7.2 Proxying Requests with ProxyHttpClient

A common requirement in Microservice environments is to proxy requests in a Gateway Microservice to other backend Microservices.

The regular HttpClient API is designed around simplifying exchange of messages and is not really designed for proxying requests. For this use case you should use the the ProxyHttpClient which can be used from a HTTP Server Filter to proxy requests to backend Microservices.

The following example demonstrates rewriting requests under the URI /proxy to the URI /real onto the same server (clearly in a real environment you would generally proxy onto another server):

Customizing the Netty pipeline for Logbook

import io.micronaut.core.async.publisher.Publishers;
import io.micronaut.core.util.StringUtils;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.MutableHttpResponse;
import io.micronaut.http.annotation.Filter;
import io.micronaut.http.client.ProxyHttpClient;
import io.micronaut.http.filter.*;
import io.micronaut.http.filter.ServerFilterChain;
import io.micronaut.runtime.server.EmbeddedServer;
import org.reactivestreams.Publisher;
@Filter("/proxy/**")
public class ProxyFilter extends OncePerRequestHttpServerFilter { (1)
    private final ProxyHttpClient client;
    private final EmbeddedServer embeddedServer;
    public ProxyFilter(ProxyHttpClient client, EmbeddedServer embeddedServer) { (2)
        this.client = client;
        this.embeddedServer = embeddedServer;
    }
    @Override
    protected Publisher<MutableHttpResponse<?>> doFilterOnce(HttpRequest<?> request, ServerFilterChain chain) {
        return Publishers.map(client.proxy( (3)
                request.mutate() (4)
                        .uri(b -> b (5)
                                .scheme("http")
                                .host(embeddedServer.getHost())
                                .port(embeddedServer.getPort())
                                .replacePath(StringUtils.prependUri(
                                        "/real",
                                        request.getPath().substring("/proxy".length())
                                ))
                        )
                        .header("X-My-Request-Header", "XXX") (6)
        ), response -> response.header("X-My-Response-Header", "YYY"));
    }
}

Customizing the Netty pipeline for Logbook

import io.micronaut.core.async.publisher.Publishers
import io.micronaut.core.util.StringUtils
import io.micronaut.http.HttpRequest
import io.micronaut.http.MutableHttpResponse
import io.micronaut.http.annotation.Filter
import io.micronaut.http.client.ProxyHttpClient
import io.micronaut.http.filter.*
import io.micronaut.http.filter.ServerFilterChain
import io.micronaut.http.uri.UriBuilder
import io.micronaut.runtime.server.EmbeddedServer
import org.reactivestreams.Publisher
@Filter("/proxy/**")
class ProxyFilter extends OncePerRequestHttpServerFilter { (1)
    private final ProxyHttpClient client
    private final EmbeddedServer embeddedServer
    ProxyFilter(ProxyHttpClient client, EmbeddedServer embeddedServer) { (2)
        this.client = client
        this.embeddedServer = embeddedServer
    }
    @Override
    protected Publisher<MutableHttpResponse<?>> doFilterOnce(HttpRequest<?> request, ServerFilterChain chain) {
        return Publishers.map(client.proxy( (3)
                request.mutate() (4)
                        .uri { UriBuilder b -> (5)
                            b.with {
                                scheme("http")
                                host(embeddedServer.getHost())
                                port(embeddedServer.getPort())
                                replacePath(StringUtils.prependUri(
                                                "/real",
                                                request.getPath().substring("/proxy".length())
                                ))
                            }
                        }
                        .header("X-My-Request-Header", "XXX") (6)
        ), { MutableHttpResponse<?> response -> response.header("X-My-Response-Header", "YYY")})
    }
}

Customizing the Netty pipeline for Logbook

import io.micronaut.core.async.publisher.Publishers
import io.micronaut.core.util.StringUtils
import io.micronaut.http.*
import io.micronaut.http.annotation.Filter
import io.micronaut.http.client.ProxyHttpClient
import io.micronaut.http.filter.*
import io.micronaut.http.uri.UriBuilder
import io.micronaut.runtime.server.EmbeddedServer
import org.reactivestreams.Publisher
import java.util.function.Function
@Filter("/proxy/**")
class ProxyFilter(
        private val client: ProxyHttpClient, (2)
        private val embeddedServer: EmbeddedServer) : OncePerRequestHttpServerFilter() { (1)
    override fun doFilterOnce(request: HttpRequest<*>, chain: ServerFilterChain): Publisher<MutableHttpResponse<*>> {
        return Publishers.map(client.proxy( (3)
                request.mutate() (4)
                        .uri { b: UriBuilder -> (5)
                            b.apply {
                                scheme("http")
                                host(embeddedServer.host)
                                port(embeddedServer.port)
                                replacePath(StringUtils.prependUri(
                                        "/real",
                                        request.path.substring("/proxy".length)
                                ))
                            }
                        }
                        .header("X-My-Request-Header", "XXX") (6)
        ), Function { response: MutableHttpResponse<*> -> response.header("X-My-Response-Header", "YYY") })
    }
}