Redirecting a signal returning an error to another signal - nsurlsession

Question

So my use case is that I have an HTTP request (fired using -[NSURLSession rac_dataWithRequest:]) that can return a status code of 403.
When this happens I would like to catch that, and redirect to another SignalProducer that requests an authentication token. When that SignalProducer successfully completes, I would like to redirect back to the original rac_dataWithRequest.
How would I best do this? I'm using ReactiveCocoa 4.x and Swift 2.

Answer 1

do you need to hand the authentication token back to the original request before retrying? If yes, then this won't help you, sorry.
I assumed that you just need to fire the authentication request once and then retry the original request. E.g. your authentication request sets the HTTP Authorization header of your HTTP client so that the next request is automatically authorised...
This gist has the contents of a Playground that illustrates the solution. This gist is the result of me playing around to find a solution, requests are mocked, ...
Lets say you have a SignalProducer for your request:
let request = SignalProducer<Response, NSError> {
// Perform your request that needs authentication here
}
And another one for your authentication request:
let authorize = SignalProducer<Void, NSError> {
// Perform your request that needs authentication here
}
Now you can use flatMapErrors (formerly catch) and retry:
request.flatMapError { error -> SignalProducer<String, NSError> in
if(error.code == 403) {
return authorize.then(SignalProducer(error: error))
} else {
return SignalProducer(error: error)
}
}.retry(1)
So, we catch errors of the original request and, if the error code is 403, we perform the authorize request. Then, we still forward the catched error. Otherwise, we just forward the error.
Forwarding the error after the authorize request is important, otherwise, retry will not restart the original request.
The problem with this however is, that it will retry on every error, not just when the original request returns 403...