[swift5][client] allow request cancellation and authentication flow to work together

[4brunu]

Fixes #11002

With the introduction of cancellable request on the swift generator, it broke the authentication flow and this PR tries to fix that.

Instead of returning the URLSessionTask, we return a class of ours, OpenAPIRequestCancellable, and the users may call the cancel method of OpenAPIRequestCancellable.

There is one OpenAPIRequestCancellable instance per request.

On the other hand, the URLSessionImplementations/AlamofireImplementations save the current request, URLSessionTask in case of URLSession or Request in case of Alamofire, in the OpenAPIRequestCancellable so that the request can be later on cancelled.

In case there is a retry of the request, we save the new URLSessionTask in the current request, so that the new request can be cancelled.

PR checklist

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  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
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• File the PR against the correct branch: master (5.3.0), 6.0.x
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@jgavris (2017/07) @ehyche (2017/08) @Edubits (2017/09) @jaz-ah (2017/09) @4brunu (2019/11)

[4brunu]

@denizdogan @davidhorvath @funzin @jarrodparkes I would appreciate if you could help to review this PR 🙂

[jarrodparkes]

@4brunu going to try and dig into this today — thanks for reaching out

[jarrodparkes]

@4brunu I was able to copy/paste the BearerRequestBuilderFactory example without modification. Was there something else I needed to check here? From what I gather, prior to this change, the example wouldn't work/compile?

[4brunu]

@4brunu I was able to copy/paste the BearerRequestBuilderFactory example without modification. Was there something else I needed to check here? From what I gather, prior to this change, the example wouldn't work/compile?

Yes, it wouldn't compile.
If you could look at the implementation of this feature, to see if you find anything wrong and if you could test the network request cancel method, it would be nice.
Just to make sure I didn't make any mistake, or introduced new bugs.

[jarrodparkes]

@4brunu just ran a little test with the Network Link Conditioner tool (so I could emulate a bad network), and the cancelling worked fine 👍

        print("starting task1")
        let task1 = PetstoreClientAPI.PetAPI.getPetById(petId: 9223372036854775807) { data, error in
            if let data = data {
                dump(data)
            }
        }
        
        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
            print("cancelling task1")
            task1.cancel()
        }
        
        print("starting task2")
        let task2 = PetstoreClientAPI.PetAPI.getPetById(petId: 9223372036854775807) { data, error in
            if let data = data {
                dump(data)
            }
        }
        
        DispatchQueue.main.asyncAfter(deadline: .now() + 15) {
            print("cancelling task2")
            task2.cancel()
        }

And the output...

starting task1
starting task2
cancelling task1
[task2 result] ▿ PetstoreClient.PetstoreClientAPI.Pet #0
  ▿ id: Optional(9223372036854775807)
    - some: 9223372036854775807
    - ... (redacted)
cancelling task2

Notice how task2 was able to finish before the delayed (15 seconds after request) cancel. While task1 was cancelled after only 2 seconds before the request could be completed — that is what its contents were not printed 👍

[4brunu]

Thanks for helping testing this.
I also made some local tests and worked as expected 👍

[4brunu]

@wing328 this one is ready to merge from me 👍