().
  bool Write(const void* data, size_t size) override;

  //! \copydoc FileWriterInterface::WriteIoVec()
  //!
  //! \note It is only valid to call this method between a successful Open() and
  //!     a Close().
  bool WriteIoVec(std::vector<WritableIoVec>* iovecs) override;

  //! \copydoc FileWriterInterface::Seek()
  //!
  //! \note It is only valid to call this method between a successful Open() and
  //!     a Close().
  off_t Seek(off_t offset, int whence) override;

 private:
  base::ScopedFD fd_;

  DISALLOW_COPY_AND_ASSIGN(FileWriter);
};

}  // namespace crashpad

#endif  // CRASHPAD_UTIL_FILE_FILE_WRITER_H_