multi: add height-based invoice expiry

This commit adds height-based invoice expiry for hodl invoices
that have active htlcs. This allows us to cancel our intentionally
held htlcs before channels are force closed. We only add this for
hodl invoices because we expect regular invoices to automatically
be resolved.

We still keep hodl invoices in the time-based expiry queue,
because we want to expire open invoices that reach their timeout
before any htlcs are added. Since htlcs are added after the
invoice is created, we add new htlcs as they arrive in the
invoice registry. In this commit, we allow adding of duplicate
entries for an invoice to be added to the expiry queue as each
htlc arrives to keep implementation simple. Our cancellation
logic can already handle the case where an entry is already
canceled, so this is ok.

config.go

@@ -344,6 +344,8 @@ type Config struct {
 
 	GcCanceledInvoicesOnTheFly bool `long:"gc-canceled-invoices-on-the-fly" description:"If true, we'll delete newly canceled invoices on the fly."`
 
+	Invoices *lncfg.Invoices `group:"invoices" namespace:"invoices"`
+
 	Routing *lncfg.Routing `group:"routing" namespace:"routing"`
 
 	Gossip *lncfg.Gossip `group:"gossip" namespace:"gossip"`
@@ -529,6 +531,9 @@ func DefaultConfig() Config {
 			MaxChannelUpdateBurst: discovery.DefaultMaxChannelUpdateBurst,
 			ChannelUpdateInterval: discovery.DefaultChannelUpdateInterval,
 		},
+		Invoices: &lncfg.Invoices{
+			HoldExpiryDelta: lncfg.DefaultHoldInvoiceExpiryDelta,
+		},
 		MaxOutgoingCltvExpiry:   htlcswitch.DefaultMaxOutgoingCltvExpiry,
 		MaxChannelFeeAllocation: htlcswitch.DefaultMaxLinkFeeAllocation,
 		MaxCommitFeeRateAnchors: lnwallet.DefaultAnchorsCommitMaxFeeRateSatPerVByte,
@@ -1369,6 +1374,18 @@ func ValidateConfig(cfg Config, usageMessage string,
 		return nil, err
 	}
 
+	// Log a warning if our expiry delta is not greater than our incoming
+	// broadcast delta. We do not fail here because this value may be set
+	// to zero to intentionally keep lnd's behavior unchanged from when we
+	// didn't auto-cancel these invoices.
+	if cfg.Invoices.HoldExpiryDelta <= lncfg.DefaultIncomingBroadcastDelta {
+		ltndLog.Warnf("Invoice hold expiry delta: %v <= incoming "+
+			"delta: %v, accepted hold invoices will force close "+
+			"channels if they are not canceled manually",
+			cfg.Invoices.HoldExpiryDelta,
+			lncfg.DefaultIncomingBroadcastDelta)
+	}
+
 	// Validate the subconfigs for workers, caches, and the tower client.
 	err = lncfg.Validate(
 		cfg.Workers,