Tested & fixed url middleware example, added comments.

examples/url-middleware.js

-/*
-  urls-middleware.js: Basic example of middleware in node-http-proxy
-
-  Copyright (c) 2010 Charlie Robbins, Mikeal Rogers, Fedor Indutny, Marak Squires, & Dominic Tarr.
-
-  Permission is hereby granted, free of charge, to any person obtaining
-  a copy of this software and associated documentation files (the
-  "Software"), to deal in the Software without restriction, including
-  without limitation the rights to use, copy, modify, merge, publish,
-  distribute, sublicense, and/or sell copies of the Software, and to
-  permit persons to whom the Software is furnished to do so, subject to
-  the following conditions:
-
-  The above copyright notice and this permission notice shall be
-  included in all copies or substantial portions of the Software.
-
-  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
-  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
-  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
-  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
-  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-
-*/
-
 var util = require('util'),
     colors = require('colors'),
     http = require('http'),
-    httpProxy = require('./../lib/node-http-proxy');
+    httpProxy = require('http-proxy');
  
 //
-// url proxying middleware example. 
+// This is an example of a url-routing middleware.
+// This is not intended for production use, but rather as
+// an example of how to write a middleware.
 //
-// this is not optimised or tested but shows the basic approch to writing a middleware.
-//
-function matcher (url, dest) {
-  var r = new RegExp (url)
 
+function matcher (url, dest) {
+  // First, turn the URL into a regex.  
+  // NOTE: Turning user input directly into a Regular Expression is NOT SAFE.
+  var r = new RegExp(url.replace(/\//, '\\/'));
+  // This next block of code may look a little confusing. 
+  // It returns a closure (anonymous function) for each URL to be matched,
+  // storing them in an array - on each request, if the URL matches one that has
+  // a function stored for it, the function will be called.
   return function (url) {
     var m = r(url)
-    if (!m) return
-    var path = url.slice(m[0].length)
-  console.log('proxy:', url, '->', path)
-    return {url: path, dest: dest}
+    if (!m) {
+      return;
+    }
+    var path = url.slice(m[0].length);
+    console.log('proxy:', url, '->', dest);
+    return {url: path, dest: dest};
   }
 }
 
 exports.urls = function (urls) {
-
-  var matchers = []
+  // This is the entry point for our middleware.
+  // 'matchers' is the array of URL matchers, as mentioned above.
+  var matchers = [];
   for (var url in urls) {
-    matchers.push(matcher(url, urls[url]))
+    // Call the 'matcher' function above, and store the resulting closure.
+    matchers.push(matcher(url, urls[url]));
   }
 
+  // This closure is returned as the request handler.
   return function (req, res, next) {
     //
-    // in nhp middlewares, `proxy` is the prototype of `next`
-    // (this means nhp middlewares support both connect API (req, res, next)
-    // and nhp API (req, res, proxy)
+    // in node-http-proxy middlewares, `proxy` is the prototype of `next`
+    // (this means node-http-proxy middlewares support both the connect API (req, res, next)
+    // and the node-http-proxy API (req, res, proxy)
     //
     var proxy = next;
-
     for (var k in matchers) {
-      var m;
-      if (m = matchers[k](req.url)) {
+      // for each URL matcher, try the request's URL.
+      var m = matchers[k](req.url);
+      // If it's a match:
+      if (m) {
+        // Replace the local URL with the destination URL.
         req.url = m.url;
-        return proxy.proxyRequest(req,res, m.dest);
+        // If routing to a server on another domain, the hostname in the request must be changed.
+        req.headers.host = m.host;
+        // Once any changes are taken care of, this line makes the magic happen.
+        proxy.proxyRequest(req, res, m.dest);
       }
     }
   }
 }
 
+// Now we set up our proxy.
 httpProxy.createServer(
-  exports.urls({'/hello': {port: 9000, host: 'localhost'}})
+  // This is where our middlewares go, with any options desired - in this case,
+  // the list of routes/URLs and their destinations.
+  exports.urls({
+    '/hello': { port: 9000, host: 'localhost' },
+    '/charlie': { port: 80, host: 'charlieistheman.com' },
+    '/google': { port: 80, host: 'google.com' } 
+  })
 ).listen(8000);
 
 //
-// Target Http Server
+// Target Http Server (to listen for requests on 'localhost')
 //
 http.createServer(
   function (req, res) {
@@ -85,5 +82,6 @@ http.createServer(
     res.end();
   }).listen(9000);
 
+// And finally, some colored startup output.
 util.puts('http proxy server'.blue + ' started '.green.bold + 'on port '.blue + '8000'.yellow);
 util.puts('http server '.blue + 'started '.green.bold + 'on port '.blue + '9000 '.yellow);
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