[Net] MultiplayerReplicator with initial state.

Move the former "spawnables" functions to a dedicated
MultiplayerReplicator class.
Support custom overrides in replicator.
Spawn/despawn messages can now contain a state.
The state can be automatically encoded/decoded by passing the desired
object properties to `spawnable_config`.
You can use script properties to optimize the state representation.
2 Callables can be also specified to completely override the default
implementation for sending and receiving the spawn/despawn event.
(9 bytes overhead, and there's room for improvement here).
When using a custom implementation `spawn` and `despawn` can be called
with any Object, `send_spawn`/`send_despawn` can receive any Variant as
a state, and the path is not required.

Two new functions, `spawn` and `despawn`, convey the implementation
independent method for requesting a spawn/despawn of an Object, while
`send_spawn` and `send_despawn` represent the more low-level send event
for a Variant to be used by the custom implementations.

5 files changed, 686 insertions, 240 deletions

diff --git a/core/io/multiplayer_api.cpp b/core/io/multiplayer_api.cpp
index f792dc6cb4..0ce9a70921 100644
--- a/core/io/multiplayer_api.cpp
+++ b/core/io/multiplayer_api.cpp
@@ -32,15 +32,11 @@
 
 #include "core/debugger/engine_debugger.h"
 #include "core/io/marshalls.h"
+#include "core/io/multiplayer_replicator.h"
 #include "scene/main/node.h"
-#include "scene/resources/packed_scene.h"
 
 #include <stdint.h>
 
-#define NODE_ID_COMPRESSION_SHIFT 3
-#define NAME_ID_COMPRESSION_SHIFT 5
-#define BYTE_ONLY_OR_NO_ARGS_SHIFT 6
-
 #ifdef DEBUG_ENABLED
 #include "core/os/os.h"
 #endif
@@ -147,7 +143,7 @@ void MultiplayerAPI::poll() {
 }
 
 void MultiplayerAPI::clear() {
-	replicated_nodes.clear();
+	replicator->clear();
 	connected_peers.clear();
 	path_get_cache.clear();
 	path_send_cache.clear();
@@ -325,10 +321,10 @@ void MultiplayerAPI::_process_packet(int p_from, const uint8_t *p_packet, int p_
 			_process_raw(p_from, p_packet, p_packet_len);
 		} break;
 		case NETWORK_COMMAND_SPAWN: {
-			_process_spawn_despawn(p_from, p_packet, p_packet_len, true);
+			replicator->process_spawn_despawn(p_from, p_packet, p_packet_len, true);
 		} break;
 		case NETWORK_COMMAND_DESPAWN: {
-			_process_spawn_despawn(p_from, p_packet, p_packet_len, false);
+			replicator->process_spawn_despawn(p_from, p_packet, p_packet_len, false);
 		} break;
 	}
 }
@@ -338,7 +334,6 @@ Node *MultiplayerAPI::_process_get_node(int p_from, const uint8_t *p_packet, uin
 
 	if (p_node_target & 0x80000000) {
 		// Use full path (not cached yet).
-
 		int ofs = p_node_target & 0x7FFFFFFF;
 
 		ERR_FAIL_COND_V_MSG(ofs >= p_packet_len, nullptr, "Invalid packet received. Size smaller than declared.");
@@ -353,25 +348,11 @@ Node *MultiplayerAPI::_process_get_node(int p_from, const uint8_t *p_packet, uin
 		if (!node) {
 			ERR_PRINT("Failed to get path from RPC: " + String(np) + ".");
 		}
+		return node;
 	} else {
 		// Use cached path.
-		int id = p_node_target;
-
-		Map<int, PathGetCache>::Element *E = path_get_cache.find(p_from);
-		ERR_FAIL_COND_V_MSG(!E, nullptr, "Invalid packet received. Requests invalid peer cache.");
-
-		Map<int, PathGetCache::NodeInfo>::Element *F = E->get().nodes.find(id);
-		ERR_FAIL_COND_V_MSG(!F, nullptr, "Invalid packet received. Unabled to find requested cached node.");
-
-		PathGetCache::NodeInfo *ni = &F->get();
-		// Do proper caching later.
-
-		node = root_node->get_node(ni->path);
-		if (!node) {
-			ERR_PRINT("Failed to get cached path from RPC: " + String(ni->path) + ".");
-		}
+		return get_cached_node(p_from, p_node_target);
 	}
-	return node;
 }
 
 void MultiplayerAPI::_process_rpc(Node *p_node, const uint16_t p_rpc_method_id, int p_from, const uint8_t *p_packet, int p_packet_len, int p_offset) {
@@ -425,7 +406,7 @@ void MultiplayerAPI::_process_rpc(Node *p_node, const uint16_t p_rpc_method_id,
 			ERR_FAIL_COND_MSG(p_offset >= p_packet_len, "Invalid packet received. Size too small.");
 
 			int vlen;
-			Error err = _decode_and_decompress_variant(args.write[i], &p_packet[p_offset], p_packet_len - p_offset, &vlen);
+			Error err = decode_and_decompress_variant(args.write[i], &p_packet[p_offset], p_packet_len - p_offset, &vlen);
 			ERR_FAIL_COND_MSG(err != OK, "Invalid packet received. Unable to decode RPC argument.");
 
 			argp.write[i] = &args[i];
@@ -514,64 +495,6 @@ void MultiplayerAPI::_process_confirm_path(int p_from, const uint8_t *p_packet,
 	E->get() = true;
 }
 
-void MultiplayerAPI::_process_spawn_despawn(int p_from, const uint8_t *p_packet, int p_packet_len, bool p_spawn) {
-	ERR_FAIL_COND_MSG(p_packet_len < 18, "Invalid spawn packet received");
-	int ofs = 1;
-	ResourceUID::ID id = decode_uint64(&p_packet[ofs]);
-	ofs += 8;
-	ERR_FAIL_COND_MSG(!spawnables.has(id), "Invalid spawn ID received " + itos(id));
-
-	uint32_t node_target = decode_uint32(&p_packet[ofs]);
-	Node *parent = _process_get_node(p_from, nullptr, node_target, 0);
-	ofs += 4;
-	ERR_FAIL_COND_MSG(parent == nullptr, "Invalid packet received. Requested node was not found.");
-
-	uint32_t name_len = decode_uint32(&p_packet[ofs]);
-	ofs += 4;
-	ERR_FAIL_COND_MSG(name_len > uint32_t(p_packet_len - ofs), vformat("Invalid spawn packet size: %d, wants: %d", p_packet_len, ofs + name_len));
-	ERR_FAIL_COND_MSG(name_len < 1, "Zero spawn name size.");
-
-	const String name = String::utf8((const char *)&p_packet[ofs], name_len);
-	// We need to make sure no trickery happens here (e.g. despawning a subpath), but we want to allow autogenerated ("@") node names.
-	ERR_FAIL_COND_MSG(name.validate_node_name() != name.replace("@", ""), vformat("Invalid node name received: '%s'", name));
-	ofs += name_len;
-	PackedByteArray data;
-	if (p_packet_len > ofs) {
-		data.resize(p_packet_len - ofs);
-		memcpy(data.ptrw(), &p_packet[ofs], data.size());
-	}
-
-	SpawnMode mode = spawnables[id];
-	if (mode == SPAWN_MODE_SERVER && p_from == 1) {
-		String scene_path = ResourceUID::get_singleton()->get_id_path(id);
-		if (p_spawn) {
-			ERR_FAIL_COND_MSG(parent->has_node(name), vformat("Unable to spawn node. Node already exists: %s/%s", parent->get_path(), name));
-			RES res = ResourceLoader::load(scene_path);
-			ERR_FAIL_COND_MSG(!res.is_valid(), "Unable to load scene to spawn at path: " + scene_path);
-			PackedScene *scene = Object::cast_to<PackedScene>(res.ptr());
-			ERR_FAIL_COND(!scene);
-			Node *node = scene->instantiate();
-			ERR_FAIL_COND(!node);
-			replicated_nodes[node->get_instance_id()] = id;
-			parent->_add_child_nocheck(node, name);
-			emit_signal(SNAME("network_spawn"), p_from, id, node, data);
-		} else {
-			ERR_FAIL_COND_MSG(!parent->has_node(name), vformat("Path not found: %s/%s", parent->get_path(), name));
-			Node *node = parent->get_node(name);
-			ERR_FAIL_COND_MSG(!replicated_nodes.has(node->get_instance_id()), vformat("Trying to despawn a Node that was not replicated: %s/%s", parent->get_path(), name));
-			emit_signal(SNAME("network_despawn"), p_from, id, node, data);
-			replicated_nodes.erase(node->get_instance_id());
-			node->queue_delete();
-		}
-	} else {
-		if (p_spawn) {
-			emit_signal(SNAME("network_spawn_request"), p_from, id, parent, name, data);
-		} else {
-			emit_signal(SNAME("network_despawn_request"), p_from, id, parent, name, data);
-		}
-	}
-}
-
 bool MultiplayerAPI::_send_confirm_path(Node *p_node, NodePath p_path, PathSentCache *psc, int p_target) {
 	bool has_all_peers = true;
 	List<int> peers_to_add; // If one is missing, take note to add it.
@@ -647,7 +570,7 @@ bool MultiplayerAPI::_send_confirm_path(Node *p_node, NodePath p_path, PathSentC
 #define ENCODE_16 1 << 5
 #define ENCODE_32 2 << 5
 #define ENCODE_64 3 << 5
-Error MultiplayerAPI::_encode_and_compress_variant(const Variant &p_variant, uint8_t *r_buffer, int &r_len) {
+Error MultiplayerAPI::encode_and_compress_variant(const Variant &p_variant, uint8_t *r_buffer, int &r_len) {
 	// Unreachable because `VARIANT_MAX` == 27 and `ENCODE_VARIANT_MASK` == 31
 	CRASH_COND(p_variant.get_type() > VARIANT_META_TYPE_MASK);
 
