Merge pull request #4455 from cfromknecht/psbt-no-publish

PSBT: add no_publish flag for safe batch channel opens v2

lnwallet/chanfunding/assembler.go

@@ -135,3 +135,18 @@ type FundingTxAssembler interface {
 	// transaction for the channel via the intent it returns.
 	FundingTxAvailable()
 }
+
+// ConditionalPublishAssembler is an assembler that can dynamically define if
+// the funding transaction should be published after channel negotiations or
+// not. Not publishing the transaction is only useful if the particular channel
+// the assembler is in charge of is part of a batch of channels. In that case
+// it is only safe to wait for all channel negotiations of the batch to complete
+// before publishing the batch transaction.
+type ConditionalPublishAssembler interface {
+	Assembler
+
+	// ShouldPublishFundingTx is a method of the assembler that signals if
+	// the funding transaction should be published after the channel
+	// negotiations are completed with the remote peer.
+	ShouldPublishFundingTx() bool
+}

lnwallet/chanfunding/psbt_assembler.go

@@ -387,6 +387,10 @@ type PsbtAssembler struct {
 	// netParams are the network parameters used to encode the P2WSH funding
 	// address.
 	netParams *chaincfg.Params
+
+	// shouldPublish specifies if the assembler should publish the
+	// transaction once the channel funding has completed.
+	shouldPublish bool
 }
 
 // NewPsbtAssembler creates a new CannedAssembler from the material required
@@ -394,12 +398,13 @@ type PsbtAssembler struct {
 // be supplied which will be used to add the channel output to instead of
 // creating a new one.
 func NewPsbtAssembler(fundingAmt btcutil.Amount, basePsbt *psbt.Packet,
-	netParams *chaincfg.Params) *PsbtAssembler {
+	netParams *chaincfg.Params, shouldPublish bool) *PsbtAssembler {
 
 	return &PsbtAssembler{
-		fundingAmt: fundingAmt,
-		basePsbt:   basePsbt,
-		netParams:  netParams,
+		fundingAmt:    fundingAmt,
+		basePsbt:      basePsbt,
+		netParams:     netParams,
+		shouldPublish: shouldPublish,
 	}
 }
 
@@ -436,16 +441,18 @@ func (p *PsbtAssembler) ProvisionChannel(req *Request) (Intent, error) {
 	return intent, nil
 }
 
-// FundingTxAvailable is an empty method that an assembler can implement to
-// signal to callers that its able to provide the funding transaction for the
-// channel via the intent it returns.
+// ShouldPublishFundingTx is a method of the assembler that signals if the
+// funding transaction should be published after the channel negotiations are
+// completed with the remote peer.
 //
-// NOTE: This method is a part of the FundingTxAssembler interface.
-func (p *PsbtAssembler) FundingTxAvailable() {}
+// NOTE: This method is a part of the ConditionalPublishAssembler interface.
+func (p *PsbtAssembler) ShouldPublishFundingTx() bool {
+	return p.shouldPublish
+}
 
-// A compile-time assertion to ensure PsbtAssembler meets the Assembler
-// interface.
-var _ Assembler = (*PsbtAssembler)(nil)
+// A compile-time assertion to ensure PsbtAssembler meets the
+// ConditionalPublishAssembler interface.
+var _ ConditionalPublishAssembler = (*PsbtAssembler)(nil)
 
 // sumUtxoInputValues tries to extract the sum of all inputs specified in the
 // UTXO fields of the PSBT. An error is returned if an input is specified that

lnwallet/chanfunding/psbt_assembler_test.go

@@ -34,7 +34,7 @@ func TestPsbtIntent(t *testing.T) {
 
 	// Create a simple assembler and ask it to provision a channel to get
 	// the funding intent.
-	a := NewPsbtAssembler(chanCapacity, nil, &params)
+	a := NewPsbtAssembler(chanCapacity, nil, &params, true)
 	intent, err := a.ProvisionChannel(&Request{LocalAmt: chanCapacity})
 	if err != nil {
 		t.Fatalf("error provisioning channel: %v", err)
@@ -215,7 +215,7 @@ func TestPsbtIntentBasePsbt(t *testing.T) {
 
 	// Now as the next step, create a new assembler/intent pair with a base
 	// PSBT to see that we can add an additional output to it.
-	a := NewPsbtAssembler(chanCapacity, pendingPsbt, &params)
+	a := NewPsbtAssembler(chanCapacity, pendingPsbt, &params, true)
 	intent, err := a.ProvisionChannel(&Request{LocalAmt: chanCapacity})
 	if err != nil {
 		t.Fatalf("error provisioning channel: %v", err)
@@ -373,7 +373,7 @@ func TestPsbtVerify(t *testing.T) {
 
 	// Create a simple assembler and ask it to provision a channel to get
 	// the funding intent.
-	a := NewPsbtAssembler(chanCapacity, nil, &params)
+	a := NewPsbtAssembler(chanCapacity, nil, &params, true)
 	intent, err := a.ProvisionChannel(&Request{LocalAmt: chanCapacity})
 	if err != nil {
 		t.Fatalf("error provisioning channel: %v", err)
@@ -500,7 +500,7 @@ func TestPsbtFinalize(t *testing.T) {
 
 	// Create a simple assembler and ask it to provision a channel to get
 	// the funding intent.
-	a := NewPsbtAssembler(chanCapacity, nil, &params)
+	a := NewPsbtAssembler(chanCapacity, nil, &params, true)
 	intent, err := a.ProvisionChannel(&Request{LocalAmt: chanCapacity})
 	if err != nil {
 		t.Fatalf("error provisioning channel: %v", err)

lnwallet/reservation.go

@@ -287,10 +287,24 @@ func NewChannelReservation(capacity, localFundingAmt btcutil.Amount,
 			chanType |= channeldb.SingleFunderBit
 		}
 
+		switch a := fundingAssembler.(type) {
+		// The first channels of a batch shouldn't publish the batch TX
+		// to avoid problems if some of the funding flows can't be
+		// completed. Only the last channel of a batch should publish.
+		case chanfunding.ConditionalPublishAssembler:
+			if !a.ShouldPublishFundingTx() {
+				chanType |= channeldb.NoFundingTxBit
+			}
+
+		// Normal funding flow, the assembler creates a TX from the
+		// internal wallet.
+		case chanfunding.FundingTxAssembler:
+			// Do nothing, a FundingTxAssembler has the transaction.
+
 		// If this intent isn't one that's able to provide us with a
 		// funding transaction, then we'll set the chanType bit to
 		// signal that we don't have access to one.
-		if _, ok := fundingAssembler.(chanfunding.FundingTxAssembler); !ok {
+		default:
 			chanType |= channeldb.NoFundingTxBit
 		}