What is the correct way to alter a Request performing an asynchronous task before the Request happens?
So any request Rn need to become transparently Tn then Rn.
A little of background here: The Task is a 3rd party SDK that dispatch a Token I need to use as Header for the original request.
My idea is to decorate the Rn, but in doing this I need to convert my Tn task into a Siesta Request I can chain then.
So I wrapped the Asynchronous Task and chained to my original request.
Thus any Rn will turn into Tn.chained { .passTo(Rn) }
In that way, this new behaviour is entirely transparent for the whole application.
The problem
Doing this my code end up crashing in a Siesta internal precondition:
precondition(completedValue == nil, "notifyOfCompletion() already called")
In my custom AsyncTaskRequest I collect the callbacks for success, failure, progress etc, in order to trigger them on the main queue when the SDK deliver the Token.
I noticed that removing all the stored callback once they are executed, the crash disappear, but honestly I didn't found the reason why.
I hope there are enough informations for some hints or suggests.
Thank you in advance.
Yes, implementing Siesta’s Request interface is no picnic. Others have had exactly the same problem — and luckily Siesta version 1.4 includes a solution.
Documentation for the new feature is still thin. To use the new API, you’ll implement the new RequestDelegate protocol, and pass your implementation to Resource.prepareRequest(using:). That will return a request that you can use in a standard Siesta request chain. The result will look something like this (WARNING – untested code):
struct MyTokenHandlerThingy: RequestDelegate {
// 3rd party SDK glue goes here
}
...
service.configure(…) {
if let authToken = self.authToken {
$0.headers["X-Auth-Token"] = authToken // authToken is an instance var or something
}
$0.decorateRequests {
self.refreshTokenOnAuthFailure(request: $1)
}
}
func refreshTokenOnAuthFailure(request: Request) -> Request {
return request.chained {
guard case .failure(let error) = $0.response, // Did request fail…
error.httpStatusCode == 401 else { // …because of expired token?
return .useThisResponse // If not, use the response we got.
}
return .passTo(
self.refreshAuthToken().chained { // If so, first request a new token, then:
if case .failure = $0.response { // If token request failed…
return .useThisResponse // …report that error.
} else {
return .passTo(request.repeated()) // We have a new token! Repeat the original request.
}
}
)
}
}
func refreshAuthToken() -> Request {
return Request.prepareRequest(using: MyTokenHandlerThingy())
.onSuccess {
self.authToken = $0.jsonDict["token"] as? String // Store the new token, then…
self.invalidateConfiguration() // …make future requests use it
}
}
}
To understand how to implement RequestDelegate, you best bet for now is to look at the new API docs directly in the code.
Since this is a brand new feature not yet released, I’d greatly appreciate a report on how it works for you and any troubles you encounter.
Related
I'm learning Swift´s Combine by making an app, trying to solve real world use cases.
A common case, I'm performing a request, and the auth token expired. I would like to refresh the token if the request fails with a 401.
Something like:
fetchData()
.flatMap { data, response
if response.statusCode == 401 {
refreshToken()
.fetchData()
} else {
Just(data)
}
}
.keepDoingThings()
Keep in mind this is just pseudo code.
I have tried a few things indeed, but it's a mess. :)
How can this be done?
Thank you!
I tried porting my RxSwift version of this to Combine, but the latter is missing some key operators (retryWhen and flatMapFirst). One solution, therefore, is to bring RxCombine and RxSwift into your project so you can use my RxSwift solution in your project.
Here's my implementation: https://medium.com/#danielt1263/retrying-a-network-request-despite-having-an-invalid-token-b8b89340d29
RxCombine: https://github.com/freak4pc/RxCombine
RxSwift: https://github.com/ReactiveX/RxSwift
I don't expect this answer to be accepted as correct, but it can be a work-around until the necessary operators are added to Combine.