@@ -722,7 +645,7 @@ Error MultiplayerAPI::_encode_and_compress_variant(const Variant &p_variant, uin
 	return OK;
 }
 
-Error MultiplayerAPI::_decode_and_decompress_variant(Variant &r_variant, const uint8_t *p_buffer, int p_len, int *r_len) {
+Error MultiplayerAPI::decode_and_decompress_variant(Variant &r_variant, const uint8_t *p_buffer, int p_len, int *r_len) {
 	const uint8_t *buf = p_buffer;
 	int len = p_len;
 
@@ -906,10 +829,10 @@ void MultiplayerAPI::_send_rpc(Node *p_from, int p_to, uint16_t p_rpc_id, const
 		ofs += 1;
 		for (int i = 0; i < p_argcount; i++) {
 			int len(0);
-			Error err = _encode_and_compress_variant(*p_arg[i], nullptr, len);
+			Error err = encode_and_compress_variant(*p_arg[i], nullptr, len);
 			ERR_FAIL_COND_MSG(err != OK, "Unable to encode RPC argument. THIS IS LIKELY A BUG IN THE ENGINE!");
 			MAKE_ROOM(ofs + len);
-			_encode_and_compress_variant(*p_arg[i], &(packet_cache.write[ofs]), len);
+			encode_and_compress_variant(*p_arg[i], &(packet_cache.write[ofs]), len);
 			ofs += len;
 		}
 	}
@@ -976,14 +899,7 @@ void MultiplayerAPI::_add_peer(int p_id) {
 	connected_peers.insert(p_id);
 	path_get_cache.insert(p_id, PathGetCache());
 	if (is_network_server()) {
-		for (const KeyValue<ObjectID, ResourceUID::ID> &E : replicated_nodes) {
-			// Only server mode adds to replicated_nodes, no need to check it.
-			Object *obj = ObjectDB::get_instance(E.key);
-			ERR_CONTINUE(!obj);
-			Node *node = Object::cast_to<Node>(obj);
-			ERR_CONTINUE(!node);
-			_send_spawn_despawn(p_id, E.value, node->get_path(), nullptr, 0, true);
-		}
+		replicator->spawn_all(p_id);
 	}
 	emit_signal(SNAME("network_peer_connected"), p_id);
 }
@@ -1000,10 +916,6 @@ void MultiplayerAPI::_del_peer(int p_id) {
 		PathSentCache *psc = path_send_cache.getptr(E);
 		psc->confirmed_peers.erase(p_id);
 	}
-	if (p_id == 1) {
-		// Erase server replicated nodes, but do not queue them for deletion.
-		replicated_nodes.clear();
-	}
 	emit_signal(SNAME("network_peer_disconnected"), p_id);
 }
 
@@ -1109,6 +1021,36 @@ void MultiplayerAPI::_process_raw(int p_from, const uint8_t *p_packet, int p_pac
 	emit_signal(SNAME("network_peer_packet"), p_from, out);
 }
 
+bool MultiplayerAPI::send_confirm_path(Node *p_node, NodePath p_path, int p_peer_id, int &r_id) {
+	// See if the path is cached.
+	PathSentCache *psc = path_send_cache.getptr(p_path);
+	if (!psc) {
+		// Path is not cached, create.
+		path_send_cache[p_path] = PathSentCache();
+		psc = path_send_cache.getptr(p_path);
+		psc->id = last_send_cache_id++;
+	}
+	r_id = psc->id;
+
+	// See if all peers have cached path (if so, call can be fast).
+	return _send_confirm_path(p_node, p_path, psc, p_peer_id);
+}
+
+Node *MultiplayerAPI::get_cached_node(int p_from, uint32_t p_node_id) {
+	Map<int, PathGetCache>::Element *E = path_get_cache.find(p_from);
+	ERR_FAIL_COND_V_MSG(!E, nullptr, vformat("No cache found for peer %d.", p_from));
+
+	Map<int, PathGetCache::NodeInfo>::Element *F = E->get().nodes.find(p_node_id);
+	ERR_FAIL_COND_V_MSG(!F, nullptr, vformat("ID %d not found in cache of peer %d.", p_node_id, p_from));
+
+	PathGetCache::NodeInfo *ni = &F->get();
+	Node *node = root_node->get_node(ni->path);
+	if (!node) {
+		ERR_PRINT("Failed to get cached path: " + String(ni->path) + ".");
+	}
+	return node;
+}
+
 int MultiplayerAPI::get_network_unique_id() const {
 	ERR_FAIL_COND_V_MSG(!network_peer.is_valid(), 0, "No network peer is assigned. Unable to get unique network ID.");
 	return network_peer->get_unique_id();
@@ -1147,97 +1089,12 @@ bool MultiplayerAPI::is_object_decoding_allowed() const {
 	return allow_object_decoding;
 }
 
-Error MultiplayerAPI::spawnable_config(const ResourceUID::ID &p_id, SpawnMode p_mode) {
-	ERR_FAIL_COND_V(p_mode < SPAWN_MODE_NONE || p_mode > SPAWN_MODE_CUSTOM, ERR_INVALID_PARAMETER);
-	ERR_FAIL_COND_V(!ResourceUID::get_singleton()->has_id(p_id), ERR_INVALID_PARAMETER);
-#ifdef TOOLS_ENABLED
-	String path = ResourceUID::get_singleton()->get_id_path(p_id);
-	RES res = ResourceLoader::load(path);
-	ERR_FAIL_COND_V(!res->is_class("PackedScene"), ERR_INVALID_PARAMETER);
-#endif
-	if (p_mode == SPAWN_MODE_NONE) {
-		if (spawnables.has(p_id)) {
-			spawnables.erase(p_id);
-		}
-	} else {
-		spawnables[p_id] = p_mode;
-	}
-	return OK;
-}
-
-Error MultiplayerAPI::send_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const NodePath &p_path, const PackedByteArray &p_data) {
-	return _send_spawn_despawn(p_peer_id, p_scene_id, p_path, p_data.ptr(), p_data.size(), false);
+MultiplayerReplicator *MultiplayerAPI::get_replicator() const {
+	return replicator;
 }
 
