forked from lightningnetwork/lnd
-
Notifications
You must be signed in to change notification settings - Fork 0
/
breacharbiter.go
1553 lines (1305 loc) · 49.2 KB
/
breacharbiter.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
package main
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io"
"sync"
"sync/atomic"
"github.com/Divicoin/btcd/blockchain"
"github.com/Divicoin/btcd/chaincfg/chainhash"
"github.com/Divicoin/btcd/txscript"
"github.com/Divicoin/btcd/wire"
"github.com/Divicoin/btcutil"
"github.com/coreos/bbolt"
"github.com/davecgh/go-spew/spew"
"github.com/lightningnetwork/lnd/chainntnfs"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/htlcswitch"
"github.com/lightningnetwork/lnd/input"
"github.com/lightningnetwork/lnd/lnwallet"
)
var (
// retributionBucket stores retribution state on disk between detecting
// a contract breach, broadcasting a justice transaction that sweeps the
// channel, and finally witnessing the justice transaction confirm on
// the blockchain. It is critical that such state is persisted on disk,
// so that if our node restarts at any point during the retribution
// procedure, we can recover and continue from the persisted state.
retributionBucket = []byte("retribution")
// justiceTxnBucket holds the finalized justice transactions for all
// breached contracts. Entries are added to the justice txn bucket just
// before broadcasting the sweep txn.
justiceTxnBucket = []byte("justice-txn")
// errBrarShuttingDown is an error returned if the breacharbiter has
// been signalled to exit.
errBrarShuttingDown = errors.New("breacharbiter shutting down")
)
// ContractBreachEvent is an event the breachArbiter will receive in case a
// contract breach is observed on-chain. It contains the necessary information
// to handle the breach, and a ProcessACK channel we will use to ACK the event
// when we have safely stored all the necessary information.
type ContractBreachEvent struct {
// ChanPoint is the channel point of the breached channel.
ChanPoint wire.OutPoint
// ProcessACK is an error channel where a nil error should be sent
// iff the breach retribution info is safely stored in the retribution
// store. In case storing the information to the store fails, a non-nil
// error should be sent.
ProcessACK chan error
// BreachRetribution is the information needed to act on this contract
// breach.
BreachRetribution *lnwallet.BreachRetribution
}
// BreachConfig bundles the required subsystems used by the breach arbiter. An
// instance of BreachConfig is passed to newBreachArbiter during instantiation.
type BreachConfig struct {
// CloseLink allows the breach arbiter to shutdown any channel links for
// which it detects a breach, ensuring now further activity will
// continue across the link. The method accepts link's channel point and
// a close type to be included in the channel close summary.
CloseLink func(*wire.OutPoint, htlcswitch.ChannelCloseType)
// DB provides access to the user's channels, allowing the breach
// arbiter to determine the current state of a user's channels, and how
// it should respond to channel closure.
DB *channeldb.DB
// Estimator is used by the breach arbiter to determine an appropriate
// fee level when generating, signing, and broadcasting sweep
// transactions.
Estimator lnwallet.FeeEstimator
// GenSweepScript generates the receiving scripts for swept outputs.
GenSweepScript func() ([]byte, error)
// Notifier provides a publish/subscribe interface for event driven
// notifications regarding the confirmation of txids.
Notifier chainntnfs.ChainNotifier
// PublishTransaction facilitates the process of broadcasting a
// transaction to the network.
PublishTransaction func(*wire.MsgTx) error
// ContractBreaches is a channel where the breachArbiter will receive
// notifications in the event of a contract breach being observed. A
// ContractBreachEvent must be ACKed by the breachArbiter, such that
// the sending subsystem knows that the event is properly handed off.
ContractBreaches <-chan *ContractBreachEvent
// Signer is used by the breach arbiter to generate sweep transactions,
// which move coins from previously open channels back to the user's
// wallet.
Signer input.Signer
// Store is a persistent resource that maintains information regarding
// breached channels. This is used in conjunction with DB to recover
// from crashes, restarts, or other failures.
