Always forward Content-Length header from origin when set (#2833)

* Always forward Content-Length from origin when set unless response is compressed and client does not support it

Fix for #2832

* Add test cases to assert behaviour with regards to the Content-Length header

spring-cloud-netflix-zuul/src/main/java/org/springframework/cloud/netflix/zuul/filters/post/SendResponseFilter.java

@@ -240,18 +240,14 @@ public class SendResponseFilter extends ZuulFilter {
 				servletResponse.addHeader(it.first(), it.second());
 			}
 		}
-		// Only inserts Content-Length if origin provides it and origin response is not
-		// gzipped
-		if (this.zuulProperties.isSetContentLength()) {
+		if (includeContentLengthHeader(context)) {
 			Long contentLength = context.getOriginContentLength();
-			if ( contentLength != null && !context.getResponseGZipped()) {
-				if(useServlet31) {
-					servletResponse.setContentLengthLong(contentLength);
-				} else {
-					//Try and set some kind of content length if we can safely convert the Long to an int
-					if (isLongSafe(contentLength)) {
-						servletResponse.setContentLength(contentLength.intValue());
-					}
+			if(useServlet31) {
+				servletResponse.setContentLengthLong(contentLength);
+			} else {
+				//Try and set some kind of content length if we can safely convert the Long to an int
+				if (isLongSafe(contentLength)) {
+					servletResponse.setContentLength(contentLength.intValue());
 				}
 			}
 		}
@@ -261,4 +257,23 @@ public class SendResponseFilter extends ZuulFilter {
 		return value <= Integer.MAX_VALUE && value >= Integer.MIN_VALUE;
 	}
 
+	protected boolean includeContentLengthHeader(RequestContext context) {
+		// Not configured to forward the header
+		if (!this.zuulProperties.isSetContentLength()) {
+			return false;
+		}
+		
+		// Only if Content-Length is provided
+		if (context.getOriginContentLength() == null) {
+			return false;
+		}
+		
+		// If response is compressed, include header only if we are not about to decompress it
+		if (context.getResponseGZipped()) {
+			return context.isGzipRequested();
+		}
+		
+		// Forward it in all other cases
+		return true;
+	}
 }

spring-cloud-netflix-zuul/src/test/java/org/springframework/cloud/netflix/zuul/filters/post/SendResponseFilterTests.java

@@ -36,6 +36,7 @@ import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.mock.web.MockHttpServletResponse;
 import org.springframework.web.util.WebUtils;
 
+import com.netflix.zuul.constants.ZuulHeaders;
 import com.netflix.zuul.context.Debug;
 import com.netflix.zuul.context.RequestContext;
 
@@ -61,6 +62,7 @@ public class SendResponseFilterTests {
 	@Before
 	public void setTestRequestcontext() {
 		RequestContext context = new RequestContext();
+		context.setResponseGZipped(false);
 		RequestContext.testSetCurrentContext(context);
 	}
 
@@ -102,6 +104,9 @@ public class SendResponseFilterTests {
 		assertThat("wrong debug header", debugHeader, equalTo("[[[test]]]"));
 	}
 
+	/*
+	 * GZip NOT requested and NOT a GZip response -> Content-Length forwarded asis
+	 */
 	@Test
 	public void runWithOriginContentLength() throws Exception {
 		ZuulProperties properties = new ZuulProperties();
@@ -117,6 +122,42 @@ public class SendResponseFilterTests {
 		assertThat("wrong origin content length", contentLength, equalTo("6"));
 	}
 
+	/*
+	 * GZip requested and GZip response -> Content-Length forwarded asis
+	 */
+	@Test
+	public void runWithOriginContentLength_gzipRequested_gzipResponse() throws Exception {
+		ZuulProperties properties = new ZuulProperties();
+		properties.setSetContentLength(true);
+
+		SendResponseFilter filter = createFilter(properties, "hello", "UTF-8", new MockHttpServletResponse(), true);
+		RequestContext.getCurrentContext().setOriginContentLength(6L); // for test
+		RequestContext.getCurrentContext().setResponseGZipped(true);
+		((MockHttpServletRequest) RequestContext.getCurrentContext().getRequest()).addHeader(ZuulHeaders.ACCEPT_ENCODING, "gzip");
+		
+		filter.run();
+
+		String contentLength = RequestContext.getCurrentContext().getResponse().getHeader("Content-Length");
+		assertThat("wrong origin content length", contentLength, equalTo("6"));
+	}
+	
+	/*
+	 * GZip NOT requested and GZip response -> Content-Length discarded
+	 */
+	@Test
+	public void runWithOriginContentLength_gzipNotRequested_gzipResponse() throws Exception {
+		ZuulProperties properties = new ZuulProperties();
+		properties.setSetContentLength(true);
+
+		SendResponseFilter filter = createFilter(properties, "hello", "UTF-8", new MockHttpServletResponse(), true);
+		RequestContext.getCurrentContext().setOriginContentLength(6L); // for test
+		RequestContext.getCurrentContext().setResponseGZipped(true);
+		
+		filter.run();
+
+		assertThat(RequestContext.getCurrentContext().getResponse().getHeader("Content-Length")).isNull();
+	}
+	
 	@Test
 	public void closeResponseOutputStreamError() throws Exception {
 		HttpServletResponse response = mock(HttpServletResponse.class);
@@ -126,6 +167,7 @@ public class SendResponseFilterTests {
 		context.setRequest(new MockHttpServletRequest());
 		context.setResponse(response);
 		context.setResponseDataStream(mockStream);
+		context.setResponseGZipped(false);
 		Closeable zuulResponse = mock(Closeable.class);
 		context.set("zuulResponse", zuulResponse);
 		RequestContext.testSetCurrentContext(context);
@@ -156,6 +198,7 @@ public class SendResponseFilterTests {
 		context.setRequest(new MockHttpServletRequest());
 		context.setResponse(response);
 		context.setResponseDataStream(mockStream);
+		context.setResponseGZipped(false);
 		Closeable zuulResponse = mock(Closeable.class);
 		context.set("zuulResponse", zuulResponse);
 		RequestContext.testSetCurrentContext(context);
@@ -200,8 +243,7 @@ public class SendResponseFilterTests {
 			context.setResponseBody(content);
 		}
 
-		context.addZuulResponseHeader(HttpHeaders.CONTENT_LENGTH, String.valueOf(content.length()));
-
+		context.setResponseGZipped(false);
 		context.set("error.status_code", HttpStatus.NOT_FOUND.value());
 		RequestContext.testSetCurrentContext(context);
 		SendResponseFilter filter = new SendResponseFilter(properties);