Components of XPC service.

main.swift

import Foundation

let delegate = MyServiceDelegate()
let listener = NSXPCListener.service()
listener.delegate = delegate
listener.resume()

MyService.swift

import Foundation

class MyService: NSObject, MyServiceProtocol {
    func upperCaseString(_ string: String, withReply reply: @escaping (String) -> Void) {
        let response = string.uppercased()
        reply(response)
    }
}

MyServiceDelegate.swift

import Foundation

class MyServiceDelegate: NSObject, NSXPCListenerDelegate {
    func listener(_ listener: NSXPCListener, shouldAcceptNewConnection newConnection: NSXPCConnection) -> Bool {
        let exportedObject = MyService()
        newConnection.exportedInterface = NSXPCInterface(with: MyServiceProtocol.self)
        newConnection.exportedObject = exportedObject
        newConnection.resume()
        return true
    }
}

MyServiceProtocol.swift

import Foundation

@objc public protocol MyServiceProtocol {
    func upperCaseString(_ string: String, withReply reply: @escaping (String) -> Void)
}

usage.swift

import MyService

...

let connection = NSXPCConnection(serviceName: "com.matthewminer.MyService")
connection.remoteObjectInterface = NSXPCInterface(with: MyServiceProtocol.self)
connection.resume()

let service = connection.remoteObjectProxyWithErrorHandler { error in
    print("Received error:", error)
} as? MyServiceProtocol

service?.upperCaseString("Hello XPC") { response in
    print("Response from XPC service:", response)
}

This is not working with macOS Mojave and Swift 4.2.

The connection to service named com.matthewminer.MyService was invalidated.

Apple's documentation is horrible. I can not figure out how to do this. Any suggestions?

So, I figured it our. In Swift 4 you have to pass @escaping to the result parameter of the service:

// MyService.swift

import Foundation

class MyService: NSObject, MyServiceProtocol {
    func upperCaseString(_ string: String, withReply reply: @escaping (String) -> Void) {
        let response = string.uppercased()
        reply(response)
    }
}

// MyServiceProtocol.swift

import Foundation

@objc public protocol MyServiceProtocol {
    func upperCaseString(_ string: String, withReply reply: @escaping (String) -> Void)
}

@adur1990: Thanks for the fix, I updated the Gist.

@mminer - listener.resume() in main.swift is throwing the following error. Any idea how to fix it?

Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)

@madscientistjaidev: I'm not too sure what might cause that error. I tried the code in the Gist in a fresh project using the Xcode 11 beta + Swift 5 and it worked without a hitch. Sorry I can't be of more help.

Thanks for making your code available.. I reference this every time I create a xpc service and want swift instead. Maybe Xcode 11 will make this obsolete (we can hope).

@tt-embodied: Glad it's helpful!

If anyone like me tried it in a command-line tool and got “The connection to service named ... was invalidated.”, it’s because it doesn’t seem to work in command-line tools at all, the same code in an app will work.

I've tried this in a SwiftUI app and I'm getting the error "The connection to service named ... was invalidated". Any ideas?

UPDATE: My problem was that the XPS Service was not copied to Contents/XPCServices. If you don't properly place the XPC Service within the app bundle, this doesn't work (also why you cannot call the XPC Service from a command line that is expecting it in it's bundle - haven't figure out how to do this yet)

@rsalesas Good to know, that’s an easy mistake to make. Thanks for the extra info.

I also just ran into this error:

Domain=NSCocoaErrorDomain Code=4099 "The connection to service on pid 0 named <service-name> was invalidated."

It turns out I just misspelled the service name when initializing the NSXPCConnection. Hope this saves someone a few hours of debugging lol.