Store RetributionStore
}
// breachArbiter is a special subsystem which is responsible for watching and
// acting on the detection of any attempted uncooperative channel breaches by
// channel counterparties. This file essentially acts as deterrence code for
// those attempting to launch attacks against the daemon. In practice it's
// expected that the logic in this file never gets executed, but it is
// important to have it in place just in case we encounter cheating channel
// counterparties.
// TODO(roasbeef): closures in config for subsystem pointers to decouple?
type breachArbiter struct {
started uint32 // To be used atomically.
stopped uint32 // To be used atomically.
cfg *BreachConfig
quit chan struct{}
wg sync.WaitGroup
sync.Mutex
}
// newBreachArbiter creates a new instance of a breachArbiter initialized with
// its dependent objects.
func newBreachArbiter(cfg *BreachConfig) *breachArbiter {
return &breachArbiter{
cfg: cfg,
quit: make(chan struct{}),
}
}
// Start is an idempotent method that officially starts the breachArbiter along
// with all other goroutines it needs to perform its functions.
func (b *breachArbiter) Start() error {
if !atomic.CompareAndSwapUint32(&b.started, 0, 1) {
return nil
}
brarLog.Tracef("Starting breach arbiter")
// Load all retributions currently persisted in the retribution store.
breachRetInfos := make(map[wire.OutPoint]retributionInfo)
if err := b.cfg.Store.ForAll(func(ret *retributionInfo) error {
breachRetInfos[ret.chanPoint] = *ret
return nil
}); err != nil {
return err
}
// Load all currently closed channels from disk, we will use the
// channels that have been marked fully closed to filter the retribution
// information loaded from disk. This is necessary in the event that the
// channel was marked fully closed, but was not removed from the
// retribution store.
closedChans, err := b.cfg.DB.FetchClosedChannels(false)
if err != nil {
brarLog.Errorf("Unable to fetch closing channels: %v", err)
return err
}
// Using the set of non-pending, closed channels, reconcile any
// discrepancies between the channeldb and the retribution store by
// removing any retribution information for which we have already
// finished our responsibilities. If the removal is successful, we also
// remove the entry from our in-memory map, to avoid any further action
// for this channel.
// TODO(halseth): no need continue on IsPending once closed channels
// actually means close transaction is confirmed.
for _, chanSummary := range closedChans {
if chanSummary.IsPending {
continue
}
chanPoint := &chanSummary.ChanPoint
if _, ok := breachRetInfos[*chanPoint]; ok {
if err := b.cfg.Store.Remove(chanPoint); err != nil {
brarLog.Errorf("Unable to remove closed "+
"chanid=%v from breach arbiter: %v",
chanPoint, err)
return err
}
delete(breachRetInfos, *chanPoint)
}
}
// Spawn the exactRetribution tasks to monitor and resolve any breaches
// that were loaded from the retribution store.
for chanPoint := range breachRetInfos {
retInfo := breachRetInfos[chanPoint]
// Register for a notification when the breach transaction is
// confirmed on chain.
breachTXID := retInfo.commitHash
breachScript := retInfo.breachedOutputs[0].signDesc.Output.PkScript
confChan, err := b.cfg.Notifier.RegisterConfirmationsNtfn(
&breachTXID, breachScript, 1, retInfo.breachHeight,
)
if err != nil {
brarLog.Errorf("Unable to register for conf updates "+
"for txid: %v, err: %v", breachTXID, err)
return err
}
// Launch a new goroutine which to finalize the channel
// retribution after the breach transaction confirms.
b.wg.Add(1)
go b.exactRetribution(confChan, &retInfo)
}
// Start watching the remaining active channels!
b.wg.Add(1)
go b.contractObserver()
return nil
}
// Stop is an idempotent method that signals the breachArbiter to execute a
// graceful shutdown. This function will block until all goroutines spawned by
// the breachArbiter have gracefully exited.
func (b *breachArbiter) Stop() error {
if !atomic.CompareAndSwapUint32(&b.stopped, 0, 1) {
return nil
}
brarLog.Infof("Breach arbiter shutting down")
close(b.quit)
b.wg.Wait()
return nil
}
// IsBreached queries the breach arbiter's retribution store to see if it is
// aware of any channel breaches for a particular channel point.
func (b *breachArbiter) IsBreached(chanPoint *wire.OutPoint) (bool, error) {
return b.cfg.Store.IsBreached(chanPoint)
}
// contractObserver is the primary goroutine for the breachArbiter. This
// goroutine is responsible for handling breach events coming from the
// contractcourt on the ContractBreaches channel. If a channel breach is
// detected, then the contractObserver will execute the retribution logic
// required to sweep ALL outputs from a contested channel into the daemon's
// wallet.