-Error MultiplayerAPI::send_spawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const NodePath &p_path, const PackedByteArray &p_data) {
-	return _send_spawn_despawn(p_peer_id, p_scene_id, p_path, p_data.ptr(), p_data.size(), true);
-}
-
-Error MultiplayerAPI::_send_spawn_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const NodePath &p_path, const uint8_t *p_data, int p_data_len, bool p_spawn) {
-	ERR_FAIL_COND_V(!root_node, ERR_UNCONFIGURED);
-	ERR_FAIL_COND_V_MSG(!spawnables.has(p_scene_id), ERR_INVALID_PARAMETER, vformat("Spawnable not found: %d", p_scene_id));
-
-	NodePath rel_path = (root_node->get_path()).rel_path_to(p_path);
-	const Vector<StringName> names = rel_path.get_names();
-	ERR_FAIL_COND_V(names.size() < 2, ERR_INVALID_PARAMETER);
-
-	NodePath parent = NodePath(names.subarray(0, names.size() - 2), false);
-	ERR_FAIL_COND_V_MSG(!root_node->has_node(parent), ERR_INVALID_PARAMETER, "Path not found: " + parent);
-
-	// See if the path is cached.
-	PathSentCache *psc = path_send_cache.getptr(parent);
-	if (!psc) {
-		// Path is not cached, create.
-		path_send_cache[parent] = PathSentCache();
-		psc = path_send_cache.getptr(parent);
-		psc->id = last_send_cache_id++;
-	}
-	_send_confirm_path(root_node->get_node(parent), parent, psc, p_peer_id);
-
-	const CharString cname = String(names[names.size() - 1]).utf8();
-	int nlen = encode_cstring(cname.get_data(), nullptr);
-	MAKE_ROOM(1 + 8 + 4 + 4 + nlen + p_data_len);
-	uint8_t *ptr = packet_cache.ptrw();
-	ptr[0] = p_spawn ? NETWORK_COMMAND_SPAWN : NETWORK_COMMAND_DESPAWN;
-	int ofs = 1;
-	ofs += encode_uint64(p_scene_id, &ptr[ofs]);
-	ofs += encode_uint32(psc->id, &ptr[ofs]);
-	ofs += encode_uint32(nlen, &ptr[ofs]);
-	ofs += encode_cstring(cname.get_data(), &ptr[ofs]);
-	memcpy(&ptr[ofs], p_data, p_data_len);
-	network_peer->set_target_peer(p_peer_id);
-	network_peer->set_transfer_channel(0);
-	network_peer->set_transfer_mode(MultiplayerPeer::TRANSFER_MODE_RELIABLE);
-	return network_peer->put_packet(ptr, ofs + p_data_len);
-}
-
-void MultiplayerAPI::scene_enter_exit_notify(const String &p_scene, const Node *p_node, bool p_enter) {
-	if (!has_network_peer()) {
-		return;
-	}
-	ERR_FAIL_COND(!p_node || !p_node->get_parent() || !root_node);
-	NodePath path = (root_node->get_path()).rel_path_to(p_node->get_parent()->get_path());
-	if (path.is_empty()) {
-		return;
-	}
-	ResourceUID::ID id = ResourceLoader::get_resource_uid(p_scene);
-	if (!spawnables.has(id)) {
-		return;
-	}
-	SpawnMode mode = spawnables[id];
-	if (p_enter) {
-		if (mode == SPAWN_MODE_SERVER && is_network_server()) {
-			replicated_nodes[p_node->get_instance_id()] = id;
-			_send_spawn_despawn(0, id, p_node->get_path(), nullptr, 0, true);
-		}
-		emit_signal(SNAME("network_spawnable_added"), id, p_node);
-	} else {
-		if (mode == SPAWN_MODE_SERVER && is_network_server() && replicated_nodes.has(p_node->get_instance_id())) {
-			replicated_nodes.erase(p_node->get_instance_id());
-			_send_spawn_despawn(0, id, p_node->get_path(), nullptr, 0, false);
-		}
-		emit_signal(SNAME("network_spawnable_removed"), id, p_node);
-	}
+void MultiplayerAPI::scene_enter_exit_notify(const String &p_scene, Node *p_node, bool p_enter) {
+	replicator->scene_enter_exit_notify(p_scene, p_node, p_enter);
 }
 
 void MultiplayerAPI::_bind_methods() {
@@ -1258,15 +1115,14 @@ void MultiplayerAPI::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("is_refusing_new_network_connections"), &MultiplayerAPI::is_refusing_new_network_connections);
 	ClassDB::bind_method(D_METHOD("set_allow_object_decoding", "enable"), &MultiplayerAPI::set_allow_object_decoding);
 	ClassDB::bind_method(D_METHOD("is_object_decoding_allowed"), &MultiplayerAPI::is_object_decoding_allowed);
-	ClassDB::bind_method(D_METHOD("spawnable_config", "scene_id", "spawn_mode"), &MultiplayerAPI::spawnable_config);
-	ClassDB::bind_method(D_METHOD("send_despawn", "peer_id", "scene_id", "path", "data"), &MultiplayerAPI::send_despawn, DEFVAL(PackedByteArray()));
-	ClassDB::bind_method(D_METHOD("send_spawn", "peer_id", "scene_id", "path", "data"), &MultiplayerAPI::send_spawn, DEFVAL(PackedByteArray()));
+	ClassDB::bind_method(D_METHOD("get_replicator"), &MultiplayerAPI::get_replicator);
 
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "allow_object_decoding"), "set_allow_object_decoding", "is_object_decoding_allowed");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "refuse_new_network_connections"), "set_refuse_new_network_connections", "is_refusing_new_network_connections");
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "network_peer", PROPERTY_HINT_RESOURCE_TYPE, "MultiplayerPeer", PROPERTY_USAGE_NONE), "set_network_peer", "get_network_peer");
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "root_node", PROPERTY_HINT_RESOURCE_TYPE, "Node", PROPERTY_USAGE_NONE), "set_root_node", "get_root_node");
 	ADD_PROPERTY_DEFAULT("refuse_new_network_connections", false);
+	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "replicator", PROPERTY_HINT_RESOURCE_TYPE, "MultiplayerReplicator", PROPERTY_USAGE_NONE), "", "get_replicator");
 
 	ADD_SIGNAL(MethodInfo("network_peer_connected", PropertyInfo(Variant::INT, "id")));
 	ADD_SIGNAL(MethodInfo("network_peer_disconnected", PropertyInfo(Variant::INT, "id")));
@@ -1274,27 +1130,19 @@ void MultiplayerAPI::_bind_methods() {
 	ADD_SIGNAL(MethodInfo("connected_to_server"));
 	ADD_SIGNAL(MethodInfo("connection_failed"));
 	ADD_SIGNAL(MethodInfo("server_disconnected"));
-	ADD_SIGNAL(MethodInfo("network_despawn", PropertyInfo(Variant::INT, "id"), PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node"), PropertyInfo(Variant::PACKED_BYTE_ARRAY, "data")));
-	ADD_SIGNAL(MethodInfo("network_spawn", PropertyInfo(Variant::INT, "id"), PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node"), PropertyInfo(Variant::PACKED_BYTE_ARRAY, "data")));
-	ADD_SIGNAL(MethodInfo("network_despawn_request", PropertyInfo(Variant::INT, "id"), PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "parent", PROPERTY_HINT_RESOURCE_TYPE, "Node"), PropertyInfo(Variant::STRING, "name"), PropertyInfo(Variant::PACKED_BYTE_ARRAY, "data")));
-	ADD_SIGNAL(MethodInfo("network_spawn_request", PropertyInfo(Variant::INT, "id"), PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "parent", PROPERTY_HINT_RESOURCE_TYPE, "Node"), PropertyInfo(Variant::STRING, "name"), PropertyInfo(Variant::PACKED_BYTE_ARRAY, "data")));
-	ADD_SIGNAL(MethodInfo("network_spawnable_added", PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node")));
-	ADD_SIGNAL(MethodInfo("network_spawnable_removed", PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node")));
 
