Improve MultiplayerAPI to enable RPC filtering

Describe the project you are working on

A game with multiplayer. it needs a reconnecting system, an authentication system. it relies on rpc calls and needs to filter these calls properly.

Describe the problem or limitation you are having in your project

Godot offers almost no control on rpc calls. you can't block certain rpc calls from reaching certain users.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Add a mechanism to filter rpc calls. also redirect failed rpc calls for more handling.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

I just have to mention when i say something like "disable rpc calls" i also mean rpc_id, reliable or unreliable. rset, reliable or unreliable

Changes to Node :

a new bool property called public_rpc with the default value of false.
a new var property called rpc_meta that will be attached to rpc calls to handle their failure if needed.

Implement a new Object type called Rpc_call with the properties below (this is just to give a gist of the idea):

NodePath node_path
String function
Array binds
var meta

Simimilarly implement a new Object type called Rset_call:

NodePath node_path
String variable_name
var value
var meta

Changes to MultiplayerAPI :

a new mechanism for the following function. when rpc is disabled for a certain peer, that peer will no longer receive rpc calls for Nodes that have their public_rpc set to false.
a new function called enable_rpc(int peer_id, bool enable). on the server side it can disable rpc calls for peer_id(incoming and outgoing). if peer_id of 0 is used, it will do it for all users. on the client side, only peer_id = 0 is allowed and it will block rpc calls coming/going from the server. the client will be responsible to decide what to do about the fact that some reliable rpc calls for some nodes have been dropped.
a new bool property called default_enable_rpc with the value of true. this will determine the initial state of rpc calls for newly connected peers. the default value will make it backwards compatible.
a new signal named rpc_failed(rpc_call, int error) . this way if a node is not found, rpc_call.meta will contain information that helps the programmer create the node if needed. for implementation note to take care of updating sender peer id to the peer that has it's rpc call failed so that we can still use get_rpc_sender_id to know who the signal is for.
a new signal named rset_failed(rset_call, int error). same as above.
a new function called last_rpc_meta() to get the rpc_meta for the latest rpc call even if it succeeded. this means that rpc_meta can also be used for other functions to reduce some of the data redundancy that it causes.
Constants describing rpc and rset fail codes.

A thing that i didn't cover is that i don't know if one should also disable rpc calls for peer_id = 1 (host itself) or just let them pass. maybe a variable could control that behavior if needed?

Also a flaw that rpc_meta has is that it will be copying the same data over and over so we have to use a data that's easy to copy to not have noticable performance drawbacks. a better approach would be to make the rpc calls more flexible with an extra argument to attach whatever we like. but that wouldn't be backwards compatible.

If this enhancement will not be used often, can it be worked around with a few lines of script?

Nope. It has to be built in.

Is there a reason why this should be core and not an add-on in the asset library?

It's one of the most important multiplayer features.

godotengine / godot-proposals