Add ChildPortServer, a MachMessageServer::Interface implementation for the child_port subsystem

util/mach/mach_message_util.h

Index: util/mach/mach_message_util.h
diff --git a/util/mach/mach_message_util.h b/util/mach/mach_message_util.h
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index 0000000000000000000000000000000000000000..afe598188d6a998f86d0c5fd64696c1097fc8d8c
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+++ b/util/mach/mach_message_util.h
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+// 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,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_UTIL_MACH_MACH_MESSAGE_UTIL_H_
+#define CRASHPAD_UTIL_MACH_MACH_MESSAGE_UTIL_H_
+
+#include <mach/mach.h>
+
+namespace crashpad {
+
+//! \brief Initializes a reply message for a MIG server routine based on its
+//!     corresponding request.
+//!
+//! If a request is handled by a server routine, it may be necessary to revise
+//! some of the fields set by this function, such as `msgh_size` and any fields
+//! defined in a routine’s reply structure type.
+//!
+//! \param[in] in_header The request message to base the reply on.
+//! \param[out] out_header The reply message to initialize. \a out_header will
+//!     be treated as a `mig_reply_error_t*` and all of its fields will be set
+//!     except for `RetCode`, which must be set by SetMIGReplyError(). 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.
+void PrepareMIGReplyFromRequest(const mach_msg_header_t* in_header,
+                                mach_msg_header_t* out_header);
+
+//! \brief Sets the error code in a reply message for a MIG server routine.
+//!
+//! \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);
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_MACH_MACH_MESSAGE_UTIL_H_