Introduce MinidumpWritable, its dependencies, and their tests

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/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 {

[Robert Sesek, 2014/08/01 14:38:04]

The assumption here is that checking errno is silly and logging is better, with
just a boolean success?

[Mark Mentovai, 2014/08/01 16:09:35]

rsesek wrote:
Yeah, basically this does the normal HANDLE_EINTR and continues after partial
writes, so from the caller’s perspective, either the operation succeeded or it
failed. The “why” of a failure isn’t normally interesting at that level.

If you do want the byte count and errno for some reason, but you also want
HANDLE_EINTR and partial write handling, use WriteFD from fd_io.{cc,h}.

+ 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()`.

[Robert Sesek, 2014/08/01 14:38:04]

Probably need to mention that you can't call this again until calling Close().

+  //!
+  //! \return `true` if the operation succeeded, `false` if it failed, with an
+  //!     error message logged.
+  bool Open(const std::string& path, int oflag, mode_t mode);

[Robert Sesek, 2014/08/01 14:38:04]

Any thought on using base::FilePath?

[Mark Mentovai, 2014/08/01 16:09:35]

rsesek wrote:
When I didn’t care about Windows support, I just wanted to use std::string
everywhere. Now that it looks like we might need Windows support in some of
this, I guess we should be using FilePath.

+
+  //! \brief Wraps `close().`
+  void Close();
+
+  virtual bool Write(const void* data, size_t size) override;

[Robert Sesek, 2014/08/01 14:38:04]

Style is typically:

// FileWriterInterface:

And then no blank lines between the overridden functions.

[Mark Mentovai, 2014/08/01 16:09:35]

rsesek wrote:
I added some extra documentation here per your previous suggestion, so the blank
lines have to stay.

+
+  virtual bool WriteIoVec(std::vector<WritableIoVec>* iovecs) override;
+
+  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_