Okhttp refresh expired token when multiple requests are sent to the server

Question

I have a ViewPager and three webservice calls are made when ViewPager is loaded simultaneously.

When first one returns 401, Authenticator is called and I refresh the token inside Authenticator, but remaining 2 requests are already sent to the server with old refresh token and fails with 498 which is captured in Interceptor and app is logged out.

This is not the ideal behaviour I would expect. I would like to keep the 2nd and 3rd request in the queue and when the token is refreshed, retry the queued request.

Currently, I have a variable to indicate if token refresh is ongoing in Authenticator, in that case, I cancel all subsequent request in the Interceptor and user has to manually refresh the page or I can logout the user and force user to login.

What is a good solution or architecture for the above problem using okhttp 3.x for Android?

EDIT: The problem I want to solve is in general and I would not like to sequence my calls. i.e. wait for one call to finish and refresh the token and then only send rest of the request on the activity and fragment level.

Code was requested. This is a standard code for Authenticator:

public class CustomAuthenticator implements Authenticator {

    @Inject AccountManager accountManager;
    @Inject @AccountType String accountType;
    @Inject @AuthTokenType String authTokenType;

    @Inject
    public ApiAuthenticator(@ForApplication Context context) {
    }

    @Override
    public Request authenticate(Route route, Response response) throws IOException {

        // Invaidate authToken
        String accessToken = accountManager.peekAuthToken(account, authTokenType);
        if (accessToken != null) {
            accountManager.invalidateAuthToken(accountType, accessToken);
        }
        try {
                // Get new refresh token. This invokes custom AccountAuthenticator which makes a call to get new refresh token.
                accessToken = accountManager.blockingGetAuthToken(account, authTokenType, false);
                if (accessToken != null) {
                    Request.Builder requestBuilder = response.request().newBuilder();

                    // Add headers with new refreshToken

                    return requestBuilder.build();
            } catch (Throwable t) {
                Timber.e(t, t.getLocalizedMessage());
            }
        }
        return null;
    }
}

Some questions similar to this: OkHttp and Retrofit, refresh token with concurrent requests

Answer 1

It is important to note, that accountManager.blockingGetAuthToken (or the non-blocking version) could still be called somewhere else, other than the interceptor. Hence the correct place to prevent this issue from happening would be within the authenticator.

We want to make sure that the first thread that needs an access token will retrieve it, and possible other threads should just register for a callback to be invoked when the first thread finished retrieving the token.
The good news is, that AbstractAccountAuthenticator already has a way of delivering asynchronous results, namely AccountAuthenticatorResponse, on which you can call onResult or onError.

---

The following sample consists of 3 blocks.

The first one is about making sure that only one thread fetches the access token while other threads just register their response for a callback.

The second part is just a dummy empty result bundle. Here, you would load your token, possibly refresh it, etc.

The third part is what you do once you have your result (or error). You have to make sure to call the response for every other thread that might have registered.

boolean fetchingToken;
List<AccountAuthenticatorResponse> queue = null;

@Override
public Bundle getAuthToken(AccountAuthenticatorResponse response, Account account, String authTokenType, Bundle options) throws NetworkErrorException {

  synchronized (this) {
    if (fetchingToken) {
      // another thread is already working on it, register for callback
      List<AccountAuthenticatorResponse> q = queue;
      if (q == null) {
        q = new ArrayList<>();
        queue = q;
      }
      q.add(response);
      // we return null, the result will be sent with the `response`
      return null;
    }
    // we have to fetch the token, and return the result other threads
    fetchingToken = true;
  }

  // load access token, refresh with refresh token, whatever
  // ... todo ...
  Bundle result = Bundle.EMPTY;

  // loop to make sure we don't drop any responses
  for ( ; ; ) {
    List<AccountAuthenticatorResponse> q;
    synchronized (this) {
      // get list with responses waiting for result
      q = queue;
      if (q == null) {
        fetchingToken = false;
        // we're done, nobody is waiting for a response, return
        return null;
      }
      queue = null;
    }

    // inform other threads about the result
    for (AccountAuthenticatorResponse r : q) {
      r.onResult(result); // return result
    }

    // repeat for the case another thread registered for callback
    // while we were busy calling others
  }
}

Just make sure to return null on all paths when using the response.

You could obviously use other means to synchronize those code blocks, like atomics as shown by @matrix in another response. I made use of synchronized, because I believe this to be the easiest to grasp implementation, since this is a great question and everyone should be doing this ;)

---

The above sample is an adapted version of an emitter loop described here, where it goes into great detail about concurrency. This blog is a great source if you're interested in how RxJava works under the hood.

