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.

config.go

@@ -455,7 +455,9 @@ 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 satoshis of a channel. This value is enforced for all channels and is independent of the channel initiator."`
 
 	Fee *lncfg.Fee `group:"fee" namespace:"fee"`
 
@@ -1717,6 +1719,20 @@ func ValidateConfig(cfg Config, interceptor signal.Interceptor, fileParser,
 		cfg.Pprof.MutexProfile = cfg.MutexProfile
 	}
 
+	// Don't allow both the old dust-threshold and the new
+	// channel-max-fee-exposure to be set.
+	defaultExposure := uint64(htlcswitch.DefaultMaxFeeExposure.ToSatoshis())
+	if cfg.DustThreshold != 0 && cfg.MaxFeeExposure != defaultExposure {
+		return nil, mkErr("cannot set both dust-threshold and " +
+			"channel-max-fee-exposure")
+	}
+
+	// Use the old dust-threshold as the max fee exposure if it is set and
+	// the new option is not (has the default value).
+	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

@@ -474,10 +474,32 @@
 ; 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.
-; dust-threshold=500000
+; 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=
+
+; 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 universally 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.
+; WARNING: 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 this situation, either increasing the limit or one side force 
+; closes 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