Sequence of actions with RxSwift - swift

Question

I'm using RxSwift to simply my code. For my current project I'd like to apply RxSwift's principles to a mess of completion blocks from the LayerKit:
layerClient.connectWithCompletion { (success, error) -> () in
if (!success) {
// Error
} else {
layerClient.requestAuthenticationNonceWithCompletion { (nonce, error) -> () in
// Even more blocks
}
}
}
I'm thinking about something like this:
// In extension
public func rx_connect() -> Observable<Bool> {
return create { observer in
self.connectWithCompletion { (success, error) -> ()in
if (success) {
observer.on(.Next(success))
observer.on(.Completed)
} else {
observer.on(.Error(error))
}
}
return NopDisposable.instance
}
}
public func rx_requestAuthenticationNonce() -> Observable<String> {
// Same for annother method
}
// In AppDelegate
self.layerClient.rx_connect()
.then() // requestAuthenticationNonceWithCompletion and use the nonce for next action
.then()
.subscribeNext(…
.onError(… // To catch all errors
RxSwift does not have a then() method. Is there another way to do this chaining stuff or am I thinking wrong on how to use ReactiveX in general?

Answer 1

Right, RxSwift doesn't have the then operator because the name is very risky.
then can be a lot of things in the Reactive Extensions world a map a flatMap or even a switchLatest, depending on the context.
In this case I would suggest to use a flatMap because that is going to be returned using a map is an Observable of Observables, that in most cases are hard to combine and manage. So I would do:
self.layerClient.rx_connect()
.flatMap(){ _ in
return rx_requestAuthenticationNonce()
.catchError(displayError)
}
.subscribeNext(…
.onError(… // To catch all errors
I would use flatMap instead of map in this case because I am then able to catch errors without terminating the sequence in case rx_requestAuthenticationNonce() fails.
Be careful in using the catchError operator, this operator will terminate the sequence after recovering and any extra event will be ignored after that.

Answer 2

This is authorization part in my project. Just an example for chaining requests. It turns the result of chained requests into a bool answer. It use 'flatMap' because result of old request is used in building new request. Otherwise, you can use 'concat' instead of 'flatMap'.
let client = RxSimpleLazyHttpClient.sharedInstance
let uuid = UIDevice().identifierForVendor!.UUIDString
let helloheaders = ["X-User-Identifier": "id:" + uuid]
let helloRequest: Observable<StringDictionary> = client.makeRequest(verb: .GET, url: NSURL(string: self.API_HOST + self.API_HELLO)!, parameters: [:], headers: helloheaders)
.map { result in
if (self.enableDebugOutput) {
self.debug(result)
}
let json = JSON(data: result.2!)
let userKey = json["user_key"].string
let userSecretHash = json["user_secret_hash"].string
return ["user_key": userKey ?? "", "user_secret_hash": userSecretHash ?? ""]
}
let jointAuthRequest: (StringDictionary -> Observable<StringDictionary>) = { [unowned self] stringDictionary in
Logger.D(stringDictionary.debugDescription)
let userKey = stringDictionary["user_key"]
let headers = ["X-User": userKey ?? ""]
return client.makeRequest(verb: .GET, url: NSURL(string: self.API_HOST + self.API_AUTH)!, parameters: [:], headers: headers)
.map { result in
if (self.enableDebugOutput) {
self.debug(result)
}
let json = JSON(data: result.2!)
let nonce = json["nonce"].string
var result = [String: String]()
result["nonce"] = nonce
return result.merge(stringDictionary)
}
}
let jointAuthNonceRequest: (StringDictionary -> Observable<StringDictionary>) = { [unowned self] stringDictionary in
Logger.D(stringDictionary.debugDescription)
let nonce = stringDictionary["nonce"] ?? ""
let userSecretHash = stringDictionary["user_secret_hash"] ?? ""
let headers = ["X-Pass": (userSecretHash + nonce).sha1().webSafeBase64()]
return client.makeRequest(verb: .GET, url: NSURL(string: self.API_HOST + self.API_AUTH + "/" + nonce)!, parameters: [:], headers: headers)
.map { result in
if (self.enableDebugOutput) {
self.debug(result)
}
let json = JSON(data: result.2!)
let sessionKey = json["session_key"].string
let sessionSecret = json["session_secret"].string
var result = [String: String]()
result["session_key"] = sessionKey
result["session_secret"] = sessionSecret
return result.merge(stringDictionary)
}
}
let jointResult: (StringDictionary -> Observable<Bool>) = { result in
let userKey = result["user_key"]
let userSecretHash = result["user_secret_hash"]
let sessionKey = result["session_key"]
let sessionSecret = result["session_secret"]
if userKey == nil || userSecretHash == nil || sessionKey == nil || sessionSecret == nil {
Logger.D("Auth Fail")
return just(false)
}
/* You can store session key here */
return just(true)
}
return helloRequest
.shareReplay(1)
.observeOn(RxScheduler.sharedInstance.mainScheduler)
.flatMap(jointAuthRequest)
.flatMap(jointAuthNonceRequest)
.flatMap(jointResult)
This is the 'makeRequest' method.
public func makeRequest(verb verb: Alamofire.Method, url: NSURL, parameters: [String : String]?, headers: [String : String]?) -> Observable<RxRequestResult> {
return create { observer in
Alamofire.request(verb, url, parameters: nil, encoding: ParameterEncoding.URL, headers: headers)
.response { request, response, data, error in
observer.onNext((request, response, data, error))
}
return AnonymousDisposable {
// when disposed
}
}
}