[MP] RPC visibility.

Implemented using MultiplayerSynchronizers.

If you didn't use the synchronizer visibility features, nothing changes.

If you were using visibility, RPCs to broadcast should now behave as
expected in most configurations (i.e. by sending the RPC to _visible_
peers).

If you want to limit the visibility of RPCs for a node, add a
synchronizer for it, and configure the visibility via
"set_visibility_for" or by adding a visibility filter.

4 files changed, 79 insertions, 21 deletions

diff --git a/modules/multiplayer/scene_multiplayer.h b/modules/multiplayer/scene_multiplayer.h
index da8c762134..4482495899 100644
--- a/modules/multiplayer/scene_multiplayer.h
+++ b/modules/multiplayer/scene_multiplayer.h
@@ -171,6 +171,7 @@ public:
 	bool is_server_relay_enabled() const;
 
 	Ref<SceneCacheInterface> get_path_cache() { return cache; }
+	Ref<SceneReplicationInterface> get_replicator() { return replicator; }
 
 	SceneMultiplayer();
 	~SceneMultiplayer();
diff --git a/modules/multiplayer/scene_replication_interface.cpp b/modules/multiplayer/scene_replication_interface.cpp
index 9302ea4f20..7d9437936a 100644
--- a/modules/multiplayer/scene_replication_interface.cpp
+++ b/modules/multiplayer/scene_replication_interface.cpp
@@ -257,15 +257,54 @@ void SceneReplicationInterface::_visibility_changed(int p_peer, ObjectID p_sid)
 	Node *node = sync->get_root_node();
 	ERR_FAIL_COND(!node); // Bug.
 	const ObjectID oid = node->get_instance_id();
-	if (spawned_nodes.has(oid)) {
+	if (spawned_nodes.has(oid) && p_peer != multiplayer->get_unique_id()) {
 		_update_spawn_visibility(p_peer, oid);
 	}
 	_update_sync_visibility(p_peer, sync);
 }
 
+bool SceneReplicationInterface::is_rpc_visible(const ObjectID &p_oid, int p_peer) const {
+	if (!tracked_nodes.has(p_oid)) {
+		return true; // Untracked nodes are always visible to RPCs.
+	}
+	ERR_FAIL_COND_V(p_peer < 0, false);
+	const TrackedNode &tnode = tracked_nodes[p_oid];
+	if (tnode.synchronizers.is_empty()) {
+		return true; // No synchronizers means no visibility restrictions.
+	}
+	if (tnode.remote_peer && uint32_t(p_peer) == tnode.remote_peer) {
+		return true; // RPCs on spawned nodes are always visible to spawner.
+	} else if (spawned_nodes.has(p_oid)) {
+		// It's a spwaned node we control, this can be fast
+		if (p_peer) {
+			return peers_info.has(p_peer) && peers_info[p_peer].spawn_nodes.has(p_oid);
+		} else {
+			for (const KeyValue<int, PeerInfo> &E : peers_info) {
+				if (!E.value.spawn_nodes.has(p_oid)) {
+					return false; // Not public.
+				}
+			}
+			return true; // All peers have this node.
+		}
+	} else {
+		// Cycle object synchronizers to check visibility.
+		for (const ObjectID &sid : tnode.synchronizers) {
+			MultiplayerSynchronizer *sync = get_id_as<MultiplayerSynchronizer>(sid);
+			ERR_CONTINUE(!sync);
+			// RPC visibility is composed using OR when multiple synchronizers are present.
+			// Note that we don't really care about authority here which may lead to unexpected
+			// results when using multiple synchronizers to control the same node.
+			if (sync->is_visible_to(p_peer)) {
+				return true;
+			}
+		}
+		return false; // Not visible.
+	}
+}
+
 Error SceneReplicationInterface::_update_sync_visibility(int p_peer, MultiplayerSynchronizer *p_sync) {
 	ERR_FAIL_COND_V(!p_sync, ERR_BUG);
-	if (!multiplayer->has_multiplayer_peer() || !p_sync->is_multiplayer_authority()) {
+	if (!multiplayer->has_multiplayer_peer() || !p_sync->is_multiplayer_authority() || p_peer == multiplayer->get_unique_id()) {
 		return OK;
 	}
 
diff --git a/modules/multiplayer/scene_replication_interface.h b/modules/multiplayer/scene_replication_interface.h
index ad68425d77..30d58f7129 100644
--- a/modules/multiplayer/scene_replication_interface.h
+++ b/modules/multiplayer/scene_replication_interface.h
@@ -125,6 +125,8 @@ public:
 	Error on_despawn_receive(int p_from, const uint8_t *p_buffer, int p_buffer_len);
 	Error on_sync_receive(int p_from, const uint8_t *p_buffer, int p_buffer_len);
 
+	bool is_rpc_visible(const ObjectID &p_oid, int p_peer) const;
+
 	SceneReplicationInterface(SceneMultiplayer *p_multiplayer) {
 		multiplayer = p_multiplayer;
 	}
diff --git a/modules/multiplayer/scene_rpc_interface.cpp b/modules/multiplayer/scene_rpc_interface.cpp
index bfe54c00ff..dbf2b3751e 100644
--- a/modules/multiplayer/scene_rpc_interface.cpp
+++ b/modules/multiplayer/scene_rpc_interface.cpp
@@ -295,7 +295,7 @@ void SceneRPCInterface::_process_rpc(Node *p_node, const uint16_t p_rpc_method_i
 	}
 }
 
