Introduce MinidumpWritable, its dependencies, and their tests

util/file/file_writer.h

Index: util/file/file_writer.h
diff --git a/util/file/file_writer.h b/util/file/file_writer.h
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+// 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().
+  virtual 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().
+  virtual 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().
+  virtual 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_