Pass Mach message trailers to server handler functions

util/mach/mach_message_util.h

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 30 matching lines @@
 //! \param[inout] out_header The reply message to operate on. \a out_header will
 //!     be treated as a `mig_reply_error_t*` and its `RetCode` field will be
 //!     set. This argument is accepted as a `mach_msg_header_t*` instead of a
 //!     `mig_reply_error_t*` because that is the type that callers are expected
 //!     to possess in the C API.
 //! \param[in] error The error code to store in \a out_header.
 //!
 //! \sa PrepareMIGReplyFromRequest()
 void SetMIGReplyError(mach_msg_header_t* out_header, kern_return_t error);
 
+//! \brief Returns a Mach message trailer for a message that has been received.
+//!
+//! This function must only be called on Mach messages that have been received
+//! via the Mach messaging interface, such as `mach_msg()`. Messages constructed
+//! for sending do not contain trailers.
+//!
+//! \param[in] header A pointer to a received Mach message.
+//!
+//! \return A pointer to the trailer following the received Mach message’s body.
+//!     The contents of the trailer depend on the options provided to
+//!     `mach_msg()` or a similar function when the message was received.
+const mach_msg_trailer_t* MachMessageTrailerFromHeader(
+    const mach_msg_header_t* header);
+
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_MACH_MACH_MESSAGE_UTIL_H_