Discover your firewall UDP output policy with this app.

• This is absolutely not secure
• Only one client at a time can use the server
• If a client does not close a port, the port will not be closed
• Use it on a server without any service listening on UDP. Or cross fingers...
• Use it on a server without any service listenging on TCP port 80 (like nginx or apache).

On your server : sudo ./server

On your client : ./client
Client will interactively ask for server IP and Port. Default port for server is 80 (so you don't need to reverse proxy it and is available anywhere).

A full log will be available in port-checker.txt

You have to authorize all UDP traffic on your test server (be careful to add a DMZ if you're behind a NAT). This app has been successfully tested on DigitalOcean servers.

Sorry, does not follow golang best practises...

go build client.go porttest.go checkerror.go
go build server.go porttest.go checkerror.go

The server binary will listen on port 80.

There is 2 available HTTP Requests :

POST /port {"port": "1005"} - Will open port 1005
DELETE /port {"port": "1005"} - Will close port 1005

The client will iterate on the following algorithm for every ports :

1. Send a request to open a port
2. Try to connect on UDP on this port
3. Wait 1 sec for the answer OK
4. will log the port as open if it receives this answer or as closed if it receives nothing or something else.
5. After that, the client will send a request to close the port.