UDP Relay

UDP app (DNS / game / VoIP / …)
  │  SOCKS5 UDP ASSOCIATE
  ▼
mqproxy-client ──────── MPQUIC DATAGRAMs (multipath) ────────► mqproxy-server
     1 UDP session = a bidi signalling stream + DATAGRAMs        │  connected
     carrying session_id-tagged packets                          │  UDP socket
                                                                 ▼
                                                             UDP target

UDP relay carries non-QUIC UDP traffic (DNS, NTP, game, VoIP, app-specific UDP) over MPQUIC DATAGRAMs. The ingress is SOCKS5 UDP ASSOCIATE (RFC 1928 §7) on the same --socks5 listener used for TCP. For each target the client opens a small bidi signalling stream (UDP_SESSION_OPEN/RESP, multiplexed alongside TCP on the one mqproxy-tcp/1 connection), then sends packets as DATAGRAMs tagged with a session id; the server keeps a connected UDP socket per session and relays both ways.

Packets larger than the path MTU are fragmented and reassembled (4-slot LRU, no retransmission — UDP stays lossy). Sessions are torn down on idle timeout (server-driven, --udp-idle-timeout), on stream close, or when the SOCKS5 control connection drops. The server advertises the capability at auth and can refuse all UDP with --no-udp.

TIP

UDP relay rides the mqproxy-tcp/1 connection, so a client running --gateway only (H3 connection) does not get it.

Quick start

UDP relay is exposed on the same --socks5 listener — any SOCKS5 client that speaks UDP ASSOCIATE can use it. The server advertises the capability at auth; pass --udp-idle-timeout <sec> to tune session lifetime, or --no-udp to refuse UDP entirely.

# Server (UDP relay on by default; 30s idle timeout shown)
./build/mqproxy server --listen 0.0.0.0:4433 --token secret123 \
  --udp-idle-timeout 30

# Client — the SOCKS5 listener handles both TCP and UDP
./build/mqproxy client \
  --server 127.0.0.1:4433 --token secret123 \
  --socks5 127.0.0.1:1080

curl does not speak SOCKS5 UDP ASSOCIATE, so use a UDP-capable SOCKS5 client. The repo ships udpsocks, a minimal test client (built by the test suite), which is handy for a quick check:

# Relay a UDP packet to a target through the client's SOCKS5 listener
./build/udpsocks --proxy 127.0.0.1:1080 --target 8.8.8.8:53 --send 32 --count 1