1// Copyright 2016 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "message.h"
6
7#include <stdint.h>
8
9_Static_assert(sizeof(mojo_message_header_t) == 16u, "mojo_message_header_t should be 16 bytes");
10
11_Static_assert(sizeof(mojo_message_header_with_request_id_t) == 24u,
12               "mojo_message_header_t should be 24 bytes");
13
14bool mojo_validate_message_header(const mojo_struct_header_t* header, size_t size) {
15    if (header->num_bytes < sizeof(mojo_message_header_t) || size < sizeof(mojo_message_header_t) ||
16        size > UINT32_MAX) {
17        return false;
18    }
19
20    const mojo_message_header_t* message_header = (const mojo_message_header_t*)header;
21
22    // Message expects response and message is response flags are mutually
23    // exclusive.
24    if ((message_header->flags & MOJO_MESSAGE_HEADER_FLAGS_EXPECTS_RESPONSE) &&
25        (message_header->flags & MOJO_MESSAGE_HEADER_FLAGS_IS_RESPONSE)) {
26        return false;
27    }
28
29    if (header->version == 0u) {
30        if (header->num_bytes != sizeof(mojo_message_header_t)) {
31            return false;
32        }
33
34        // Version 0 has no request id and should not have either of these flags.
35        if ((message_header->flags & MOJO_MESSAGE_HEADER_FLAGS_EXPECTS_RESPONSE) ||
36            (message_header->flags & MOJO_MESSAGE_HEADER_FLAGS_IS_RESPONSE)) {
37            return false;
38        }
39    } else if (header->version == 1u) {
40        if (header->num_bytes != sizeof(mojo_message_header_with_request_id_t)) {
41            return false;
42        }
43    }
44    // Accept unknown versions of the message header to be future-proof.
45
46    return true;
47}
48