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fix(server): T3 Connect remembers when the relay client falls back to HTTP/2 on its own
When cloudflared, started with `auto`, gave up on QUIC and registered over HTTP/2 by itself, T3 recorded the protocol but not the fallback, so every later start went back to QUIC and spent minutes relearning it. Persist that fallback the same way as T3's own switch, for the same 24-hour window. Fixes #33928 Co-Authored-By: Claude Opus 5.5 <[email protected]>
1 parent 0f13d2c commit efea810

2 files changed

Lines changed: 69 additions & 6 deletions

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‎apps/server/src/cloud/ManagedEndpointRuntime.test.ts‎

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Original file line numberDiff line numberDiff line change
@@ -516,6 +516,57 @@ describe("CloudManagedEndpointRuntime", () => {
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}),
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);
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519+
it.effect("remembers an HTTP/2 fallback the relay client made on its own", () =>
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Effect.gen(function* () {
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const context = yield* Layer.build(
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ServerSecretStore.layer.pipe(
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Layer.provide(ServerConfig.layerTest(process.cwd(), { prefix: "t3-transport-test-" })),
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Layer.provide(Layer.mergeAll(NodeServices.layer, NodeCrypto.layer)),
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),
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);
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const secretStoreLayer = Layer.succeed(
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ServerSecretStore.ServerSecretStore,
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context.pipe(Context.get(ServerSecretStore.ServerSecretStore)),
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);
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const start = (spawner: ReturnType<typeof ChildProcessSpawner.make>) =>
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buildCloudManagedEndpointRuntime(
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spawner,
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layerRelayClientAvailable,
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unusedHttpClient,
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secretStoreLayer,
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);
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const registered = (protocol: string) =>
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`2026-11-10T01:43:17Z INF Registered tunnel connection connIndex=0 connection=c1 event=0 ip=198.41.192.7 location=fra08 protocol=${protocol}\n`;
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yield* Effect.gen(function* () {
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const fixture = yield* makeTransportSpawner();
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const runtime = yield* start(fixture.spawner);
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yield* runtime.applyConfig(tunnelConfig);
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yield* fixture.emit(0, registered("quic"));
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yield* Stream.runHead(runtime.tunnelConnected);
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}).pipe(Effect.scoped);
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yield* Effect.gen(function* () {
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const fixture = yield* makeTransportSpawner();
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const runtime = yield* start(fixture.spawner);
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yield* runtime.applyConfig(tunnelConfig);
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expect(fixture.spawned[0]!.args).not.toContain("--protocol");
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// cloudflared, started with `auto`, gave up on QUIC itself.
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yield* fixture.emit(0, registered("http2"));
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yield* Stream.runHead(runtime.tunnelConnected);
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// The connector already runs on HTTP/2, so it is not restarted.
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expect(fixture.spawned).toHaveLength(1);
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expect(fixture.killed).toEqual([]);
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}).pipe(Effect.scoped);
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yield* Effect.gen(function* () {
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const fixture = yield* makeTransportSpawner();
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const runtime = yield* start(fixture.spawner);
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yield* runtime.applyConfig(tunnelConfig);
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expect(fixture.spawned[0]!.args.slice(-3)).toEqual(["--protocol", "http2", "run"]);
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}).pipe(Effect.scoped);
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}),
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);
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it.effect(
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"ignores invalid or unreadable fallback state and still falls back if persistence fails",
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() =>

‎apps/server/src/cloud/ManagedEndpointRuntime.ts‎

Lines changed: 18 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -571,10 +571,7 @@ export const make = Effect.gen(function* () {
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}
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});
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574-
const switchToHttp2 = Effect.fnUntraced(function* (connector: ActiveConnector) {
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const active = yield* Ref.get(activeRef);
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const desiredConfig = yield* Ref.get(desiredConfigRef);
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if ((yield* Ref.get(http2Ref)) || active !== connector || !desiredConfig) return;
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const rememberHttp2Fallback = Effect.fnUntraced(function* () {
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yield* Ref.set(http2Ref, true);
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yield* secrets
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.set(
@@ -586,6 +583,13 @@ export const make = Effect.gen(function* () {
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.pipe(
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Effect.catch(() => Effect.logWarning("Could not persist the relay client HTTP/2 fallback")),
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);
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});
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const switchToHttp2 = Effect.fnUntraced(function* (connector: ActiveConnector) {
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const active = yield* Ref.get(activeRef);
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const desiredConfig = yield* Ref.get(desiredConfigRef);
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if ((yield* Ref.get(http2Ref)) || active !== connector || !desiredConfig) return;
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yield* rememberHttp2Fallback();
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yield* Effect.logWarning("Relay client keeps losing QUIC connections; switching to HTTP/2", {
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pid: Number(connector.child.pid),
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tunnelId: connector.config.tunnelId,
@@ -630,11 +634,18 @@ export const make = Effect.gen(function* () {
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output,
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};
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switch (classifyRelayClientOutput(line)) {
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case "connected":
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case "connected": {
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rejectedRegistrations = 0;
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const protocol = RELAY_CLIENT_PROTOCOL.exec(line)?.[1] ?? null;
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return Deferred.succeed(connector.registered, undefined).pipe(
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Effect.andThen(Ref.set(connector.protocol, protocol)),
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// cloudflared started with `auto` fell back on its own; later starts skip QUIC too.
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Effect.andThen(
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Ref.set(connector.protocol, RELAY_CLIENT_PROTOCOL.exec(line)?.[1] ?? null),
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protocol === "http2" && !transportChosenByUser
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? Ref.get(http2Ref).pipe(
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Effect.flatMap((http2) => (http2 ? Effect.void : rememberHttp2Fallback())),
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)
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: Effect.void,
638649
),
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Effect.andThen(
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Effect.logInfo("Relay client tunnel connection registered", attributes),
@@ -652,6 +663,7 @@ export const make = Effect.gen(function* () {
652663
),
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Effect.asVoid,
654665
);
666+
}
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case "unregistered":
656668
return Effect.logInfo("Relay client tunnel connection unregistered", attributes);
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case "warning":

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