[Net] Modularize multiplayer, expose MultiplayerAPI to extensions.

- RPC configurations are now dictionaries.
- Script.get_rpc_methods renamed to Script.get_rpc_config.
- Node.rpc[_id] and Callable.rpc now return an Error.
- Refactor MultiplayerAPI to allow extension.
- New MultiplayerAPI.rpc method with Array argument (for scripts).
- Move the default MultiplayerAPI implementation to a module.

12 files changed, 47 insertions, 66 deletions

diff --git a/modules/gdscript/gdscript.cpp b/modules/gdscript/gdscript.cpp
index a34bf6ef82..0216a710d7 100644
--- a/modules/gdscript/gdscript.cpp
+++ b/modules/gdscript/gdscript.cpp
@@ -954,8 +954,8 @@ void GDScript::get_members(HashSet<StringName> *p_members) {
 	}
 }
 
-const Vector<Multiplayer::RPCConfig> GDScript::get_rpc_methods() const {
-	return rpc_functions;
+const Variant GDScript::get_rpc_config() const {
+	return rpc_config;
 }
 
 Variant GDScript::callp(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error) {
@@ -1212,9 +1212,9 @@ void GDScript::_save_orphaned_subclasses() {
 
 void GDScript::_init_rpc_methods_properties() {
 	// Copy the base rpc methods so we don't mask their IDs.
-	rpc_functions.clear();
+	rpc_config.clear();
 	if (base.is_valid()) {
-		rpc_functions = base->rpc_functions;
+		rpc_config = base->rpc_config.duplicate();
 	}
 
 	GDScript *cscript = this;
@@ -1222,12 +1222,9 @@ void GDScript::_init_rpc_methods_properties() {
 	while (cscript) {
 		// RPC Methods
 		for (KeyValue<StringName, GDScriptFunction *> &E : cscript->member_functions) {
-			Multiplayer::RPCConfig config = E.value->get_rpc_config();
-			if (config.rpc_mode != Multiplayer::RPC_MODE_DISABLED) {
-				config.name = E.value->get_name();
-				if (rpc_functions.find(config) == -1) {
-					rpc_functions.push_back(config);
-				}
+			Variant config = E.value->get_rpc_config();
+			if (config.get_type() != Variant::NIL) {
+				rpc_config[E.value->get_name()] = config;
 			}
 		}
 
@@ -1241,9 +1238,6 @@ void GDScript::_init_rpc_methods_properties() {
 			cscript = nullptr;
 		}
 	}
-
-	// Sort so we are 100% that they are always the same.
-	rpc_functions.sort_custom<Multiplayer::SortRPCConfig>();
 }
 
 GDScript::~GDScript() {
@@ -1408,9 +1402,7 @@ bool GDScriptInstance::get(const StringName &p_name, Variant &r_ret) const {
 			while (sl) {
 				HashMap<StringName, GDScriptFunction *>::ConstIterator E = sl->member_functions.find(p_name);
 				if (E) {
-					Multiplayer::RPCConfig config;
-					config.name = p_name;
-					if (sptr->rpc_functions.find(config) != -1) {
+					if (sptr->rpc_config.has(p_name)) {
 						r_ret = Callable(memnew(GDScriptRPCCallable(this->owner, E->key)));
 					} else {
 						r_ret = Callable(this->owner, E->key);
@@ -1629,8 +1621,8 @@ ScriptLanguage *GDScriptInstance::get_language() {
 	return GDScriptLanguage::get_singleton();
 }
 
-const Vector<Multiplayer::RPCConfig> GDScriptInstance::get_rpc_methods() const {
-	return script->get_rpc_methods();
+const Variant GDScriptInstance::get_rpc_config() const {
+	return script->get_rpc_config();
 }
 
 void GDScriptInstance::reload_members() {
diff --git a/modules/gdscript/gdscript.h b/modules/gdscript/gdscript.h
index e9a206f48b..47de3ad088 100644
--- a/modules/gdscript/gdscript.h
+++ b/modules/gdscript/gdscript.h
@@ -87,7 +87,7 @@ class GDScript : public Script {
 	HashMap<StringName, MemberInfo> member_indices; //members are just indices to the instantiated script.
 	HashMap<StringName, Ref<GDScript>> subclasses;
 	HashMap<StringName, Vector<StringName>> _signals;
-	Vector<Multiplayer::RPCConfig> rpc_functions;
+	Dictionary rpc_config;
 
