multi: fix payment failure overwrite #9543

ziggie1984 · 2025-02-22T10:42:33Z

We are not consistent when handling payment failures so we need to make sure we do not fail a payment twice overwriting its previous failure reason.

Thanks @feelancer21 for reporting. Fixes #9542

Observed in the sendtoroute cmd. When tracking the payment it can be observed that we overwrite the payment failure.

coderabbitai · 2025-02-22T10:45:04Z

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ziggie1984 · 2025-02-22T10:47:42Z

If the approach is ok, will add a unit-test.
I don't think we should allow swapping the payment error tbh, a payment should only fail once and I think this is a relict in the codebase fromer the prior behaviour, we should only fail a payment if all shards are resolved.

lnd/channeldb/payment_control_test.go

Lines 891 to 894 in 5fe900d

    
           // Check that we can override any perevious terminal 
        
           // failure. This is to allow multiple concurrent shard 
        
           // write a terminal failure to the database without 
        
           // syncing.

yyforyongyu · 2025-02-24T06:43:33Z

Why did we fail the payment twice? Can we make it fail it once instead?

ziggie1984 · 2025-02-24T07:37:51Z

We fail it almost certainly twice in SendToRouteV2 because we don't know whether we only fail the attempt or the attempt and the payment in the result collector:

lnd/routing/router.go

Lines 1189 to 1206 in 5fe900d

    
           result, err = p.collectAndHandleResult(attempt) 
        
           if err != nil { 
        
           	return nil, err 
        
           } 
        
           // We got a successful result. 
        
           if result.err == nil { 
        
           	return result.attempt, nil 
        
           } 
        
           // An error returned from collecting the result, we'll mark the payment 
        
           // as failed if we don't skip temp error. 
        
           if !skipTempErr { 
        
           	err := r.cfg.Control.FailPayment(paymentIdentifier, reason) 
        
           	if err != nil { 
        
           		return nil, err 
        
           	} 
        
           }

yyforyongyu · 2025-02-26T14:01:44Z

routing/router.go

@@ -1200,7 +1200,12 @@ func (r *ChannelRouter) sendToRoute(htlcHash lntypes.Hash, rt *route.Route,
 	// as failed if we don't skip temp error.
 	if !skipTempErr {
 		err := r.cfg.Control.FailPayment(paymentIdentifier, reason)
-		if err != nil {
+


I think a better approach is to perform a check on this payment, if it's already failed, we skip calling the above FailPayment. We don't wanna this single case to change the underlying logic/assumptions for our CRUD.

Yes, I think that’s a better approach too.

ok added a check into the fail method so that we just return nil if it is already failed.

lightninglabs-deploy · 2025-03-14T20:08:31Z

@ziggie1984, remember to re-request review from reviewers when ready

yyforyongyu

I think we should just do another payment check in sendToRoute and exit if it's already failed,

diff --git a/routing/router.go b/routing/router.go
index 323fe7616..6e95a5ffd 100644
--- a/routing/router.go
+++ b/routing/router.go
@@ -1199,7 +1199,21 @@ func (r *ChannelRouter) sendToRoute(htlcHash lntypes.Hash, rt *route.Route,
 	// An error returned from collecting the result, we'll mark the payment
 	// as failed if we don't skip temp error.
 	if !skipTempErr {
-		err := r.cfg.Control.FailPayment(paymentIdentifier, reason)
+		// We now look up the payment to see if it's already failed.
+		payment, err := p.router.cfg.Control.FetchPayment(p.identifier)
+		if err != nil {
+			return result.attempt, err
+		}
+
+		// Exit if the above error has caused the payment to be failed, we also
+		// return the error from sending attempt to mimic the old behavior of
+		// this method.
+		_, failedReason := payment.TerminalInfo()
+		if failedReason != nil {
+			return result.attempt, result.err
+		}
+
+		err = r.cfg.Control.FailPayment(paymentIdentifier, reason)
 		if err != nil {
 			return nil, err
 		}

routing/control_tower.go

routing/router.go

yyforyongyu

Pending linter fix otherwise good to go🚢

yyforyongyu · 2025-03-21T01:15:02Z

routing/router.go

+		// already failed.
+		_, failedReason := payment.TerminalInfo()
+		if failedReason != nil {
+			return nil


previously we'd return return result.attempt, result.err when there's a failed reason, but it's no longer returned?

