call callback once on listen error

lib/application.js

@@ -24,6 +24,7 @@ var compileTrust = require('./utils').compileTrust;
 var flatten = require('array-flatten');
 var merge = require('utils-merge');
 var resolve = require('path').resolve;
+var once = require('once')
 var Router = require('router');
 var slice = Array.prototype.slice;
 
@@ -598,10 +599,15 @@ app.render = function render(name, options, callback) {
  * @public
  */
 
-app.listen = function listen() {
-  var server = http.createServer(this);
-  return server.listen.apply(server, arguments);
-};
+app.listen = function listen () {
+  var server = http.createServer(this)
+  var args = Array.prototype.slice.call(arguments)
+  if (typeof args[args.length - 1] === 'function') {
+    var done = args[args.length - 1] = once(args[args.length - 1])
+    server.once('error', done)
+  }
+  return server.listen.apply(server, args)
+}
 
 /**
  * Log error using console.error.

package.json

@@ -43,6 +43,7 @@
     "merge-descriptors": "1.0.1",
     "methods": "~1.1.2",
     "on-finished": "~2.3.0",
+    "once": "1.4.0",
     "parseurl": "~1.3.1",
     "path-is-absolute": "1.0.1",
     "path-to-regexp": "0.1.7",

test/app.listen.js

@@ -1,6 +1,7 @@
 
 var express = require('../')
-  , request = require('supertest');
+var assert = require('assert')
+var request = require('supertest')
 
 describe('app.listen()', function(){
   it('should wrap with an HTTP server', function(done){
@@ -15,4 +16,17 @@ describe('app.listen()', function(){
       done();
     });
   })
+  it('should callback on HTTP server errors', function (done) {
+    var app1 = express()
+    var app2 = express()
+
+    var server1 = app1.listen(0, function (err) {
+      assert(!err)
+      var server2 = app2.listen(server1.address().port, function (err) {
+        assert(err.code === 'EADDRINUSE')
+        server1.close()
+        done()
+      })
+    })
+  })
 })