config: expose distinct accept-amp flag

This mirrors the accept-keysend flag, but also permits users to
eventually toggle off keysend separately from AMP.

config.go

@@ -338,6 +338,8 @@ type Config struct {
 
 	AcceptKeySend bool `long:"accept-keysend" description:"If true, spontaneous payments through keysend will be accepted. [experimental]"`
 
+	AcceptAMP bool `long:"accept-amp" description:"If true, spontaneous payments via AMP will be accepted."`
+
 	KeysendHoldTime time.Duration `long:"keysend-hold-time" description:"If non-zero, keysend payments are accepted but not immediately settled. If the payment isn't settled manually after the specified time, it is canceled automatically. [experimental]"`
 
 	GcCanceledInvoicesOnStartup bool `long:"gc-canceled-invoices-on-startup" description:"If true, we'll attempt to garbage collect canceled invoices upon start."`

invoices/invoiceregistry.go

@@ -57,6 +57,10 @@ type RegistryConfig struct {
 	// send payments.
 	AcceptKeySend bool
 
+	// AcceptAMP indicates whether we want to accept spontaneous AMP
+	// payments.
+	AcceptAMP bool
+
 	// GcCanceledInvoicesOnStartup if set, we'll attempt to garbage collect
 	// all canceled invoices upon start.
 	GcCanceledInvoicesOnStartup bool
@@ -884,11 +888,12 @@ func (i *InvoiceRegistry) NotifyExitHopHtlc(rHash lntypes.Hash,
 		amp:                  payload.AMPRecord(),
 	}
 
-	// Process keysend if present. Do this outside of the lock, because
-	// AddInvoice obtains its own lock. This is no problem, because the
-	// operation is idempotent.
-	if i.cfg.AcceptKeySend {
-		if ctx.amp != nil {
+	switch {
+
+	// If we are accepting spontaneous AMP payments and this payload
+	// contains an AMP record, create an AMP invoice that will be settled
+	// below.
+	case i.cfg.AcceptAMP && ctx.amp != nil:
 		err := i.processAMP(ctx)
 		if err != nil {
 			ctx.log(fmt.Sprintf("amp error: %v", err))
@@ -897,7 +902,12 @@ func (i *InvoiceRegistry) NotifyExitHopHtlc(rHash lntypes.Hash,
 				circuitKey, currentHeight, ResultAmpError,
 			), nil
 		}
-		} else {
+
+	// If we are accepting spontaneous keysend payments, create a regular
+	// invoice that will be settled below. We also enforce that this is only
+	// done when no AMP payload is present since it will only be settle-able
+	// by regular HTLCs.
+	case i.cfg.AcceptKeySend && ctx.amp == nil:
 		err := i.processKeySend(ctx)
 		if err != nil {
 			ctx.log(fmt.Sprintf("keysend error: %v", err))
@@ -907,7 +917,6 @@ func (i *InvoiceRegistry) NotifyExitHopHtlc(rHash lntypes.Hash,
 			), nil
 		}
 	}
-	}
 
 	// Execute locked notify exit hop logic.
 	i.Lock()

invoices/invoiceregistry_test.go

@@ -1290,7 +1290,7 @@ func TestAMPWithoutMPPPayload(t *testing.T) {
 	ctx := newTestContext(t)
 	defer ctx.cleanup()
 
