C types and utilities to validate and access struct and message headers

mojo/public/c/bindings/message.h

Index: mojo/public/c/bindings/message.h
diff --git a/mojo/public/c/bindings/message.h b/mojo/public/c/bindings/message.h
new file mode 100644
index 0000000000000000000000000000000000000000..f9eb4467a2110de2cc4277afb727fb88240929f5
--- /dev/null
+++ b/mojo/public/c/bindings/message.h
@@ -0,0 +1,36 @@
+// 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_MESSAGE_H_
+#define MOJO_PUBLIC_C_BINDINGS_MESSAGE_H_
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "mojo/public/c/bindings/struct.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Validates that the buffer started at a (validated) mojo_struct_header with a
+// given size contains a valid mojo message header.
+bool mojo_validate_message_header(mojo_struct_header_t* header, uint32_t size);

[viettrungluu, 2016/02/02 00:48:47]

const mojo_struct_header_t*?

|size_t| for size?

[jamesr, 2016/02/02 00:55:04]

Sure (although it's meaningless here)
I'm sticking with uint32_t for sizes as that's what the mojo archive format uses
for struct sizes+offsets and to avoid <stddef.h>.  Wouldn't mind switching if
you think it's strictly better.

+

[viettrungluu, 2016/02/02 00:48:47]

Probably you want suitable pack pragmas, no?

[jamesr, 2016/02/02 00:55:04]

I'm relying on the static assertions to tell me if these need to be packed.  So
far the asserts seem to be holding true without any pragmas.

+typedef struct mojo_message_header {
+  mojo_struct_header_t struct_header;
+  uint32_t name;
+  uint32_t flags;
+} mojo_message_header_t;

[viettrungluu, 2016/02/02 00:48:47]

Note that POSIX sez that _t names are reserved for implementors of systems,
which is fine when we're the implementor, but not so good if people want to use
these headers on other systems.

[jamesr, 2016/02/02 00:55:04]

That's super annoying.  Is there another naming convention I could use or should
I just drop the convenience typedefs? I want to leave the real struct names so
forward decls can work

+
+typedef struct mojo_message_header_with_request_id {
+  mojo_message_header_t message_header;
+  uint64_t request_id;
+} mojo_message_header_with_request_id_t;
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // MOJO_PUBLIC_C_BINDINGS_MESSAGE_H_