 #ifdef TOOLS_ENABLED
 
@@ -250,7 +250,7 @@ public:
 	virtual void get_constants(HashMap<StringName, Variant> *p_constants) override;
 	virtual void get_members(HashSet<StringName> *p_members) override;
 
-	virtual const Vector<Multiplayer::RPCConfig> get_rpc_methods() const override;
+	virtual const Variant get_rpc_config() const override;
 
 #ifdef TOOLS_ENABLED
 	virtual bool is_placeholder_fallback_enabled() const override { return placeholder_fallback_enabled; }
@@ -304,7 +304,7 @@ public:
 
 	void reload_members();
 
-	virtual const Vector<Multiplayer::RPCConfig> get_rpc_methods() const;
+	virtual const Variant get_rpc_config() const;
 
 	GDScriptInstance();
 	~GDScriptInstance();
diff --git a/modules/gdscript/gdscript_byte_codegen.cpp b/modules/gdscript/gdscript_byte_codegen.cpp
index a1a28e7675..2c9150abde 100644
--- a/modules/gdscript/gdscript_byte_codegen.cpp
+++ b/modules/gdscript/gdscript_byte_codegen.cpp
@@ -158,7 +158,7 @@ void GDScriptByteCodeGenerator::end_parameters() {
 	function->default_arguments.reverse();
 }
 
-void GDScriptByteCodeGenerator::write_start(GDScript *p_script, const StringName &p_function_name, bool p_static, Multiplayer::RPCConfig p_rpc_config, const GDScriptDataType &p_return_type) {
+void GDScriptByteCodeGenerator::write_start(GDScript *p_script, const StringName &p_function_name, bool p_static, Variant p_rpc_config, const GDScriptDataType &p_return_type) {
 	function = memnew(GDScriptFunction);
 	debug_stack = EngineDebugger::is_active();
 
diff --git a/modules/gdscript/gdscript_byte_codegen.h b/modules/gdscript/gdscript_byte_codegen.h
index ffc3178c83..7dd51845df 100644
--- a/modules/gdscript/gdscript_byte_codegen.h
+++ b/modules/gdscript/gdscript_byte_codegen.h
@@ -419,7 +419,7 @@ public:
 	virtual void start_block() override;
 	virtual void end_block() override;
 
-	virtual void write_start(GDScript *p_script, const StringName &p_function_name, bool p_static, Multiplayer::RPCConfig p_rpc_config, const GDScriptDataType &p_return_type) override;
+	virtual void write_start(GDScript *p_script, const StringName &p_function_name, bool p_static, Variant p_rpc_config, const GDScriptDataType &p_return_type) override;
 	virtual GDScriptFunction *write_end() override;
 
 #ifdef DEBUG_ENABLED
diff --git a/modules/gdscript/gdscript_codegen.h b/modules/gdscript/gdscript_codegen.h
index 7b5f133ec5..5972481c3a 100644
--- a/modules/gdscript/gdscript_codegen.h
+++ b/modules/gdscript/gdscript_codegen.h
@@ -31,7 +31,6 @@
 #ifndef GDSCRIPT_CODEGEN_H
 #define GDSCRIPT_CODEGEN_H
 
-#include "core/multiplayer/multiplayer.h"
 #include "core/string/string_name.h"
 #include "core/variant/variant.h"
 #include "gdscript_function.h"
@@ -80,7 +79,7 @@ public:
 	virtual void start_block() = 0;
 	virtual void end_block() = 0;
 
-	virtual void write_start(GDScript *p_script, const StringName &p_function_name, bool p_static, Multiplayer::RPCConfig p_rpc_config, const GDScriptDataType &p_return_type) = 0;
+	virtual void write_start(GDScript *p_script, const StringName &p_function_name, bool p_static, Variant p_rpc_config, const GDScriptDataType &p_return_type) = 0;
 	virtual GDScriptFunction *write_end() = 0;
 