-	ctx.registry.cfg.AcceptKeySend = true
+	ctx.registry.cfg.AcceptAMP = true
 
 	const (
 		shardAmt = lnwire.MilliSatoshi(10)
@@ -1320,37 +1320,37 @@ func TestAMPWithoutMPPPayload(t *testing.T) {
 func TestSpontaneousAmpPayment(t *testing.T) {
 	tests := []struct {
 		name               string
-		keySendEnabled     bool
+		ampEnabled         bool
 		failReconstruction bool
 		numShards          int
 	}{
 		{
 			name:               "enabled valid one shard",
-			keySendEnabled:     true,
+			ampEnabled:         true,
 			failReconstruction: false,
 			numShards:          1,
 		},
 		{
 			name:               "enabled valid multiple shards",
-			keySendEnabled:     true,
+			ampEnabled:         true,
 			failReconstruction: false,
 			numShards:          3,
 		},
 		{
 			name:               "enabled invalid one shard",
-			keySendEnabled:     true,
+			ampEnabled:         true,
 			failReconstruction: true,
 			numShards:          1,
 		},
 		{
 			name:               "enabled invalid multiple shards",
-			keySendEnabled:     true,
+			ampEnabled:         true,
 			failReconstruction: true,
 			numShards:          3,
 		},
 		{
 			name:               "disabled valid multiple shards",
-			keySendEnabled:     false,
+			ampEnabled:         false,
 			failReconstruction: false,
 			numShards:          3,
 		},
@@ -1360,7 +1360,7 @@ func TestSpontaneousAmpPayment(t *testing.T) {
 		test := test
 		t.Run(test.name, func(t *testing.T) {
 			testSpontaneousAmpPayment(
-				t, test.keySendEnabled, test.failReconstruction,
+				t, test.ampEnabled, test.failReconstruction,
 				test.numShards,
 			)
 		})
@@ -1369,14 +1369,14 @@ func TestSpontaneousAmpPayment(t *testing.T) {
 
 // testSpontaneousAmpPayment runs a specific spontaneous AMP test case.
 func testSpontaneousAmpPayment(
-	t *testing.T, keySendEnabled, failReconstruction bool, numShards int) {
+	t *testing.T, ampEnabled, failReconstruction bool, numShards int) {
 
 	defer timeout()()
 
 	ctx := newTestContext(t)
 	defer ctx.cleanup()
 
-	ctx.registry.cfg.AcceptKeySend = keySendEnabled
+	ctx.registry.cfg.AcceptAMP = ampEnabled
 
 	allSubscriptions, err := ctx.registry.SubscribeNotifications(0, 0)
 	require.Nil(t, err)
@@ -1471,7 +1471,7 @@ func testSpontaneousAmpPayment(
 		// When keysend is disabled all HTLC should fail with invoice
 		// not found, since one is not inserted before executing
 		// UpdateInvoice.
-		if !keySendEnabled {
+		if !ampEnabled {
 			require.NotNil(t, resolution)
 			checkFailResolution(t, resolution, ResultInvoiceNotFound)
 			continue
@@ -1515,7 +1515,7 @@ func testSpontaneousAmpPayment(
 	}
 
 	// No need to check the hodl chans when keysend is not enabled.
-	if !keySendEnabled {
+	if !ampEnabled {
 		return
 	}
 

lntest/node.go

@@ -210,6 +210,7 @@ type NodeConfig struct {
 	ProfilePort int
 
 	AcceptKeySend bool
+	AcceptAMP     bool
 
 	FeeURL string
 
@@ -297,6 +298,10 @@ func (cfg NodeConfig) genArgs() []string {
 		args = append(args, "--accept-keysend")
 	}
 
+	if cfg.AcceptAMP {
+		args = append(args, "--accept-amp")
+	}
+
 	if cfg.Etcd {
 		args = append(args, "--db.backend=etcd")
 		args = append(args, "--db.etcd.embedded")

sample-lnd.conf

@@ -375,6 +375,10 @@
 ; automatically. [experimental]
 ; keysend-hold-time=true
 
+; If true, spontaneous payments through AMP will be accepted. Payments to AMP
+; invoices will be accepted regardless of this setting.
+; accept-amp=true
+
 ; If set, lnd will use anchor channels by default if the remote channel party
 ; supports them. Note that lnd will require 1 UTXO to be reserved for this
 ; channel type if it is enabled.

server.go

@@ -427,6 +427,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		HtlcHoldDuration:            invoices.DefaultHtlcHoldDuration,
 		Clock:                       clock.NewDefaultClock(),
 		AcceptKeySend:               cfg.AcceptKeySend,
+		AcceptAMP:                   cfg.AcceptAMP,
 		GcCanceledInvoicesOnStartup: cfg.GcCanceledInvoicesOnStartup,
 		GcCanceledInvoicesOnTheFly:  cfg.GcCanceledInvoicesOnTheFly,
 		KeysendHoldTime:             cfg.KeysendHoldTime,