Avoid code duplication

core/src/main/java/hudson/Functions.java

@@ -1765,4 +1765,24 @@ public class Functions {
                 .replaceAll("(\\w{10})(?=\\w{3})", "$1<wbr>")
         ;
     }
+
+    /**
+     * Advertises the minimum set of HTTP headers that assist programmatic
+     * discovery of Jenkins.
+     */
+    public static void advertiseHeaders(HttpServletResponse rsp) {
+        Jenkins j = Jenkins.getInstance();
+
+        rsp.setHeader("X-Hudson","1.395");
+        rsp.setHeader("X-Jenkins", Jenkins.VERSION);
+        rsp.setHeader("X-Jenkins-Session", Jenkins.SESSION_HASH);
+
+        TcpSlaveAgentListener tal = j.tcpSlaveAgentListener;
+        if (tal !=null) {
+            rsp.setIntHeader("X-Hudson-CLI-Port", tal.getPort());
+            rsp.setIntHeader("X-Jenkins-CLI-Port", tal.getPort());
+            rsp.setIntHeader("X-Jenkins-CLI2-Port", tal.getPort());
+            rsp.setHeader("X-Jenkins-CLI-Host", TcpSlaveAgentListener.CLI_HOST_NAME);
+        }
+    }
 }

core/src/main/java/hudson/security/HudsonAuthenticationEntryPoint.java

@@ -23,6 +23,7 @@
  */
 package hudson.security;
 
+import hudson.Functions;
 import jenkins.model.Jenkins;
 import hudson.TcpSlaveAgentListener;
 
@@ -84,14 +85,7 @@ public class HudsonAuthenticationEntryPoint extends AuthenticationProcessingFilt
             rsp.setStatus(SC_FORBIDDEN);
             rsp.setContentType("text/html;charset=UTF-8");
 
-            // advertise the CLI TCP port
-            TcpSlaveAgentListener tal = Jenkins.getInstance().getTcpSlaveAgentListener();
-            if (tal!=null) {
-                rsp.setIntHeader("X-Hudson-CLI-Port", tal.getPort());
-                rsp.setIntHeader("X-Jenkins-CLI-Port", tal.getPort());
-                rsp.setIntHeader("X-Jenkins-CLI2-Port", tal.getPort());
-                rsp.setHeader("X-Jenkins-CLI-Host", TcpSlaveAgentListener.CLI_HOST_NAME);
-            }
+            Functions.advertiseHeaders(rsp);
 
             AccessDeniedException2 cause = null;
             // report the diagnosis information if possible

core/src/main/resources/lib/layout/layout.jelly

@@ -71,16 +71,7 @@ ${h.initPageVariables(context)}
 <j:set var="_" value="${h.configureAutoRefresh(request, response, attrs.norefresh!=null)}"/>
 
   <j:if test="${request.servletPath=='/' || request.servletPath==''}">
-    <st:setHeader name="X-Hudson" value="1.395"/>
-    <st:setHeader name="X-Jenkins" value="${servletContext.getAttribute('version')}"/>
-    <st:setHeader name="X-Jenkins-Session" value="${app.SESSION_HASH}"/>
-    <j:if test="${app.tcpSlaveAgentListener!=null}">
-      <!-- advertise the CLI TCP port -->
-      <st:setHeader name="X-Hudson-CLI-Port" value="${app.tcpSlaveAgentListener.port}"/>
-      <st:setHeader name="X-Jenkins-CLI-Port" value="${app.tcpSlaveAgentListener.port}"/>
-      <st:setHeader name="X-Jenkins-CLI2-Port" value="${app.tcpSlaveAgentListener.port}"/>
-      <st:setHeader name="X-Jenkins-CLI-Host" value="${app.tcpSlaveAgentListener.CLI_HOST_NAME}"/>
-    </j:if>
+    ${h.advertiseHeaders(response)}
     <j:forEach var="pd" items="${h.pageDecorators}">
       <st:include it="${pd}" page="httpHeaders.jelly" optional="true"/>
     </j:forEach>