mojo/public/c/bindings/lib/message.c

// 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.

#include "mojo/public/c/bindings/message.h"

#include <stdint.h>

_Static_assert(sizeof(mojo_message_header_t) == 16u,
               "mojo_message_header_t should be 16 bytes");

_Static_assert(sizeof(mojo_message_header_with_request_id_t) == 24u,
               "mojo_message_header_t should be 24 bytes");

bool mojo_validate_message_header(const mojo_struct_header_t* header,
                                  size_t size) {
  if (header->num_bytes < sizeof(mojo_message_header_t) ||
      size < sizeof(mojo_message_header_t) || size > UINT32_MAX) {
    return false;
  }

  const mojo_message_header_t* message_header =
      (const mojo_message_header_t*)header;

  // Message expects response and message is response flags are mutually
  // exclusive.
  if ((message_header->flags & MOJO_MESSAGE_HEADER_FLAGS_EXPECTS_RESPONSE) &&
      (message_header->flags & MOJO_MESSAGE_HEADER_FLAGS_IS_RESPONSE)) {
    return false;
  }

  if (header->version == 0u) {
    if (header->num_bytes != sizeof(mojo_message_header_t)) {
      return false;
    }

    // Version 0 has no request id and should not have either of these flags.
    if ((message_header->flags & MOJO_MESSAGE_HEADER_FLAGS_EXPECTS_RESPONSE) ||
        (message_header->flags & MOJO_MESSAGE_HEADER_FLAGS_IS_RESPONSE)) {
      return false;
    }
  } else if (header->version == 1u) {
    if (header->num_bytes != sizeof(mojo_message_header_with_request_id_t)) {
      return false;
    }
  }
  // Accept unknown versions of the message header to be future-proof.

  return true;
}