I ran into a similar scenario where I wanted to write a unit test for the various compression scenarios, however, the WebTestClient always returns the decompressed response. Here's my workaround to access the raw response as well as the original headers.

@Honey were you able to figure out any other alternatives?

1. Disable compression on the WebClient. This will disable both response decompression as well as the "Accept-Encoding=gzip" request header.

   @Bean
   public WebClient webClient() {
     return WebClient
       .builder()
       .clientConnector(
         new ReactorClientHttpConnector(HttpClient.create().compress(false)))
         // ^ disabling compression
       .build();
   }
   

2. Manually add the "Accept-Encoding=gzip" request header. This will ensure that the server responds with the compressed payload, but the client doesn't decompress it.

   public Mono<Response> reactiveSendRequest(
     String body, URI url, String method, HttpHeaders headers) {
     return webClient
       .method(HttpMethod.valueOf(method.toUpperCase()))
       .uri(url)
       .bodyValue(body)
       .headers(h -> h.addAll(headers))
       .header("Accept-Encoding", "gzip")
       // ^ manually adding the header back
       .retrieve()
       .toEntity(byte[].class)
       .timeout(this.timeout)
       .map(rawResponse -> {
         return new Response(rawResponse);
       });
   }