routing+lnrpc+lncli: allow setting min htlc policy

cmd/lncli/commands.go

@@ -3459,6 +3459,12 @@ var updateChannelPolicyCommand = cli.Command{
 			Usage: "the CLTV delta that will be applied to all " +
 				"forwarded HTLCs",
 		},
+		cli.Uint64Flag{
+			Name: "min_htlc_msat",
+			Usage: "if set, the min HTLC size that will be applied " +
+				"to all forwarded HTLCs. If unset, the min HTLC " +
+				"is left unchanged.",
+		},
 		cli.Uint64Flag{
 			Name: "max_htlc_msat",
 			Usage: "if set, the max HTLC size that will be applied " +
@@ -3581,6 +3587,11 @@ func updateChannelPolicy(ctx *cli.Context) error {
 		MaxHtlcMsat:   ctx.Uint64("max_htlc_msat"),
 	}
 
+	if ctx.IsSet("min_htlc_msat") {
+		req.MinHtlcMsat = ctx.Uint64("min_htlc_msat")
+		req.MinHtlcMsatSpecified = true
+	}
+
 	if chanPoint != nil {
 		req.Scope = &lnrpc.PolicyUpdateRequest_ChanPoint{
 			ChanPoint: chanPoint,

lnrpc/rpc.proto

@@ -2686,6 +2686,12 @@ message PolicyUpdateRequest {
 
     /// If set, the maximum HTLC size in milli-satoshis. If unset, the maximum HTLC will be unchanged.
     uint64 max_htlc_msat = 6 [json_name = "max_htlc_msat"];
+
+    /// The minimum HTLC size in milli-satoshis. Only applied if min_htlc_msat_specified is true.
+    uint64 min_htlc_msat = 7 [json_name = "min_htlc_msat"];
+
+    /// If true, min_htlc_msat is applied.
+    bool min_htlc_msat_specified = 8 [json_name = "set_min_htlc_msat"];
 }
 message PolicyUpdateResponse {
 }

lnrpc/rpc.swagger.json

@@ -3538,6 +3538,16 @@
           "type": "string",
           "format": "uint64",
           "description": "/ If set, the maximum HTLC size in milli-satoshis. If unset, the maximum HTLC will be unchanged."
+        },
+        "min_htlc_msat": {
+          "type": "string",
+          "format": "uint64",
+          "description": "/ The minimum HTLC size in milli-satoshis. Only applied if min_htlc_msat_specified is true."
+        },
+        "min_htlc_msat_specified": {
+          "type": "boolean",
+          "format": "boolean",
+          "description": "/ If true, min_htlc_msat is applied."
         }
       }
     },

routing/localchans/manager.go

@@ -160,6 +160,11 @@ func (r *Manager) updateEdge(chanPoint wire.OutPoint,
 		edge.MaxHTLC = amtMax
 	}
 
+	// If a new min htlc is specified, update the edge.
+	if newSchema.MinHTLC != nil {
+		edge.MinHTLC = *newSchema.MinHTLC
+	}
+
 	// If the MaxHtlc flag wasn't already set, we can set it now.
 	edge.MessageFlags |= lnwire.ChanUpdateOptionMaxHtlc
 

routing/router.go

@@ -224,6 +224,10 @@ type ChannelPolicy struct {
 	// MaxHTLC is the maximum HTLC size including fees we are allowed to
 	// forward over this channel.
 	MaxHTLC lnwire.MilliSatoshi
+
+	// MinHTLC is the minimum HTLC size including fees we are allowed to
+	// forward over this channel.
+	MinHTLC *lnwire.MilliSatoshi
 }
 
 // Config defines the configuration for the ChannelRouter. ALL elements within

rpcserver.go

@@ -4864,15 +4864,25 @@ func (r *rpcServer) UpdateChannelPolicy(ctx context.Context,
 		FeeRate: feeRateFixed,
 	}
 
+	maxHtlc := lnwire.MilliSatoshi(req.MaxHtlcMsat)
+	var minHtlc *lnwire.MilliSatoshi
+	if req.MinHtlcMsatSpecified {
+		min := lnwire.MilliSatoshi(req.MinHtlcMsat)
+		minHtlc = &min
+	}
+
 	chanPolicy := routing.ChannelPolicy{
 		FeeSchema:     feeSchema,
 		TimeLockDelta: req.TimeLockDelta,
-		MaxHTLC:       lnwire.MilliSatoshi(req.MaxHtlcMsat),
+		MaxHTLC:       maxHtlc,
+		MinHTLC:       minHtlc,
 	}
 
 	rpcsLog.Debugf("[updatechanpolicy] updating channel policy base_fee=%v, "+
-		"rate_float=%v, rate_fixed=%v, time_lock_delta: %v, targets=%v",
+		"rate_float=%v, rate_fixed=%v, time_lock_delta: %v, "+
+		"min_htlc=%v, max_htlc=%v, targets=%v",
 		req.BaseFeeMsat, req.FeeRate, feeRateFixed, req.TimeLockDelta,
+		minHtlc, maxHtlc,
 		spew.Sdump(targetChans))
 
 	// With the scope resolved, we'll now send this to the local channel