 #ifdef DEBUG_ENABLED
diff --git a/modules/gdscript/gdscript_compiler.cpp b/modules/gdscript/gdscript_compiler.cpp
index e36252ada5..00e8223b9a 100644
--- a/modules/gdscript/gdscript_compiler.cpp
+++ b/modules/gdscript/gdscript_compiler.cpp
@@ -1975,7 +1975,7 @@ GDScriptFunction *GDScriptCompiler::_parse_function(Error &r_error, GDScript *p_
 
 	StringName func_name;
 	bool is_static = false;
-	Multiplayer::RPCConfig rpc_config;
+	Variant rpc_config;
 	GDScriptDataType return_type;
 	return_type.has_type = true;
 	return_type.kind = GDScriptDataType::BUILTIN;
diff --git a/modules/gdscript/gdscript_function.h b/modules/gdscript/gdscript_function.h
index 53c75648a0..e44038d6da 100644
--- a/modules/gdscript/gdscript_function.h
+++ b/modules/gdscript/gdscript_function.h
@@ -477,7 +477,7 @@ private:
 
 	int _initial_line = 0;
 	bool _static = false;
-	Multiplayer::RPCConfig rpc_config;
+	Variant rpc_config;
 
 	GDScript *_script = nullptr;
 
@@ -599,7 +599,7 @@ public:
 	void disassemble(const Vector<String> &p_code_lines) const;
 #endif
 
-	_FORCE_INLINE_ Multiplayer::RPCConfig get_rpc_config() const { return rpc_config; }
+	_FORCE_INLINE_ const Variant get_rpc_config() const { return rpc_config; }
 	GDScriptFunction();
 	~GDScriptFunction();
 };
diff --git a/modules/gdscript/gdscript_parser.cpp b/modules/gdscript/gdscript_parser.cpp
index e8fa2981ba..6f5397e1a3 100644
--- a/modules/gdscript/gdscript_parser.cpp
+++ b/modules/gdscript/gdscript_parser.cpp
@@ -35,6 +35,7 @@
 #include "core/io/resource_loader.h"
 #include "core/math/math_defs.h"
 #include "gdscript.h"
+#include "scene/main/multiplayer_api.h"
 
 #ifdef DEBUG_ENABLED
 #include "core/os/os.h"
@@ -145,7 +146,7 @@ GDScriptParser::GDScriptParser() {
 	// Warning annotations.
 	register_annotation(MethodInfo("@warning_ignore", PropertyInfo(Variant::STRING, "warning")), AnnotationInfo::CLASS | AnnotationInfo::VARIABLE | AnnotationInfo::SIGNAL | AnnotationInfo::CONSTANT | AnnotationInfo::FUNCTION | AnnotationInfo::STATEMENT, &GDScriptParser::warning_annotations, varray(), true);
 	// Networking.
-	register_annotation(MethodInfo("@rpc", PropertyInfo(Variant::STRING, "mode"), PropertyInfo(Variant::STRING, "sync"), PropertyInfo(Variant::STRING, "transfer_mode"), PropertyInfo(Variant::INT, "transfer_channel")), AnnotationInfo::FUNCTION, &GDScriptParser::network_annotations<Multiplayer::RPC_MODE_AUTHORITY>, varray("", "", "", 0), true);
+	register_annotation(MethodInfo("@rpc", PropertyInfo(Variant::STRING, "mode"), PropertyInfo(Variant::STRING, "sync"), PropertyInfo(Variant::STRING, "transfer_mode"), PropertyInfo(Variant::INT, "transfer_channel")), AnnotationInfo::FUNCTION, &GDScriptParser::rpc_annotation, varray("", "", "", 0), true);
 }
 
 GDScriptParser::~GDScriptParser() {
@@ -3867,16 +3868,21 @@ bool GDScriptParser::warning_annotations(const AnnotationNode *p_annotation, Nod
 #endif // DEBUG_ENABLED
 }
 
-template <Multiplayer::RPCMode t_mode>
-bool GDScriptParser::network_annotations(const AnnotationNode *p_annotation, Node *p_node) {
-	ERR_FAIL_COND_V_MSG(p_node->type != Node::VARIABLE && p_node->type != Node::FUNCTION, false, vformat(R"("%s" annotation can only be applied to variables and functions.)", p_annotation->name));
+bool GDScriptParser::rpc_annotation(const AnnotationNode *p_annotation, Node *p_node) {
+	ERR_FAIL_COND_V_MSG(p_node->type != Node::FUNCTION, false, vformat(R"("%s" annotation can only be applied to functions.)", p_annotation->name));
 
