Add CompositeMachMessageServer and its test

util/mach/composite_mach_message_server.h

Index: util/mach/composite_mach_message_server.h
diff --git a/util/mach/composite_mach_message_server.h b/util/mach/composite_mach_message_server.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_COMPOSITE_MACH_MESSAGE_SERVER_H_
+#define CRASHPAD_UTIL_MACH_COMPOSITE_MACH_MESSAGE_SERVER_H_
+
+#include <mach/mach.h>
+
+#include <map>
+#include <set>
+
+#include "base/basictypes.h"
+#include "util/mach/mach_message_server.h"
+
+namespace crashpad {
+
+//! \brief Adapts multiple MachMessageServer::Interface implementations for
+//!     simultaneous use in a single MachMessageServer::Run() call.
+//!
+//! This class implements a MachMessageServer::Interface that contains other
+//! other MachMessageServer::Interface objects.
+//!
+//! In some situations, it may be desirable for a Mach message server to handle
+//! messages from distinct MIG subsystems with distinct
+//! MachMessageServer::Interface implementations. This may happen if a single
+//! receive right is shared for multiple subsystems, or if distinct receive
+//! rights are combined in a Mach port set. In these cases, this class performs
+//! a first-level demultiplexing to forward request messages to the proper
+//! subsystem-level demultiplexers.
+class CompositeMachMessageServer : public MachMessageServer::Interface {
+ public:
+  CompositeMachMessageServer();
+  ~CompositeMachMessageServer();
+
+  //! \brief Adds a handler that messages can be dispatched to based on request
+  //!     message ID.
+  //!
+  //! \param[in] handler A MachMessageServer handler. Ownership of this object
+  //!     is not taken. Cycles must not be created between objects. It is
+  //!     invalid to add an object as its own handler.
+  //!
+  //! If \a handler claims to support any request ID that this object is already
+  //! able to handle, execution will be terminated.
+  void AddHandler(MachMessageServer::Interface* handler);
+
+  // MachMessageServer::Interface:
+
+  //! \copydoc MachMessageServer::Interface::MachMessageServerFunction()
+  //!
+  //! This implementation forwards the message to an appropriate handler added
+  //! by AddHandler() on the basis of the \a in request message’s message ID.
+  //! If no appropriate handler exists, the \a out reply message is treated as
+  //! a `mig_reply_error_t`, its return code is set to `MIG_BAD_ID`, and `false`
+  //! is returned.
+  bool MachMessageServerFunction(const mach_msg_header_t* in,
+                                 mach_msg_header_t* out,
+                                 bool* destroy_complex_request) override;
+
+  //! \copydoc MachMessageServer::Interface::MachMessageServerRequestIDs()
+  //!
+  //! This implementation returns the set of all request message Mach message
+  //! IDs of all handlers added by AddHandler().
+  std::set<mach_msg_id_t> MachMessageServerRequestIDs() override;
+
+  //! \copydoc MachMessageServer::Interface::MachMessageServerRequestSize()
+  //!
+  //! This implementation returns the maximum request message size of all
+  //! handlers added by AddHandler(). If no handlers are present, returns the
+  //! size of `mach_msg_header_t`, the minimum size of a MIG request message
+  //! that can be received for demultiplexing purposes.
+  mach_msg_size_t MachMessageServerRequestSize() override;
+
+  //! \copydoc MachMessageServer::Interface::MachMessageServerReplySize()
+  //!
+  //! This implementation returns the maximum reply message size of all handlers
+  //! added by AddHandler(). If no handlers are present, returns the size of
+  //! `mig_reply_error_t`, the minimum size of a MIG reply message.
+  mach_msg_size_t MachMessageServerReplySize() override;
+
+ private:
+  using HandlerMap = std::map<mach_msg_id_t, MachMessageServer::Interface*>;
+
+  HandlerMap handler_map_;  // weak
+  mach_msg_size_t request_size_;
+  mach_msg_size_t reply_size_;
+
+  DISALLOW_COPY_AND_ASSIGN(CompositeMachMessageServer);
+};
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_MACH_COMPOSITE_MACH_MESSAGE_SERVER_H_