mac: Add NotifyServer::DefaultInterface, a default no-op implementation

util/mach/notify_server.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 19 matching lines @@
 //! href="https://lists.apple.com/archives/darwin-development/2001/Sep/msg00451.html">mach
 //! port notifications</a> thread on the <a
 //! href="https://lists.apple.com/archives/darwin-development/">darwin-development</a>
 //! mailing list (now known as <a
 //! href="https://lists.apple.com/mailman/listinfo/darwin-dev">darwin-dev</a>)
 //! is good background for the various notification types.
 class NotifyServer : public MachMessageServer::Interface {
  public:
   //! \brief An interface that the different request messages that are a part of
   //!     the `notify` Mach subsystem can be dispatched to.
+  //!
+  //! Default implementations of all methods are available in the
+  //! DefaultInterface class.
   class Interface {
    public:
     //! \brief Handles port-deleted notifications sent by
     //!     `mach_notify_port_deleted()`.
     //!
     //! A port-deleted notification is generated when a port with a dead-name
     //! notification request is destroyed and the port name becomes available
     //! for reuse.
     //!
     //! This behaves equivalently to a `do_mach_notify_port_deleted()` function
@@ skipping 109 matching lines @@
     //!     not complex Mach messages.
     virtual kern_return_t DoMachNotifyDeadName(
         notify_port_t notify,
         mach_port_name_t name,
         const mach_msg_trailer_t* trailer) = 0;
 
    protected:
     ~Interface() {}
   };
 
+  //! \brief A concrete implementation of Interface that provides a default
+  //!     behavior for all `notify` routines.
+  //!
+  //! The Mach `notify` subsystem contains a collection of unrelated routines,
+  //! and a single server would rarely need to implement all of them. To make it
+  //! easier to use NotifyServer, a server can inherit from DefaultInterface
+  //! instead of Interface. Unless overridden, each routine in DefaultInterface
+  //! returns `MIG_BAD_ID` to indicate to the caller that the `notify` message
+  //! was unexpected and not processed.
+  class DefaultInterface : public Interface {
+   public:
+    // Interface:
+
+    kern_return_t DoMachNotifyPortDeleted(
+        notify_port_t notify,
+        mach_port_name_t name,
+        const mach_msg_trailer_t* trailer) override;
+
+    kern_return_t DoMachNotifyPortDestroyed(
+        notify_port_t notify,
+        mach_port_t rights,
+        const mach_msg_trailer_t* trailer,
+        bool* destroy_request) override;
+
+    kern_return_t DoMachNotifyNoSenders(
+        notify_port_t notify,
+        mach_port_mscount_t mscount,
+        const mach_msg_trailer_t* trailer) override;
+
+    kern_return_t DoMachNotifySendOnce(
+        notify_port_t notify,
+        const mach_msg_trailer_t* trailer) override;
+
+    kern_return_t DoMachNotifyDeadName(
+        notify_port_t notify,
+        mach_port_name_t name,
+        const mach_msg_trailer_t* trailer) override;
+
+   protected:
+    DefaultInterface() : Interface() {}
+    ~DefaultInterface() {}
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(DefaultInterface);
+  };
+
   //! \brief Constructs an object of this class.
   //!
   //! \param[in] interface The interface to dispatch requests to. Weak.
   explicit NotifyServer(Interface* interface);
 
   // MachMessageServer::Interface:
 
   bool MachMessageServerFunction(const mach_msg_header_t* in_header,
                                  mach_msg_header_t* out_header,
                                  bool* destroy_complex_request) override;
 
   std::set<mach_msg_id_t> MachMessageServerRequestIDs() override;
 
   mach_msg_size_t MachMessageServerRequestSize() override;
   mach_msg_size_t MachMessageServerReplySize() override;
 
  private:
   Interface* interface_;  // weak
 
   DISALLOW_COPY_AND_ASSIGN(NotifyServer);
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_MACH_NOTIFY_SERVER_H_