# Sans-I/O Pattern

URL: /docs/concepts/sans-io/
Section: concepts

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What is sans-I/O? Sans-I/O means the protocol library never touches sockets, files, or any I/O primitives. It consumes bytes and produces bytes. The caller owns I/O. datagram in → QuicConnection.datagram_received() → [QuicEvent, ...] → QuicConnection.send_datagrams() → [bytes, ...] Why? Testable — Feed bytes in, assert on events out. No mocks needed. Portable — Works with asyncio, threading, bare sockets, or any event loop. Composable — Pounce (ASGI server) wraps Zoomies with its own I/O layer. You can too. The contract Every Zoomies API follows the same pattern: Input: Call a method with raw bytes or protocol data Process: Internal state machine advances Output: Get events (what happened) and datagrams (what to send) # You own the socket events = conn.datagram_received(datagram, addr) # React to events for event in events: match event: case HandshakeComplete(): ... case StreamDataReceived(stream_id=sid, data=data): ... # Send what the connection produced for dg in conn.send_datagrams(): sock.sendto(dg, addr) Timer callbacks Loss recovery requires timers (PTO, idle timeout). Zoomies exposes a get_timer() method. You call it, schedule a wakeup, and call handle_timer() when it fires. timeout = conn.get_timer() if timeout is not None: # schedule a wakeup at `timeout` (absolute time) ... # When the timer fires: events = conn.handle_timer() for dg in conn.send_datagrams(): sock.sendto(dg, addr) See also sans-I/O manifesto — the original proposal Architecture — how Zoomies layers compose

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Metadata:
- Author: lbliii
- Word Count: 221
- Reading Time: 1 minutes