Add persistent unique identifiers for objects (#14135)

src/server/luaentity_sao.cpp

@@ -50,7 +50,14 @@ LuaEntitySAO::LuaEntitySAO(ServerEnvironment *env, v3f pos, const std::string &d
 		rotation.X = readF1000(is);
 		rotation.Z = readF1000(is);
 
-		// if (version2 < 2)
+		if (version2 < 2) {
+			m_guid = env->getGUIDGenerator().next();
+			break;
+		}
+
+		m_guid.deSerialize(is);
+
+		// if (version2 < 3)
 		//     break;
 		// <read new values>
 		break;
@@ -70,6 +77,14 @@ LuaEntitySAO::LuaEntitySAO(ServerEnvironment *env, v3f pos, const std::string &d
 	m_rotation = rotation;
 }
 
+LuaEntitySAO::LuaEntitySAO(ServerEnvironment *env, v3f pos, const std::string &name,
+		const std::string &state) :
+		UnitSAO(env, pos),
+		m_init_name(name), m_init_state(state),
+		m_guid(env->getGUIDGenerator().next())
+{
+}
+
 LuaEntitySAO::~LuaEntitySAO()
 {
 	if(m_registered){
@@ -294,11 +309,13 @@ void LuaEntitySAO::getStaticData(std::string *result) const
 	writeF1000(os, m_rotation.Y);
 
 	// version2. Increase this variable for new values
-	writeU8(os, 1); // PROTOCOL_VERSION >= 37
+	writeU8(os, 2);
 
 	writeF1000(os, m_rotation.X);
 	writeF1000(os, m_rotation.Z);
 
+	m_guid.serialize(os);
+
 	// <write new values>
 
 	*result = os.str();
@@ -414,6 +431,13 @@ u16 LuaEntitySAO::getHP() const
 	return m_hp;
 }
 
+std::string LuaEntitySAO::getGUID() const
+{
+	// The "@" ensures that entity GUIDs are easily recognizable
+	// and makes it obvious that they can't collide with player names.
+	return "@" + m_guid.base64();
+}
+
 void LuaEntitySAO::setVelocity(v3f velocity)
 {
 	m_velocity = velocity;

src/server/luaentity_sao.h

@@ -6,6 +6,7 @@
 #pragma once
 
 #include "unit_sao.h"
+#include "util/guid.h"
 
 class LuaEntitySAO : public UnitSAO
 {
@@ -15,11 +16,7 @@ public:
 	LuaEntitySAO(ServerEnvironment *env, v3f pos, const std::string &data);
 	// Used by the Lua API
 	LuaEntitySAO(ServerEnvironment *env, v3f pos, const std::string &name,
-			const std::string &state) :
-			UnitSAO(env, pos),
-			m_init_name(name), m_init_state(state)
-	{
-	}
+			const std::string &state);
 	~LuaEntitySAO();
 
 	ActiveObjectType getType() const { return ACTIVEOBJECT_TYPE_LUAENTITY; }
@@ -47,6 +44,7 @@ public:
 
 	void setHP(s32 hp, const PlayerHPChangeReason &reason);
 	u16 getHP() const;
+	std::string getGUID() const;
 
 	/* LuaEntitySAO-specific */
 	void setVelocity(v3f velocity);
@@ -86,6 +84,8 @@ private:
 	std::string m_init_state;
 	bool m_registered = false;
 
+	MyGUID m_guid;
+
 	v3f m_velocity;
 	v3f m_acceleration;
 

src/server/player_sao.cpp

@@ -14,6 +14,7 @@ PlayerSAO::PlayerSAO(ServerEnvironment *env_, RemotePlayer *player_, session_t p
 		bool is_singleplayer):
 	UnitSAO(env_, v3f(0,0,0)),
 	m_player(player_),
+	m_player_name(player_->getName()),
 	m_peer_id_initial(peer_id_),
 	m_is_singleplayer(is_singleplayer)
 {

src/server/player_sao.h

@@ -78,6 +78,7 @@ public:
 	void addPos(const v3f &added_pos) override;
 	void moveTo(v3f pos, bool continuous) override;
 	void setPlayerYaw(const float yaw);
+	std::string getGUID() const override { return m_player_name; }
 	// Data should not be sent at player initialization
 	void setPlayerYawAndSend(const float yaw);
 	void setLookPitch(const float pitch);
@@ -182,6 +183,8 @@ private:
 	std::string generateUpdatePhysicsOverrideCommand() const;
 
 	RemotePlayer *m_player = nullptr;
+	// Extra variable because during shutdown m_player is unavailable, but we still need to know.
+	std::string m_player_name; ///< used as GUID
 	session_t m_peer_id_initial = 0; ///< only used to initialize RemotePlayer
 
 	// Cheat prevention

src/server/serveractiveobject.h

@@ -141,6 +141,10 @@ public:
 	virtual u16 getHP() const
 	{ return 0; }
 
+	/// @brief Returns an unique ID for this object (persistent across unload, server restarts).
+	/// @note Because these strings are very short, copying them is not expensive.
+	virtual std::string getGUID() const = 0;
+
 	virtual void setArmorGroups(const ItemGroupList &armor_groups)
 	{}
 	virtual const ItemGroupList &getArmorGroups() const