Answer 2

You can do this:

Add those as data members:

// these two static variables serve for the pattern to refresh a token
private final static ConditionVariable LOCK = new ConditionVariable(true);
private static final AtomicBoolean mIsRefreshing = new AtomicBoolean(false);

and then on the intercept method:

@Override
    public Response intercept(@NonNull Chain chain) throws IOException {
        Request request = chain.request();

        // 1. sign this request
        ....

        // 2. proceed with the request
        Response response = chain.proceed(request);

        // 3. check the response: have we got a 401?
        if (response.code() == HttpURLConnection.HTTP_UNAUTHORIZED) {

            if (!TextUtils.isEmpty(token)) {
                /*
                *  Because we send out multiple HTTP requests in parallel, they might all list a 401 at the same time.
                *  Only one of them should refresh the token, because otherwise we'd refresh the same token multiple times
                *  and that is bad. Therefore we have these two static objects, a ConditionVariable and a boolean. The
                *  first thread that gets here closes the ConditionVariable and changes the boolean flag.
                */
                if (mIsRefreshing.compareAndSet(false, true)) {
                    LOCK.close();

                    /* we're the first here. let's refresh this token.
                    *  it looks like our token isn't valid anymore.
                    *  REFRESH the actual token here
                    */

                    LOCK.open();
                    mIsRefreshing.set(false);
                } else {
                    // Another thread is refreshing the token for us, let's wait for it.
                    boolean conditionOpened = LOCK.block(REFRESH_WAIT_TIMEOUT);

                    // If the next check is false, it means that the timeout expired, that is - the refresh
                    // stuff has failed.
                    if (conditionOpened) {

                        // another thread has refreshed this for us! thanks!
                        // sign the request with the new token and proceed
                        // return the outcome of the newly signed request
                        response = chain.proceed(newRequest);
                    }
                }
            }
        }

        // check if still unauthorized (i.e. refresh failed)
        if (response.code() == HttpURLConnection.HTTP_UNAUTHORIZED) {
            ... // clean your access token and prompt for request again.
        }

        // returning the response to the original request
        return response;
    }

In this way you will only send 1 request to refresh the token and then for every other you will have the refreshed token.

Answer 3

You can try with this application level interceptor

 private class HttpInterceptor implements Interceptor {

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();

        //Build new request
        Request.Builder builder = request.newBuilder();
        builder.header("Accept", "application/json"); //if necessary, say to consume JSON

        String token = settings.getAccessToken(); //save token of this request for future
        setAuthHeader(builder, token); //write current token to request

        request = builder.build(); //overwrite old request
        Response response = chain.proceed(request); //perform request, here original request will be executed

        if (response.code() == 401) { //if unauthorized
            synchronized (httpClient) { //perform all 401 in sync blocks, to avoid multiply token updates
                String currentToken = settings.getAccessToken(); //get currently stored token

                if(currentToken != null && currentToken.equals(token)) { //compare current token with token that was stored before, if it was not updated - do update

                    int code = refreshToken() / 100; //refresh token
                    if(code != 2) { //if refresh token failed for some reason
                        if(code == 4) //only if response is 400, 500 might mean that token was not updated
                            logout(); //go to login screen
                        return response; //if token refresh failed - show error to user
                    }
                }

                if(settings.getAccessToken() != null) { //retry requires new auth token,
                    setAuthHeader(builder, settings.getAccessToken()); //set auth token to updated
                    request = builder.build();
                    return chain.proceed(request); //repeat request with new token
                }
            }
        }

        return response;
    }

    private void setAuthHeader(Request.Builder builder, String token) {
        if (token != null) //Add Auth token to each request if authorized
            builder.header("Authorization", String.format("Bearer %s", token));
    }

    private int refreshToken() {
        //Refresh token, synchronously, save it, and return result code
        //you might use retrofit here
    }

    private int logout() {
        //logout your user
    }
}

You can set interceptor like this to okHttp instance

    Gson gson = new GsonBuilder().create();

    OkHttpClient httpClient = new OkHttpClient();
    httpClient.interceptors().add(new HttpInterceptor());

    final RestAdapter restAdapter = new RestAdapter.Builder()
            .setEndpoint(BuildConfig.REST_SERVICE_URL)
            .setClient(new OkClient(httpClient))
            .setConverter(new GsonConverter(gson))
            .setLogLevel(RestAdapter.LogLevel.BASIC)
            .build();

    remoteService = restAdapter.create(RemoteService.class);

Hope this helps!!!!