Transport

The bottom of the stack is the IO layer: getting raw bytes from one peer to another.

The [Link] component is the type-erased struct that will send/receive raw bytes. It holds a send queue and a receive queue of raw payloads, plus the link state (Linking, Linked, Unlinked) and some stats. Lightyear systems only ever talk to the Link; they don’t know or care how the bytes actually travel.

How the bytes travel is decided by the IO component you pair with the Link:

• UdpIo / ServerUdpIo: plain UDP sockets
• WebTransportClientIo / WebTransportServerIo: WebTransport (QUIC)
• WebSocketClientIo / WebSocketServerIo: WebSocket
• CrossbeamIo: in-memory channels, used for tests and host-server mode
• SteamClientIo / SteamServerIo: Steam sockets

So a UDP client is Link + UdpIo, a WebTransport client is Link + WebTransportClientIo, and so on. Swapping transports means swapping one component.