👌 [backedn/eth/channel] Add isConcluded to Adj.

Signed-off-by: Oliver Tale-Yazdi <oliver@perun.network>

Author: ggwpez

backend/ethereum/channel/conclude.go

@@ -33,33 +33,25 @@ const secondaryWaitBlocks = 2
 // ensureConcluded ensures that conclude or concludeFinal (for non-final and
 // final states, resp.) is called on the adjudicator.
 // - a subscription on Concluded events is established
-// - it searches for a past concluded event
+// - it searches for a past concluded event by calling `isConcluded`
 //   - if found, channel is already concluded and success is returned
 //   - if none found, conclude/concludeFinal is called on the adjudicator
 // - it waits for a Concluded event from the blockchain.
-// nolint: funlen
 func (a *Adjudicator) ensureConcluded(ctx context.Context, req channel.AdjudicatorReq, subStates channel.StateMap) error {
-	// Listen for Concluded event.
-	events := make(chan *subscription.Event, 10)
-	subErr := make(chan error, 1)
 	sub, err := subscription.NewEventSub(ctx, a.ContractBackend, a.bound, updateEventType(req.Params.ID()), startBlockOffset)
 	if err != nil {
 		return errors.WithMessage(err, "subscribing")
 	}
 	defer sub.Close()
-	// Check for past event
-	if err := sub.ReadPast(ctx, events); err != nil {
-		return errors.WithMessage(err, "reading past events")
-	}
-	select {
-	case _e := <-events:
-		e := _e.Data.(*adjudicator.AdjudicatorChannelUpdate)
-		if e.Phase == phaseConcluded {
-			return nil
-		}
-	default:
+	// Check whether it is already concluded.
+	if concluded, err := a.isConcluded(ctx, sub); err != nil {
+		return errors.WithMessage(err, "isConcluded")
+	} else if concluded {
+		return nil
 	}
 
+	events := make(chan *subscription.Event, 10)
+	subErr := make(chan error, 1)
 	waitCtx, cancel := context.WithCancel(ctx)
 	go func() {
 		subErr <- sub.Read(ctx, events)
@@ -108,6 +100,25 @@ func (a *Adjudicator) ensureConcluded(ctx context.Context, req channel.Adjudicat
 	}
 }
 
+// isConcluded returns whether a channel is already concluded.
+func (a *Adjudicator) isConcluded(ctx context.Context, sub *subscription.EventSub) (bool, error) {
+	events := make(chan *subscription.Event, 10)
+	subErr := make(chan error, 1)
+	// Write the events into events.
+	go func() {
+		defer close(events)
+		subErr <- sub.ReadPast(ctx, events)
+	}()
+	// Read all events and check for concluded.
+	for _e := range events {
+		e := _e.Data.(*adjudicator.AdjudicatorChannelUpdate)
+		if e.Phase == phaseConcluded {
+			return true, nil
+		}
+	}
+	return false, errors.WithMessage(<-subErr, "reading past events")
+}
+
 func updateEventType(channelID [32]byte) subscription.EventFactory {
 	return func() *subscription.Event {
 		return &subscription.Event{