 	BIND_ENUM_CONSTANT(RPC_MODE_DISABLED);
 	BIND_ENUM_CONSTANT(RPC_MODE_REMOTE);
 	BIND_ENUM_CONSTANT(RPC_MODE_MASTER);
 	BIND_ENUM_CONSTANT(RPC_MODE_PUPPET);
-
-	BIND_ENUM_CONSTANT(SPAWN_MODE_NONE);
-	BIND_ENUM_CONSTANT(SPAWN_MODE_SERVER);
-	BIND_ENUM_CONSTANT(SPAWN_MODE_CUSTOM);
 }
 
 MultiplayerAPI::MultiplayerAPI() {
+	replicator = memnew(MultiplayerReplicator(this));
 	clear();
 }
 
 MultiplayerAPI::~MultiplayerAPI() {
 	clear();
+	memdelete(replicator);
 }
diff --git a/core/io/multiplayer_api.h b/core/io/multiplayer_api.h
index 9552a0bf35..5853541efa 100644
--- a/core/io/multiplayer_api.h
+++ b/core/io/multiplayer_api.h
@@ -35,6 +35,8 @@
 #include "core/io/resource_uid.h"
 #include "core/object/ref_counted.h"
 
+class MultiplayerReplicator;
+
 class MultiplayerAPI : public RefCounted {
 	GDCLASS(MultiplayerAPI, RefCounted);
 
@@ -46,12 +48,6 @@ public:
 		RPC_MODE_PUPPET, // Using rpc() on it will call method for all puppets
 	};
 
-	enum SpawnMode {
-		SPAWN_MODE_NONE,
-		SPAWN_MODE_SERVER,
-		SPAWN_MODE_CUSTOM,
-	};
-
 	struct RPCConfig {
 		StringName name;
 		RPCMode rpc_mode = RPC_MODE_DISABLED;
@@ -71,6 +67,32 @@ public:
 		}
 	};
 
+	enum NetworkCommands {
+		NETWORK_COMMAND_REMOTE_CALL = 0,
+		NETWORK_COMMAND_SIMPLIFY_PATH,
+		NETWORK_COMMAND_CONFIRM_PATH,
+		NETWORK_COMMAND_RAW,
+		NETWORK_COMMAND_SPAWN,
+		NETWORK_COMMAND_DESPAWN,
+	};
+
+	enum NetworkNodeIdCompression {
+		NETWORK_NODE_ID_COMPRESSION_8 = 0,
+		NETWORK_NODE_ID_COMPRESSION_16,
+		NETWORK_NODE_ID_COMPRESSION_32,
+	};
+
+	enum NetworkNameIdCompression {
+		NETWORK_NAME_ID_COMPRESSION_8 = 0,
+		NETWORK_NAME_ID_COMPRESSION_16,
+	};
+
+	enum {
+		NODE_ID_COMPRESSION_SHIFT = 3,
+		NAME_ID_COMPRESSION_SHIFT = 5,
+		BYTE_ONLY_OR_NO_ARGS_SHIFT = 6,
+	};
+
 private:
 	//path sent caches
 	struct PathSentCache {
@@ -89,16 +111,15 @@ private:
 	};
 
 	Ref<MultiplayerPeer> network_peer;
-	Map<ResourceUID::ID, SpawnMode> spawnables;
 	int rpc_sender_id = 0;
 	Set<int> connected_peers;
 	HashMap<NodePath, PathSentCache> path_send_cache;
 	Map<int, PathGetCache> path_get_cache;
-	Map<ObjectID, ResourceUID::ID> replicated_nodes;
 	int last_send_cache_id;
 	Vector<uint8_t> packet_cache;
 	Node *root_node = nullptr;
 	bool allow_object_decoding = false;
+	MultiplayerReplicator *replicator = nullptr;
 
 protected:
 	static void _bind_methods();
@@ -106,7 +127,6 @@ protected:
 	void _process_packet(int p_from, const uint8_t *p_packet, int p_packet_len);
 	void _process_simplify_path(int p_from, const uint8_t *p_packet, int p_packet_len);
 	void _process_confirm_path(int p_from, const uint8_t *p_packet, int p_packet_len);
-	void _process_spawn_despawn(int p_from, const uint8_t *p_packet, int p_packet_len, bool p_spawn);
 	Node *_process_get_node(int p_from, const uint8_t *p_packet, uint32_t p_node_target, int p_packet_len);
 	void _process_rpc(Node *p_node, const uint16_t p_rpc_method_id, int p_from, const uint8_t *p_packet, int p_packet_len, int p_offset);
 	void _process_raw(int p_from, const uint8_t *p_packet, int p_packet_len);
@@ -114,30 +134,7 @@ protected:
 	void _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);
 	bool _send_confirm_path(Node *p_node, NodePath p_path, PathSentCache *psc, int p_target);
 
-	Error _encode_and_compress_variant(const Variant &p_variant, uint8_t *p_buffer, int &r_len);
-	Error _decode_and_decompress_variant(Variant &r_variant, const uint8_t *p_buffer, int p_len, int *r_len);
-
 public:
-	enum NetworkCommands {
-		NETWORK_COMMAND_REMOTE_CALL = 0,
-		NETWORK_COMMAND_SIMPLIFY_PATH,
-		NETWORK_COMMAND_CONFIRM_PATH,
-		NETWORK_COMMAND_RAW,
-		NETWORK_COMMAND_SPAWN,
-		NETWORK_COMMAND_DESPAWN,
-	};
-
-	enum NetworkNodeIdCompression {
-		NETWORK_NODE_ID_COMPRESSION_8 = 0,
-		NETWORK_NODE_ID_COMPRESSION_16,
-		NETWORK_NODE_ID_COMPRESSION_32,
-	};
-
-	enum NetworkNameIdCompression {
-		NETWORK_NAME_ID_COMPRESSION_8 = 0,
-		NETWORK_NAME_ID_COMPRESSION_16,
-	};
-
 	void poll();
 	void clear();
 	void set_root_node(Node *p_node);
@@ -146,8 +143,16 @@ public:
 	Ref<MultiplayerPeer> get_network_peer() const;
 	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);
 
+	Error encode_and_compress_variant(const Variant &p_variant, uint8_t *p_buffer, int &r_len);
+	Error decode_and_decompress_variant(Variant &r_variant, const uint8_t *p_buffer, int p_len, int *r_len);
+
 	// Called by Node.rpc
 	void rpcp(Node *p_node, int p_peer_id, bool p_unreliable, const StringName &p_method, const Variant **p_arg, int p_argcount);
+	// Called by Node._notification
+	void scene_enter_exit_notify(const String &p_scene, Node *p_node, bool p_enter);
+	// Called by replicator
+	bool send_confirm_path(Node *p_node, NodePath p_path, int p_target, int &p_id);
+	Node *get_cached_node(int p_from, uint32_t p_node_id);
 
 	void _add_peer(int p_id);
 	void _del_peer(int p_id);
@@ -166,17 +171,12 @@ public:
 	void set_allow_object_decoding(bool p_enable);
 	bool is_object_decoding_allowed() const;
 
-	Error spawnable_config(const ResourceUID::ID &p_id, SpawnMode p_mode);
-	Error send_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const NodePath &p_path, const PackedByteArray &p_data = PackedByteArray());
-	Error send_spawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const NodePath &p_path, const PackedByteArray &p_data = PackedByteArray());
-	Error _send_spawn_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const NodePath &p_path, const uint8_t *p_data, int p_data_len, bool p_spawn);
-	void scene_enter_exit_notify(const String &p_scene, const Node *p_node, bool p_enter);
+	MultiplayerReplicator *get_replicator() const;
 
 	MultiplayerAPI();
 	~MultiplayerAPI();
 };
 
 VARIANT_ENUM_CAST(MultiplayerAPI::RPCMode);
-VARIANT_ENUM_CAST(MultiplayerAPI::SpawnMode);
 