-	Multiplayer::RPCConfig rpc_config;
-	rpc_config.rpc_mode = t_mode;
+	FunctionNode *function = static_cast<FunctionNode *>(p_node);
+	if (function->rpc_config.get_type() != Variant::NIL) {
+		push_error(R"(RPC annotations can only be used once per function.)", p_annotation);
+		return false;
+	}
+
+	Dictionary rpc_config;
+	rpc_config["rpc_mode"] = MultiplayerAPI::RPC_MODE_AUTHORITY;
 	if (p_annotation->resolved_arguments.size()) {
 		int last = p_annotation->resolved_arguments.size() - 1;
 		if (p_annotation->resolved_arguments[last].get_type() == Variant::INT) {
-			rpc_config.channel = p_annotation->resolved_arguments[last].operator int();
+			rpc_config["channel"] = p_annotation->resolved_arguments[last].operator int();
 			last -= 1;
 		}
 		if (last > 3) {
@@ -3886,37 +3892,25 @@ bool GDScriptParser::network_annotations(const AnnotationNode *p_annotation, Nod
 		for (int i = last; i >= 0; i--) {
 			String mode = p_annotation->resolved_arguments[i].operator String();
 			if (mode == "any_peer") {
-				rpc_config.rpc_mode = Multiplayer::RPC_MODE_ANY_PEER;
+				rpc_config["rpc_mode"] = MultiplayerAPI::RPC_MODE_ANY_PEER;
 			} else if (mode == "authority") {
-				rpc_config.rpc_mode = Multiplayer::RPC_MODE_AUTHORITY;
+				rpc_config["rpc_mode"] = MultiplayerAPI::RPC_MODE_AUTHORITY;
 			} else if (mode == "call_local") {
-				rpc_config.call_local = true;
+				rpc_config["call_local"] = true;
 			} else if (mode == "call_remote") {
-				rpc_config.call_local = false;
+				rpc_config["call_local"] = false;
 			} else if (mode == "reliable") {
-				rpc_config.transfer_mode = Multiplayer::TRANSFER_MODE_RELIABLE;
+				rpc_config["transfer_mode"] = MultiplayerPeer::TRANSFER_MODE_RELIABLE;
 			} else if (mode == "unreliable") {
-				rpc_config.transfer_mode = Multiplayer::TRANSFER_MODE_UNRELIABLE;
+				rpc_config["transfer_mode"] = MultiplayerPeer::TRANSFER_MODE_UNRELIABLE;
 			} else if (mode == "unreliable_ordered") {
-				rpc_config.transfer_mode = Multiplayer::TRANSFER_MODE_UNRELIABLE_ORDERED;
+				rpc_config["transfer_mode"] = MultiplayerPeer::TRANSFER_MODE_UNRELIABLE_ORDERED;
 			} else {
 				push_error(R"(Invalid RPC argument. Must be one of: 'call_local'/'call_remote' (local calls), 'any_peer'/'authority' (permission), 'reliable'/'unreliable'/'unreliable_ordered' (transfer mode).)", p_annotation);
 			}
 		}
 	}
-	switch (p_node->type) {
-		case Node::FUNCTION: {
-			FunctionNode *function = static_cast<FunctionNode *>(p_node);
-			if (function->rpc_config.rpc_mode != Multiplayer::RPC_MODE_DISABLED) {
-				push_error(R"(RPC annotations can only be used once per function.)", p_annotation);
-				return false;
-			}
-			function->rpc_config = rpc_config;
-			break;
-		}
-		default:
-			return false; // Unreachable.
-	}
+	function->rpc_config = rpc_config;
 	return true;
 }
 
diff --git a/modules/gdscript/gdscript_parser.h b/modules/gdscript/gdscript_parser.h
index 9c97f98fbc..d4efab173b 100644
--- a/modules/gdscript/gdscript_parser.h
+++ b/modules/gdscript/gdscript_parser.h
@@ -32,7 +32,6 @@
 #define GDSCRIPT_PARSER_H
 
