moq-net: negotiate Lite03+ via legacy SETUP when ALPN is unavailable

js/net/src/connection/accept.ts

@@ -134,7 +134,17 @@ async function acceptNegotiated(transport: WebTransport, url: URL, props?: Accep
 	await server.encode(stream.writer, setupVersion);
 
 	if (Object.values(Lite.Version).includes(selectedVersion as Lite.Version)) {
-		return new Lite.Connection(url, transport, selectedVersion as Lite.Version, stream);
+		const version = selectedVersion as Lite.Version;
+		// Lite03+ has no SessionInfo protocol on the control stream. When it's
+		// negotiated via this Draft14 SETUP fallback (e.g. Firefox WebTransport,
+		// which can't select an ALPN), close the bootstrap stream after the
+		// exchange and run the session as if it had been ALPN-negotiated directly.
+		const isLegacy = version === Lite.Version.DRAFT_01 || version === Lite.Version.DRAFT_02;
+		if (isLegacy) {
+			return new Lite.Connection(url, transport, version, stream);
+		}
+		stream.writer.close();
+		return new Lite.Connection(url, transport, version, undefined);
 	} else if (Object.values(Ietf.Version).includes(selectedVersion as Ietf.Version)) {
 		const maxRequestId = client.parameters.getVarint(Ietf.SetupOption.MaxRequestId) ?? 0n;
 		return new Ietf.Connection({

js/net/src/connection/connect.ts

@@ -9,6 +9,40 @@ import { exchangeSetup } from "./handshake.ts";
 // Default head start for WebTransport before attempting the WebSocket fallback.
 const DEFAULT_WEBSOCKET_DELAY_MS = 500;
 
+// Versions advertised in the Draft14 SETUP fallback (bare `moql` ALPN or no ALPN
+// at all, e.g. Firefox WebTransport, which can't select an ALPN). Listing every
+// shipped moq-lite version lets the server pick Lite03+ even without ALPN
+// selection. Lite05Wip is intentionally omitted: it's work-in-progress and not
+// advertised by default.
+const LITE_FALLBACK_VERSIONS = [
+	Lite.Version.DRAFT_04,
+	Lite.Version.DRAFT_03,
+	Lite.Version.DRAFT_02,
+	Lite.Version.DRAFT_01,
+	Ietf.Version.DRAFT_14,
+];
+
+// Lite01/Lite02 still run the SessionInfo protocol on the SETUP control stream.
+function isLiteLegacy(v: Lite.Version): boolean {
+	return v === Lite.Version.DRAFT_01 || v === Lite.Version.DRAFT_02;
+}
+
+// Build a Lite connection negotiated via the Draft14 SETUP fallback. Lite03+ has
+// no SessionInfo protocol, so close the bootstrap stream we borrowed for the
+// exchange and run the session as if it had been ALPN-negotiated directly.
+function liteFallbackConnection(
+	url: URL,
+	session: WebTransport,
+	version: Lite.Version,
+	stream: Stream,
+): Lite.Connection {
+	if (isLiteLegacy(version)) {
+		return new Lite.Connection(url, session, version, stream);
+	}
+	stream.writer.close();
+	return new Lite.Connection(url, session, version, undefined);
+}
+
 /** Tuning for the WebSocket fallback used when WebTransport is unavailable or loses the connect race. */
 export interface WebSocketOptions {
 	// If true (default), enable the WebSocket fallback.
@@ -162,12 +196,14 @@ export async function connect(url: URL, props?: ConnectProps): Promise<Establish
 	const client = new Ietf.ClientSetup({
 		// NOTE: draft 15 onwards does not use CLIENT_SETUP to negotiate the version.
 		// We still echo it just to make sure we're not accidentally trying to negotiate the version.
+		// For the Draft14 fallback (ALPN_LITE or no ALPN, e.g. Firefox WebTransport),
+		// advertise every shipped moq-lite version so we can negotiate Lite03+ without ALPN.
 		versions:
 			setupVersion === Ietf.Version.DRAFT_16
 				? [Ietf.Version.DRAFT_16]
 				: setupVersion === Ietf.Version.DRAFT_15
 					? [Ietf.Version.DRAFT_15]
-					: [Lite.Version.DRAFT_02, Lite.Version.DRAFT_01, Ietf.Version.DRAFT_14],
+					: LITE_FALLBACK_VERSIONS,
 		parameters: params,
 	});
 	console.debug(url.toString(), "sending client setup", client);
@@ -184,7 +220,7 @@ export async function connect(url: URL, props?: ConnectProps): Promise<Establish
 	console.debug(url.toString(), "received server setup", server);
 