//
// NOTE: This MUST be run as a goroutine.
func (b *breachArbiter) contractObserver() {
defer b.wg.Done()
brarLog.Infof("Starting contract observer, watching for breaches.")
for {
select {
case breachEvent := <-b.cfg.ContractBreaches:
// We have been notified about a contract breach!
// Handle the handoff, making sure we ACK the event
// after we have safely added it to the retribution
// store.
b.wg.Add(1)
go b.handleBreachHandoff(breachEvent)
case <-b.quit:
return
}
}
}
// convertToSecondLevelRevoke takes a breached output, and a transaction that
// spends it to the second level, and mutates the breach output into one that
// is able to properly sweep that second level output. We'll use this function
// when we go to sweep a breached commitment transaction, but the cheating
// party has already attempted to take it to the second level
func convertToSecondLevelRevoke(bo *breachedOutput, breachInfo *retributionInfo,
spendDetails *chainntnfs.SpendDetail) {
// In this case, we'll modify the witness type of this output to
// actually prepare for a second level revoke.
bo.witnessType = input.HtlcSecondLevelRevoke
// We'll also redirect the outpoint to this second level output, so the
// spending transaction updates it inputs accordingly.
spendingTx := spendDetails.SpendingTx
oldOp := bo.outpoint
bo.outpoint = wire.OutPoint{
Hash: spendingTx.TxHash(),
Index: 0,
}
// Next, we need to update the amount so we can do fee estimation
// properly, and also so we can generate a valid signature as we need
// to know the new input value (the second level transactions shaves
// off some funds to fees).
newAmt := spendingTx.TxOut[0].Value
bo.amt = btcutil.Amount(newAmt)
bo.signDesc.Output.Value = newAmt
bo.signDesc.Output.PkScript = spendingTx.TxOut[0].PkScript
// Finally, we'll need to adjust the witness program in the
// SignDescriptor.
bo.signDesc.WitnessScript = bo.secondLevelWitnessScript
brarLog.Warnf("HTLC(%v) for ChannelPoint(%v) has been spent to the "+
"second-level, adjusting -> %v", oldOp, breachInfo.chanPoint,
bo.outpoint)
}
// waitForSpendEvent waits for any of the breached outputs to get spent, and
// mutates the breachInfo to be able to sweep it. This method should be used
// when we fail to publish the justice tx because of a double spend, indicating
// that the counter party has taken one of the breached outputs to the second
// level. The spendNtfns map is a cache used to store registered spend
// subscriptions, in case we must call this method multiple times.
func (b *breachArbiter) waitForSpendEvent(breachInfo *retributionInfo,
spendNtfns map[wire.OutPoint]*chainntnfs.SpendEvent) error {
inputs := breachInfo.breachedOutputs
// spend is used to wrap the index of the output that gets spent
// together with the spend details.
type spend struct {
index int
detail *chainntnfs.SpendDetail
}
// We create a channel the first goroutine that gets a spend event can
// signal. We make it buffered in case multiple spend events come in at
// the same time.
anySpend := make(chan struct{}, len(inputs))
// The allSpends channel will be used to pass spend events from all the
// goroutines that detects a spend before they are signalled to exit.
allSpends := make(chan spend, len(inputs))
// exit will be used to signal the goroutines that they can exit.
exit := make(chan struct{})
var wg sync.WaitGroup
// We'll now launch a goroutine for each of the HTLC outputs, that will
// signal the moment they detect a spend event.
for i := range inputs {
breachedOutput := &inputs[i]
brarLog.Infof("Checking spend from %v(%v) for ChannelPoint(%v)",
breachedOutput.witnessType, breachedOutput.outpoint,
breachInfo.chanPoint)
// If we have already registered for a notification for this
// output, we'll reuse it.
