ZipException occurs when content-encoding-header is set for 304-response

Test scenario

• Setup http server
• Execute Request twice
• First response
  • Status: 200
  • Cache-Control: public
  • ETag: 123
  • Body: some text
• Second response
  • Status: 304
  • Content-Encoding: gzip
• Effect: java.util.zip.ZipException: Not in GZIP format
• Expected: Cached response

JUnit-Test

• Dependencies: junit 4.11, commons-io 2.4, com.github.tomakehurst:wiremock 1.57

  import com.github.tomakehurst.wiremock.junit.WireMockRule;
  import org.apache.commons.io.IOUtils;
  import org.apache.http.client.methods.CloseableHttpResponse;
  import org.apache.http.client.methods.HttpGet;
  import org.apache.http.impl.client.CloseableHttpClient;
  import org.apache.http.impl.client.HttpClientBuilder;
  import org.apache.http.impl.client.cache.CacheConfig;
  import org.apache.http.impl.client.cache.CachingHttpClientBuilder;
  import org.junit.Assert;
  import org.junit.Rule;
  import org.junit.Test;
  
  import java.io.IOException;
  
  import static com.github.tomakehurst.wiremock.client.WireMock.aResponse;
  import static com.github.tomakehurst.wiremock.client.WireMock.equalTo;
  import static com.github.tomakehurst.wiremock.client.WireMock.get;
  import static com.github.tomakehurst.wiremock.client.WireMock.stubFor;
  import static com.github.tomakehurst.wiremock.client.WireMock.urlEqualTo;
  
  public class GZipCachingHttpClientBuilderTest  {
  
    private static final String TEST_BODY = "Sometext";
  
    @Rule
    public WireMockRule wireMockRule = new WireMockRule(0);
  
    @Test
    public void testGzipError() throws Exception {
  
      stubFor(get(urlEqualTo("/my/resource"))
          .willReturn(aResponse()
                  .withStatus(200)
                  .withHeader("Cache-Control", "public")
                  .withHeader("ETag", "123")
                  .withBody(TEST_BODY)
  
          ));
  
  
      stubFor(get(urlEqualTo("/my/resource"))
          .withHeader("If-None-Match", equalTo("123"))
          .willReturn(aResponse()
                  .withHeader("Content-Encoding", "gzip")
                  .withStatus(304)
          ));
  
  
      CacheConfig.Builder cfgBuilder = CacheConfig.custom();
      CacheConfig cfg = cfgBuilder.setMaxCacheEntries(1024).build();
      HttpClientBuilder bld = CachingHttpClientBuilder.create().setCacheConfig(cfg);
  
      CloseableHttpClient client = bld.build();
  
      executeRequest(client);
      executeRequest(client); // second request causes Exception :-(
    }
  
  
    private void executeRequest(CloseableHttpClient client) throws IOException {
      int port = wireMockRule.port();
      CloseableHttpResponse resp = client.execute(new HttpGet("http://localhost:"+port+"/my/resource"));
      Assert.assertEquals(TEST_BODY, IOUtils.toString(resp.getEntity().getContent()));
    }
  
  }