Xcode+Swift+XPC: How to start and deploy a Swift XPC target on MacOS - swift

Question

DISCLAIMER: I am relatively new to MacOS/Xcode
I want to build a simple XPC Launch Agent in Swift (ie: in ~/Library/LaunchAgents) but I could not find much documentation.
I started with Xcode XPC template but I do not know if it was a good idea for my Swift project.
I notice I should also have ~/Library/LaunchAgents/com.demo.myservice.plist
Versions:
- MacOS: 10.13.2
- Xcode: 9.2
Instruction to create the Xcode XPC Project:
File > New project
I chose the MacOS template: XPC
I create the bundle ‘com.demo.myservice’
It creates me an Objective-C project. So I delete all files (ie: myserviceProtocol.h, myservice.h, myservice.m, main.m and Info.plist
Create the files:
myserviceProtocol.swift
import Foundation
#objc(myserviceProtocol) protocol myserviceProtocol {
func ping()
}
myservice.swift
import Foundation
class myservice : NSObject, myserviceProtocol {
func ping() {
print("ping")
}
}
main.swift
import Foundation
class ServiceDelegate : NSObject, NSXPCListenerDelegate {
func listener(_ listener: NSXPCListener, shouldAcceptNewConnection newConnection: NSXPCConnection) -> Bool {
newConnection.exportedInterface = NSXPCInterface(with:myserviceProtocol.self)
let exportedObject = myservice()
newConnection.exportedObject = exportedObject
newConnection.resume()
return true
}
}
// Create the listener and resume it:
//
let delegate = ServiceDelegate()
let listener = NSXPCListener.service()
listener.delegate = delegate;
listener.resume()
Info.plist
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>KeepAlive</key>
<true/>
<key>Label</key>
<string>com.demo.myservice</string>
<key>ProgramArguments</key>
<array>
<string>myservice</string>
</array>
<key>RunAtLoad</key>
<true/>
</dict>
</plist>
I build it:
I copied Info.plist into ~/Library/LaunchAgents/ : cp ~/Documents/myservice/myservice/Info.plist ~/Library/LaunchAgents/com.demo.myservice.plist
I retrieve my userid with id -u
And then I try to execute it from the command line (as it does not seem to do anything from Xcode):
sudo launchctl debug user/501/com.demo.myservice /Users/olivier/Library/Developer/Xcode/DerivedData/myservice-hbwefcgibyqbajguvblgcmxsnrmd/Build/Products/Debug/myservice.xpc
Configuration failed: 113: Could not find specified service
Could not find service "com.demo.myservice" in domain for uid: 501
I am not really sure of what I am doing. Was I right to use XPC template to create my swift XPC.

Answer 1

If you want your Agent to provide an XPC service, you need to expose it as a Mach Service.
The way you are initialising your Listener is for an XPC Service (notice capital S), an XPC Service is a bundle that is part of your application's bundle, located inside the Contents/XPCServices/ directory.
So in summary, you would have to:
1.) Create an Agent that exposes an XPC service via mach service. Your listener would look like:
let listener = NSXPCListener(machServiceName: "com.rderik.exampleXPC" )
2.) To consume your Agent's service you'll need to build the connection to that mach service.
let connection = NSXPCConnection(machServiceName: "com.rderik.exampleXPC")
I hope that helps.
If you want to read more, I wrote a tutorial on how to do that here:
https://rderik.com/blog/creating-a-launch-agent-that-provides-an-xpc-service-on-macos/

Answer 2

I'm not sure what your goal is. If you just want a daemon that is managed by launchd, then you don't need XPC. Just create a daemon (probably with the Command Line Tool project template) and create a launchd plist configuration file (see man launchd.plist).
XPC is intended to communicate with a host app. The service binary should be embedded in your app bundle and launchd will launch it when your app tries to connect. You don't need to modify ~/Library/LaunchAgents for this.
Your app needs to setup an NSXPCConnection to connect to the XPCListener you created.
Something like:
let connection = NSXPCConnection(serviceName: "com.demo.myservice")
let interface = NSXPCInterface(with: myserviceProtocol.self)
connection.remoteObjectInterface = interface
connection.resume()
let proxy = connection.remoteObjectProxyWithErrorHandler {(error) in
os_log("Connection Error: %{public}#", error.localizedDescription)
} as! myserviceProtocol
// message proxy here to communicate with service
Both scenarios are covered in more detail in the Daemons and Services Programming Guide