Use API for setting content length on responses (#15504)

Change-Id: Ic8f29163442a1476406a1f2b617a4ecaf577ba93

server/src/com/vaadin/server/VaadinPortletResponse.java

@@ -96,6 +96,14 @@ public class VaadinPortletResponse implements VaadinResponse {
         }
     }
 
+    @Override
+    public void setContentLength(int len) {
+        if (response instanceof ResourceResponse) {
+            ((ResourceResponse) response).setContentLength(len);
+        }
+
+    }
+
     @Override
     public PrintWriter getWriter() throws IOException {
         if (response instanceof MimeResponse) {

server/src/com/vaadin/server/VaadinResponse.java

@@ -169,4 +169,17 @@ public interface VaadinResponse extends Serializable {
      * @see PortletResponse#addProperty(Cookie)
      */
     public void addCookie(Cookie cookie);
+
+    /**
+     * Sets the length of the content body in the response In HTTP servlets,
+     * this method sets the HTTP Content-Length header. For some portlet
+     * responses, this method sets the content-length header, for others this
+     * method does nothing.
+     *
+     * @param len
+     *            an integer specifying the length of the content being returned
+     *            to the client
+     * @since 7.3.8
+     */
+    public void setContentLength(int len);
 }

server/src/com/vaadin/server/communication/UIInitHandler.java

@@ -112,7 +112,7 @@ public abstract class UIInitHandler extends SynchronizedRequestHandler {
         response.setHeader("Cache-Control", "no-cache");
 
         byte[] b = json.getBytes("UTF-8");
-        response.setHeader("Content-Length", String.valueOf(b.length));
+        response.setContentLength(b.length);
 
         OutputStream outputStream = response.getOutputStream();
         outputStream.write(b);