I found a problem where a process tries to connect to System Extension and connection is invalidated. XPC listener has to be disposed and initialized again. This happens when System Extension executes tasks in following order: NSXPCListener initialized NSXPCListener.resume() NSProvider.startSystemExtensionMode() Result: Connection is invalidated and not only that the client has to retry connection, nut also System Extension must reinitialize listener (execute step 1 and 2). However if I call NSProvider.startSystemExtensionMode() NSXPCListener initialized NSXPCListener.resume() It works as expected and even if the connection is invalidated/interrupted, client process can always reconnect and no other action is necessary in System Extension (no need to reinitialize XPC listener), In Apple docs about NSProvider.startSystemExtensionMode() it says that this method starts handling request, but in another online article written by Scott Knight I found that startSystemExtensionMode() also starts listener server. Is that right? PLease could you add this info into the docs if it is so? https://knight.sc/reverse%20engineering/2019/08/24/system-extension-internals.html I would like to use following logic: Call NSProvider.startSystemExtensionMode() only under certain circumstances - I have received some configuration that I need to process and do some setup. If I don't receive it, there is no reason to call startSystemExtensionMode() yet, I don't need to handle handleNewFlow() yet. Connect XPC client to System Extension under certain conditions. Ideally communicate with client even though System Extension is not handling network requests yet, that is without receiving handleNewFlow(). Basically I consider XPC and System Extension handling network requests as separate things. Is that correct, are they separate and independent? Does XPC communication really depend on calling startSystemExtensionMode()? Another potential issue: Is it possible that XPC listener fails to validate connection when client tries to connect before System Extension manages to complete init and park the main thread in CFRunLoop? Note: These querstions arose mostly from handling upgrades of System Extension (extension is already running, network filter is created and is connected and new version of the app upgrades System Exension). Thanks.

Our app has a network extension (as I've mentioned lots 😄). We do an upgrade by downloading the new package, stopping & removing all of our components except for the network extension, and then installing the new package, which then loads a LaunchAgent causing the containing app to run. (The only difference between a new install and upgrade is the old extension is left running, but not having anything to tell it what to do, just logs and continues.) On some (but not all) upgrades... nothing ends up able to communicate via XPC with the Network Extension. My simplest cli program to talk to it gets Could not create proxy: Error Domain=NSCocoaErrorDomain Code=4099 "The connection to service named blah was invalidated: failed at lookup with error 3 - No such process." UserInfo={NSDebugDescription=The connection to service named bla was invalidated: failed at lookup with error 3 - No such process.} Could not communicate with blah Restarting the extension by doing a kill -9 doesn't fix it; neither does restarting the control daemon. The only solution we've come across so far is rebooting. I filed FB11086599 about this, but has anyone thoughts about this?