channeldb+routing: continue payment lifecycle on register error

channeldb/payment_control.go

@@ -115,6 +115,10 @@ var (
 	// amount exceed the total amount.
 	ErrSentExceedsTotal = errors.New("total sent exceeds total amount")
 
+	// ErrRegisterAttempt is returned when a new htlc attempt cannot be
+	// registered.
+	ErrRegisterAttempt = errors.New("cannot register htlc attempt")
+
 	// errNoAttemptInfo is returned when no attempt info is stored yet.
 	errNoAttemptInfo = errors.New("unable to find attempt info for " +
 		"inflight payment")
@@ -342,7 +346,8 @@ func (p *PaymentControl) RegisterAttempt(paymentHash lntypes.Hash,
 
 		// Check if registering a new attempt is allowed.
 		if err := payment.Registrable(); err != nil {
-			return err
+			return fmt.Errorf("%w: %v", ErrRegisterAttempt,
+				err.Error())
 		}
 
 		// If the final hop has encrypted data, then we know this is a

routing/payment_lifecycle.go

@@ -262,6 +262,16 @@ lifecycle:
 		// We found a route to try, create a new HTLC attempt to try.
 		attempt, err := p.registerAttempt(rt, ps.RemainingAmt)
 		if err != nil {
+			// If the error is due to we cannot register another
+			// HTLC, we will skip this iteration and continue to
+			// the next one in case there are inflight HTLCs.
+			//
+			// TODO(yy): remove this check once we have a finer
+			// control over errors returned from the switch.
+			if errors.Is(err, channeldb.ErrRegisterAttempt) {
+				continue lifecycle
+			}
+
 			return exitWithErr(err)
 		}