move getIP function to its own module

extra_modules/getip.js

@@ -0,0 +1,12 @@
+/**
+ * gets ip of a request
+ * @param {request} req 
+ * @returns ip of the given request, after taking preferred headers into account
+ */
+ function getIP(req) {
+    let ip = req.socket.remoteAddress;
+    if(req.headers[config.preferred_ip_header] != undefined && ip == config.only_prefer_when_ip)ip = req.headers[config.preferred_ip_header]
+    return ip
+  }
+
+module.exports = getIP

extra_modules/unsign.js

@@ -1,6 +1,7 @@
 const signature = require('cookie-signature')
 const fs = require('fs');
 const cookiesecret = fs.readFileSync("cookiesecret.txt").toString()
+const getIP = require("./extra_modules/getip.js")
 /**
  * usignes a string
  * @param  {string} text               text to unsign
@@ -9,7 +10,7 @@ const cookiesecret = fs.readFileSync("cookiesecret.txt").toString()
  * @return {string/boolean}      unsigned text, or if unsigning was unsuccessful, false
  */
 function unsign(text,req,res) {
-  let ip = req.socket.remoteAddress
+  let ip = getIP(req)
   let unsigned = signature.unsign(text,cookiesecret+ip)
   if(!unsigned) {
     return false