receiveCompletion and receiveValue are not being called

Question

I'm trying to leverage combine when making some API calls and I'm at a loss for why the sink methods are not being called.

I've included what I believe are all the relevant parts of the code and also the output in the logs.

What should I be doing differently?

    private var authorization: GTMAppAuthFetcherAuthorization?
    private let service = GTLRGmailService()
    private var cancellables = Set<AnyCancellable>()

...

    private func executeQuery(query: GTLRGmailQuery) -> AnyPublisher<Any, Error> {
        print("in executeQuery")
        return Future<Any, Error> { promise in
            self.service.executeQuery(query) {ticket, result, error in
                if let error = error {
                    return promise(.failure(error))
                } else {
                    print ("GOT ME SOME RESULTS")
                    print(result!)
                    return promise(.success(result!))
                }
            }
        }.eraseToAnyPublisher()
    }
    
    func getThreads() {
        print("in getThreads")
        let query = GTLRGmailQuery_UsersThreadsList.query(
            withUserId: authorization?.userEmail ?? "me"
        )
        
        print("getting threads")
        self.executeQuery(query: query)
            .sink(
                receiveCompletion: { completion in
                    print("GOT COMPLETION")
                    print(completion)
                    switch completion {
                    case .failure(let error):
                        print("ERROR EXECUTING QUERY")
                        print(error)
                    case .finished:
                        break
                    }
                },

                receiveValue: { value in
                    print("VALUE FROM QUERY")
                    print(value)
                }
            )
            .store(in: &cancellables)
    }

Log output:

in getThreads
getting threads
in executeQuery
2022-01-15 22:27:57.875615-0500 mail[30582:6728076] GTMSessionFetcher invoking fetch callbacks, data {length = 32719, bytes = 0x7b227468 72656164 73223a5b 7b226964 ... 7465223a 3533387d }, error (null)
2022-01-15 22:27:57.878231-0500 mail[30582:6728134] Executing GTLRGmailQuery_UsersThreadsList has additional pages of results not fetched because shouldFetchNextPages is not enabled
GOT ME SOME RESULTS
GTLRGmail_ListThreadsResponse 0x600000c4fc30: {nextPageToken:"..." resultSizeEstimate:538 threads:[100]}

Answer 1

I read this and added a .print("debugging") before .sink and the logs now include the following:

appeared and getting threads
in getThreads
getting threads
in executeQuery
debugging: receive subscription: (Future)
debugging: request unlimited
debugging: receive cancel

What this made me realize is that before my sink methods could be called the Future was being cancelled. So, I looked at where I was instantiating this class and realized that it was in a short-lived method (onAppear of a view). I moved instantiation to somewhere longer-lived and that allowed for the operations to complete and for the sink methods to be called.