Mojo: Add a C++-style SharedBuffer API.

mojo/public/cpp/system/buffer.h

 // Copyright 2014 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 shared buffers,
 // replacing the prefix of "Mojo" with a "mojo" namespace, and using more
 // strongly-typed representations of |MojoHandle|s.
 //
 // Please see "mojo/public/c/system/buffer.h" for complete documentation of the
 // API.
 
 #ifndef MOJO_PUBLIC_CPP_SYSTEM_BUFFER_H_
 #define MOJO_PUBLIC_CPP_SYSTEM_BUFFER_H_
 
 #include <stdint.h>
 
+#include <memory>
+
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "mojo/public/c/system/buffer.h"
 #include "mojo/public/cpp/system/handle.h"
 
 namespace mojo {
+namespace internal {
+
+struct Unmapper {
+  void operator()(void* buffer) {
+    MojoResult result = MojoUnmapBuffer(buffer);
+    DCHECK_EQ(MOJO_RESULT_OK, result);
+  }
+};
+
+}  // namespace internal
+
+using ScopedSharedBufferMapping = std::unique_ptr<void, internal::Unmapper>;
+
+class SharedBufferHandle;
+
+typedef ScopedHandleBase<SharedBufferHandle> ScopedSharedBufferHandle;
 
 // A strongly-typed representation of a |MojoHandle| referring to a shared
 // buffer.
 class SharedBufferHandle : public Handle {
  public:
+  enum class AccessMode {
+    READ_WRITE,
+    READ_ONLY,
+  };
+
   SharedBufferHandle() {}
   explicit SharedBufferHandle(MojoHandle value) : Handle(value) {}
 
   // Copying and assignment allowed.
+
+  // Clones this shared buffer handle. If |access_mode| is READ_ONLY or this is
+  // a read-only handle, the new handle will be read-only. On failure, this will
+  // return an empty result.
+  ScopedSharedBufferHandle Clone(AccessMode = AccessMode::READ_WRITE) const;
+
+  // Maps |size| bytes of this shared buffer. On failure, this will return a
+  // null mapping.
+  ScopedSharedBufferMapping Map(uint64_t size) const;
+
+  // Maps |size| bytes of this shared buffer, starting |offset| bytes into the
+  // buffer. On failure, this will return a null mapping.
+  ScopedSharedBufferMapping MapAtOffset(uint64_t size, uint64_t offset) const;
 };
 
 static_assert(sizeof(SharedBufferHandle) == sizeof(Handle),
               "Bad size for C++ SharedBufferHandle");
-
-typedef ScopedHandleBase<SharedBufferHandle> ScopedSharedBufferHandle;
 static_assert(sizeof(ScopedSharedBufferHandle) == sizeof(SharedBufferHandle),
               "Bad size for C++ ScopedSharedBufferHandle");
 
 // Creates a shared buffer. See |MojoCreateSharedBuffer()| for complete
 // documentation.
 inline MojoResult CreateSharedBuffer(
     const MojoCreateSharedBufferOptions* options,
     uint64_t num_bytes,
     ScopedSharedBufferHandle* shared_buffer) {
   DCHECK(shared_buffer);
@@ skipping 76 matching lines @@
   ALLOW_UNUSED_LOCAL(result);
   DCHECK_EQ(MOJO_RESULT_OK, result);
 }
 
 inline SharedBuffer::~SharedBuffer() {
 }
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_SYSTEM_BUFFER_H_