mojo/public/cpp/system/platform_handle.h

// Copyright 2016 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.

// This file provides a C++ wrapping around the Mojo C API for platform handles,
// replacing the prefix of "Mojo" with a "mojo" namespace.
//
// Please see "mojo/public/c/system/platform_handle.h" for complete
// documentation of the API.

#ifndef MOJO_PUBLIC_CPP_SYSTEM_PLATFORM_HANDLE_H_
#define MOJO_PUBLIC_CPP_SYSTEM_PLATFORM_HANDLE_H_

#include <stdint.h>

#include "base/compiler_specific.h"
#include "base/files/file.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/shared_memory_handle.h"
#include "base/process/process_handle.h"
#include "mojo/public/c/system/platform_handle.h"
#include "mojo/public/cpp/system/buffer.h"
#include "mojo/public/cpp/system/handle.h"
#include "mojo/public/cpp/system/system_export.h"

#if defined(OS_WIN)
#include <windows.h>
#endif

namespace mojo {

#if defined(OS_POSIX)
const MojoPlatformHandleType kPlatformFileHandleType =
    MOJO_PLATFORM_HANDLE_TYPE_FILE_DESCRIPTOR;

#if defined(OS_MACOSX) && !defined(OS_IOS)
const MojoPlatformHandleType kPlatformSharedBufferHandleType =
    MOJO_PLATFORM_HANDLE_TYPE_MACH_PORT;
#elif defined(OS_FUCHSIA)
const MojoPlatformHandleType kPlatformSharedBufferHandleType =
    MOJO_PLATFORM_HANDLE_TYPE_FUCHSIA_HANDLE;
#else
const MojoPlatformHandleType kPlatformSharedBufferHandleType =
    MOJO_PLATFORM_HANDLE_TYPE_FILE_DESCRIPTOR;
#endif  // defined(OS_MACOSX) && !defined(OS_IOS)

#elif defined(OS_WIN)
const MojoPlatformHandleType kPlatformFileHandleType =
    MOJO_PLATFORM_HANDLE_TYPE_WINDOWS_HANDLE;

const MojoPlatformHandleType kPlatformSharedBufferHandleType =
    MOJO_PLATFORM_HANDLE_TYPE_WINDOWS_HANDLE;
#endif  // defined(OS_POSIX)

// Used to specify the protection status of a base::SharedMemoryHandle memory
// handle wrapped or unwrapped by mojo::WrapSharedMemoryHandle or
// mojo::UnwrapSharedMemoryHandle below. See those functions for additional
// details.
enum class UnwrappedSharedMemoryHandleProtection {
  // Indicates that the base::SharedMemoryHandle supports being mapped to
  // writable memory regions.
  kReadWrite,

  // Indicates that the base::SharedMemoryHandle supports being mapped only to
  // read-only memory regions.
  kReadOnly,
};

// Wraps a PlatformFile as a Mojo handle. Takes ownership of the file object.
MOJO_CPP_SYSTEM_EXPORT
ScopedHandle WrapPlatformFile(base::PlatformFile platform_file);

// Unwraps a PlatformFile from a Mojo handle.
MOJO_CPP_SYSTEM_EXPORT
MojoResult UnwrapPlatformFile(ScopedHandle handle, base::PlatformFile* file);

// Wraps a base::SharedMemoryHandle as a Mojo handle. Takes ownership of the
// SharedMemoryHandle. |size| indicates the size of the underlying
// base::SharedMemory object, and |current_protection| indicates whether or
// not |memory_handle| supports being mapped to writable memory segments.
//
// ***** IMPORTANT. PLEASE READ BELOW CAREFULLY. *****
//
// THIS CALL DOES NOT IN ANY WAY AFFECT THE MEMORY PROTECTION STATUS OF THE
// WRAPPED HANDLE.
//
// The |current_protection| argument is only an indication of the current memory
// protection status of |memory_handle| as known by the caller.
//
// DO NOT wrap a writable |memory_handle| with |current_protection| set to
// |UnwrappedSharedMemoryHandleProtection::kReadOnly|, as this will mislead
// corresponding callers to |UnwrapSharedMemoryHandle()|: the subsequently
// unwrapped SharedMemoryHandle will appear to be read-only on the surface, but
// will still be mappable to a writable memory segment.
//
// Use base::SharedMemory::GetReadOnlyHandle() to acquire a read-only handle to
// a shared memory object if you intend to wrap the handle with
// |UnwrappedSharedMemoryHandleProtection::kReadOnly|.
MOJO_CPP_SYSTEM_EXPORT
ScopedSharedBufferHandle WrapSharedMemoryHandle(
    const base::SharedMemoryHandle& memory_handle,
    size_t size,
    UnwrappedSharedMemoryHandleProtection current_protection);

// Unwraps a base::SharedMemoryHandle from a Mojo handle. The caller assumes
// responsibility for the lifetime of the SharedMemoryHandle. On success,
// |*memory_handle| is set to a valid handle, |*size| is is set to the size of
// that handle's underlying base::SharedMemory object, and
// |*protection| indicates whether or not the handle may only be mapped
// to a read-only memory segment.
//
// Note that if |*protection| is
// |UnwrappedSharedMemoryHandleProtection::kReadOnly| upon return, writable
// mapping of |*memory_handle| should not be attempted, and (unless there
// is buggy code misusing WrapSharedMemoryHandle above) will always fail.
MOJO_CPP_SYSTEM_EXPORT MojoResult
UnwrapSharedMemoryHandle(ScopedSharedBufferHandle handle,
                         base::SharedMemoryHandle* memory_handle,
                         size_t* size,
                         UnwrappedSharedMemoryHandleProtection* protection);

#if defined(OS_MACOSX) && !defined(OS_IOS)
// Wraps a mach_port_t as a Mojo handle. This takes a reference to the
// Mach port.
MOJO_CPP_SYSTEM_EXPORT ScopedHandle WrapMachPort(mach_port_t port);

// Unwraps a mach_port_t from a Mojo handle. The caller gets ownership of the
// Mach port.
MOJO_CPP_SYSTEM_EXPORT MojoResult UnwrapMachPort(ScopedHandle handle,
                                                 mach_port_t* port);
#endif  // defined(OS_MACOSX) && !defined(OS_IOS)

}  // namespace mojo

#endif  // MOJO_PUBLIC_CPP_SYSTEM_PLATFORM_HANDLE_H_