[SOLVED] Allow selection of local_port for sending UDP packets.

[CabalCrow]

EDIT

Apperantly this already exist and it is done via the PackedPeerUDP.bind method.

Suggestion

Currently you can send UDP packets via

	var peer = PacketPeerUDP.new()
	peer.set_dest_address(address, port)
	peer.put_packet(buffer)

however those packets would be send with a random local_port. Instead add a way to specify the local port via the set_dest_address as a 3rd optional argument.

Why is this important

To enable NAT traversal. It is vital for many NAT traversal techniques to specify the port you send packets from.
This can then be used to improve the internet play of any peer to peer game, even without a STUN server.

Example use case

Two players with ipv6 want to connect over the internet without port forwarding.
Since ipv6 is rarely masks ports, you don't need a STUN server to determine their public_port, as it would coincide with the local_port.
This means the players can connect directly via hole punching in the following way:

1. Player A sends packets to Player B via:

	var peer = PacketPeerUDP.new()
	peer.set_dest_address(player_b_address, player_b_local_port, player_a_local_port)
	peer.put_packet(buffer)

2. Player B sends packets back to Player A via:

	var peer = PacketPeerUDP.new()
	peer.set_dest_address(player_a_address, player_a_local_port, player_b_local_port)
	peer.put_packet(buffer)

3. This should be enough for the players to successfully establish connection and recieve each other packets. In order words the players have punched thourgh and can now connect and play via the player_a_local_port and player_b_local_port.

Possible workarounds

Do not use Godot's PacketPeerUDP, and instead package netcat-openbsd as a binary and run it from godot to send packets. This is undesireable since trying package and run binaries on different machines and OSes would create a lot of additional problems.

That being said here how currently you can achive the same result as the example use case, using the external program net-cat-openbsd.

1. Player A sends packets to Player B via (nc is netcat-openbsd):

echo "buffer content" | nc -6u player_b_address player_b_local_port -p player_a_local_port

2. Player B sends packets back to Player A via:

echo "buffer content" | nc -6u player_a_address player_a_local_port -p player_b_local_port

3. This should be enough for the players to successfully establish connection and recieve each other packets. In order words the players have punched thourgh and can now connect and play via the player_a_local_port and player_b_local_port.

[dustdfg]

I am not familiar with networking but isn't bind method what you need?

[CabalCrow]

The bind method affects listening, not sending of packets.

[Faless]

Bind "binds" the socket (see bind(2)) which effectively selects the outgoing port.

If a socket is not bound, the OS selects the outgoing port at random (on Linux in the range 32768 - 60999 by default)

[Calinou]

Since ipv6 is rarely masks ports, you don't need a STUN server to determine their public_port, as it would coincide with the local_port.

Most ISPs have an IPv6 firewall active by default that blocks all incoming connections at the router level, so this won't work reliably unless the app uses UPnPv6 to open ports.

This firewall is sometimes not controllable on some connection types (mainly mobile connections where you can't open any ports on it, including residential 4G/5G connections).

[CabalCrow]

This is why I'm using the NAT traversal technique explained above to punch a hole through the firewall.
The possible workaround I've given at the bottom of the proposal works with IPv6 firewalls.