[MP] New default multiplayer_peer acting as server.

Adds a OfflineMultiplayerPeer class which behaves like a server with no
connected peers.

Use OfflineMultiplayerPeer as default for SceneMultiplayer.

This means that the SceneTree will act as the multiplayer authority by
default.
Calls to is_server will return true, and calls to get_unique_id will
return TARGET_PEER_SERVER.

4 files changed, 39 insertions, 0 deletions

diff --git a/doc/classes/OfflineMultiplayerPeer.xml b/doc/classes/OfflineMultiplayerPeer.xml
new file mode 100644
index 0000000000..5e15992d54
--- /dev/null
+++ b/doc/classes/OfflineMultiplayerPeer.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="OfflineMultiplayerPeer" inherits="MultiplayerPeer" version="4.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+	<brief_description>
+		A [MultiplayerPeer] which is always connected and acts as a server.
+	</brief_description>
+	<description>
+		This is the default [member MultiplayerAPI.multiplayer_peer] for the [member Node.multiplayer]. It mimics the behavior of a server with no peers connected.
+		This means that the [SceneTree] will act as the multiplayer authority by default. Calls to [method MultiplayerAPI.is_server] will return [code]true[/code], and calls to [method MultiplayerAPI.get_unique_id] will return [constant MultiplayerPeer.TARGET_PEER_SERVER].
+	</description>
+	<tutorials>
+	</tutorials>
+</class>
diff --git a/modules/multiplayer/register_types.cpp b/modules/multiplayer/register_types.cpp
index 2bf1041029..ca85a46f31 100644
--- a/modules/multiplayer/register_types.cpp
+++ b/modules/multiplayer/register_types.cpp
@@ -47,6 +47,7 @@ void initialize_multiplayer_module(ModuleInitializationLevel p_level) {
 		GDREGISTER_CLASS(SceneReplicationConfig);
 		GDREGISTER_CLASS(MultiplayerSpawner);
 		GDREGISTER_CLASS(MultiplayerSynchronizer);
+		GDREGISTER_CLASS(OfflineMultiplayerPeer);
 		GDREGISTER_CLASS(SceneMultiplayer);
 		MultiplayerAPI::set_default_interface("SceneMultiplayer");
 		MultiplayerDebugger::initialize();
diff --git a/modules/multiplayer/scene_multiplayer.cpp b/modules/multiplayer/scene_multiplayer.cpp
index e0a21fca9a..5042a0502d 100644
--- a/modules/multiplayer/scene_multiplayer.cpp
+++ b/modules/multiplayer/scene_multiplayer.cpp
@@ -661,6 +661,7 @@ SceneMultiplayer::SceneMultiplayer() {
 	replicator = Ref<SceneReplicationInterface>(memnew(SceneReplicationInterface(this)));
 	rpc = Ref<SceneRPCInterface>(memnew(SceneRPCInterface(this)));
 	cache = Ref<SceneCacheInterface>(memnew(SceneCacheInterface(this)));
+	set_multiplayer_peer(Ref<OfflineMultiplayerPeer>(memnew(OfflineMultiplayerPeer)));
 }
 
 SceneMultiplayer::~SceneMultiplayer() {
diff --git a/modules/multiplayer/scene_multiplayer.h b/modules/multiplayer/scene_multiplayer.h
index da8c762134..10b04de346 100644
--- a/modules/multiplayer/scene_multiplayer.h
+++ b/modules/multiplayer/scene_multiplayer.h
@@ -37,6 +37,31 @@
 #include "scene_replication_interface.h"
 #include "scene_rpc_interface.h"
 
+class OfflineMultiplayerPeer : public MultiplayerPeer {
+	GDCLASS(OfflineMultiplayerPeer, MultiplayerPeer);
+
+public:
+	virtual int get_available_packet_count() const override { return 0; }
+	virtual Error get_packet(const uint8_t **r_buffer, int &r_buffer_size) override {
+		*r_buffer = nullptr;
+		r_buffer_size = 0;
+		return OK;
+	}
+	virtual Error put_packet(const uint8_t *p_buffer, int p_buffer_size) override { return OK; }
+	virtual int get_max_packet_size() const override { return 0; }
+
+	virtual void set_target_peer(int p_peer_id) override {}
+	virtual int get_packet_peer() const override { return 0; }
+	virtual TransferMode get_packet_mode() const override { return TRANSFER_MODE_RELIABLE; };
+	virtual int get_packet_channel() const override { return 0; }
+	virtual void disconnect_peer(int p_peer, bool p_force = false) override {}
+	virtual bool is_server() const override { return true; }
+	virtual void poll() override {}
+	virtual void close() override {}
+	virtual int get_unique_id() const override { return TARGET_PEER_SERVER; }
+	virtual ConnectionStatus get_connection_status() const override { return CONNECTION_CONNECTED; };
+};
+
 class SceneMultiplayer : public MultiplayerAPI {
 	GDCLASS(SceneMultiplayer, MultiplayerAPI);