[minor] add middleware to node-http-proxy

lib/node-http-proxy.js

@@ -112,6 +112,30 @@ exports.getMaxSockets = function () {
 exports.setMaxSockets = function (value) {
   maxSockets = value;
 };
+//
+// stack
+// adapted from https://github.com/creationix/stack
+//
+
+function stack (middlewares, proxy) {
+  var handle;
+  middlewares.reverse().forEach(function (layer) {
+    
+    var child = handle;
+    var next = function (err) {
+        if (err) {
+          throw err;
+          //return error(req, res, err); 
+        }
+        child(req, res);
+      }
+    next.__proto__ = proxy;
+    handle = function (req, res) {
+      layer(req, res, next);
+    };
+  });
+  return handle;
+}
 
 //
 // ### function createServer ([port, host, options, handler])
@@ -127,55 +151,54 @@ exports.setMaxSockets = function (value) {
 //
 exports.createServer = function () {
   var args = Array.prototype.slice.call(arguments), 
-      callback = typeof args[0] === 'function' && args.shift(),
-      options = {}, port, host, forward, silent, proxy, server;
+      callback,
+      options = {}, port, host, forward, silent, proxy, server, middleware = [];
   
-  if (args.length >= 2) {
-    port = args[0];
-    host = args[1];
-    options = args[2] || {};
-  } 
-  else if (args.length === 1) {
-    options = args[0] || {};
-    if (!options.router && !callback) {
-      throw new Error('Cannot create server with no router and no callback');
-    }
-  }
+  args.forEach(function (arg) {
   
-  proxy = new HttpProxy(options);
+    switch (typeof arg) {
+      case 'string': host = arg; break;
+      case 'number': port = arg; break;
+      case 'function': middleware.push(arg); break;
+      case 'object': options = arg; break;
+    };
   
-  handler = function (req, res) {
-    if (callback) {
-      //
-      // If we were passed a callback to process the request
-      // or response in some way, then call it.
-      //
-      callback(req, res, proxy);
-    } 
-    else if (port && host) {
+  });
+
+  var proxy = new HttpProxy(options);
+
+  if(middleware.length)
+    //handler = callback = middleware.shift()
+  //else if (middleware.length)
+    handler = callback = stack(middleware, proxy);
+
+    if (port && host) {
       //
       // If we have a target host and port for the request
       // then proxy to the specified location.
       //
+      handler = function (req, res) {
         proxy.proxyRequest(req, res, {
           port: port, 
           host: host
         });
       }
+    }
     else if (proxy.proxyTable) {
       //
       // If the proxy is configured with a ProxyTable
       // instance then use that before failing.
       //
+      handler = function (req, res) {
         proxy.proxyRequest(req, res);
       }
-    else {
+    }
+    else if (!handler) {
       //
       // Otherwise this server is improperly configured.
       //
       throw new Error('Cannot proxy without port, host, or router.')
     }
-  };
 
   server = options.https 
     ? https.createServer(options.https, handler)