 	if (Object.values(Lite.Version).includes(server.version as Lite.Version)) {
-		return new Lite.Connection(url, session, server.version as Lite.Version, stream);
+		return liteFallbackConnection(url, session, server.version as Lite.Version, stream);
 	} else if (Object.values(Ietf.Version).includes(server.version as Ietf.Version)) {
 		const maxRequestId = server.parameters.getVarint(Ietf.SetupOption.MaxRequestId) ?? 0n;
 		return new Ietf.Connection({
@@ -242,7 +278,7 @@ async function connectTransport(url: URL, session: WebTransport): Promise<Establ
 				? [Ietf.Version.DRAFT_16]
 				: setupVersion === Ietf.Version.DRAFT_15
 					? [Ietf.Version.DRAFT_15]
-					: [Lite.Version.DRAFT_02, Lite.Version.DRAFT_01, Ietf.Version.DRAFT_14],
+					: LITE_FALLBACK_VERSIONS,
 		parameters: params,
 	});
 	await client.encode(stream.writer, setupVersion);
@@ -255,7 +291,7 @@ async function connectTransport(url: URL, session: WebTransport): Promise<Establ
 	const server = await Ietf.ServerSetup.decode(stream.reader, setupVersion);
 
 	if (Object.values(Lite.Version).includes(server.version as Lite.Version)) {
-		return new Lite.Connection(url, session, server.version as Lite.Version, stream);
+		return liteFallbackConnection(url, session, server.version as Lite.Version, stream);
 	} else if (Object.values(Ietf.Version).includes(server.version as Ietf.Version)) {
 		const maxRequestId = server.parameters.getVarint(Ietf.SetupOption.MaxRequestId) ?? 0n;
 		return new Ietf.Connection({

js/net/src/integration.test.ts

@@ -64,6 +64,21 @@ test("integration: lite draft-03", async () => {
 	await runPublishSubscribeFlow(Lite.ALPN_03);
 });
 
+test("integration: lite draft-04", async () => {
+	await runPublishSubscribeFlow(Lite.ALPN_04);
+});
+
+// No-ALPN fallback (e.g. Firefox WebTransport, which can't select an ALPN).
+// The SETUP exchange advertises every shipped moq-lite version, so the server
+// can pick Lite03+ even without ALPN selection.
+test("integration: lite draft-03 via SETUP fallback (no ALPN)", async () => {
+	await runPublishSubscribeFlow("", Lite.Version.DRAFT_03);
+});
+
+test("integration: lite draft-04 via SETUP fallback (no ALPN)", async () => {
+	await runPublishSubscribeFlow("", Lite.Version.DRAFT_04);
+});
+
 test("integration: ietf draft-14", async () => {
 	await runPublishSubscribeFlow("", Ietf.Version.DRAFT_14);
 });

js/net/src/lite/version.ts

@@ -11,7 +11,10 @@ export const Version = {
 export type Version = (typeof Version)[keyof typeof Version];
 
 /// The WebTransport subprotocol identifier for moq-lite.
-/// Version negotiation still happens via SETUP when this is used.
+/// Version negotiation still happens via SETUP when this is used, or when no
+/// ALPN selection is available at all (e.g. Firefox WebTransport). In both
+/// cases we advertise every shipped moq-lite version in the legacy SETUP
+/// versions list, so Lite03+ can still be negotiated without a dedicated ALPN.
 export const ALPN = "moql";
 
 /// The ALPN string for Draft03, which uses ALPN-based version negotiation.

rs/moq-net/src/client.rs

@@ -205,10 +205,21 @@ impl Client {
 
 		let recv_bw = match version {
 			Version::Lite(v) => {
-				let stream = stream.with_version(v);
+				// Lite03+ has no SessionInfo protocol on the control stream. When it's
+				// negotiated via this legacy SETUP fallback (because ALPN selection
+				// wasn't available, e.g. Firefox WebTransport), close the bootstrap
+				// stream after the exchange and run the session as if it had been
+				// ALPN-negotiated directly.
+				let setup_stream = match v {
+					lite::Version::Lite01 | lite::Version::Lite02 => Some(stream.with_version(v)),
+					_ => {
+						let _ = stream.writer.finish();
+						None
+					}
+				};
 				lite::start(
 					session.clone(),
-					Some(stream),
+					setup_stream,
 					self.publish.clone(),
 					self.consume.clone(),
 					self.stats.clone(),
@@ -454,6 +465,7 @@ mod tests {
 		assert_eq!(
 			advertised,
 			vec![
+				Version::Lite(lite::Version::Lite03),
 				Version::Lite(lite::Version::Lite02),
 				Version::Lite(lite::Version::Lite01),
 				Version::Ietf(ietf::Version::Draft14),
@@ -466,6 +478,49 @@ mod tests {
 		assert_eq!(code, Error::Cancel.to_code());
 	}
 