yes I kept it the same, failPayment returns nil, and then we return:

return result.attempt, result.err ?

routing/router.go

starius

LGTM!
The code and the concept looks good to me!
I propose to add an itest to help prevent this bug in the future.

starius · 2025-03-21T14:09:39Z

routing/router.go

@@ -1048,6 +1048,29 @@ func (r *ChannelRouter) sendToRoute(htlcHash lntypes.Hash, rt *route.Route,
 	firstHopCustomRecords lnwire.CustomRecords) (*channeldb.HTLCAttempt,
 	error) {

+	// Helper function to fail a payment. It makes sure the payment is only
+	// failed once so that the failure reason is not overwritten.
+	failPayment := func(paymentIdentifier lntypes.Hash,


In the bug report it is said that the bug is reproducible with bos probe. I propose to add an itest reproducing the original bug to make sure it won't re-occur in the future if the code is changed. The itest would fail if run without this patch and pass if the patch is applied.

added an itest.

itest/lnd_trackpayments_test.go

routing/router.go

yyforyongyu

LGTM🚢

ziggie1984 requested a review from yyforyongyu February 22, 2025 10:45

ziggie1984 force-pushed the fix-payment-inconsitency branch from ab5cd5f to 4eca3b9 Compare February 22, 2025 10:47

ziggie1984 marked this pull request as ready for review February 22, 2025 10:47

yyforyongyu reviewed Feb 26, 2025

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saubyk assigned ziggie1984 Mar 3, 2025

ziggie1984 force-pushed the fix-payment-inconsitency branch from 4eca3b9 to 38bbcaf Compare March 18, 2025 23:08

saubyk added this to the v0.19.0 milestone Mar 18, 2025

ziggie1984 requested review from yyforyongyu and MPins March 18, 2025 23:30

ziggie1984 added this to lnd v0.19 Mar 18, 2025

ziggie1984 added payments Related to invoices/payments notifications labels Mar 18, 2025

saubyk moved this to In Progress in lnd v0.19 Mar 18, 2025

ziggie1984 force-pushed the fix-payment-inconsitency branch 2 times, most recently from f74c370 to bee1eba Compare March 19, 2025 00:19

yyforyongyu requested changes Mar 19, 2025

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ziggie1984 force-pushed the fix-payment-inconsitency branch 3 times, most recently from 91a37c4 to fc69b22 Compare March 19, 2025 07:44

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ziggie1984 force-pushed the fix-payment-inconsitency branch from fc69b22 to e01814a Compare March 19, 2025 15:26

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ziggie1984 force-pushed the fix-payment-inconsitency branch from e01814a to 398f4ab Compare March 19, 2025 17:53

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ziggie1984 force-pushed the fix-payment-inconsitency branch from 0e37e4e to 76a6296 Compare March 21, 2025 18:22

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ziggie1984 added 3 commits March 24, 2025 09:17

routing: Ensure to not fail a payment twice

4bdd375

docs: add release-notes

9e683a3

itest: add itest to test duplicate failure notification

b010e95

ziggie1984 force-pushed the fix-payment-inconsitency branch from 76a6296 to b010e95 Compare March 24, 2025 14:17

ziggie1984 requested a review from yyforyongyu March 24, 2025 14:18

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yyforyongyu merged commit 3351a17 into lightningnetwork:master Mar 25, 2025
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github-project-automation bot moved this from In Progress to Done in lnd v0.19 Mar 25, 2025

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multi: fix payment failure overwrite #9543

multi: fix payment failure overwrite #9543

ziggie1984 commented Feb 22, 2025 •

edited by saubyk

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multi: fix payment failure overwrite #9543

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ziggie1984 commented Feb 22, 2025 •

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