 #endif // MULTIPLAYER_API_H
diff --git a/core/io/multiplayer_replicator.cpp b/core/io/multiplayer_replicator.cpp
new file mode 100644
index 0000000000..ba0fe32b58
--- /dev/null
+++ b/core/io/multiplayer_replicator.cpp
@@ -0,0 +1,497 @@
+/*************************************************************************/
+/*  multiplayer_replicator.cpp                                           */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "core/io/multiplayer_replicator.h"
+
+#include "core/io/marshalls.h"
+#include "scene/main/node.h"
+#include "scene/resources/packed_scene.h"
+
+#define MAKE_ROOM(m_amount)             \
+	if (packet_cache.size() < m_amount) \
+		packet_cache.resize(m_amount);
+
+Error MultiplayerReplicator::_send_default_spawn_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, Object *p_obj, const NodePath &p_path, bool p_spawn) {
+	ERR_FAIL_COND_V(p_spawn && !p_obj, ERR_INVALID_PARAMETER);
+	ERR_FAIL_COND_V(!replications.has(p_scene_id), ERR_INVALID_PARAMETER);
+	Error err;
+	// Prepare state
+	List<Variant> state_variants;
+	int state_len = 0;
+	const SceneConfig &cfg = replications[p_scene_id];
+	if (p_spawn) {
+		if ((err = _get_state(cfg.properties, p_obj, state_variants)) != OK) {
+			return err;
+		}
+	}
+
+	bool is_raw = false;
+	if (state_variants.size() == 1 && state_variants[0].get_type() == Variant::PACKED_BYTE_ARRAY) {
+		is_raw = true;
+	} else if (state_variants.size()) {
+		err = _encode_state(state_variants, nullptr, state_len);
+		ERR_FAIL_COND_V(err, err);
+	} else {
+		is_raw = true;
+	}
+
+	int ofs = 0;
+
+	// Prepare simplified path
+	const Node *root_node = multiplayer->get_root_node();
+	ERR_FAIL_COND_V(!root_node, ERR_UNCONFIGURED);
+	NodePath rel_path = (root_node->get_path()).rel_path_to(p_path);
+	const Vector<StringName> names = rel_path.get_names();
+	ERR_FAIL_COND_V(names.size() < 2, ERR_INVALID_PARAMETER);
+
+	NodePath parent = NodePath(names.subarray(0, names.size() - 2), false);
+	ERR_FAIL_COND_V_MSG(!root_node->has_node(parent), ERR_INVALID_PARAMETER, "Path not found: " + parent);
+
+	int path_id = 0;
+	multiplayer->send_confirm_path(root_node->get_node(parent), parent, p_peer_id, path_id);
+
+	// Encode name and parent ID.
+	CharString cname = String(names[names.size() - 1]).utf8();
+	int nlen = encode_cstring(cname.get_data(), nullptr);
+	MAKE_ROOM(SPAWN_CMD_OFFSET + 4 + 4 + nlen + state_len);
+	uint8_t *ptr = packet_cache.ptrw();
+	ptr[0] = (p_spawn ? MultiplayerAPI::NETWORK_COMMAND_SPAWN : MultiplayerAPI::NETWORK_COMMAND_DESPAWN) + ((is_raw ? 1 : 0) << MultiplayerAPI::BYTE_ONLY_OR_NO_ARGS_SHIFT);
+	ofs = 1;
+	ofs += encode_uint64(p_scene_id, &ptr[ofs]);
+	ofs += encode_uint32(path_id, &ptr[ofs]);
+	ofs += encode_uint32(nlen, &ptr[ofs]);
+	ofs += encode_cstring(cname.get_data(), &ptr[ofs]);
+
+	// Encode state.
+	if (!is_raw) {
+		_encode_state(state_variants, &ptr[ofs], state_len);
+	} else if (state_len) {
+		PackedByteArray pba = state_variants[0];
+		memcpy(&ptr[ofs], pba.ptr(), state_len);
+	}
+
+	Ref<MultiplayerPeer> network_peer = multiplayer->get_network_peer();
+	network_peer->set_target_peer(p_peer_id);
+	network_peer->set_transfer_channel(0);
+	network_peer->set_transfer_mode(MultiplayerPeer::TRANSFER_MODE_RELIABLE);
+	return network_peer->put_packet(ptr, ofs + state_len);
+}
+
+void MultiplayerReplicator::_process_default_spawn_despawn(int p_from, const ResourceUID::ID &p_scene_id, const uint8_t *p_packet, int p_packet_len, bool p_spawn) {
+	ERR_FAIL_COND_MSG(p_packet_len < SPAWN_CMD_OFFSET + 9, "Invalid spawn packet received");
+	int ofs = SPAWN_CMD_OFFSET;
+	uint32_t node_target = decode_uint32(&p_packet[ofs]);
+	Node *parent = multiplayer->get_cached_node(p_from, node_target);
+	ofs += 4;
+	ERR_FAIL_COND_MSG(parent == nullptr, "Invalid packet received. Requested node was not found.");
+
+	uint32_t name_len = decode_uint32(&p_packet[ofs]);
+	ofs += 4;
+	ERR_FAIL_COND_MSG(name_len > uint32_t(p_packet_len - ofs), vformat("Invalid spawn packet size: %d, wants: %d", p_packet_len, ofs + name_len));
+	ERR_FAIL_COND_MSG(name_len < 1, "Zero spawn name size.");
+
+	const String name = String::utf8((const char *)&p_packet[ofs], name_len);
+	// We need to make sure no trickery happens here (e.g. despawning a subpath), but we want to allow autogenerated ("@") node names.
+	ERR_FAIL_COND_MSG(name.validate_node_name() != name.replace("@", ""), vformat("Invalid node name received: '%s'", name));
+	ofs += name_len;
+
+	const SceneConfig &cfg = replications[p_scene_id];
+	if (cfg.mode == REPLICATION_MODE_SERVER && p_from == 1) {
+		String scene_path = ResourceUID::get_singleton()->get_id_path(p_scene_id);
+		if (p_spawn) {
+			const bool is_raw = ((p_packet[0] & 64) >> MultiplayerAPI::BYTE_ONLY_OR_NO_ARGS_SHIFT) == 1;
+
+			ERR_FAIL_COND_MSG(parent->has_node(name), vformat("Unable to spawn node. Node already exists: %s/%s", parent->get_path(), name));
+			RES res = ResourceLoader::load(scene_path);
+			ERR_FAIL_COND_MSG(!res.is_valid(), "Unable to load scene to spawn at path: " + scene_path);
+			PackedScene *scene = Object::cast_to<PackedScene>(res.ptr());
+			ERR_FAIL_COND(!scene);
+			Node *node = scene->instantiate();
+			ERR_FAIL_COND(!node);
+			replicated_nodes[node->get_instance_id()] = p_scene_id;
+			int size;
+			_decode_state(cfg.properties, node, &p_packet[ofs], p_packet_len - ofs, size, is_raw);
+			parent->_add_child_nocheck(node, name);
+			emit_signal(SNAME("spawned"), p_scene_id, node);
+		} else {
+			ERR_FAIL_COND_MSG(!parent->has_node(name), vformat("Path not found: %s/%s", parent->get_path(), name));
+			Node *node = parent->get_node(name);
+			ERR_FAIL_COND_MSG(!replicated_nodes.has(node->get_instance_id()), vformat("Trying to despawn a Node that was not replicated: %s/%s", parent->get_path(), name));
+			emit_signal(SNAME("despawned"), p_scene_id, node);
+			replicated_nodes.erase(node->get_instance_id());
+			node->queue_delete();
+		}
+	} else {
+		PackedByteArray data;
+		if (p_packet_len > ofs) {
+			data.resize(p_packet_len - ofs);
+			memcpy(data.ptrw(), &p_packet[ofs], data.size());
+		}
+		if (p_spawn) {
+			emit_signal(SNAME("spawn_requested"), p_from, p_scene_id, parent, name, data);
+		} else {
+			emit_signal(SNAME("despawn_requested"), p_from, p_scene_id, parent, name, data);
+		}
+	}
+}
+
+void MultiplayerReplicator::process_spawn_despawn(int p_from, const uint8_t *p_packet, int p_packet_len, bool p_spawn) {