You can use tryMap() to throw Error before refreshToken, then do retry.
fetchData()
.tryMap { data, response in
if response.statusCode == 401 {
refreshToken()
.fetchData()
throw __MYERROR__.invalidServerResponse
} else {
return data
}
}
.retry(3)
.keepDoingThings()
I am unable to get values filled in the map after making a web client call and using the response of the previous Mono.Here is the code I have tried.The value of parameters.size() comes out to zero.Not able to get the reason as to why the value is not filled.I basically want to return age ( and not Mono object)
from this method.Using block gives an error block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-3.
Map<String, String> parameters = new HashMap<String,String>();
Mono<Person> obj = webClient
.post()
.uri("dummy url")
.accept(MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML)
.retrieve()
.bodyToMono(Person.class)
.flatMap(resp -> {
parameters.put("name", resp.getName());
parameters.put("age", resp.getAge());
return Mono.just(new Person(resp.getName(),resp.getAge()));
}
);
System.out.println(parameters.size());
Please suggest where I am wrong and solution to fix the same.
Since this is about collecting and using a token of some sort collected from a previous HTTP call, your best bet is to delegate all that to an ExchangeFilterFunction.
An ExchangeFilterFunction is a filter that is executed on the client side for each outgoing request. Here is a very, very naïve implementation of such a filter:
class TokenFilterFunction implements ExchangeFilterFunction {
private final AtomicReference<String> token = new AtomicReference<>();
#Override
public Mono<ClientResponse> filter(ClientRequest req, ExchangeFunction next) {
if (this.token.get() == null) {
return fetchToken(next).then(sendRequest(req, next));
}
else {
return sendRequest(req, next);
}
}
private Mono<ClientResponse> sendRequest(ClientRequest req, ExchangeFunction next) {
ClientRequest request = ClientRequest.from(req)
.header("Token", this.token.get()).build();
return next.exchange(request);
}
private Mono<Void> fetchToken(ExchangeFunction next) {
ClientRequest tokenRequest = ClientRequest.create(HttpMethod.GET,
URI.create("https://example.com/token")).build();
return next.exchange(tokenRequest).doOnNext(res -> {
this.token.set(res.headers().header("Token").get(0));
}).then();
}
}
This could automatically call the token endpoint to fetch a token when needed and directly chain with the request you asked in the first place. Again, such an implementation should be much more complex than that, handling domains, errors, and more.
If you're using some authentication technology, such a filter might be implemented already in Spring Security in a much, much better way.
You can configure it on your client during the building phase, like:
WebClient webClient = WebClient.builder().filter(new TokenFilterFunction()).build();
the documentation shows how to make targets require bearer tokens, which I did like this
extension MyService: AccessTokenAuthorizable {
var authorizationType: AuthorizationType {
switch self {
case .resetPassword, .postTextBook, .bookmarkBook, .getBookmarks, .logout, .verify:
return .bearer
default:
return .none
}
}
}
then it shows how to add tokens to the providers, which I did like this
let token = "abc123"
let authPlugin = AccessTokenPlugin(tokenClosure: token)
let provider = MoyaProvider<MyService>(plugins: [authPlugin])
but when the token expires, how can I change the token? and does Moya offer a way to automate this process, where if I get a forbidden http response (meaning I am not authorized), it automatically requests a token?
The implementation details of authentication/authorization can be quite different for each API out there. This is the reason why Moya will not handle the auth for you.
That said, implementing your own authentication/authorization can be done in many ways. It will depend on your constraints and/or preferences. As of today, you can find a few solutions sparsely outlined in Moya documentation:
Use the PluginType to add your auth to the requests. But think that this can potentially be used to refresh the token if needed. You may also need to intercept the completion of the request to detect authorization errors and apply your preferred recovery scenario (eg. refresh the token and retry the call).
Same can be implemented using the endpointClosure and/or requestClosure.
You can also consider implementing Alamofire's RequestAdapter and RequestRetrier. Depending on your needs, this can make retries easier. However, on them you will not have straightforward access to your TargetType, so you may need to find a way to recognize the different auth methods needed (ie. your bearer or none).
