Spring Webflux-based proxying controller

DefaultController.java

import org.springframework.core.io.buffer.DefaultDataBufferFactory;
import org.springframework.http.MediaType;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.stereotype.Controller;
import org.springframework.util.Assert;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;

@Controller
public class DefaultController {


  private DefaultDataBufferFactory defaultDataBufferFactory = new DefaultDataBufferFactory();

  @RequestMapping(value = "/api/**", method = RequestMethod.GET)
  @ResponseBody
  public Mono<Void> defaultGetHandler(ServerHttpRequest serverRequest, ServerHttpResponse serverHttpResponse) {

    WebClient client = WebClient.create("http://example.com");

    String path = serverRequest.getPath().value();

    System.out.println("Path=" + path);

    // Note http://example.com/api/... returns a badly formatted content header

    return client.get()
            .uri("/foo/" + path)
            .accept(serverRequest.getHeaders().getAccept().toArray(new MediaType[0]))
            .exchange()
            .flatMap(clientResponse -> {
              Assert.isTrue(serverHttpResponse.setStatusCode(clientResponse.statusCode()));
              serverHttpResponse.getHeaders().addAll(clientResponse.headers().asHttpHeaders());
              return serverHttpResponse.writeWith(clientResponse.bodyToFlux(String.class).map(s -> defaultDataBufferFactory.wrap(s.getBytes())));
            });
  }
  
}

Hi there!

Your solution does not handle non-text responses correctly, e.g. when the proxied server responds with some PDF document.

I assume the following (using Kotlin, excuse me!) code snippet works better (and provides better performance probably):

.exchange()
.flatMap {
    serverHttpResponse.headers.addAll(it.headers().asHttpHeaders())
    serverHttpResponse.statusCode = it.statusCode()
    it.body { clientHttpResponse, _ -> serverHttpResponse.writeWith(clientHttpResponse.body) }
}

The idea is to use a BodyExtractor to directly access ReactiveHttpInputMessage#getBody (which returns Flux<DataBuffer>).

Best regards,
Justus