+	ERR_FAIL_COND_MSG(p_packet_len < SPAWN_CMD_OFFSET, "Invalid spawn packet received");
+	ResourceUID::ID id = decode_uint64(&p_packet[1]);
+	ERR_FAIL_COND_MSG(!replications.has(id), "Invalid spawn ID received " + itos(id));
+
+	const SceneConfig &cfg = replications[id];
+	if (cfg.on_spawn_despawn_receive.is_valid()) {
+		int ofs = SPAWN_CMD_OFFSET;
+		bool is_raw = ((p_packet[0] & 64) >> MultiplayerAPI::BYTE_ONLY_OR_NO_ARGS_SHIFT) == 1;
+		Variant data;
+		int left = p_packet_len - ofs;
+		if (is_raw && left) {
+			PackedByteArray pba;
+			pba.resize(left);
+			memcpy(pba.ptrw(), &p_packet[ofs], pba.size());
+			data = pba;
+		} else if (left) {
+			ERR_FAIL_COND(decode_variant(data, &p_packet[ofs], left) != OK);
+		}
+
+		Variant args[4];
+		args[0] = p_from;
+		args[1] = id;
+		args[2] = data;
+		args[3] = p_spawn;
+		const Variant *argp[] = { &args[0], &args[1], &args[2], &args[3] };
+		Callable::CallError ce;
+		Variant ret;
+		cfg.on_spawn_despawn_receive.call(argp, 4, ret, ce);
+		ERR_FAIL_COND_MSG(ce.error != Callable::CallError::CALL_OK, "Custom receive function failed");
+	} else {
+		_process_default_spawn_despawn(p_from, id, p_packet, p_packet_len, p_spawn);
+	}
+}
+
+Error MultiplayerReplicator::_get_state(const List<StringName> &p_properties, const Object *p_obj, List<Variant> &r_variant) {
+	ERR_FAIL_COND_V_MSG(!p_obj, ERR_INVALID_PARAMETER, "Cannot encode null object");
+	for (const StringName &prop : p_properties) {
+		bool valid = false;
+		const Variant v = p_obj->get(prop, &valid);
+		ERR_FAIL_COND_V_MSG(!valid, ERR_INVALID_DATA, vformat("Property '%s' not found.", prop));
+		r_variant.push_back(v);
+	}
+	return OK;
+}
+
+Error MultiplayerReplicator::_encode_state(const List<Variant> &p_variants, uint8_t *p_buffer, int &r_len, bool *r_raw) {
+	r_len = 0;
+	int size = 0;
+
+	// Try raw encoding optimization.
+	if (r_raw && p_variants.size() == 1) {
+		*r_raw = false;
+		const Variant v = p_variants[0];
+		if (v.get_type() == Variant::PACKED_BYTE_ARRAY) {
+			*r_raw = true;
+			const PackedByteArray pba = v;
+			if (p_buffer) {
+				memcpy(p_buffer, pba.ptr(), pba.size());
+			}
+			r_len += pba.size();
+		} else {
+			multiplayer->encode_and_compress_variant(v, p_buffer, size);
+			r_len += size;
+		}
+		return OK;
+	}
+
+	// Regular encoding.
+	for (const Variant &v : p_variants) {
+		multiplayer->encode_and_compress_variant(v, p_buffer ? p_buffer + r_len : nullptr, size);
+		r_len += size;
+	}
+	return OK;
+}
+
+Error MultiplayerReplicator::_decode_state(const List<StringName> &p_properties, Object *p_obj, const uint8_t *p_buffer, int p_len, int &r_len, bool p_raw) {
+	r_len = 0;
+	int argc = p_properties.size();
+	if (argc == 0 && p_raw) {
+		ERR_FAIL_COND_V_MSG(p_len != 0, ERR_INVALID_DATA, "Buffer has trailing bytes.");
+		return OK;
+	}
+	ERR_FAIL_COND_V(p_raw && argc != 1, ERR_INVALID_DATA);
+	if (p_raw) {
+		r_len = p_len;
+		PackedByteArray pba;
+		pba.resize(p_len);
+		memcpy(pba.ptrw(), p_buffer, p_len);
+		p_obj->set(p_properties[0], pba);
+		return OK;
+	}
+
+	Vector<Variant> args;
+	Vector<const Variant *> argp;
+	args.resize(argc);
+
+	for (int i = 0; i < argc; i++) {
+		ERR_FAIL_COND_V_MSG(r_len >= p_len, ERR_INVALID_DATA, "Invalid packet received. Size too small.");
+
+		int vlen;
+		Error err = multiplayer->decode_and_decompress_variant(args.write[i], &p_buffer[r_len], p_len - r_len, &vlen);
+		ERR_FAIL_COND_V_MSG(err != OK, err, "Invalid packet received. Unable to decode state variable.");
+		r_len += vlen;
+	}
+	ERR_FAIL_COND_V_MSG(p_len - r_len != 0, ERR_INVALID_DATA, "Buffer has trailing bytes.");
+
+	int i = 0;
+	for (const StringName &prop : p_properties) {
+		p_obj->set(prop, args[i]);
+		i += 1;
+	}
+	return OK;
+}
+
+Error MultiplayerReplicator::spawn_config(const ResourceUID::ID &p_id, ReplicationMode p_mode, const TypedArray<StringName> &p_props, const Callable &p_on_send, const Callable &p_on_recv) {
+	ERR_FAIL_COND_V(p_mode < REPLICATION_MODE_NONE || p_mode > REPLICATION_MODE_CUSTOM, ERR_INVALID_PARAMETER);
+	ERR_FAIL_COND_V(!ResourceUID::get_singleton()->has_id(p_id), ERR_INVALID_PARAMETER);
+	ERR_FAIL_COND_V_MSG(p_on_send.is_valid() != p_on_recv.is_valid(), ERR_INVALID_PARAMETER, "Send and receive custom callables must be both valid or both empty");
+#ifdef TOOLS_ENABLED
+	if (!p_on_send.is_valid()) {
+		// We allow non scene spawning with custom callables.
+		String path = ResourceUID::get_singleton()->get_id_path(p_id);
+		RES res = ResourceLoader::load(path);
+		ERR_FAIL_COND_V(!res->is_class("PackedScene"), ERR_INVALID_PARAMETER);
+	}
+#endif
+	if (p_mode == REPLICATION_MODE_NONE) {
+		if (replications.has(p_id)) {
+			replications.erase(p_id);
+		}
+	} else {
+		SceneConfig cfg;
+		cfg.mode = p_mode;
+		for (int i = 0; i < p_props.size(); i++) {
+			cfg.properties.push_back(StringName(p_props[i]));
+		}
+		cfg.on_spawn_despawn_send = p_on_send;
+		cfg.on_spawn_despawn_receive = p_on_recv;
+		replications[p_id] = cfg;
+	}
+	return OK;
+}
+
+Error MultiplayerReplicator::_send_spawn_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data, bool p_spawn) {
+	int data_size = 0;
+	int is_raw = false;
+	if (p_data.get_type() == Variant::PACKED_BYTE_ARRAY) {
+		const PackedByteArray pba = p_data;
+		is_raw = true;
+		data_size = p_data.operator PackedByteArray().size();
+	} else if (p_data.get_type() == Variant::NIL) {
+		is_raw = true;
+	} else {
+		Error err = encode_variant(p_data, nullptr, data_size);
+		ERR_FAIL_COND_V(err, err);
+	}
+	MAKE_ROOM(SPAWN_CMD_OFFSET + data_size);
+	uint8_t *ptr = packet_cache.ptrw();
+	ptr[0] = (p_spawn ? MultiplayerAPI::NETWORK_COMMAND_SPAWN : MultiplayerAPI::NETWORK_COMMAND_DESPAWN) + ((is_raw ? 1 : 0) << MultiplayerAPI::BYTE_ONLY_OR_NO_ARGS_SHIFT);
+	encode_uint64(p_scene_id, &ptr[1]);
+	if (p_data.get_type() == Variant::PACKED_BYTE_ARRAY) {
+		const PackedByteArray pba = p_data;
+		memcpy(&ptr[SPAWN_CMD_OFFSET], pba.ptr(), pba.size());
+	} else if (data_size) {
+		encode_variant(p_data, &ptr[SPAWN_CMD_OFFSET], data_size);
+	}
+	Ref<MultiplayerPeer> network_peer = multiplayer->get_network_peer();
+	network_peer->set_target_peer(p_peer_id);
+	network_peer->set_transfer_channel(0);
+	network_peer->set_transfer_mode(MultiplayerPeer::TRANSFER_MODE_RELIABLE);
+	return network_peer->put_packet(ptr, SPAWN_CMD_OFFSET + data_size);
+}
+