A few direct references to their documentation:
Plugins
Endpoints
Authentication
Alamofire Automatic Validation
Also, I highly encourage anybody to learn/get inspiration from Eilodon's Networking source code.
for change/refresh token i used this
static func send(request: TargetType) -> PrimitiveSequence<SingleTrait, Response> {
return provider.rx.request(request)
.retry(1)
.observeOn(ConcurrentDispatchQueueScheduler.init(qos: .default))
.filterSuccessfulStatusAndRedirectCodes()
.retryWhen({ (errorObservable: Observable<Error>) in
errorObservable.flatMap({ (error) -> Single<String> in
if let moyaError: MoyaError = error as? MoyaError, let response: Response = moyaError.response {
if **check forbidden http responses here** {
return provider.rx.request(.refreshToken(*your refresh token here*))
.filterSuccessfulStatusCodes()
.mapString(atKeyPath: "*json path to new access token*")
.catchError { (_) in
logout()
throw error
}
.flatMap({ (newAccessToken) -> PrimitiveSequence<SingleTrait, String> in
changeAccessToken()
return Single.just(newAccessToken)
})
}
}
throw error
})
})
}
static func logout() {
// logout action
}
static func changeAccessToken() {
// set new access token
}
I find transactions (https://www.firebase.com/docs/transactions.html) to be a cool way of handling concurrency, however it seems they can only be done from clients.
The way we use Firebase is mainly by writing data from our servers and observing them on clients. Is there a way to achieve optimistic concurrency model when writing data via REST API?
Thanks!
You could utilize an update counter to make write ops work in a similar way to transactions. (I'm going to use some pseudo-code below; sorry for that but I didn't want to write out a full REST API for an example.)
For example, if I have an object like this:
{
total: 100,
update_counter: 0
}
And a write rule like this:
{
".write": "newData.hasChild('update_counter')",
"update_counter": {
".validate": "newData.val() === data.val()+1"
}
}
I could now prevent concurrent modifications by simply passing in the update_counter with each operation. For example:
var url = 'https://<INSTANCE>.firebaseio.com/path/to/data.json';
addToTotal(url, 25, function(data) {
console.log('new total is '+data.total);
});
function addToTotal(url, amount, next) {
getCurrentValue(url, function(in) {
var data = { total: in.total+amount, update_counter: in.update_counter+1 };
setCurrentValue(ref, data, next, addToTotal.bind(null, ref, amount, next));
});
}
function getCurrentValue(url, next) {
// var data = (results of GET request to the URL)
next( data );
}
function setCurrentValue(url, data, next, retryMethod) {
// set the data with a PUT request to the URL
// if the PUT fails with 403 (permission denied) then
// we assume there was a concurrent edit and we need
// to try our pseudo-transaction again
// we have to make some assumptions that permission_denied does not
// occur for any other reasons, so we might want some extra checking, fallbacks,
// or a max number of retries here
// var statusCode = (server's response code to PUT request)
if( statusCode === 403 ) {
retryMethod();
}
else {
next(data);
}
}
FYI, Firebase Realtime Database officially supports this now.
Read the blog and the docs for more info.
check out Firebase-Transactions project: https://github.com/vacuumlabs/firebase-transactions
I believe, this may be quite handy for your case, especially if you do a lot of writes from the server.
(disclaimer: I'm one of the authors)
I'm about to set up a stupid play/scala app whose only job will be to make some http call once it receives calls itself
GET /abracadabra controllers.Application.abracadabra(stuff: String)
and then
def abracadabra(stuff: String) = Action {
Logger.info("called for stuff: "+stuff);
// call this other URL with 'stuff' as get parameter
// log http return status code and return Ok/200 anyways
}
Now for the second (commented) part I thought about using Dispatch.
I've read the docs but I can't just figure out how to use Promises and all that.
If anybody could point me to some sample code or something, it will be much appreciated
Since Play! has a built in Async library, you should probably go ahead and use that unless there's a feature in Dispatch that you specifically need.
Here's a short example:
def abracadabra(stuff: String) = Action {
Logger.info("called for stuff: "+stuff);
Async {
WS.url("http://stackoverflow.com/").get().map { response =>
Ok("I got it: " + response)
}
}
}
The documentation is here: https://github.com/playframework/Play20/wiki/ScalaWS