From 7b3f78d70c9cac87806d0a0140b22a2976518940 Mon Sep 17 00:00:00 2001
From: Jiri Spac <capajj@gmail.com>
Date: Tue, 23 Aug 2016 02:00:37 +0200
Subject: [PATCH] check the server parameter

---
 index.js | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/index.js b/index.js
index 1023b0e..5e7687c 100644
--- a/index.js
+++ b/index.js
@@ -68,6 +68,9 @@ const gatherOsMetrics = (io, span) => {
 const encoding = {encoding: 'utf8'}
 
 const middlewareWrapper = (app, config) => {
+  if (!app.listen) {
+    throw new Error('First parameter must be an http server')
+  }
   io = require('socket.io')(app)
   Object.assign(defaultConfig, config)
   config = defaultConfig