include rejecting if cheque rejected plus metric (#795)

pkg/settlement/swap/metrics.go

@@ -13,8 +13,9 @@ type metrics struct {
 	// all metrics fields must be exported
 	// to be able to return them by Metrics()
 	// using reflection
-	TotalReceived prometheus.Counter
-	TotalSent     prometheus.Counter
+	TotalReceived   prometheus.Counter
+	TotalSent       prometheus.Counter
+	ChequesRejected prometheus.Counter
 }
 
 func newMetrics() metrics {
@@ -32,7 +33,14 @@ func newMetrics() metrics {
 			Subsystem: subsystem,
 			Name:      "total_sent",
 			Help:      "Amount of tokens sent to peers (costs paid by the node)",
-		})}
+		}),
+		ChequesRejected: prometheus.NewCounter(prometheus.CounterOpts{
+			Namespace: m.Namespace,
+			Subsystem: subsystem,
+			Name:      "cheques_rejected",
+			Help:      "Number of cheques rejected",
+		}),
+	}
 }
 
 func (s *Service) Metrics() []prometheus.Collector {

pkg/settlement/swap/swap.go

@@ -7,6 +7,7 @@ package swap
 import (
 	"context"
 	"errors"
+	"fmt"
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -88,7 +89,8 @@ func (s *Service) ReceiveCheque(ctx context.Context, peer swarm.Address, cheque
 
 	amount, err := s.chequeStore.ReceiveCheque(ctx, cheque)
 	if err != nil {
-		return err
+		s.metrics.ChequesRejected.Inc()
+		return fmt.Errorf("rejecting cheque: %w", err)
 	}
 
 	if !known {