Example of Alamofire RxSwift response serialization extension.

Alamofire+Rx.swift

import Alamofire
import RxSwift

extension Request: ReactiveCompatible {}

extension Reactive where Base: DataRequest {

    func responseJSON() -> Observable<Any> {
        return Observable.create { observer in
            let request = self.base.responseJSON { response in
                switch response.result {
                case .success(let value):
                    observer.onNext(value)
                    observer.onCompleted()

                case .failure(let error):
                    observer.onError(error)
                }
            }

            return Disposables.create(with: request.cancel)
        }
    }
}


// Example usage:

_ = Alamofire.request("https://httpbin.org/get").rx.responseJSON()
    .map { value in
        let json = value as? [String: Any] ?? [:]
        let origin = json["origin"] as? String ?? "unknown"
        return origin
    }
    .subscribe(onNext: { print("Origin:", $0) })

How would the map work in an error case?

map would be skipped entirely and you would need to handle the error case by supplying an onError handler.

_ = Alamofire.request("https://httpbin.org/get").rx.responseJSON()
    .map { ... }
    .subscribe(
        onNext: { print("Origin:", $0) },
        onError: { print("Received error:", $0) }
    )

The downside is that onError lacks the body of the response, which is problematic if you want to parse it. If you require this, you need to change the argument passed to observer.onError.