spendNtfn, ok := spendNtfns[breachedOutput.outpoint]
if !ok {
var err error
spendNtfn, err = b.cfg.Notifier.RegisterSpendNtfn(
&breachedOutput.outpoint,
breachedOutput.signDesc.Output.PkScript,
breachInfo.breachHeight,
)
if err != nil {
brarLog.Errorf("Unable to check for spentness "+
"of outpoint=%v: %v",
breachedOutput.outpoint, err)
// Registration may have failed if we've been
// instructed to shutdown. If so, return here
// to avoid entering an infinite loop.
select {
case <-b.quit:
return errBrarShuttingDown
default:
continue
}
}
spendNtfns[breachedOutput.outpoint] = spendNtfn
}
// Launch a goroutine waiting for a spend event.
b.wg.Add(1)
wg.Add(1)
go func(index int, spendEv *chainntnfs.SpendEvent) {
defer b.wg.Done()
defer wg.Done()
select {
// The output has been taken to the second level!
case sp, ok := <-spendEv.Spend:
if !ok {
return
}
brarLog.Infof("Detected spend on %s(%v) by "+
"txid(%v) for ChannelPoint(%v)",
inputs[index].witnessType,
inputs[index].outpoint,
sp.SpenderTxHash,
breachInfo.chanPoint)
// First we send the spend event on the
// allSpends channel, such that it can be
// handled after all go routines have exited.
allSpends <- spend{index, sp}
// Finally we'll signal the anySpend channel
// that a spend was detected, such that the
// other goroutines can be shut down.
anySpend <- struct{}{}
case <-exit:
return
case <-b.quit:
return
}
}(i, spendNtfn)
}
// We'll wait for any of the outputs to be spent, or that we are
// signalled to exit.
select {
// A goroutine have signalled that a spend occurred.
case <-anySpend:
// Signal for the remaining goroutines to exit.
close(exit)
wg.Wait()
// At this point all goroutines that can send on the allSpends
// channel have exited. We can therefore safely close the
// channel before ranging over its content.
close(allSpends)
doneOutputs := make(map[int]struct{})
for s := range allSpends {
breachedOutput := &inputs[s.index]
delete(spendNtfns, breachedOutput.outpoint)
switch breachedOutput.witnessType {
case input.HtlcAcceptedRevoke:
fallthrough
case input.HtlcOfferedRevoke:
brarLog.Infof("Spend on second-level"+
"%s(%v) for ChannelPoint(%v) "+
"transitions to second-level output",
breachedOutput.witnessType,
breachedOutput.outpoint,
breachInfo.chanPoint)
// In this case we'll morph our initial revoke
// spend to instead point to the second level
// output, and update the sign descriptor in the
// process.
convertToSecondLevelRevoke(
breachedOutput, breachInfo, s.detail,
)
continue
}
brarLog.Infof("Spend on %s(%v) for ChannelPoint(%v) "+
"transitions output to terminal state, "+
"removing input from justice transaction",
breachedOutput.witnessType,
breachedOutput.outpoint, breachInfo.chanPoint)
doneOutputs[s.index] = struct{}{}
}
// Filter the inputs for which we can no longer proceed.
var nextIndex int
for i := range inputs {
if _, ok := doneOutputs[i]; ok {
continue
}
inputs[nextIndex] = inputs[i]
nextIndex++
}
// Update our remaining set of outputs before continuing with
// another attempt at publication.
breachInfo.breachedOutputs = inputs[:nextIndex]
case <-b.quit:
return errBrarShuttingDown
}
return nil
}
// exactRetribution is a goroutine which is executed once a contract breach has
// been detected by a breachObserver. This function is responsible for
// punishing a counterparty for violating the channel contract by sweeping ALL
// the lingering funds within the channel into the daemon's wallet.
