Chaining API calls - ios

Question

I've built myself an APIService class, handling all interaction with APIs my App is using
func callEndpointX(token: String, completion: #escaping(Result<User, APIError>) -> Void) {
guard let endpoint = URL(string: apiBaseUrl + "/endpointX") else {fatalError()}
var request = URLRequest(url: endpoint)
request.addValue("Bearer " + token, forHTTPHeaderField: "Authorization")
request.httpMethod = "GET"
let dataTask = URLSession.shared.dataTask(with: request) { data, response, error in
guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200, let jsonData = data
else { ... completion(.failure(.responseError)); return }
do {
let response = try JSONDecoder()...
completion(.success(response.detailresponse!))
} catch {
...
completion(.failure(.decodingError))
}
}
dataTask.resume()
}
My challenge is that the Bearer Tokens I'm passing along do expire. What I would like to do in case of an expired token is to silently refresh the token for the user before hitting the api.
So I've got a mini function func tokenExpired() -> Bool {...} checking if the Token has alreaady expired and I have access to another API all refreshToken in a similar way as func callEndpointX above.
What I'm struggling with is how to chain these together to avoid race conditions - i.e. when func callEndpointX gets called, it should check func tokenExpired() and not continue any other work until that's done. If expired, it should first execute refreshToken and only after that returns continue with finally executing the ret of func callEndpointX.
All this chaining is messing with my brain and I was hoping someone would be able to guide me here.
Many thanks!!!

Answer 1

A solution is to call recursively callEndPointX after token refresh is completed.
Assume your token request is like this:
func requestToken(completion:#escaping((String) -> Void))
then
func callEndpointX(token: String, completion: #escaping(Result<User, APIError>) -> Void) {
if tokenExpired() {
requestToken(completion: { newToken in
callEndpointX(token: newToken, completion: completion)
})
}
else {
// your code for callendpointX
}
}