Godot Multiplayer. Errors when spawning other player characters.

[なかの31]

I'm having a issue that is burning my head, even more since the error message itself is cryptic.

I'm doing the host and join part of the multiplayer, but one of the instances of the game (probably the one where joins the server) gives the following error:

E 0:00:05:0114   on_spawn_receive: Condition "parent->has_node(name)" is true. Returning: ERR_INVALID_DATA
  <C++ Source>   modules/multiplayer/scene_replication_interface.cpp:604 @ on_spawn_receive()

Based on part of the error, it gives the impression that there's an object with repeated name being set on a node, but I checked the scripts, and also did some debug message checking and, the clients themselves doesn't seems to be trying to spawn repeated objects, based on what debug messages returns (each call on the character spawning script happens once per client object on the clients).

This is my character spawning script. I thought it was the "call_defered" that could be causing the issue, but that causes another issue to happen, where the character isn't spawned in the right place (???).

func AddPlayer(ID):
	#print_debug(str(multiplayer.get_unique_id()) + "| Creating Player ID " + str(ID))
	var NewPlayer : PlayerScript = SpawnPlayerCharacter(Global.SpawnX, Global.SpawnY, ID)
	return NewPlayer

func SpawnPlayerCharacter(X, Y, ID) -> PlayerScript:
	var NewCharacter : PlayerScript = load("res://Objects/player.tscn").instantiate()
	NewCharacter.WhoAmI = ID
	NewCharacter.name = "ID" + str(ID)
	PlayersContainer.call_deferred("add_child", NewCharacter)
	NewCharacter.Teleport(X, Y)
	return NewCharacter

Other than that, on both clients, the character of the players spawns on the game world, but no sync or rpc calls happens.

Any clues of what I might be doing wrong? I'm literally running in circles about this issue...

[Romløk]

That error message indicates that the client is receiving a node to spawn from the server, but the spawning fails because there's already a node with that name. Are you creating the Player on the client as well as on the server? When does AddPlayer get called?

[なかの31]

AddPlayer is called right after server starts hosting, and also when a player connects.

[Romløk]

Is the "when a player connects" guarded by an `is_server()` check of some variety? Eg. If you're just listening for `multiplayer.peer_connected`, then clients will get that for the server's peer too.

[なかの31]

Nope. That's called for both servers and clients?

[なかの31]

I added a "is_server()" check to player connect, and now it no longer show errors once other player enters server :).

Thanks. I guess better I add a comment to a 3 minute video saying how to make a multiplayer game heh.

[Romløk]

Yeah, every instance is a "peer", including the server, so peer_connected signals get fired for everyone. And by default the server will propagate other peer information too, so every peer would get a peer_connected for every other peer except themselves!

Godot networking can be confusing sometimes. It feels like a somewhat muddled bag of client-server concepts and peer-to-peer concepts, all kinda mixed together and stretched across multiple objects and APIs. :/

[なかの31]

I actually find it a bit confusing. I've been reading documentations and am being unable to get the grasp of how it works.
I'm even having troubles getting rpcs to work. They seem to only fire locally.

[なかの31]

I think I got it. When calling a rpc method, lets say, move(position):, instead of calling it like "move(position)", must call it like "move.rpc(position)" instead. Like, with the ".rpc" next to the method, and with a parenthesis with the arguments of the method.

I only found out about that after checking a documentation about scene replication.