//
// NOTE: This MUST be run as a goroutine.
func (b *breachArbiter) exactRetribution(confChan *chainntnfs.ConfirmationEvent,
breachInfo *retributionInfo) {
defer b.wg.Done()
// TODO(roasbeef): state needs to be checkpointed here
var breachConfHeight uint32
select {
case breachConf, ok := <-confChan.Confirmed:
// If the second value is !ok, then the channel has been closed
// signifying a daemon shutdown, so we exit.
if !ok {
return
}
breachConfHeight = breachConf.BlockHeight
// Otherwise, if this is a real confirmation notification, then
// we fall through to complete our duty.
case <-b.quit:
return
}
brarLog.Debugf("Breach transaction %v has been confirmed, sweeping "+
"revoked funds", breachInfo.commitHash)
// We may have to wait for some of the HTLC outputs to be spent to the
// second level before broadcasting the justice tx. We'll store the
// SpendEvents between each attempt to not re-register uneccessarily.
spendNtfns := make(map[wire.OutPoint]*chainntnfs.SpendEvent)
finalTx, err := b.cfg.Store.GetFinalizedTxn(&breachInfo.chanPoint)
if err != nil {
brarLog.Errorf("Unable to get finalized txn for"+
"chanid=%v: %v", &breachInfo.chanPoint, err)
return
}
// If this retribution has not been finalized before, we will first
// construct a sweep transaction and write it to disk. This will allow
// the breach arbiter to re-register for notifications for the justice
// txid.
justiceTxBroadcast:
if finalTx == nil {
// With the breach transaction confirmed, we now create the
// justice tx which will claim ALL the funds within the
// channel.
finalTx, err = b.createJusticeTx(breachInfo)
if err != nil {
brarLog.Errorf("Unable to create justice tx: %v", err)
return
}
// Persist our finalized justice transaction before making an
// attempt to broadcast.
err := b.cfg.Store.Finalize(&breachInfo.chanPoint, finalTx)
if err != nil {
brarLog.Errorf("Unable to finalize justice tx for "+
"chanid=%v: %v", &breachInfo.chanPoint, err)
return
}
}
brarLog.Debugf("Broadcasting justice tx: %v", newLogClosure(func() string {
return spew.Sdump(finalTx)
}))
// We'll now attempt to broadcast the transaction which finalized the
// channel's retribution against the cheating counter party.
err = b.cfg.PublishTransaction(finalTx)
if err != nil {
brarLog.Errorf("Unable to broadcast justice tx: %v", err)
if err == lnwallet.ErrDoubleSpend {
// Broadcasting the transaction failed because of a
// conflict either in the mempool or in chain. We'll
// now create spend subscriptions for all HTLC outputs
// on the commitment transaction that could possibly
// have been spent, and wait for any of them to
// trigger.
brarLog.Infof("Waiting for a spend event before " +
"attempting to craft new justice tx.")
finalTx = nil
err := b.waitForSpendEvent(breachInfo, spendNtfns)
if err != nil {
if err != errBrarShuttingDown {
brarLog.Errorf("error waiting for "+
"spend event: %v", err)
}
return
}
if len(breachInfo.breachedOutputs) == 0 {
brarLog.Debugf("No more outputs to sweep for "+
"breach, marking ChannelPoint(%v) "+
"fully resolved", breachInfo.chanPoint)
err = b.cleanupBreach(&breachInfo.chanPoint)
if err != nil {
brarLog.Errorf("Failed to cleanup "+
"breached ChannelPoint(%v): %v",
breachInfo.chanPoint, err)
}
return
}
brarLog.Infof("Attempting another justice tx "+
"with %d inputs",
len(breachInfo.breachedOutputs))
goto justiceTxBroadcast
}
}
// As a conclusionary step, we register for a notification to be
// dispatched once the justice tx is confirmed. After confirmation we
// notify the caller that initiated the retribution workflow that the
// deed has been done.
justiceTXID := finalTx.TxHash()
justiceScript := finalTx.TxOut[0].PkScript
confChan, err = b.cfg.Notifier.RegisterConfirmationsNtfn(
&justiceTXID, justiceScript, 1, breachConfHeight,
)
if err != nil {
brarLog.Errorf("Unable to register for conf for txid(%v): %v",
justiceTXID, err)
return
}
select {
case _, ok := <-confChan.Confirmed:
if !ok {
return
}
// Compute both the total value of funds being swept and the
// amount of funds that were revoked from the counter party.