+Error MultiplayerReplicator::send_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data, const NodePath &p_path) {
+	ERR_FAIL_COND_V_MSG(!replications.has(p_scene_id), ERR_INVALID_PARAMETER, vformat("Spawnable not found: %d", p_scene_id));
+	const SceneConfig &cfg = replications[p_scene_id];
+	if (cfg.on_spawn_despawn_send.is_valid()) {
+		return _send_spawn_despawn(p_peer_id, p_scene_id, p_data, true);
+	} else {
+		ERR_FAIL_COND_V_MSG(cfg.mode == REPLICATION_MODE_SERVER && multiplayer->is_network_server(), ERR_UNAVAILABLE, "Manual despawn is restricted in default server mode implementation. Use custom mode if you desire control over server spawn requests.");
+		NodePath path = p_path;
+		Object *obj = p_data.get_type() == Variant::OBJECT ? p_data.get_validated_object() : nullptr;
+		if (path.is_empty() && obj) {
+			Node *node = Object::cast_to<Node>(obj);
+			if (node && node->is_inside_tree()) {
+				path = node->get_path();
+			}
+		}
+		ERR_FAIL_COND_V_MSG(path.is_empty(), ERR_INVALID_PARAMETER, "Despawn default implementation requires a despawn path, or the data to be a node inside the SceneTree");
+		return _send_default_spawn_despawn(p_peer_id, p_scene_id, obj, path, false);
+	}
+}
+
+Error MultiplayerReplicator::send_spawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data, const NodePath &p_path) {
+	ERR_FAIL_COND_V_MSG(!replications.has(p_scene_id), ERR_INVALID_PARAMETER, vformat("Spawnable not found: %d", p_scene_id));
+	const SceneConfig &cfg = replications[p_scene_id];
+	if (cfg.on_spawn_despawn_send.is_valid()) {
+		return _send_spawn_despawn(p_peer_id, p_scene_id, p_data, false);
+	} else {
+		ERR_FAIL_COND_V_MSG(cfg.mode == REPLICATION_MODE_SERVER && multiplayer->is_network_server(), ERR_UNAVAILABLE, "Manual spawn is restricted in default server mode implementation. Use custom mode if you desire control over server spawn requests.");
+		NodePath path = p_path;
+		Object *obj = p_data.get_type() == Variant::OBJECT ? p_data.get_validated_object() : nullptr;
+		ERR_FAIL_COND_V_MSG(!obj, ERR_INVALID_PARAMETER, "Spawn default implementation requires the data to be an object.");
+		if (path.is_empty()) {
+			Node *node = Object::cast_to<Node>(obj);
+			if (node && node->is_inside_tree()) {
+				path = node->get_path();
+			}
+		}
+		ERR_FAIL_COND_V_MSG(path.is_empty(), ERR_INVALID_PARAMETER, "Spawn default implementation requires a spawn path, or the data to be a node inside the SceneTree");
+		return _send_default_spawn_despawn(p_peer_id, p_scene_id, obj, path, true);
+	}
+}
+
+Error MultiplayerReplicator::_spawn_despawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer, bool p_spawn) {
+	ERR_FAIL_COND_V_MSG(!replications.has(p_scene_id), ERR_INVALID_PARAMETER, vformat("Spawnable not found: %d", p_scene_id));
+
+	const SceneConfig &cfg = replications[p_scene_id];
+	if (cfg.on_spawn_despawn_send.is_valid()) {
+		Variant args[4];
+		args[0] = p_peer;
+		args[1] = p_scene_id;
+		args[2] = p_obj;
+		args[3] = true;
+		const Variant *argp[] = { &args[0], &args[1], &args[2], &args[3] };
+		Callable::CallError ce;
+		Variant ret;
+		cfg.on_spawn_despawn_send.call(argp, 4, ret, ce);
+		ERR_FAIL_COND_V_MSG(ce.error != Callable::CallError::CALL_OK, FAILED, "Custom send function failed");
+		return OK;
+	} else {
+		Node *node = Object::cast_to<Node>(p_obj);
+		ERR_FAIL_COND_V_MSG(!p_obj, ERR_INVALID_PARAMETER, "Only nodes can be replicated by the default implementation");
+		return _send_default_spawn_despawn(p_peer, p_scene_id, node, node->get_path(), p_spawn);
+	}
+}
+
+Error MultiplayerReplicator::spawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer) {
+	return _spawn_despawn(p_scene_id, p_obj, p_peer, true);
+}
+
+Error MultiplayerReplicator::despawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer) {
+	return _spawn_despawn(p_scene_id, p_obj, p_peer, false);
+}
+
+PackedByteArray MultiplayerReplicator::encode_state(const ResourceUID::ID &p_scene_id, const Object *p_obj) {
+	PackedByteArray state;
+	ERR_FAIL_COND_V_MSG(!replications.has(p_scene_id), state, vformat("Spawnable not found: %d", p_scene_id));
+	const SceneConfig &cfg = replications[p_scene_id];
+	int len = 0;
+	List<Variant> state_vars;
+	Error err = _get_state(cfg.properties, p_obj, state_vars);
+	ERR_FAIL_COND_V_MSG(err != OK, state, "Unable to retrieve object state.");
+	err = _encode_state(state_vars, nullptr, len);
+	ERR_FAIL_COND_V_MSG(err != OK, state, "Unable to encode object state.");
+	state.resize(len);
+	_encode_state(state_vars, state.ptrw(), len);
+	return state;
+}
+
+Error MultiplayerReplicator::decode_state(const ResourceUID::ID &p_scene_id, Object *p_obj, const PackedByteArray p_data) {
+	ERR_FAIL_COND_V_MSG(!replications.has(p_scene_id), ERR_INVALID_PARAMETER, vformat("Spawnable not found: %d", p_scene_id));
+	const SceneConfig &cfg = replications[p_scene_id];
+	int size;
+	return _decode_state(cfg.properties, p_obj, p_data.ptr(), p_data.size(), size);
+}
+
+void MultiplayerReplicator::scene_enter_exit_notify(const String &p_scene, Node *p_node, bool p_enter) {
+	if (!multiplayer->has_network_peer()) {
+		return;
+	}
+	Node *root_node = multiplayer->get_root_node();
+	ERR_FAIL_COND(!p_node || !p_node->get_parent() || !root_node);
+	NodePath path = (root_node->get_path()).rel_path_to(p_node->get_parent()->get_path());
+	if (path.is_empty()) {
+		return;
+	}
+	ResourceUID::ID id = ResourceLoader::get_resource_uid(p_scene);
+	if (!replications.has(id)) {
+		return;
+	}
+	const SceneConfig &cfg = replications[id];
+	if (p_enter) {
+		if (cfg.mode == REPLICATION_MODE_SERVER && multiplayer->is_network_server()) {
+			replicated_nodes[p_node->get_instance_id()] = id;
+			spawn(id, p_node, 0);
+		}
+		emit_signal(SNAME("replicated_instance_added"), id, p_node);
+	} else {
+		if (cfg.mode == REPLICATION_MODE_SERVER && multiplayer->is_network_server() && replicated_nodes.has(p_node->get_instance_id())) {
+			replicated_nodes.erase(p_node->get_instance_id());
+			despawn(id, p_node, 0);
+		}
+		emit_signal(SNAME("replicated_instance_removed"), id, p_node);
+	}
+}
+
+void MultiplayerReplicator::spawn_all(int p_peer) {
+	for (const KeyValue<ObjectID, ResourceUID::ID> &E : replicated_nodes) {
+		// Only server mode adds to replicated_nodes, no need to check it.
+		Object *obj = ObjectDB::get_instance(E.key);
+		ERR_CONTINUE(!obj);
+		Node *node = Object::cast_to<Node>(obj);
+		ERR_CONTINUE(!node);
+		spawn(E.value, node, p_peer);
+	}
