[swift5] Cancellable requests

Created by: DavidHorvath

resolve #8658 (closed)

Previously the generated clients didn't support cancellation of requests

I've added request cancellation for:

• Both URLSession & Alamofire library
• Combine configuration
• RxSwift configuration
• Result configuration
• AsyncAwait configuration

For these clients I have updated the RequestBuilder's execute function so it returns an optional URLSessionDataTask. I've also added @discardableResult to keep backward compatibility.

Default

I've added to return the URLSessionDataTask so the user will be able to control the request's lifecycle.

    @discardableResult
    open class func addPet(body: Pet, apiResponseQueue: DispatchQueue = PetstoreClientAPI.apiResponseQueue, completion: @escaping ((_ data: Void?, _ error: Error?) -> Void)) -> URLSessionDataTask? {
        return addPetWithRequestBuilder(body: body).execute(apiResponseQueue) { result in
            switch result {
            case .success:
                completion((), nil)
            case let .failure(error):
                completion(nil, error)
            }
        }
    }

Result

I've added to return the URLSessionDataTask so the user will be able to control the request's lifecycle.

    @discardableResult
    open class func addPet(body: Pet, apiResponseQueue: DispatchQueue = PetstoreClientAPI.apiResponseQueue, completion: @escaping ((_ result: Swift.Result<Void, ErrorResponse>) -> Void)) -> URLSessionTask? {
        return addPetWithRequestBuilder(body: body).execute(apiResponseQueue) { result in
            switch result {
            case .success:
                completion(.success(()))
            case let .failure(error):
                completion(.failure(error))
            }
        }
    }

Combine

I've implemented handeEvents(receiveCompletion: where I cancel the returned URLSessionDataTask when the stream is cancelled

open class func addPet(body: Pet, apiResponseQueue: DispatchQueue = PetstoreClientAPI.apiResponseQueue) -> AnyPublisher<Void, Error> {
        var dataTask: URLSessionDataTask?
        return Future<Void, Error> { promise in
            dataTask = addPetWithRequestBuilder(body: body).execute(apiResponseQueue) { result in
                switch result {
                case .success:
                    promise(.success(()))
                case let .failure(error):
                    promise(.failure(error))
                }
            }
        }
        .handleEvents(receiveCancel: {
            dataTask?.cancel()
        })
        .eraseToAnyPublisher()
    }

RxSwift

I've added to cancel the returned URLSessionDataTask in Disposables.create when the stream is cancelled

    open class func addPet(body: Pet, apiResponseQueue: DispatchQueue = PetstoreClientAPI.apiResponseQueue) -> Observable<Void> {
        return Observable.create { observer -> Disposable in
            let dataTask = addPetWithRequestBuilder(body: body).execute(apiResponseQueue) { result in
                switch result {
                case .success:
                    observer.onNext(())
                case let .failure(error):
                    observer.onError(error)
                }
                observer.onCompleted()
            }
            
            return Disposables.create {
                dataTask?.cancel()
            }
        }
    }

Async Await

I've added to cancel the returned URLSessionDataTask in withTaskCancellationHandler.onCancel:

    open class func addPet(body: Pet, apiResponseQueue: DispatchQueue = PetstoreClientAPI.apiResponseQueue) async throws {
        var task: URLSessionTask?
        return try await withTaskCancellationHandler {
            try Task.checkCancellation()
            return try await withCheckedThrowingContinuation { continuation in
                guard !Task.isCancelled else {
                  continuation.resume(throwing: CancellationError())
                  return
                }

                task = addPetWithRequestBuilder(body: body).execute(apiResponseQueue) { result in
                    switch result {
                    case .success:
                        continuation.resume(returning: ())
                    case let .failure(error):
                        continuation.resume(throwing: error)
                    }
                }
            }
        } onCancel: { [task] in
            task?.cancel()
        }
    }

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./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. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
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