[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, 18 insertions, 0 deletions

diff --git a/modules/multiplayer/scene_multiplayer.h b/modules/multiplayer/scene_multiplayer.h
index a99cca7b21..06d7b2c7a7 100644
--- a/modules/multiplayer/scene_multiplayer.h
+++ b/modules/multiplayer/scene_multiplayer.h
@@ -49,6 +49,17 @@ public:
 		NETWORK_COMMAND_SPAWN,
 		NETWORK_COMMAND_DESPAWN,
 		NETWORK_COMMAND_SYNC,
+		NETWORK_COMMAND_SYS,
+	};
+
+	enum SysCommands {
+		SYS_COMMAND_ADD_PEER,
+		SYS_COMMAND_DEL_PEER,
+		SYS_COMMAND_RELAY,
+	};
+
+	enum {
+		SYS_CMD_SIZE = 6, // Command + sys command + peer_id (+ optional payload).
 	};
 
 	// For each command, the 4 MSB can contain custom flags, as defined by subsystems.
@@ -74,6 +85,8 @@ private:
 
 	NodePath root_path;
 	bool allow_object_decoding = false;
+	bool server_relay = true;
+	Ref<StreamPeerBuffer> relay_buffer;
 
 	Ref<SceneCacheInterface> cache;
 	Ref<SceneReplicationInterface> replicator;
@@ -84,6 +97,7 @@ protected:
 
 	void _process_packet(int p_from, const uint8_t *p_packet, int p_packet_len);
 	void _process_raw(int p_from, const uint8_t *p_packet, int p_packet_len);
+	void _process_sys(int p_from, const uint8_t *p_packet, int p_packet_len, MultiplayerPeer::TransferMode p_mode, int p_channel);
 
 	void _add_peer(int p_id);
 	void _del_peer(int p_id);
@@ -111,6 +125,7 @@ public:
 	void set_root_path(const NodePath &p_path);
 	NodePath get_root_path() const;
 
+	Error send_command(int p_to, const uint8_t *p_packet, int p_packet_len); // Used internally to relay packets when needed.
 	Error send_bytes(Vector<uint8_t> p_data, int p_to = MultiplayerPeer::TARGET_PEER_BROADCAST, MultiplayerPeer::TransferMode p_mode = MultiplayerPeer::TRANSFER_MODE_RELIABLE, int p_channel = 0);
 	String get_rpc_md5(const Object *p_obj);
 
@@ -123,6 +138,9 @@ public:
 	void set_allow_object_decoding(bool p_enable);
 	bool is_object_decoding_allowed() const;
 
+	void set_server_relay_enabled(bool p_enabled);
+	bool is_server_relay_enabled() const;
+
 	Ref<SceneCacheInterface> get_path_cache() { return cache; }
 
 #ifdef DEBUG_ENABLED