htlcswitch: add ForwardingError constructor

Add a constructor for the creation of forwarding errors.
A special constructor is added for the case where we have
an unknown wire failure, and must set a nil failure message.

htlcswitch/failure.go

@@ -40,6 +40,27 @@ func (f *ForwardingError) Error() string {
 	)
 }
 
+// NewForwardingError creates a new payment error which wraps a wire error
+// with additional metadata.
+func NewForwardingError(failure lnwire.FailureMessage, index int,
+	extraMsg string) *ForwardingError {
+
+	return &ForwardingError{
+		FailureSourceIdx: index,
+		FailureMessage:   failure,
+		ExtraMsg:         extraMsg,
+	}
+}
+
+// NewUnknownForwardingError returns a forwarding error which has a nil failure
+// message. This constructor should only be used in the case where we cannot
+// decode the failure we have received from a peer.
+func NewUnknownForwardingError(index int) *ForwardingError {
+	return &ForwardingError{
+		FailureSourceIdx: index,
+	}
+}
+
 // ErrorDecrypter is an interface that is used to decrypt the onion encrypted
 // failure reason an extra out a well formed error.
 type ErrorDecrypter interface {
@@ -94,15 +115,10 @@ func (s *SphinxErrorDecrypter) DecryptError(reason lnwire.OpaqueReason) (
 	r := bytes.NewReader(failure.Message)
 	failureMsg, err := lnwire.DecodeFailure(r, 0)
 	if err != nil {
-		return &ForwardingError{
-			FailureSourceIdx: failure.SenderIdx,
-		}, nil
+		return NewUnknownForwardingError(failure.SenderIdx), nil
 	}
 
-	return &ForwardingError{
-		FailureSourceIdx: failure.SenderIdx,
-		FailureMessage:   failureMsg,
-	}, nil
+	return NewForwardingError(failureMsg, failure.SenderIdx, ""), nil
 }
 
 // A compile time check to ensure ErrorDecrypter implements the Deobfuscator

htlcswitch/mock.go

@@ -400,10 +400,7 @@ func (o *mockDeobfuscator) DecryptError(reason lnwire.OpaqueReason) (*Forwarding
 		return nil, err
 	}
 
-	return &ForwardingError{
-		FailureSourceIdx: 1,
-		FailureMessage:   failure,
-	}, nil
+	return NewForwardingError(failure, 1, ""), nil
 }
 
 var _ ErrorDecrypter = (*mockDeobfuscator)(nil)

htlcswitch/switch.go

@@ -756,10 +756,9 @@ func (s *Switch) handleLocalDispatch(pkt *htlcPacket) error {
 		s.indexMtx.RUnlock()
 		if err != nil {
 			log.Errorf("Link %v not found", pkt.outgoingChanID)
-			return &ForwardingError{
-				FailureSourceIdx: 0,
-				FailureMessage:   &lnwire.FailUnknownNextPeer{},
-			}
+			return NewForwardingError(
+				&lnwire.FailUnknownNextPeer{}, 0, "",
+			)
 		}
 
 		if !link.EligibleToForward() {
@@ -770,11 +769,7 @@ func (s *Switch) handleLocalDispatch(pkt *htlcPacket) error {
 			// The update does not need to be populated as the error
 			// will be returned back to the router.
 			htlcErr := lnwire.NewTemporaryChannelFailure(nil)
-			return &ForwardingError{
-				FailureSourceIdx: 0,
-				ExtraMsg:         err.Error(),
-				FailureMessage:   htlcErr,
-			}
+			return NewForwardingError(htlcErr, 0, err.Error())
 		}
 
 		// Ensure that the htlc satisfies the outgoing channel policy.
@@ -788,10 +783,7 @@ func (s *Switch) handleLocalDispatch(pkt *htlcPacket) error {
 			log.Errorf("Link %v policy for local forward not "+
 				"satisfied", pkt.outgoingChanID)
 
-			return &ForwardingError{
-				FailureSourceIdx: 0,
-				FailureMessage:   htlcErr,
-			}
+			return NewForwardingError(htlcErr, 0, "")
 		}
 
 		return link.HandleSwitchPacket(pkt)
@@ -930,11 +922,7 @@ func (s *Switch) parseFailedPayment(deobfuscator ErrorDecrypter,
 			failureMsg = lnwire.NewTemporaryChannelFailure(nil)
 		}
 
-		return &ForwardingError{
-			FailureSourceIdx: 0,
-			ExtraMsg:         userErr,
-			FailureMessage:   failureMsg,
-		}
+		return NewForwardingError(failureMsg, 0, userErr)
 
 	// A payment had to be timed out on chain before it got past
 	// the first hop. In this case, we'll report a permanent
@@ -945,11 +933,9 @@ func (s *Switch) parseFailedPayment(deobfuscator ErrorDecrypter,
 			"on-chain, then canceled back (hash=%v, pid=%d)",
 			paymentHash, paymentID)
 
-		return &ForwardingError{
-			FailureSourceIdx: 0,
-			ExtraMsg:         userErr,
-			FailureMessage:   &lnwire.FailPermanentChannelFailure{},
-		}
+		return NewForwardingError(
+			&lnwire.FailPermanentChannelFailure{}, 0, userErr,
+		)
 
 	// A regular multi-hop payment error that we'll need to
 	// decrypt.