Fixed large DoS vector in the middleware implementation

lib/node-http-proxy.js

@@ -222,12 +222,19 @@ exports.stack = function stack (middlewares, proxy) {
     handle = function (req, res) {
       var next = function (err) {
         if (err) {
-          throw err;
-          //
-          // TODO: figure out where to send errors.
-          // return error(req, res, err);
-          //
+          if (res._headerSent) {
+            res.destroy();
+          } 
+          else {
+            res.statusCode = 500;
+            res.setHeader('Content-Type', 'text/plain');
+            res.end('Internal Server Error');
+          }
+          
+          console.error('Error in middleware(s): %s', err.stack);
+          return;
         }
+        
         child(req, res);
       }