 #include "core/io/resource.h"
-#include "core/multiplayer/multiplayer.h"
 #include "core/object/ref_counted.h"
 #include "core/object/script_language.h"
 #include "core/string/string_name.h"
@@ -750,7 +749,7 @@ public:
 		SuiteNode *body = nullptr;
 		bool is_static = false;
 		bool is_coroutine = false;
-		Multiplayer::RPCConfig rpc_config;
+		Variant rpc_config;
 		MethodInfo info;
 		LambdaNode *source_lambda = nullptr;
 #ifdef TOOLS_ENABLED
@@ -1371,8 +1370,7 @@ private:
 	template <PropertyUsageFlags t_usage>
 	bool export_group_annotations(const AnnotationNode *p_annotation, Node *p_target);
 	bool warning_annotations(const AnnotationNode *p_annotation, Node *p_target);
-	template <Multiplayer::RPCMode t_mode>
-	bool network_annotations(const AnnotationNode *p_annotation, Node *p_target);
+	bool rpc_annotation(const AnnotationNode *p_annotation, Node *p_target);
 	// Statements.
 	Node *parse_statement();
 	VariableNode *parse_variable();
diff --git a/modules/gdscript/gdscript_rpc_callable.cpp b/modules/gdscript/gdscript_rpc_callable.cpp
index 63ebd8acf5..4e12419357 100644
--- a/modules/gdscript/gdscript_rpc_callable.cpp
+++ b/modules/gdscript/gdscript_rpc_callable.cpp
@@ -76,11 +76,11 @@ GDScriptRPCCallable::GDScriptRPCCallable(Object *p_object, const StringName &p_m
 	ERR_FAIL_COND_MSG(!node, "RPC can only be defined on class that extends Node.");
 }
 
-void GDScriptRPCCallable::rpc(int p_peer_id, const Variant **p_arguments, int p_argcount, Callable::CallError &r_call_error) const {
+Error GDScriptRPCCallable::rpc(int p_peer_id, const Variant **p_arguments, int p_argcount, Callable::CallError &r_call_error) const {
 	if (unlikely(!node)) {
 		r_call_error.error = Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL;
-		return;
+		return ERR_UNCONFIGURED;
 	}
 	r_call_error.error = Callable::CallError::CALL_OK;
-	node->rpcp(p_peer_id, method, p_arguments, p_argcount);
+	return node->rpcp(p_peer_id, method, p_arguments, p_argcount);
 }
diff --git a/modules/gdscript/gdscript_rpc_callable.h b/modules/gdscript/gdscript_rpc_callable.h
index c8a91d6259..83b9c7e2df 100644
--- a/modules/gdscript/gdscript_rpc_callable.h
+++ b/modules/gdscript/gdscript_rpc_callable.h
@@ -52,7 +52,7 @@ public:
 	CompareLessFunc get_compare_less_func() const override;
 	ObjectID get_object() const override;
 	void call(const Variant **p_arguments, int p_argcount, Variant &r_return_value, Callable::CallError &r_call_error) const override;
-	void rpc(int p_peer_id, const Variant **p_arguments, int p_argcount, Callable::CallError &r_call_error) const override;
+	Error rpc(int p_peer_id, const Variant **p_arguments, int p_argcount, Callable::CallError &r_call_error) const override;
 
 	GDScriptRPCCallable(Object *p_object, const StringName &p_method);
 	virtual ~GDScriptRPCCallable() = default;
diff --git a/modules/gdscript/language_server/gdscript_extend_parser.cpp b/modules/gdscript/language_server/gdscript_extend_parser.cpp
index 03e93821c7..46a9b33eb0 100644
--- a/modules/gdscript/language_server/gdscript_extend_parser.cpp
+++ b/modules/gdscript/language_server/gdscript_extend_parser.cpp
@@ -690,9 +690,7 @@ Dictionary ExtendGDScriptParser::dump_function_api(const GDScriptParser::Functio
 	ERR_FAIL_NULL_V(p_func, func);
 	func["name"] = p_func->identifier->name;
 	func["return_type"] = p_func->get_datatype().to_string();
-	func["rpc_mode"] = p_func->rpc_config.rpc_mode;
-	func["rpc_transfer_mode"] = p_func->rpc_config.transfer_mode;
-	func["rpc_transfer_channel"] = p_func->rpc_config.channel;
+	func["rpc_config"] = p_func->rpc_config;
 	Array parameters;
 	for (int i = 0; i < p_func->parameters.size(); i++) {
 		Dictionary arg;