Mojo C bindings library pt1: MojomBuffer

mojo/public/c/bindings/buffer.h

Index: mojo/public/c/bindings/buffer.h
diff --git a/mojo/public/c/bindings/buffer.h b/mojo/public/c/bindings/buffer.h
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+// 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.
+
+#ifndef MOJO_PUBLIC_C_BINDINGS_BUFFER_H_
+#define MOJO_PUBLIC_C_BINDINGS_BUFFER_H_
+
+#include <stdint.h>
+
+#include "mojo/public/c/system/macros.h"
+
+MOJO_BEGIN_EXTERN_C
+
+// |MojomBuffer| is used to track a buffer state for mojom serialization. The
+// user must initialize this struct themselves. See the fields for details.
+struct MojomBuffer {
+  char* buf;
+  // The number of bytes described by |buf|.
+  uint32_t buf_size;
+  // Must be initialized to 0. MojomBuffer_Allocate() will update it as it
+  // consumes |buf|.
+  uint32_t num_bytes_used;
+};
+
+// Allocates |num_bytes| (rounded to 8 bytes) from |buf|. Returns NULL if
+// there isn't enough space left to allocate, or when |num_bytes| is 0.
+void* MojomBuffer_Allocate(struct MojomBuffer* buf, uint32_t num_bytes);
+
+MOJO_END_EXTERN_C
+
+#endif  // MOJO_PUBLIC_C_BINDINGS_BUFFER_H_