var totalFunds, revokedFunds btcutil.Amount
for _, inp := range breachInfo.breachedOutputs {
totalFunds += inp.Amount()
// If the output being revoked is the remote commitment
// output or an offered HTLC output, it's amount
// contributes to the value of funds being revoked from
// the counter party.
switch inp.WitnessType() {
case input.CommitmentRevoke:
revokedFunds += inp.Amount()
case input.HtlcOfferedRevoke:
revokedFunds += inp.Amount()
default:
}
}
brarLog.Infof("Justice for ChannelPoint(%v) has "+
"been served, %v revoked funds (%v total) "+
"have been claimed", breachInfo.chanPoint,
revokedFunds, totalFunds)
err = b.cleanupBreach(&breachInfo.chanPoint)
if err != nil {
brarLog.Errorf("Failed to cleanup breached "+
"ChannelPoint(%v): %v", breachInfo.chanPoint,
err)
}
// TODO(roasbeef): add peer to blacklist?
// TODO(roasbeef): close other active channels with offending
// peer
return
case <-b.quit:
return
}
}
// cleanupBreach marks the given channel point as fully resolved and removes the
// retribution for that the channel from the retribution store.
func (b *breachArbiter) cleanupBreach(chanPoint *wire.OutPoint) error {
// With the channel closed, mark it in the database as such.
err := b.cfg.DB.MarkChanFullyClosed(chanPoint)
if err != nil {
return fmt.Errorf("unable to mark chan as closed: %v", err)
}
// Justice has been carried out; we can safely delete the retribution
// info from the database.
err = b.cfg.Store.Remove(chanPoint)
if err != nil {
return fmt.Errorf("unable to remove retribution from db: %v",
err)
}
return nil
}
// handleBreachHandoff handles a new breach event, by writing it to disk, then
// notifies the breachArbiter contract observer goroutine that a channel's
// contract has been breached by the prior counterparty. Once notified the
// breachArbiter will attempt to sweep ALL funds within the channel using the
// information provided within the BreachRetribution generated due to the
// breach of channel contract. The funds will be swept only after the breaching
// transaction receives a necessary number of confirmations.
//
// NOTE: This MUST be run as a goroutine.
func (b *breachArbiter) handleBreachHandoff(breachEvent *ContractBreachEvent) {
defer b.wg.Done()
chanPoint := breachEvent.ChanPoint
brarLog.Debugf("Handling breach handoff for ChannelPoint(%v)",
chanPoint)
// A read from this channel indicates that a channel breach has been
// detected! So we notify the main coordination goroutine with the
// information needed to bring the counterparty to justice.
breachInfo := breachEvent.BreachRetribution
brarLog.Warnf("REVOKED STATE #%v FOR ChannelPoint(%v) "+
"broadcast, REMOTE PEER IS DOING SOMETHING "+
"SKETCHY!!!", breachInfo.RevokedStateNum,
chanPoint)
// Immediately notify the HTLC switch that this link has been
// breached in order to ensure any incoming or outgoing
// multi-hop HTLCs aren't sent over this link, nor any other
// links associated with this peer.
b.cfg.CloseLink(&chanPoint, htlcswitch.CloseBreach)
// TODO(roasbeef): need to handle case of remote broadcast
// mid-local initiated state-transition, possible
// false-positive?
// Acquire the mutex to ensure consistency between the call to
// IsBreached and Add below.
b.Lock()
// We first check if this breach info is already added to the
// retribution store.
breached, err := b.cfg.Store.IsBreached(&chanPoint)
if err != nil {
b.Unlock()
brarLog.Errorf("Unable to check breach info in DB: %v", err)
select {
case breachEvent.ProcessACK <- err:
case <-b.quit:
}
return
}
// If this channel is already marked as breached in the retribution
// store, we already have handled the handoff for this breach. In this
// case we can safely ACK the handoff, and return.
if breached {
b.Unlock()
select {
case breachEvent.ProcessACK <- nil:
case <-b.quit:
}
return
}
// Using the breach information provided by the wallet and the
// channel snapshot, construct the retribution information that
// will be persisted to disk.