+	async fn run_alpn_lite_fallback_lite03_case(protocol: Option<&'static str>) {
+		// Server negotiates Lite03 via the legacy SETUP versions list.
+		// No SessionInfo frame is appended: Lite03+ has no SETUP stream protocol.
+		let mut server_bytes = Vec::new();
+		let server = setup::Server {
+			version: Version::Lite(lite::Version::Lite03).into(),
+			parameters: Bytes::new(),
+		};
+		server
+			.encode(&mut server_bytes, Version::Ietf(ietf::Version::Draft14))
+			.unwrap();
+
+		let fake = FakeSession::new(protocol, server_bytes);
+		let client = Client::new().with_versions(
+			[
+				Version::Lite(lite::Version::Lite04),
+				Version::Lite(lite::Version::Lite03),
+				Version::Lite(lite::Version::Lite02),
+				Version::Lite(lite::Version::Lite01),
+				Version::Ietf(ietf::Version::Draft14),
+			]
+			.into(),
+		);
+
+		let session = client.connect(fake.clone()).await.unwrap();
+		assert_eq!(session.version(), Version::Lite(lite::Version::Lite03));
+
+		// The client advertises every shipped moq-lite version in the SETUP list.
+		let mut setup_bytes = Bytes::from(fake.control_writes());
+		let setup = setup::Client::decode(&mut setup_bytes, Version::Ietf(ietf::Version::Draft14)).unwrap();
+		let advertised: Vec<Version> = setup.versions.iter().map(|v| Version::try_from(*v).unwrap()).collect();
+		assert_eq!(
+			advertised,
+			vec![
+				Version::Lite(lite::Version::Lite04),
+				Version::Lite(lite::Version::Lite03),
+				Version::Lite(lite::Version::Lite02),
+				Version::Lite(lite::Version::Lite01),
+				Version::Ietf(ietf::Version::Draft14),
+			]
+		);
+	}
+
 	#[tokio::test(start_paused = true)]
 	async fn alpn_lite_falls_back_to_draft14_and_switches_version_post_setup() {
 		run_alpn_lite_fallback_case(Some(ALPN_LITE)).await;
@@ -475,4 +530,14 @@ mod tests {
 	async fn no_alpn_falls_back_to_draft14_and_switches_version_post_setup() {
 		run_alpn_lite_fallback_case(None).await;
 	}
+
+	#[tokio::test(start_paused = true)]
+	async fn alpn_lite_fallback_negotiates_lite03() {
+		run_alpn_lite_fallback_lite03_case(Some(ALPN_LITE)).await;
+	}
+
+	#[tokio::test(start_paused = true)]
+	async fn no_alpn_fallback_negotiates_lite03() {
+		run_alpn_lite_fallback_lite03_case(None).await;
+	}
 }

rs/moq-net/src/server.rs

@@ -207,10 +207,21 @@ impl Server {
 
 		let recv_bw = match version {
 			Version::Lite(v) => {
-				let stream = stream.with_version(v);
+				// Lite03+ has no SessionInfo protocol on the control stream. When it's
+				// negotiated via this legacy SETUP fallback (because ALPN selection
+				// wasn't available, e.g. Firefox WebTransport), close the bootstrap
+				// stream after the exchange and run the session as if it had been
+				// ALPN-negotiated directly.
+				let setup_stream = match v {
+					lite::Version::Lite01 | lite::Version::Lite02 => Some(stream.with_version(v)),
+					_ => {
+						let _ = stream.writer.finish();
+						None
+					}
+				};
 				lite::start(
 					session.clone(),
-					Some(stream),
+					setup_stream,
 					self.publish.clone(),
 					self.consume.clone(),
 					self.stats.clone(),

rs/moq-net/src/version.rs

@@ -6,9 +6,22 @@ use crate::{coding, ietf, lite};
 /// The versions of MoQ that are negotiated via SETUP.
 ///
 /// Ordered by preference, with the client's preference taking priority.
-/// This intentionally includes only SETUP-negotiated versions (Lite02, Lite01, Draft14);
-/// Lite03 and newer IETF drafts negotiate via dedicated ALPNs instead.
-pub(crate) const NEGOTIATED: [Version; 3] = [
+///
+/// This path is used when ALPN-based selection is unavailable: a bare `"moql"`
+/// ALPN, or no ALPN at all (e.g. Firefox's WebTransport, which doesn't expose
+/// an ALPN selection API). To avoid stranding such peers on the oldest drafts,
+/// we advertise every shipped moq-lite version in the legacy SETUP versions
+/// list so Lite03+ can still be negotiated without a dedicated ALPN.
+///
+/// Lite03+ borrows the draft-14 SETUP framing *only* for this bootstrap
+/// exchange. Once negotiated, the SETUP stream is closed and the rest of the
+/// session follows the dedicated-ALPN semantics (no SessionInfo messages).
+///
+/// Lite05Wip is intentionally excluded: it is work-in-progress and must not be
+/// advertised by default, matching [`ALPNS`].
+pub(crate) const NEGOTIATED: [Version; 5] = [
+	Version::Lite(lite::Version::Lite04),
+	Version::Lite(lite::Version::Lite03),
 	Version::Lite(lite::Version::Lite02),
 	Version::Lite(lite::Version::Lite01),
 	Version::Ietf(ietf::Version::Draft14),