Thank you for your answer. But doing what you explained, the error is nearly the same. NSXPCConnection: 0x12d834ab0 connection on anonymousListener or serviceListener from pid 36952: Exception caught during decoding of received selector hello, dropping incoming message. Exception: NSXPCDecoder: 0x10c9e6000 received a message or reply block that is not in the interface of the remote object (hello), dropping. ( 0  CoreFoundation           0x00007fff205f56af __exceptionPreprocess + 242 1  libobjc.A.dylib           0x00007fff2032d3c9 objc_exception_throw + 48 2  Foundation             0x00007fff212c73e4 -[NSXPCDecoder __decodeXPCObject:allowingSimpleMessageSend:outInvocation:outArguments:outArgumentsMaxCount:outMethodSignature:outSelector:isReply:replySelector:interface:] + 2244 3  Foundation             0x00007fff21312001 -[NSXPCDecoder _decodeMessageFromXPCObject:allowingSimpleMessageSend:outInvocation:outArguments:outArgumentsMaxCount:outMethodSignature:outSelector:interface:] + 33 4  Foundation             0x00007fff21310e3b -[NSXPCConnection _decodeAndInvokeMessageWithEvent:flags:] + 418 5  Foundation             0x00007fff212c8d49 message_handler + 206 6  libxpc.dylib            0x00007fff201c6c28 _xpc_connection_call_event_handler + 56 7  libxpc.dylib            0x00007fff201c5a9c _xpc_connection_mach_event + 935 8  libdispatch.dylib          0x00007fff202d8867 _dispatch_client_callout4 + 9 9  libdispatch.dylib          0x00007fff202efa47 _dispatch_mach_msg_invoke + 441 10 libdispatch.dylib          0x00007fff202de4a7 _dispatch_lane_serial_drain + 263 11 libdispatch.dylib          0x00007fff202f05b8 _dispatch_mach_invoke + 498 12 libdispatch.dylib          0x00007fff202de4a7 _dispatch_lane_serial_drain + 263 13 libdispatch.dylib          0x00007fff202df0fe _dispatch_lane_invoke + 426 14 libdispatch.dylib          0x00007fff202e8c5d _dispatch_workloop_worker_thread + 819 15 libsystem_pthread.dylib       0x00007fff20480499 _pthread_wqthread + 314 16 libsystem_pthread.dylib       0x00007fff2047f467 start_wqthread + 15

I finally managed to make it working. The thing is initWithMachServiceName must be called with: from the app: the full path of the login item bundle, i.e. /Applications/myApp.app/Contents/Library/LoginItems/a.b.c.d.e.LoginItemAgent.app from the FinderSync ext: the bundle id of the login item, i.e. a.b.c.d.e.LoginItemAgent

So, I've been able to set my bundle id starting with a figure from the Build Settings tab... Now my app can communicate with the login item agent, but the FinderSync, still not... I found this error in the Console: Sandbox: Extension(7145) deny(1) file-read-data .....myApp.app/Contents/Library/LoginItems/a.b.c.d.e.LoginItemAgent.app The app, FinderSync ext and login item agent are all in the same App Group, sandboxed and signed with "Apple Development" (debuging in XCode). Any idea?

Ok, thank you. So I'm trying to make working the AppLoginItemXPCDemo example. In the readme, I found that "The bundle identifier of a login item must start with your Team ID", but my Team ID starts with a figure and this is not accepted by XCode. Is there a solution?

I have also tried without success to set com.apple.security.temporary-exception.mach-register.global-name/com.apple.security.temporary-exception.mach-lookup.global-name entitlements. In myApp.entitlements: ... keycom.apple.security.temporary-exception.mach-register.global-name/key array stringa.b.c.d.e.f/string /array And in Extension.entitlements: ... keycom.apple.security.temporary-exception.mach-lookup.global-name/key array stringa.b.c.d.e.f/string /array Should I use an XPC login item app between the app and the extension? myApp = XPC login item app = FinderSync ext By dint of searching, I came across the AppLoginItemXPCDemo example, but it dates from 2012 ... No better solution has been proposed by Apple since? It seems like it's a common problem to get an application to communicate with a FinderSync extension ...

Finally, I managed to make it work, I did not understand that the sys ext had to be the listener. Thank you for your help. It's really solved this time!

Not solved, but I cannot remove the "Solved" badge I set by mistake...

If you add an XPC Service to an app then the service is registered in the app’s namespace. Only that app can access it. So, what should I do to communicate between my app and my sys ext?

Hello! So, I have added an XPC service to my application. I'm able to communicate between the app and the service but still not between the system extension and the service. The code is almost the same for the app and the system extension The only difference is: _xpcConnection = [[NSXPCConnection alloc] initWithServiceName:_serviceName]; // App code _xpcConnection = [[NSXPCConnection alloc] initWithMachServiceName:_serviceName options:0]; // Sys ext code The interruptionHandler and invalidationHandler don't catch any error. I don't see any error in the Console. The service and sys ext belong to the same app group. I have added NSEndpointSecurityMachServiceName to the Info.plist of the sys ext. I have also tried to add it to the Info.plist of the service (not sure it's usefull or not). "sudo launchctl procinfo ... " for the service: endpoints = { "a.b.c.d.e" = { port = 0x105c77 active = 1 managed = 1 reset = 0 hide = 0 } } "sudo launchctl procinfo ... " for the sys ext: endpoints = { "a.b.c.d.e" = { port = 0xf5d5b active = 0 managed = 1 reset = 0 hide = 0 } } How can I debug that? Thank you.

Thank you for your answer. Yikes! You’re using Distributed Objects (DO). Don’t do that. It’s been deprecated for a while now and for good reason. It’s deeply broken. It's an old app and I didn't want to rewrite everything (now). The migration is not trivial... The standard way to set up comms between an app and an ES sysex is via NSEndpointSecurityMachServiceName. Ok, I will try to get by using this.