retInfo := newRetributionInfo(&chanPoint, breachInfo)
// Persist the pending retribution state to disk.
err = b.cfg.Store.Add(retInfo)
b.Unlock()
if err != nil {
brarLog.Errorf("Unable to persist retribution "+
"info to db: %v", err)
}
// Now that the breach has been persisted, try to send an
// acknowledgment back to the close observer with the error. If
// the ack is successful, the close observer will mark the
// channel as pending-closed in the channeldb.
select {
case breachEvent.ProcessACK <- err:
// Bail if we failed to persist retribution info.
if err != nil {
return
}
case <-b.quit:
return
}
// Now that a new channel contract has been added to the retribution
// store, we first register for a notification to be dispatched once
// the breach transaction (the revoked commitment transaction) has been
// confirmed in the chain to ensure we're not dealing with a moving
// target.
breachTXID := &retInfo.commitHash
breachScript := retInfo.breachedOutputs[0].signDesc.Output.PkScript
cfChan, err := b.cfg.Notifier.RegisterConfirmationsNtfn(
breachTXID, breachScript, 1, retInfo.breachHeight,
)
if err != nil {
brarLog.Errorf("Unable to register for conf updates for "+
"txid: %v, err: %v", breachTXID, err)
return
}
brarLog.Warnf("A channel has been breached with txid: %v. Waiting "+
"for confirmation, then justice will be served!", breachTXID)
// With the retribution state persisted, channel close persisted, and
// notification registered, we launch a new goroutine which will
// finalize the channel retribution after the breach transaction has
// been confirmed.
b.wg.Add(1)
go b.exactRetribution(cfChan, retInfo)
}
// breachedOutput contains all the information needed to sweep a breached
// output. A breached output is an output that we are now entitled to due to a
// revoked commitment transaction being broadcast.
type breachedOutput struct {
amt btcutil.Amount
outpoint wire.OutPoint
witnessType input.WitnessType
signDesc input.SignDescriptor
confHeight uint32
secondLevelWitnessScript []byte
witnessFunc input.WitnessGenerator
}
// makeBreachedOutput assembles a new breachedOutput that can be used by the
// breach arbiter to construct a justice or sweep transaction.
func makeBreachedOutput(outpoint *wire.OutPoint,
witnessType input.WitnessType,
secondLevelScript []byte,
signDescriptor *input.SignDescriptor,
confHeight uint32) breachedOutput {
amount := signDescriptor.Output.Value
return breachedOutput{
amt: btcutil.Amount(amount),
outpoint: *outpoint,
secondLevelWitnessScript: secondLevelScript,
witnessType: witnessType,
signDesc: *signDescriptor,
confHeight: confHeight,
}
}
// Amount returns the number of satoshis contained in the breached output.
func (bo *breachedOutput) Amount() btcutil.Amount {
return bo.amt
}
// OutPoint returns the breached output's identifier that is to be included as a
// transaction input.
func (bo *breachedOutput) OutPoint() *wire.OutPoint {
return &bo.outpoint
}
// WitnessType returns the type of witness that must be generated to spend the
// breached output.
func (bo *breachedOutput) WitnessType() input.WitnessType {
return bo.witnessType
}
// SignDesc returns the breached output's SignDescriptor, which is used during
// signing to compute the witness.
func (bo *breachedOutput) SignDesc() *input.SignDescriptor {
return &bo.signDesc
}
// CraftInputScript computes a valid witness that allows us to spend from the
// breached output. It does so by first generating and memoizing the witness
// generation function, which parameterized primarily by the witness type and
// sign descriptor. The method then returns the witness computed by invoking
// this function on the first and subsequent calls.
func (bo *breachedOutput) CraftInputScript(signer input.Signer, txn *wire.MsgTx,
hashCache *txscript.TxSigHashes, txinIdx int) (*input.Script, error) {
// First, we ensure that the witness generation function has been
// initialized for this breached output.
bo.witnessFunc = bo.witnessType.GenWitnessFunc(
signer, bo.SignDesc(),
)
// Now that we have ensured that the witness generation function has
// been initialized, we can proceed to execute it and generate the
// witness for this particular breached output.
