multi: deprecate dust-treshold config value

Replace ambigious config value "dust-treshold" with a more clear
"channel-max-fee-exposure" exposure value. The old value is
deprecated and will be removed in the near future.

Author: ziggie1984

config.go

@@ -454,7 +454,9 @@ type Config struct {
 
 	GcCanceledInvoicesOnTheFly bool `long:"gc-canceled-invoices-on-the-fly" description:"If true, we'll delete newly canceled invoices on the fly."`
 
-	MaxFeeExposure uint64 `long:"dust-threshold" description:"Sets the max fee exposure in satoshis for a channel after which HTLC's will be failed."`
+	DustThreshold uint64 `long:"dust-threshold" description:"DEPRECATED: Sets the max fee exposure in satoshis for a channel after which HTLC's will be failed." hidden:"true"`
+
+	MaxFeeExposure uint64 `long:"channel-max-fee-exposure" description:" Limits the maximum fee exposure in sathosis of a channel. This value is enforced for all channels and is independent of the channel initiator."`
 
 	Fee *lncfg.Fee `group:"fee" namespace:"fee"`
 
@@ -714,6 +716,7 @@ func DefaultConfig() Config {
 		MaxChannelFeeAllocation:   htlcswitch.DefaultMaxLinkFeeAllocation,
 		MaxCommitFeeRateAnchors:   lnwallet.DefaultAnchorsCommitMaxFeeRateSatPerVByte,
 		MaxFeeExposure:            uint64(htlcswitch.DefaultMaxFeeExposure.ToSatoshis()),
+		DustThreshold:             uint64(htlcswitch.DefaultMaxFeeExposure.ToSatoshis()),
 		LogWriter:                 build.NewRotatingLogWriter(),
 		DB:                        lncfg.DefaultDB(),
 		Cluster:                   lncfg.DefaultCluster(),
@@ -1700,6 +1703,18 @@ func ValidateConfig(cfg Config, interceptor signal.Interceptor, fileParser,
 		return nil, mkErr("custom-message: %v", err)
 	}
 
+	// Don't allow both the old dust-threshold and the new
+	// channel-max-fee-exposure to be set.
+	if cfg.DustThreshold != 0 && cfg.MaxFeeExposure != 0 {
+		return nil, mkErr("cannot set both dust-threshold and " +
+			"channel-max-fee-exposure")
+	}
+
+	// Map the old dust-threshold to the new channel-max-fee-exposure.
+	if cfg.DustThreshold != 0 {
+		cfg.MaxFeeExposure = cfg.DustThreshold
+	}
+
 	// Validate the subconfigs for workers, caches, and the tower client.
 	err = lncfg.Validate(
 		cfg.Workers,

htlcswitch/switch_test.go

@@ -4522,8 +4522,8 @@ func TestSwitchDustForwarding(t *testing.T) {
 }
 
 // sendDustHtlcs is a helper function used to send many dust HTLC's to test the
-// Switch's dust-threshold logic. It takes a boolean denoting whether or not
-// Alice is the sender.
+// Switch's channel-max-fee-exposure logic. It takes a boolean denoting whether
+// or not Alice is the sender.
 func sendDustHtlcs(t *testing.T, n *threeHopNetwork, alice bool,
 	amt lnwire.MilliSatoshi, sid lnwire.ShortChannelID, numHTLCs int) {
 

itest/lnd_payment_test.go

@@ -820,7 +820,7 @@ func testBidirectionalAsyncPayments(ht *lntest.HarnessTest) {
 	args := []string{
 		// Increase the dust threshold to avoid the payments fail due
 		// to threshold limit reached.
-		"--dust-threshold=10000000",
+		"--channel-max-fee-exposure=10000000",
 
 		// Increase the pending commit interval since there are lots of
 		// commitment dances.

lntest/harness.go

@@ -316,7 +316,7 @@ func (h *HarnessTest) SetupStandbyNodes() {
 
 	lndArgs := []string{
 		"--default-remote-max-htlcs=483",
-		"--dust-threshold=5000000",
+		"--channel-max-fee-exposure=5000000",
 	}
 
 	// Start the initial seeder nodes within the test network.

sample-lnd.conf

@@ -467,11 +467,33 @@
 ; propagation 
 ; max-commit-fee-rate-anchors=10
 
-; A threshold defining the maximum amount of dust a given channel can have
-; after which forwarding and sending dust HTLC's to and from the channel will
-; fail. This amount is expressed in satoshis.
+; DEPRECATED: This value will be deprecated please use the new setting 
+; 'channel-max-fee-exposure'. This value is equivalent to the new fee exposure
+; limit but was removed because the name was ambigious.
 ; dust-threshold=500000
 
+; This value replaces the old 'dust-threshold' setting and defines the maximum
+; amount of satoshis that a channel pays in fees in case the commitment 
+; transaction is broadcasted. This is enforced in both directions either when
+; we are the channel intiator hence paying the fees but also applies to the 
+; channel fee if we are NOT the channel initiator. It is
+; important to note that every HTLC adds fees to the channel state. Non-dust 
+; HTLCs add just a new output onto the commitment transaction whereas dust 
+; HTLCs are completely attributed the commitment fee. So this limit can also 
+; influence adding new HTLCs onto the state. When the limit is reached we won't 
+; allow any new HTLCs onto the channel state (outgoing and incoming). So 
+; choosing a right limit here must be done with caution. Moreover this is a 
+; limit for all channels universially meaning there is no difference made due to
+; the channel size. So it is recommended to use the default value. However if
+; you have a very small channel average size you might want to reduce this 
+; value.
+; Setting this value too low might cause force closes because the lightning
+; protocol has no way to roll back a channel state when your peer proposes a
+; channel update which exceeds this limit there are only two options to resolve
+; the situation. You can either increase the limit and the channel should be
+; fully functional again or one side has to force close the channel.
+; channel-max-fee-exposure=500000 
+
 ; If true, lnd will abort committing a migration if it would otherwise have been
 ; successful. This leaves the database unmodified, and still compatible with the
 ; previously active version of lnd.

server.go

@@ -661,7 +661,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 
 	s.htlcNotifier = htlcswitch.NewHtlcNotifier(time.Now)
 
-	thresholdSats := btcutil.Amount(cfg.MaxFeeExposure)
+	thresholdSats := htlcswitch.DefaultMaxFeeExposure.ToSatoshis()
 	thresholdMSats := lnwire.NewMSatFromSatoshis(thresholdSats)
 
 	linkUpdater := func(shortID lnwire.ShortChannelID) error {
@@ -4105,7 +4105,7 @@ func (s *server) peerConnected(conn net.Conn, connReq *connmgr.ConnReq,
 		towerClient = s.towerClientMgr
 	}
 
-	thresholdSats := btcutil.Amount(s.cfg.MaxFeeExposure)
+	thresholdSats := htlcswitch.DefaultMaxFeeExposure.ToSatoshis()
 	thresholdMSats := lnwire.NewMSatFromSatoshis(thresholdSats)
 
 	// Now that we've established a connection, create a peer, and it to the