htlcswitch: add failure details to incoming failures

This commit adds LinkErrors with failure details to htlcs which fail on
our incoming link. This change is made with the intention of notifying
detailed htlc failure reasons in sendHTLCError. The FailureDetail
interface is implemented on FailureResolutionResults so that they can
directly be used to enrich LinkErrors. sendHtlcError is updated to
take a LinkError in preparation for the addition of a htlcnotifier
which will notify the detail of the error.

htlcswitch/link.go

@@ -1220,8 +1220,8 @@ func (l *channelLink) processHtlcResolution(resolution invoices.HtlcResolution,
 		failure := getResolutionFailure(res, htlc.pd.Amount)
 
 		l.sendHTLCError(
-			htlc.pd.HtlcIndex, failure, htlc.obfuscator,
+			htlc.pd.HtlcIndex, failure,
-			htlc.pd.SourceRef,
+			htlc.obfuscator, htlc.pd.SourceRef,
 		)
 		return nil
 
@@ -1236,21 +1236,25 @@ func (l *channelLink) processHtlcResolution(resolution invoices.HtlcResolution,
 // getResolutionFailure returns the wire message that a htlc resolution should
 // be failed with.
 func getResolutionFailure(resolution *invoices.HtlcFailResolution,
-	amount lnwire.MilliSatoshi) lnwire.FailureMessage {
+	amount lnwire.MilliSatoshi) *LinkError {
 
 	// If the resolution has been resolved as part of a MPP timeout,
 	// we need to fail the htlc with lnwire.FailMppTimeout.
 	if resolution.Outcome == invoices.ResultMppTimeout {
-		return &lnwire.FailMPPTimeout{}
+		return NewDetailedLinkError(
+			&lnwire.FailMPPTimeout{}, resolution.Outcome,
+		)
 	}
 
 	// If the htlc is not a MPP timeout, we fail it with
 	// FailIncorrectDetails. This error is sent for invoice payment
 	// failures such as underpayment/ expiry too soon and hodl invoices
 	// (which return FailIncorrectDetails to avoid leaking information).
-	return lnwire.NewFailIncorrectDetails(
+	incorrectDetails := lnwire.NewFailIncorrectDetails(
 		amount, uint32(resolution.AcceptHeight),
 	)
+
+	return NewDetailedLinkError(incorrectDetails, resolution.Outcome)
 }
 
 // randomFeeUpdateTimeout returns a random timeout between the bounds defined
@@ -2650,9 +2654,10 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 			// for TLV payloads that also supports injecting invalid
 			// payloads. Deferring this non-trival effort till a
 			// later date
+			failure := lnwire.NewInvalidOnionPayload(failedType, 0)
 			l.sendHTLCError(
 				pd.HtlcIndex,
-				lnwire.NewInvalidOnionPayload(failedType, 0),
+				NewLinkError(failure),
 				obfuscator, pd.SourceRef,
 			)
 
@@ -2766,7 +2771,10 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 				)
 
 				l.sendHTLCError(
-					pd.HtlcIndex, failure, obfuscator, pd.SourceRef,
+					pd.HtlcIndex,
+					NewLinkError(failure),
+					obfuscator,
+					pd.SourceRef,
 				)
 				continue
 			}
@@ -2849,7 +2857,9 @@ func (l *channelLink) processExitHop(pd *lnwallet.PaymentDescriptor,
 			"value: expected %v, got %v", pd.RHash,
 			pd.Amount, fwdInfo.AmountToForward)
 
-		failure := lnwire.NewFinalIncorrectHtlcAmount(pd.Amount)
+		failure := NewLinkError(
+			lnwire.NewFinalIncorrectHtlcAmount(pd.Amount),
+		)
 		l.sendHTLCError(pd.HtlcIndex, failure, obfuscator, pd.SourceRef)
 
 		return nil
@@ -2862,7 +2872,9 @@ func (l *channelLink) processExitHop(pd *lnwallet.PaymentDescriptor,
 			"time-lock: expected %v, got %v",
 			pd.RHash[:], pd.Timeout, fwdInfo.OutgoingCTLV)
 
-		failure := lnwire.NewFinalIncorrectCltvExpiry(pd.Timeout)
+		failure := NewLinkError(
+			lnwire.NewFinalIncorrectCltvExpiry(pd.Timeout),
+		)
 		l.sendHTLCError(pd.HtlcIndex, failure, obfuscator, pd.SourceRef)
 
 		return nil
@@ -2979,10 +2991,10 @@ func (l *channelLink) handleBatchFwdErrs(errChan chan error) {
 
 // sendHTLCError functions cancels HTLC and send cancel message back to the
 // peer from which HTLC was received.
-func (l *channelLink) sendHTLCError(htlcIndex uint64, failure lnwire.FailureMessage,
+func (l *channelLink) sendHTLCError(htlcIndex uint64, failure *LinkError,
 	e hop.ErrorEncrypter, sourceRef *channeldb.AddRef) {
 
-	reason, err := e.EncryptFirstHop(failure)
+	reason, err := e.EncryptFirstHop(failure.WireMessage())
 	if err != nil {
 		l.log.Errorf("unable to obfuscate error: %v", err)
 		return

invoices/resolution_result.go

@@ -107,8 +107,10 @@ const (
 	ResultMppInProgress
 )
 
-// String returns a string representation of the result.
+// FailureString returns a string representation of the result.
-func (f FailResolutionResult) String() string {
+//
+// Note: it is part of the FailureDetail interface.
+func (f FailResolutionResult) FailureString() string {
 	switch f {
 	case resultInvalidFailure:
 		return "invalid failure result"