cmd/tsconnect/src/lib/start-ipn.ts

@@ -19,14 +19,12 @@ export async function startIPN(
   const name = `__tsconnectInit_${Math.random().toString(36).slice(2)}`
   const globals = globalThis as Record<string, unknown>
 
-  const ready = new Promise<(config: IPNConfig) => Promise<IPN>>(
-    (resolve) => {
-      globals[name] = (newIPN: (config: IPNConfig) => Promise<IPN>) => {
-        delete globals[name]
-        resolve(newIPN)
-      }
+  const ready = new Promise<[NewIPN, Terminate]>((resolve) => {
+    globals[name] = (newIPN: NewIPN, terminate: Terminate) => {
+      delete globals[name]
+      resolve([newIPN, terminate])
     }
-  )
+  })
 
   go.env[INIT_CALLBACK_ENV] = name
   const exited = go.run(instance).then(() => {
@@ -35,9 +33,20 @@ export async function startIPN(
     throw new Error("Go runtime exited before the IPN was ready")
   })
 
-  const newIPN = await Promise.race([ready, exited])
-  return newIPN(config)
+  const [newIPN, terminate] = await Promise.race([ready, exited])
+  try {
+    return await newIPN(config)
+  } catch (err) {
+    // Nothing was built, so nothing can shut the runtime down. Exit it here and
+    // wait for it, or the page keeps a blocked runtime for a failed startup.
+    terminate()
+    await exited.catch(() => {})
+    throw err
+  }
 }
 
+type NewIPN = (config: IPNConfig) => Promise<IPN>
+type Terminate = () => void
+
 /** Must match initCallbackEnv in wasm_js.go. */
 const INIT_CALLBACK_ENV = "TSCONNECT_INIT_CALLBACK"

cmd/tsconnect/wasm/wasm_js.go

@@ -85,8 +85,11 @@ func main() {
 	}
 
 	shutdownCh := make(chan struct{})
+	var terminateOnce sync.Once
+	terminate := func() { terminateOnce.Do(func() { close(shutdownCh) }) }
+
 	var claimed atomic.Bool
-	callback.Invoke(js.FuncOf(func(this js.Value, args []js.Value) any {
+	newIPNFn := js.FuncOf(func(this js.Value, args []js.Value) any {
 		return makePromise(func() (any, error) {
 			if len(args) != 1 {
 				return nil, errors.New("newIPN takes exactly one argument")
@@ -96,16 +99,27 @@ func main() {
 			if !claimed.CompareAndSwap(false, true) {
 				return nil, errors.New("this WASM runtime already has an IPN; start another runtime instead")
 			}
-			return newIPN(args[0], shutdownCh)
+			return newIPN(args[0], terminate)
 		})
-	}))
+	})
+
+	// A failed newIPN leaves the runtime blocked below with nothing to shut it
+	// down, so the loader gets a way to exit it. Leaving that to the loader
+	// keeps the ordering right: closing shutdownCh here would let main return
+	// before makePromise had delivered the rejection.
+	terminateFn := js.FuncOf(func(this js.Value, args []js.Value) any {
+		terminate()
+		return nil
+	})
+
+	callback.Invoke(newIPNFn, terminateFn)
 
 	// Block until shutdown() is called on the IPN, then let main return so the
 	// Go runtime (and all its goroutines) can be collected by the JS engine.
 	<-shutdownCh
 }
 
-func newIPN(jsConfig js.Value, shutdownCh chan struct{}) (map[string]any, error) {
+func newIPN(jsConfig js.Value, terminate func()) (map[string]any, error) {
 	netns.SetEnabled(false)
 
 	var store ipn.StateStore
@@ -221,7 +235,7 @@ func newIPN(jsConfig js.Value, shutdownCh chan struct{}) (map[string]any, error)
 		hostname:    hostname,
 		logID:       logid,
 		funnelPorts: make(map[uint16]*funnelListenerEntry),
-		shutdownCh:  shutdownCh,
+		terminate:   terminate,
 	}
 	lb.SetTCPHandlerForFunnelFlow(jsIPN.handleFunnelTCP)
 
@@ -416,7 +430,7 @@ type jsIPN struct {
 	funnelMu    sync.Mutex
 	funnelPorts map[uint16]*funnelListenerEntry
 
-	shutdownCh   chan struct{} // closed by shutdown() to unblock main()
+	terminate    func() // unblocks main() so the Go runtime can exit
 	shutdownOnce sync.Once
 }
 
@@ -627,16 +641,15 @@ func (i *jsIPN) logout() {
 
 // shutdown tears down the backend and lets main return, which exits the whole
 // Go runtime. Callers should await the runtime's exit rather than the promise
-// returned here: closing shutdownCh races with makePromise resolving, so the
-// promise may never settle. There is exactly one IPN per runtime, so the once
-// and the channel belong to the same instance and a second call is a no-op.
+// returned here: terminating races with makePromise resolving, so the promise
+// may never settle.
 func (i *jsIPN) shutdown() js.Value {
 	return makePromise(func() (any, error) {
 		i.shutdownOnce.Do(func() {
 			if i.lb != nil {
 				i.lb.Shutdown()
 			}
-			close(i.shutdownCh)
+			i.terminate()
 		})
 		return nil, nil
 	})