-void SceneRPCInterface::_send_rpc(Node *p_from, int p_to, uint16_t p_rpc_id, const RPCConfig &p_config, const StringName &p_name, const Variant **p_arg, int p_argcount) {
+void SceneRPCInterface::_send_rpc(Node *p_node, int p_to, uint16_t p_rpc_id, const RPCConfig &p_config, const StringName &p_name, const Variant **p_arg, int p_argcount) {
 	Ref<MultiplayerPeer> peer = multiplayer->get_multiplayer_peer();
 	ERR_FAIL_COND_MSG(peer.is_null(), "Attempt to call RPC without active multiplayer peer.");
 
@@ -311,12 +311,35 @@ void SceneRPCInterface::_send_rpc(Node *p_from, int p_to, uint16_t p_rpc_id, con
 		ERR_FAIL_MSG("Attempt to call RPC with unknown peer ID: " + itos(p_to) + ".");
 	}
 
-	// See if all peers have cached path (if so, call can be fast).
-	int psc_id;
-	const bool has_all_peers = multiplayer->get_path_cache()->send_object_cache(p_from, p_to, psc_id);
+	// See if all peers have cached path (if so, call can be fast) while building the RPC target list.
+	HashSet<int> targets;
+	Ref<SceneCacheInterface> cache = multiplayer->get_path_cache();
+	int psc_id = -1;
+	bool has_all_peers = true;
+	const ObjectID oid = p_node->get_instance_id();
+	if (p_to > 0) {
+		ERR_FAIL_COND_MSG(!multiplayer->get_replicator()->is_rpc_visible(oid, p_to), "Attempt to call an RPC to a peer that cannot see this node. Peer ID: " + itos(p_to));
+		targets.insert(p_to);
+		has_all_peers = cache->send_object_cache(p_node, p_to, psc_id);
+	} else {
+		bool restricted = !multiplayer->get_replicator()->is_rpc_visible(oid, 0);
+		for (const int &P : multiplayer->get_connected_peers()) {
+			if (p_to < 0 && P == -p_to) {
+				continue; // Excluded peer.
+			}
+			if (restricted && !multiplayer->get_replicator()->is_rpc_visible(oid, P)) {
+				continue; // Not visible to this peer.
+			}
+			targets.insert(P);
+			bool has_peer = cache->send_object_cache(p_node, P, psc_id);
+			has_all_peers = has_all_peers && has_peer;
+		}
+	}
+	if (targets.is_empty()) {
+		return; // No one in sight.
+	}
 
 	// Create base packet, lots of hardcode because it must be tight.
-
 	int ofs = 0;
 
 #define MAKE_ROOM(m_amount)             \
@@ -399,7 +422,7 @@ void SceneRPCInterface::_send_rpc(Node *p_from, int p_to, uint16_t p_rpc_id, con
 	ERR_FAIL_COND(name_id_compression > 1);
 
 #ifdef DEBUG_ENABLED
-	_profile_node_data("rpc_out", p_from->get_instance_id(), ofs);
+	_profile_node_data("rpc_out", p_node->get_instance_id(), ofs);
 #endif
 
 	// We can now set the meta
@@ -410,8 +433,9 @@ void SceneRPCInterface::_send_rpc(Node *p_from, int p_to, uint16_t p_rpc_id, con
 	peer->set_transfer_mode(p_config.transfer_mode);
 
 	if (has_all_peers) {
-		// They all have verified paths, so send fast.
-		multiplayer->send_command(p_to, packet_cache.ptr(), ofs);
+		for (const int P : targets) {
+			multiplayer->send_command(P, packet_cache.ptr(), ofs);
+		}
 	} else {
 		// Unreachable because the node ID is never compressed if the peers doesn't know it.
 		CRASH_COND(node_id_compression != NETWORK_NODE_ID_COMPRESSION_32);
@@ -419,23 +443,15 @@ void SceneRPCInterface::_send_rpc(Node *p_from, int p_to, uint16_t p_rpc_id, con
 		// Not all verified path, so send one by one.
 
 		// Append path at the end, since we will need it for some packets.
-		NodePath from_path = multiplayer->get_root_path().rel_path_to(p_from->get_path());
+		NodePath from_path = multiplayer->get_root_path().rel_path_to(p_node->get_path());
 		CharString pname = String(from_path).utf8();
 		int path_len = encode_cstring(pname.get_data(), nullptr);
 		MAKE_ROOM(ofs + path_len);
 		encode_cstring(pname.get_data(), &(packet_cache.write[ofs]));
 
-		for (const int &P : multiplayer->get_connected_peers()) {
-			if (p_to < 0 && P == -p_to) {
-				continue; // Continue, excluded.
-			}
-
-			if (p_to > 0 && P != p_to) {
-				continue; // Continue, not for this peer.
-			}
-
+		// Not all verified path, so check which needs the longer packet.
+		for (const int P : targets) {
 			bool confirmed = multiplayer->get_path_cache()->is_cache_confirmed(from_path, P);
-
 			if (confirmed) {
 				// This one confirmed path, so use id.
 				encode_uint32(psc_id, &(packet_cache.write[1]));