[MP] Let MultiplayerAPI handle packet relaying and peer signaling.

MultiplayerPeer changes:

- Adds is_server_relay_supported virtual method

Informs the upper MultiplayerAPI layer if it can signal peers connected
to the server to other clients, and perform packet relaying among them.

- Adds get_packet_channel and get_packet_mode virtual methods

Allows the MultiplayerAPI to retrieve the channel and transfer modes to
use when relaying the last received packet.

SceneMultiplayerPeer changes:

- Implement peer signaling and packet relaying when the MultiplayerPeer
  advertise they are supported.

ENet, WebRTC, WebSocket changes:

- Removed custom code for relaying from WebSocket and ENet, and let it
  be handled by the upper layer.
- Update WebRTC to split create_client, create_server, and create_mesh,
  with the latter behaving like the old initialize with
  "server_compatibility = false", and the first two supporting the upper
  layer relaying protocol.

1 files changed, 16 insertions, 0 deletions

diff --git a/scene/main/multiplayer_peer.cpp b/scene/main/multiplayer_peer.cpp
index 9b63118f7c..462dc1babb 100644
--- a/scene/main/multiplayer_peer.cpp
+++ b/scene/main/multiplayer_peer.cpp
@@ -78,6 +78,10 @@ bool MultiplayerPeer::is_refusing_new_connections() const {
 	return refuse_connections;
 }
 
+bool MultiplayerPeer::is_server_relay_supported() const {
+	return false;
+}
+
 void MultiplayerPeer::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_transfer_channel", "channel"), &MultiplayerPeer::set_transfer_channel);
 	ClassDB::bind_method(D_METHOD("get_transfer_channel"), &MultiplayerPeer::get_transfer_channel);
@@ -86,6 +90,8 @@ void MultiplayerPeer::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_target_peer", "id"), &MultiplayerPeer::set_target_peer);
 
 	ClassDB::bind_method(D_METHOD("get_packet_peer"), &MultiplayerPeer::get_packet_peer);
+	ClassDB::bind_method(D_METHOD("get_packet_channel"), &MultiplayerPeer::get_packet_channel);
+	ClassDB::bind_method(D_METHOD("get_packet_mode"), &MultiplayerPeer::get_packet_mode);
 
 	ClassDB::bind_method(D_METHOD("poll"), &MultiplayerPeer::poll);
 
@@ -96,6 +102,8 @@ void MultiplayerPeer::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_refuse_new_connections", "enable"), &MultiplayerPeer::set_refuse_new_connections);
 	ClassDB::bind_method(D_METHOD("is_refusing_new_connections"), &MultiplayerPeer::is_refusing_new_connections);
 
+	ClassDB::bind_method(D_METHOD("is_server_relay_supported"), &MultiplayerPeer::is_server_relay_supported);
+
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "refuse_new_connections"), "set_refuse_new_connections", "is_refusing_new_connections");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "transfer_mode", PROPERTY_HINT_ENUM, "Unreliable,Unreliable Ordered,Reliable"), "set_transfer_mode", "get_transfer_mode");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "transfer_channel", PROPERTY_HINT_RANGE, "0,255,1"), "set_transfer_channel", "get_transfer_channel");
@@ -177,6 +185,14 @@ bool MultiplayerPeerExtension::is_refusing_new_connections() const {
 	return MultiplayerPeer::is_refusing_new_connections();
 }
 
+bool MultiplayerPeerExtension::is_server_relay_supported() const {
+	bool can_relay;
+	if (GDVIRTUAL_CALL(_is_server_relay_supported, can_relay)) {
+		return can_relay;
+	}
+	return MultiplayerPeer::is_server_relay_supported();
+}
+
 void MultiplayerPeerExtension::_bind_methods() {
 	GDVIRTUAL_BIND(_get_packet, "r_buffer", "r_buffer_size");
 	GDVIRTUAL_BIND(_put_packet, "p_buffer", "p_buffer_size");