Add isPortTaken function

packages/cli-utils/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@aragon/cli-utils",
-  "version": "0.0.5",
+  "version": "0.0.6",
   "description": "Common building blocks for CLI tools",
   "main": "",
   "scripts": {

packages/cli-utils/src/util.js

@@ -0,0 +1,27 @@
+const net = require('net')
+
+const isPortTaken = async (port, opts) => {
+  opts = Object.assign({ timeout: 1000 }, opts)
+
+  return new Promise(resolve => {
+    const socket = new net.Socket()
+
+    const onError = () => {
+      socket.destroy()
+      resolve(false)
+    }
+
+    socket.setTimeout(opts.timeout)
+    socket.on('error', onError)
+    socket.on('timeout', onError)
+
+    socket.connect(port, opts.host, () => {
+      socket.end()
+      resolve(true)
+    })
+  })
+}
+
+module.exports = {
+  isPortTaken,
+}