How can I queue up and delay retrofit requests to avoid hitting an api rate limit?

Question

I'm using an api that implements throttling. One of the limits is 1 request/second. ugh. I have the following scenario which hits the limit right away.

• Check the status of the api with api/status

• if the api is up, get a users subscriptions

• load a page from the list of subscriptions

Is there anything I can plug into retrofit that can queue each network request to only run at least 1000ms after the last? I am using/learning rxjava, can debounce be of any use here?

Answer 1

You can throttle your observable.

    Observable<String> text = ...
text.throttleLast(1, SECONDS)
    .flatMap(retrofitApiCall())
    .subscribe(result -> System.out.println("result: " + result));

Another solution is to set a dispatcher in your okhttp builder, and add an interceptor that sleeps for one second. This may not be the most elegant solution and kills some of the benefits of using async because it limits you to one thread at a time.

OkHttpClient.Builder builder = new OkHttpClient.Builder();


    Dispatcher dispatcher = new Dispatcher();
    dispatcher.setMaxRequests(1);

    Interceptor interceptor = new Interceptor() {
        @Override
        public Response intercept(Chain chain) throws IOException {
            SystemClock.sleep(1000);
            return chain.proceed(chain.request());
        }
    };

    builder.addNetworkInterceptor(interceptor);
    builder.dispatcher(dispatcher);
    builder.build();

Answer 2

Actually, you can use already made OkHttp Delay Interceptor library. Just call .addInterceptor(DelayInterceptor(Long, TimeUnit)) method on your's OkHttp client builder object.

Answer 3

An interceptor (from OkHttpClient) combined with a RateLimiter (from Guava) is a good solution to avoid HTTP 429 error code.

Let's suppose we want a limit of 3 calls per second:

import java.io.IOException;

import com.google.common.util.concurrent.RateLimiter;

import okhttp3.Interceptor;
import okhttp3.Response;

public class RateLimitInterceptor implements Interceptor {
    private RateLimiter limiter = RateLimiter.create(3);

    @Override
    public Response intercept(Chain chain) throws IOException {
        limiter.acquire(1);
        return chain.proceed(chain.request());
    }
}