fn: Remove error channel for container exits (#1287)

The channel is unnecessary and unreliable since exits
trigger I/O failure on UDS earlier than we detect
the exit.

api/agent/agent.go

@@ -555,7 +555,6 @@ func (a *agent) waitHot(ctx context.Context, call *call) (Slot, error) {
 // implements Slot
 type hotSlot struct {
 	done          chan struct{} // signal we are done with slot
-	errC          <-chan error  // container error
 	container     *container    // TODO mask this
 	cfg           *Config
 	udsClient     http.Client
@@ -599,9 +598,6 @@ func (s *hotSlot) exec(ctx context.Context, call *call) error {
 	errApp := s.dispatch(ctx, call)
 
 	select {
-	case err := <-s.errC: // error from container
-		s.trySetError(err)
-		return err
 	case err := <-errApp: // from dispatch
 		if err != nil {
 			if models.IsAPIError(err) {
@@ -814,9 +810,6 @@ func (a *agent) runHot(ctx context.Context, call *call, tok ResourceToken, state
 		return
 	}
 
-	// buffered, in case someone has slot when waiter returns but isn't yet listening
-	errC := make(chan error, 1)
-
 	go func() {
 		defer shutdownContainer() // also close if we get an agent shutdown / idle timeout
 
@@ -849,7 +842,6 @@ func (a *agent) runHot(ctx context.Context, call *call, tok ResourceToken, state
 
 			slot := &hotSlot{
 				done:          make(chan struct{}),
-				errC:          errC,
 				container:     container,
 				cfg:           &a.cfg,
 				udsClient:     udsClient,
@@ -870,17 +862,6 @@ func (a *agent) runHot(ctx context.Context, call *call, tok ResourceToken, state
 	}()
 
 	res := waiter.Wait(ctx)
-	if err := res.Error(); err != nil {
-		if err == context.Canceled {
-			// TODO consider removal after format biz mellows out (t-minus 30 days)
-			// we can turn this into a user visible error (for now) if the container
-			// exits because they are using the wrong format, say, and try to guess/
-			// help them out for now. context.Canceled only comes from container exit.
-			errC <- models.ErrContainerExitedEarly
-		} else {
-			errC <- err // TODO: race condition, no guaranteed delivery fix this... we can't really, if nobody is there it's working as intended for idle timeout?
-		}
-	}
 	if res.Error() != context.Canceled {
 		logger.WithError(res.Error()).Info("hot function terminated")
 	}