[doc] Added sample for custom error messages using the `proxyError` event

examples/custom-proxy-error.js

+/*
+  custom-proxy-error.js: Example of using the custom `proxyError` event.
+
+  Copyright (c) 2010 Charlie Robbins, Mikeal Rogers, Fedor Indutny, & Marak Squires.
+
+  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');
+
+//
+// Http Proxy Server with Latency
+//
+var server = httpProxy.createServer(function (req, res, proxy) {
+  proxy.proxyRequest(req, res, {
+    port: 9000,
+    host: 'localhost'
+  });
+})
+
+//
+// Tell the server to listen on port 8002
+//
+server.listen(8002);
+
+//
+// Listen for the `proxyError` event on `server.proxy`. _It will not
+// be raised on the server itself._
+server.proxy.on('proxyError', function (err, req, res) {
+  res.writeHead(500, {
+    'Content-Type': 'text/plain'
+  });
+  
+  res.end('Something went wrong. And we are reporting a custom error message.');
+});
+
+
+util.puts('http proxy server '.blue + 'started '.green.bold + 'on port '.blue + '8002 '.yellow + 'with custom error message'.magenta.underline);
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