dot-peer-to-peer

dot-peer-to-peer is for games played on a session one of the players hosts, rather than on a dedicated server: join codes, membership, readiness and host migration.

Requires dot-core. WebRTC is optional and is reached without being named.

It is a lobby problem before it is a transport problem

The transport half is a dozen calls into an engine module. What goes wrong is in the lobby: two people joining the same slot, a code that was already used, a host leaving and nobody agreeing who takes over, two peers that both think they are the host. None of that involves a socket, which is why DotP2PLobby holds no connection and all of it is covered by a headless suite.

Usage

var p2p := DotP2PSession.new()
p2p.config = my_config
p2p.signaller = DotP2PSignallerHttp.new(url, my_id, http)
add_child(p2p)
p2p.setup()

var code = p2p.host("Ada").value      # show this to a friend
p2p.join("K7M4PX", "Bob")             # or type theirs

DotP2PSignaller is four verbs. A loopback one ships for suites and split screen, and an HTTP one for anything with a URL and four routes; a backbone, a lobby service or a WebSocket the game already has are all subclasses.

The host election is a pure function

lobby.elect_host()     # stable first, then longest here, then lowest id

Every peer computes it from a member list they all have. An election requiring agreement needs a round of messages, and the moment a host disappears is precisely the moment messages are not arriving.

The tie-break is total and deterministic, because two peers picking differently is a split session neither can detect. Longest-joined rather than lowest latency: latency is measured differently by everybody, and a value two peers disagree about can elect two hosts.

Three things it will not hide

Peer-to-peer needs a server to start: Two machines behind two routers cannot find each other without something both can reach. What P2P removes is the server carrying the game traffic, which is the expensive part; the rendezvous is a few kilobytes, once.
Without a relay, some pairs cannot connect: Between five and fifteen per cent: symmetric NAT on both sides, carrier-grade NAT, some corporate and mobile networks. relay_servers is empty by default because a relay costs bandwidth and nobody can choose that for you — and with none configured those pairs fail quickly and by name, because “we could not find a route to that player” is something a person can act on and a spinner is not.
A host is a player, and can cheat: DotP2PConfig.Trust makes it a decision: host-authoritative (right for co-op among friends), verified (catches a careless host, not a determined one), or sandboxed, where nothing leaves the session — no records, no statistics, no leaderboard. A host who can cheat and a leaderboard are not two features; they are one exploit.

The transport is never named

Godot’s WebRTC ships as an optional GDExtension on native and is built into the web export. On a desktop build without it every WebRTC class is absent, and a script that mentions the identifier fails to compile, taking every script that references it down with it.

Everything therefore goes through ClassDB.instantiate by string, and a build without it still parses, still runs, and says which of the two reasons it is:

if not DotP2PSession.available():
    push_warning(DotP2PSession.unavailable_reason())

The join-code alphabet

23456789ABCDEFGHJKLMNPQRSTUVWXYZ — no 0, O, 1, I or l. A player reading a code aloud and the other person typing a different one is the commonest support request any game with a join code has. Six characters is about a billion codes.

A code is checked for shape before anything is looked up, which is both a better answer for a typo and not a way to find out which sessions exist.