+}
+
+void MultiplayerReplicator::clear() {
+	replicated_nodes.clear();
+}
+
+void MultiplayerReplicator::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("spawn_config", "scene_id", "spawn_mode", "properties", "custom_send", "custom_receive"), &MultiplayerReplicator::spawn_config, DEFVAL(TypedArray<StringName>()), DEFVAL(Callable()), DEFVAL(Callable()));
+	ClassDB::bind_method(D_METHOD("despawn", "scene_id", "object", "peer_id"), &MultiplayerReplicator::despawn, DEFVAL(0));
+	ClassDB::bind_method(D_METHOD("spawn", "scene_id", "object", "peer_id"), &MultiplayerReplicator::spawn, DEFVAL(0));
+	ClassDB::bind_method(D_METHOD("send_despawn", "peer_id", "scene_id", "data", "path"), &MultiplayerReplicator::send_despawn, DEFVAL(Variant()), DEFVAL(NodePath()));
+	ClassDB::bind_method(D_METHOD("send_spawn", "peer_id", "scene_id", "data", "path"), &MultiplayerReplicator::send_spawn, DEFVAL(Variant()), DEFVAL(NodePath()));
+	ClassDB::bind_method(D_METHOD("encode_state", "scene_id", "object"), &MultiplayerReplicator::encode_state);
+	ClassDB::bind_method(D_METHOD("decode_state", "scene_id", "object", "data"), &MultiplayerReplicator::decode_state);
+
+	ADD_SIGNAL(MethodInfo("despawned", PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node")));
+	ADD_SIGNAL(MethodInfo("spawned", PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node")));
+	ADD_SIGNAL(MethodInfo("despawn_requested", PropertyInfo(Variant::INT, "id"), PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "parent", PROPERTY_HINT_RESOURCE_TYPE, "Node"), PropertyInfo(Variant::STRING, "name"), PropertyInfo(Variant::PACKED_BYTE_ARRAY, "data")));
+	ADD_SIGNAL(MethodInfo("spawn_requested", PropertyInfo(Variant::INT, "id"), PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "parent", PROPERTY_HINT_RESOURCE_TYPE, "Node"), PropertyInfo(Variant::STRING, "name"), PropertyInfo(Variant::PACKED_BYTE_ARRAY, "data")));
+	ADD_SIGNAL(MethodInfo("replicated_instance_added", PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node")));
+	ADD_SIGNAL(MethodInfo("replicated_instance_removed", PropertyInfo(Variant::INT, "scene_id"), PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node")));
+
+	BIND_ENUM_CONSTANT(REPLICATION_MODE_NONE);
+	BIND_ENUM_CONSTANT(REPLICATION_MODE_SERVER);
+	BIND_ENUM_CONSTANT(REPLICATION_MODE_CUSTOM);
+}
diff --git a/core/io/multiplayer_replicator.h b/core/io/multiplayer_replicator.h
new file mode 100644
index 0000000000..e19dd80602
--- /dev/null
+++ b/core/io/multiplayer_replicator.h
@@ -0,0 +1,99 @@
+/*************************************************************************/
+/*  multiplayer_replicator.h                                             */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef MULTIPLAYER_REPLICATOR_H
+#define MULTIPLAYER_REPLICATOR_H
+
+#include "core/io/multiplayer_api.h"
+#include "core/variant/typed_array.h"
+
+class MultiplayerReplicator : public Object {
+	GDCLASS(MultiplayerReplicator, Object);
+
+public:
+	enum {
+		SPAWN_CMD_OFFSET = 9,
+	};
+
+	enum ReplicationMode {
+		REPLICATION_MODE_NONE,
+		REPLICATION_MODE_SERVER,
+		REPLICATION_MODE_CUSTOM,
+	};
+
+	struct SceneConfig {
+		ReplicationMode mode;
+		List<StringName> properties;
+		Callable on_spawn_despawn_send;
+		Callable on_spawn_despawn_receive;
+	};
+
+protected:
+	static void _bind_methods();
+
+private:
+	MultiplayerAPI *multiplayer = nullptr;
+	Vector<uint8_t> packet_cache;
+	Map<ResourceUID::ID, SceneConfig> replications;
+	Map<ObjectID, ResourceUID::ID> replicated_nodes;
+
+	Error _encode_state(const List<Variant> &p_variants, uint8_t *p_buffer, int &r_len, bool *r_raw = nullptr);
+	Error _decode_state(const List<StringName> &p_cfg, Object *p_obj, const uint8_t *p_buffer, int p_len, int &r_len, bool p_raw = false);
+	Error _get_state(const List<StringName> &p_properties, const Object *p_obj, List<Variant> &r_variant);
+	Error _spawn_despawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer, bool p_spawn);
+	Error _send_spawn_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data, bool p_spawn);
+	void _process_default_spawn_despawn(int p_from, const ResourceUID::ID &p_scene_id, const uint8_t *p_packet, int p_packet_len, bool p_spawn);
+	Error _send_default_spawn_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, Object *p_obj, const NodePath &p_path, bool p_spawn);
+
+public:
+	void clear();
+
+	Error spawn_config(const ResourceUID::ID &p_id, ReplicationMode p_mode, const TypedArray<StringName> &p_props = TypedArray<StringName>(), const Callable &p_on_send = Callable(), const Callable &p_on_recv = Callable());
+	Error spawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer = 0);
+	Error despawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer = 0);
+
+	Error send_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data = Variant(), const NodePath &p_path = NodePath());
+	Error send_spawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data = Variant(), const NodePath &p_path = NodePath());
+	PackedByteArray encode_state(const ResourceUID::ID &p_scene_id, const Object *p_node);
+	Error decode_state(const ResourceUID::ID &p_scene_id, Object *p_node, PackedByteArray p_data);
+
+	// Used by MultiplayerAPI
+	void spawn_all(int p_peer);
+	void process_spawn_despawn(int p_from, const uint8_t *p_packet, int p_packet_len, bool p_spawn);
+	void scene_enter_exit_notify(const String &p_scene, Node *p_node, bool p_enter);
+
+	MultiplayerReplicator(MultiplayerAPI *p_multiplayer) {
+		multiplayer = p_multiplayer;
+	}
+};
+
+VARIANT_ENUM_CAST(MultiplayerReplicator::ReplicationMode);
+
+#endif // MULTIPLAYER_REPLICATOR_H
diff --git a/core/register_core_types.cpp b/core/register_core_types.cpp
index f801be3db3..4fabd1551e 100644
--- a/core/register_core_types.cpp
+++ b/core/register_core_types.cpp
@@ -49,6 +49,7 @@
 #include "core/io/marshalls.h"
 #include "core/io/multiplayer_api.h"
 #include "core/io/multiplayer_peer.h"
+#include "core/io/multiplayer_replicator.h"
 #include "core/io/packed_data_container.h"
 #include "core/io/packet_peer.h"
 #include "core/io/packet_peer_dtls.h"
@@ -193,6 +194,7 @@ void register_core_types() {
 	ResourceLoader::add_resource_format_loader(resource_format_loader_crypto);
 
 	GDREGISTER_VIRTUAL_CLASS(MultiplayerPeer);
+	GDREGISTER_VIRTUAL_CLASS(MultiplayerReplicator);
 	GDREGISTER_CLASS(MultiplayerAPI);
 	GDREGISTER_CLASS(MainLoop);
 	GDREGISTER_CLASS(Translation);