Get public ip address using project reactor and jbang

GetIpAddressFromHostWithReactor.java

///usr/bin/env jbang "$0" "$@" ; exit $?

//DEPS io.projectreactor:reactor-core:3.6.0

import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;

import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpClient.Version;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.net.http.HttpResponse.BodyHandlers;
import java.time.Duration;
import java.util.concurrent.CountDownLatch;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * @author rubn
 */
public class GetIpAddressFromHostWithReactor {

    private static final String IFCONFIG_CO = "http://ifconfig.cao";
    private static final String CHECKIP_AMAZON_COM = "http://checkip.amazonaws.com";

    public GetIpAddressFromHostWithReactor() {
        System.out.println("Initial host: " + IFCONFIG_CO);
        final CountDownLatch countDownLatch = new CountDownLatch(1);
        Mono.fromCallable(GetIpAddressFromHostWithReactor::makeRequest)
                .subscribeOn(Schedulers.boundedElastic())
                .flatMap(Function.identity())
                .map(HttpResponse::body)
                .flatMap(GetIpAddressFromHostWithReactor::extractIp)
                .onErrorResume(fallback)
                .doOnNext(ip -> System.out.println("ip " + ip))
                .doOnTerminate(countDownLatch::countDown)
                .subscribe();
        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

    private static HttpClient client() {
        return HttpClient.newBuilder()
                .version(Version.HTTP_2)
                .connectTimeout(Duration.ofSeconds(5))
                .build();
    }

    private static Mono<HttpResponse<String>> makeRequest() {
        return Mono.just(client())
                .flatMap(httpClient -> send(httpClient, IFCONFIG_CO))
                .doOnError(throwable -> System.out.println("Request error on: " + IFCONFIG_CO + " " + throwable.getMessage()));
    }

    private static Mono<HttpResponse<String>> send(HttpClient client, final String url) {
        try {
            return Mono.just(client.send(request(url), BodyHandlers.ofString()));
        } catch (IOException | InterruptedException e) {
            return Mono.error(new RequestWTFHostException(e));
        }
    }

    private static HttpRequest request(final String url) {
        return HttpRequest.newBuilder(URI.create(url))
                .GET()
                .build();
    }

    private static Mono<String> extractIp(String body) {
        return Mono.just(Stream.of(body.split("<ip>"))
                .map(internalData -> internalData.split("class=\"ip\">")[1])
                .map(ip -> ip.split("</code")[0])
                .collect(Collectors.joining()));
    }

    static Function<Throwable, Mono<String>> fallback = (throwable) -> {
        System.out.println("Fallback host " + CHECKIP_AMAZON_COM);
        return Mono.just(client())
                .flatMap(httpClient -> send(httpClient, CHECKIP_AMAZON_COM))
                .doOnError(onError -> System.out.println("Request error on: " + CHECKIP_AMAZON_COM + " " + throwable.getMessage()))
                .map(HttpResponse::body);
    };

    public static class RequestWTFHostException extends Exception {

        public RequestWTFHostException(Throwable error) {
            super(error);
        }
    }

    public static void main(String... bull$hXt) {
        new GetIpAddressFromHostWithReactor();
    }

}

rubn ⲁƛ ▸ jbang GetIpAddressFromHostWithReactor.java
[jbang] Building jar for GetIpAddressFromHostWithReactor.java...
Initial host: http://ifconfig.co <1>
ip 139.XX.XX.XXX

• (1) good

rubn ⲁƛ ▸ jbang GetIpAddressFromHostWithReactor.java
Initial host: http://ifconfig.cao <1>
Request error on: http://ifconfig.cao java.net.ConnectException
Fallback host http://checkip.amazonaws.com <2>
ip 139.XX.XX.XXX

• (1) bad url
• (2) good host