How to return an error from a HTTPS Cloud Function?

Question

Calling a Cloud Function from an iOS app looks like this:

var functions = Functions.functions() functions.httpsCallable(name).call(data){ (result, error) in // Code here }

How can I send an error from my Cloud Function, so it will get picked up in the above code? For example:

Cloud Function:

exports.joinGame = functions.https.onCall((data, context) => { return Error("The game is full") })

SwiftUI:

var functions = Functions.functions() functions.httpsCallable("joinGame").call(data){ (result, error) in print(error) // "The game is full" }

The Cloud Function is just returning an HTTP response. If you catch an error on the function's side, you should return an appropiate HTTP response code: tools.ietf.org/html/rfc7231#section-6 . Then, you handle that HTTP response code from your local code as any regular response from an HTTP request. — Jofre
– Jofre, Commented Nov 24, 2020 at 8:58
Calling the cloud function will return: (HTTPSCallableResult?, Error?) in SwiftUI - I want to return an error message from my cloud function that will appear under the 2nd parameter of the response (Error). @Asperi — Zorgan
– Zorgan, Commented Nov 24, 2020 at 9:10
@Paulw11 That makes sense. I will return { error: "error message" } or { success: "success message" } depending on the scenario. Thanks. — Zorgan
– Zorgan, Commented Nov 24, 2020 at 9:12
Yes, I think that is a better approach. You could also return { "success": true/false, "message":null/"Game full" } or whatever — Paulw11
– Paulw11, Commented Nov 24, 2020 at 9:16

Asperi · Accepted Answer · 2020-11-24 09:19:58Z

I'm still not sure where do you want to return error... but here is some variants of possible handling:

@State private var error: Error? var body: some View { VStack { Text("Wait for Error") .onAppear { functions.httpsCallable("joinGame").call(data){ (result, error) in print(error) // "The game is full" DispatchQueue.main.async { self.error = error } } } if nil != error { Text("Got error!") // << do anything with error here } } .onChange(of: error) { newError in // << or here } }

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