Issue #5214 - Use known content_length when in HEAD mode

+ Adding DefaultServlet.doHead() to avoid servlet wrapping
+ Making ResourceService HEAD aware

Signed-off-by: Joakim Erdfelt <joakim.erdfelt@gmail.com>

jetty-server/src/main/java/org/eclipse/jetty/server/ResourceService.java

@@ -673,11 +673,16 @@ public class ResourceService
                 // write without headers
                 content.getResource().writeTo(out, 0, content_length);
             }
+            // we are working with a HEAD request
+            else if (isHead(request) && content_length > 0)
+            {
+                putHeaders(response, content, content_length);
+            }
             // else if we can't do a bypass write because of wrapping
             else if (written || !(out instanceof HttpOutput))
             {
                 // write normally
-                putHeaders(response, content, content_length);
+                putHeaders(response, content, written ? -1 : 0);
                 ByteBuffer buffer = content.getIndirectBuffer();
                 if (buffer != null)
                     BufferUtil.writeTo(buffer, out);
@@ -846,6 +851,11 @@ public class ResourceService
         }
     }
 
+    private boolean isHead(HttpServletRequest request)
+    {
+        return "HEAD".equalsIgnoreCase(request.getMethod());
+    }
+
     public interface WelcomeFactory
     {
 

jetty-servlet/src/main/java/org/eclipse/jetty/servlet/DefaultServlet.java

@@ -462,20 +462,28 @@ public class DefaultServlet extends HttpServlet implements ResourceFactory, Welc
         doGet(request, response);
     }
 
+    @Override
+    protected void doHead(HttpServletRequest request, HttpServletResponse response)
+        throws ServletException, IOException
+    {
+        doGet(request, response);
+    }
+
     /* (non-Javadoc)
      * @see javax.servlet.http.HttpServlet#doTrace(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
      */
     @Override
-    protected void doTrace(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
+    protected void doTrace(HttpServletRequest request, HttpServletResponse response)
+        throws ServletException, IOException
     {
-        resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
+        response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
     }
 
     @Override
-    protected void doOptions(HttpServletRequest req, HttpServletResponse resp)
+    protected void doOptions(HttpServletRequest request, HttpServletResponse response)
         throws ServletException, IOException
     {
-        resp.setHeader("Allow", "GET,HEAD,POST,OPTIONS");
+        response.setHeader("Allow", "GET,HEAD,POST,OPTIONS");
     }
 
     /*