return bo.witnessFunc(txn, hashCache, txinIdx)
}
// BlocksToMaturity returns the relative timelock, as a number of blocks, that
// must be built on top of the confirmation height before the output can be
// spent.
func (bo *breachedOutput) BlocksToMaturity() uint32 {
return 0
}
// HeightHint returns the minimum height at which a confirmed spending tx can
// occur.
func (bo *breachedOutput) HeightHint() uint32 {
return bo.confHeight
}
// Add compile-time constraint ensuring breachedOutput implements the Input
// interface.
var _ input.Input = (*breachedOutput)(nil)
// retributionInfo encapsulates all the data needed to sweep all the contested
// funds within a channel whose contract has been breached by the prior
// counterparty. This struct is used to create the justice transaction which
// spends all outputs of the commitment transaction into an output controlled
// by the wallet.
type retributionInfo struct {
commitHash chainhash.Hash
chanPoint wire.OutPoint
chainHash chainhash.Hash
breachHeight uint32
breachedOutputs []breachedOutput
}
// newRetributionInfo constructs a retributionInfo containing all the
// information required by the breach arbiter to recover funds from breached
// channels. The information is primarily populated using the BreachRetribution
// delivered by the wallet when it detects a channel breach.
func newRetributionInfo(chanPoint *wire.OutPoint,
breachInfo *lnwallet.BreachRetribution) *retributionInfo {
// Determine the number of second layer HTLCs we will attempt to sweep.
nHtlcs := len(breachInfo.HtlcRetributions)
// Initialize a slice to hold the outputs we will attempt to sweep. The
// maximum capacity of the slice is set to 2+nHtlcs to handle the case
// where the local, remote, and all HTLCs are not dust outputs. All
// HTLC outputs provided by the wallet are guaranteed to be non-dust,
// though the commitment outputs are conditionally added depending on
// the nil-ness of their sign descriptors.
breachedOutputs := make([]breachedOutput, 0, nHtlcs+2)
// First, record the breach information for the local channel point if
// it is not considered dust, which is signaled by a non-nil sign
// descriptor. Here we use CommitmentNoDelay since this output belongs
// to us and has no time-based constraints on spending.
if breachInfo.LocalOutputSignDesc != nil {
localOutput := makeBreachedOutput(
&breachInfo.LocalOutpoint,
input.CommitmentNoDelay,
// No second level script as this is a commitment
// output.
nil,
breachInfo.LocalOutputSignDesc,
breachInfo.BreachHeight)
breachedOutputs = append(breachedOutputs, localOutput)
}
// Second, record the same information regarding the remote outpoint,
// again if it is not dust, which belongs to the party who tried to
// steal our money! Here we set witnessType of the breachedOutput to
// CommitmentRevoke, since we will be using a revoke key, withdrawing
// the funds from the commitment transaction immediately.
if breachInfo.RemoteOutputSignDesc != nil {
remoteOutput := makeBreachedOutput(
&breachInfo.RemoteOutpoint,
input.CommitmentRevoke,
// No second level script as this is a commitment
// output.
nil,
breachInfo.RemoteOutputSignDesc,
breachInfo.BreachHeight)
breachedOutputs = append(breachedOutputs, remoteOutput)
}
// Lastly, for each of the breached HTLC outputs, record each as a
// breached output with the appropriate witness type based on its
// directionality. All HTLC outputs provided by the wallet are assumed
// to be non-dust.
for i, breachedHtlc := range breachInfo.HtlcRetributions {
// Using the breachedHtlc's incoming flag, determine the
// appropriate witness type that needs to be generated in order
// to sweep the HTLC output.
var htlcWitnessType input.WitnessType
if breachedHtlc.IsIncoming {
htlcWitnessType = input.HtlcAcceptedRevoke
} else {
htlcWitnessType = input.HtlcOfferedRevoke
}
htlcOutput := makeBreachedOutput(
&breachInfo.HtlcRetributions[i].OutPoint,
htlcWitnessType,
breachInfo.HtlcRetributions[i].SecondLevelWitnessScript,
&breachInfo.HtlcRetributions[i].SignDesc,
breachInfo.BreachHeight)