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UPNP¶

Inherits: RefCounted < Object

Universal Plug and Play (UPnP) functions for network device discovery, querying and port forwarding.

Description¶

This class can be used to discover compatible UPNPDevices on the local network and execute commands on them, like managing port mappings (for port forwarding/NAT traversal) and querying the local and remote network IP address. Note that methods on this class are synchronous and block the calling thread.

To forward a specific port (here 7777, note both discover and add_port_mapping can return errors that should be checked):

var upnp = UPNP.new()
upnp.discover()
upnp.add_port_mapping(7777)

To close a specific port (e.g. after you have finished using it):

upnp.delete_port_mapping(port)

Note: UPnP discovery blocks the current thread. To perform discovery without blocking the main thread, use Threads like this:

# Emitted when UPnP port mapping setup is completed (regardless of success or failure).
signal upnp_completed(error)

# Replace this with your own server port number between 1024 and 65535.
const SERVER_PORT = 3928
var thread = null

func _upnp_setup(server_port):
    # UPNP queries take some time.
    var upnp = UPNP.new()
    var err = upnp.discover()

    if err != OK:
        push_error(str(err))
        emit_signal("upnp_completed", err)
        return

    if upnp.get_gateway() and upnp.get_gateway().is_valid_gateway():
        upnp.add_port_mapping(server_port, server_port, ProjectSettings.get_setting("application/config/name"), "UDP")
        upnp.add_port_mapping(server_port, server_port, ProjectSettings.get_setting("application/config/name"), "TCP")
        emit_signal("upnp_completed", OK)

func _ready():
    thread = Thread.new()
    thread.start(_upnp_setup.bind(SERVER_PORT))

func _exit_tree():
    # Wait for thread finish here to handle game exit while the thread is running.
    thread.wait_to_finish()

Terminology: In the context of UPnP networking, "gateway" (or "internet gateway device", short IGD) refers to network devices that allow computers in the local network to access the internet ("wide area network", WAN). These gateways are often also called "routers".

Pitfalls:

As explained above, these calls are blocking and shouldn't be run on the main thread, especially as they can block for multiple seconds at a time. Use threading!
Networking is physical and messy. Packets get lost in transit or get filtered, addresses, free ports and assigned mappings change, and devices may leave or join the network at any time. Be mindful of this, be diligent when checking and handling errors, and handle these gracefully if you can: add clear error UI, timeouts and re-try handling.
Port mappings may change (and be removed) at any time, and the remote/external IP address of the gateway can change likewise. You should consider re-querying the external IP and try to update/refresh the port mapping periodically (for example, every 5 minutes and on networking failures).
Not all devices support UPnP, and some users disable UPnP support. You need to handle this (e.g. documenting and requiring the user to manually forward ports, or adding alternative methods of NAT traversal, like a relay/mirror server, or NAT hole punching, STUN/TURN, etc.).
Consider what happens on mapping conflicts. Maybe multiple users on the same network would like to play your game at the same time, or maybe another application uses the same port. Make the port configurable, and optimally choose a port automatically (re-trying with a different port on failure).

Further reading: If you want to know more about UPnP (and the Internet Gateway Device (IGD) and Port Control Protocol (PCP) specifically), Wikipedia is a good first stop, the specification can be found at the Open Connectivity Foundation and Godot's implementation is based on the MiniUPnP client.

Properties¶

bool	discover_ipv6	`false`
int	discover_local_port	`0`
String	discover_multicast_if	`""`

Methods¶

void	add_device ( UPNPDevice device )
int	add_port_mapping ( int port, int port_internal=0, String desc="", String proto="UDP", int duration=0 ) const
void	clear_devices ( )
int	delete_port_mapping ( int port, String proto="UDP" ) const
int	discover ( int timeout=2000, int ttl=2, String device_filter="InternetGatewayDevice" )
UPNPDevice	get_device ( int index ) const
int	get_device_count ( ) const
UPNPDevice	get_gateway ( ) const
String	query_external_address ( )