error message when localhost app isn't running

lib/sorting-hat.js

@@ -100,7 +100,7 @@ module.exports.assign = function (state, tun, cb) {
     state.defaultHttpServer.emit('connection', tlsSocket);
   };
 
-  function getNetConn(port) {
+  function getNetConn(port, cb) {
     var netOpts = {
       port: port
     , host: '127.0.0.1'
@@ -117,8 +117,12 @@ module.exports.assign = function (state, tun, cb) {
       // this will happen before 'data' or 'readable' is triggered
       // We use the data from the netOpts object so that the createConnection function has
       // the oppurtunity of removing/changing it if it wants/needs to handle it differently.
+      cb(null, conn);
+      cb = function () {}; // for error events
+    });
+    conn.on('error', function (err) {
+      cb(err);
     });
-    return conn;
   }
 
   function redirectHttp(cb) {
@@ -194,8 +198,7 @@ module.exports.assign = function (state, tun, cb) {
   function invokeTcpHandler(conf, socket, tun, id, cb) {
     var conn;
     if (parseInt(conf.handler, 10)) {
-      conn = getNetConn(conf.handler);
-      cb(null, conn);
+      getNetConn(conf.handler, cb);
       return conn;
     }
 
@@ -232,13 +235,20 @@ module.exports.assign = function (state, tun, cb) {
   }
   var handlerservers = {};
   function invokeHandler(conf, tlsSocket, tun, id) {
-    var conn;
     if (parseInt(conf.handler, 10)) {
       // TODO http-proxy with proper headers and ws support
-      conn = getNetConn(conf.handler);
-      console.info("Port-Forwarding '" + (tun.name || tun.serviceport) + "' to '" + conf.handler + "'");
-      conn.pipe(tlsSocket);
-      tlsSocket.pipe(conn);
+      getNetConn(conf.handler, function (err, conn) {
+        if (err) {
+          // TODO direct to site with error page
+          console.error("probably couldn't connect to handler");
+          tlsSocket.write("Couldn't connect to localhost:" + conf.handler);
+          tlsSocket.end();
+          return;
+        }
+        console.info("Port-Forwarding '" + (tun.name || tun.serviceport) + "' to '" + conf.handler + "'");
+        conn.pipe(tlsSocket);
+        tlsSocket.pipe(conn);
+      });
       return;
     }
     var handle = tun.name || tun.port;