Interoperability

js-udx speaks UDX wire version 3. go-udx is the reference for the wire format, and js-udx’s codec tests check its encoding byte for byte against vectors generated from go-udx.

Versions

Peer	Works with	Notes
go-udx	v0.1.3 and later	Earlier v3 releases work, but don’t acknowledge PINGs, so conn.ping() always resolves false
dart_udx	3.1.0 and later	Before 3.1.0, a second stream opened by the Dart side, or a stream opened right after another closed, can get mixed up
go-libp2p-udx-transport	v0.1.4 and later	Built on go-udx v0.1.3
dart-libp2p	3.0.0 and later	Earlier releases miss the end of a stream that js-libp2p ends with a FIN on a Yamux window update, and can crash when js-libp2p aborts a connection

UDX v2 and earlier don’t interoperate with v3. js-udx answers a packet on another version with a version negotiation packet, and a js-udx dialer that gets one before the peer has answered gives up at once instead of timing out.

js-udx has some features go-udx lacks, and does some of them differently from dart_udx. Each is built so it still works with both:

Feature	With go-udx	With dart_udx
Path MTU discovery	Rises to 1472-byte datagrams (v0.1.3 and later)	Rises to 1472-byte datagrams
Anti-amplification	Works: go-udx answers the address challenge	Works: dart_udx answers the address challenge
Path migration	js-udx follows a go-udx peer that moves; go-udx doesn’t follow js-udx	Both follow each other
Stateless reset	No effect: go-udx ignores reset tokens	No effect: dart_udx doesn’t use reset tokens

Stateless reset works between js-udx peers only. Turning it on is safe with go-udx and dart_udx peers: they ignore or drop the packet that carries the token, and that packet carries nothing else.

How it’s tested

The test suite runs against real peers over real UDP, when their source is checked out next to js-udx (../go-udx, ../dart-udx, ../go-libp2p-udx-transport, ../dart-libp2p) and the Go and Dart toolchains are installed. It skips what’s missing.

Test	Covers
packages/udx/test/go-interop.test.ts	js-udx with go-udx, both directions: handshake, bulk transfer, many streams, ping, path MTU discovery
packages/udx/test/dart-interop.test.ts	The same with dart_udx, plus streams opened back to back and concurrently from each side
npm run interop:go-udx	go-udx’s own bulk and multi-stream interop suite, with js-udx in place of its Dart peer
packages/libp2p-udx/test/compliance.test.ts	js-libp2p’s transport compliance suite
packages/libp2p-udx/test/interop.test.ts	js-libp2p with go-libp2p and with dart-libp2p, each side dialing the other: Noise, Yamux, ping, identify and a 1 MiB echo
examples/examples.test.ts	Every program in examples/, which the code samples in these guides come from

UDX_SLOW_TESTS=1 adds tests that leave connections idle for 45 seconds, to check that keep-alives hold them open at both ends.