Refractoring and add thumbnails support (without tests)

server/helpers/utils.js

@@ -1,9 +1,20 @@
 'use strict'
 
+const crypto = require('crypto')
+
 const logger = require('./logger')
 
 const utils = {
-  cleanForExit: cleanForExit
+  cleanForExit: cleanForExit,
+  generateRandomString: generateRandomString
+}
+
+function generateRandomString (size, callback) {
+  crypto.pseudoRandomBytes(size, function (err, raw) {
+    if (err) return callback(err)
+
+    callback(null, raw.toString('hex'))
+  })
 }
 
 function cleanForExit (webtorrent_process) {