Tinygo crashes on http.Client{}.Do() with Timeout #58

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1. Nico-Mayer commented on Jun 27, 2026

   

   Nico-Mayer

   on Jun 27, 2026

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   It seems that, at the moment, there is no way to cancel an in-flight request. Any http.Get or http.Post to an unreachable destination blocks indefinitely, effectively deadlocking the entire process and requiring a manual reset.
2. Darckfast commented on Jun 30, 2026

   

   Darckfast

   on Jun 30, 2026

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   yeah, i gave a shot porting Go's timeout solution and it seems to work fine, might bring this here
3. Nico-Mayer commented on Jun 30, 2026

   

   Nico-Mayer

   on Jun 30, 2026

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   yeah, i gave a shot porting Go's timeout solution and it seems to work fine, might bring this here

   Could you please share your solution? I’m curious to know how you approached it.
4. Darckfast commented on Jun 30, 2026

   

   Darckfast

   on Jun 30, 2026

   Last edited by Darckfast

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   Could you please share your solution? I’m curious to know how you approached it.

   ofc, it's nothing too amazing, i just grabbed Go net/http/client.go code and removed some part like http2 and legacy CancelRequest (Go 1.6)

   //net/http/client.go
   // setRequestCancel sets req.Cancel and adds a deadline context to req
   // if deadline is non-zero. The RoundTripper's type is used to
   // determine whether the legacy CancelRequest behavior should be used.
   //
   // As background, there are three ways to cancel a request:
   // First was Transport.CancelRequest. (deprecated)
   // Second was Request.Cancel.
   // Third was Request.Context.
   // This function populates the second and third, and uses the first if it really needs to.  TINYGO: Removed the third option as we dont support Go 1.6
   func setRequestCancel(req *Request, rt RoundTripper, deadline time.Time) (stopTimer func(), didTimeout func() bool) {
   	if deadline.IsZero() {
   		return nop, alwaysFalse
   	}
   	knownTransport := knownRoundTripperImpl(rt, req) // switch that check if rt.(type) is *Transport
   	oldCtx := req.Context()
   
   	if req.Cancel == nil && knownTransport {
   		// If they already had a Request.Context that's
   		// expiring sooner, do nothing:
   		if !timeBeforeContextDeadline(deadline, oldCtx) {
   			return nop, alwaysFalse
   		}
   
   		var cancelCtx func()
   		req.ctx, cancelCtx = context.WithDeadline(oldCtx, deadline)
   		return cancelCtx, func() bool { return time.Now().After(deadline) }
   	}
   	initialReqCancel := req.Cancel // the user's original Request.Cancel, if any
   
   	var cancelCtx func()
   	if timeBeforeContextDeadline(deadline, oldCtx) { // timeBeforeContextDeadline checks if ctx.Deadline() is before deadline
   		req.ctx, cancelCtx = context.WithDeadline(oldCtx, deadline)
   	}
   
   	cancel := make(chan struct{})
   	req.Cancel = cancel
   
   	doCancel := func() {
   		// The second way in the func comment above:
   		close(cancel)
   		// TINYGO: Removed logic using CancelRequest (implementation for <= Go 1.6)
   	}
   
   	stopTimerCh := make(chan struct{})
   	stopTimer = sync.OnceFunc(func() {
   		close(stopTimerCh)
   		if cancelCtx != nil {
   			cancelCtx()
   		}
   	})
   
   	timer := time.NewTimer(time.Until(deadline))
   	var timedOut atomic.Bool
   
   	go func() {
   		select {
   		case <-initialReqCancel:
   			doCancel()
   			timer.Stop()
   		case <-timer.C:
   			timedOut.Store(true)
   			doCancel()
   		case <-stopTimerCh:
   			timer.Stop()
   		}
   	}()
   
   	return stopTimer, timedOut.Load
   }

   then on roundtrip i added this before writing to the connection

   ctx, cancel := context.WithCancelCause(req.Context())
   defer func() {
   	if err != nil {
   		cancel(err)
   	}
   }()
   
   // TINYGO: TODO handle timeouts
   select {
   case <-ctx.Done():
   	req.closeBody()
   	return nil, context.Cause(ctx)
   default:
   }

   the setRequestCancel() get called a line before calling the roundTrip() in the send() function

   stopTimer, didTimeout := setRequestCancel(req, rt, deadline)
   
   resp, err = rt.RoundTrip(req)

   i still need to test with tinygo own roundTrip(), but for JS roundTrip it works fine

   there is more code, like the error types, extra helper functions on transport and client, but the part above is the gist of it

   ❤️React with ❤️1Reacted by Nico Mayer
5. Darckfast

   added a commit that references this issue on Jul 12, 2026

   feat: port Go net/http timeout handling

   ...

   ba49238
6. 0pcom commented on Sep 5, 2026

   

   0pcom

   on Sep 5, 2026

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   This is fixed on main by 70037cf ("net/http: fix nil didTimeout deref when a client dial fails"): send now returns an alwaysFalse func on the error path, so c.do's didTimeout() call no longer dereferences a nil func value when the dial fails with Client.Timeout set.

   Relatedly, #83 (open) makes the nil-Transport client dispatch through DefaultTransport / the fetch API on js/wasm instead of always dialing through the netdev — the other half of what your POC runs into (#66). With main as of 70037cf your reproducer should report the dial error instead of panicking; worth a re-test and closing if it checks out.