sweep: allow force sweeps

cmd/lncli/walletrpc_active.go

@@ -4,7 +4,6 @@ package main
 
 import (
 	"context"
-	"fmt"
 	"sort"
 
 	"github.com/lightningnetwork/lnd/lnrpc/walletrpc"
@@ -113,7 +112,13 @@ var bumpFeeCommand = cli.Command{
 	Note that this command currently doesn't perform any validation checks
 	on the fee preference being provided. For now, the responsibility of
 	ensuring that the new fee preference is sufficient is delegated to the
-	user.`,
+	user.
+
+	The force flag enables sweeping of inputs that are negatively yielding.
+	Normally it does not make sense to lose money on sweeping, unless a
+	parent transaction needs to get confirmed and there is only a small
+	output available to attach the child transaction to.
+	`,
 	Flags: []cli.Flag{
 		cli.Uint64Flag{
 			Name: "conf_target",
@@ -125,14 +130,18 @@ var bumpFeeCommand = cli.Command{
 			Usage: "a manual fee expressed in sat/byte that " +
 				"should be used when sweeping the output",
 		},
+		cli.BoolFlag{
+			Name:  "force",
+			Usage: "sweep even if the yield is negative",
+		},
 	},
 	Action: actionDecorator(bumpFee),
 }
 
 func bumpFee(ctx *cli.Context) error {
 	// Display the command's help message if we do not have the expected
 	// number of arguments/flags.
-	if ctx.NArg() != 1 || ctx.NumFlags() != 1 {
+	if ctx.NArg() != 1 {
 		return cli.ShowCommandHelp(ctx, "bumpfee")
 	}
 
@@ -142,24 +151,14 @@ func bumpFee(ctx *cli.Context) error {
 		return err
 	}
 
-	var confTarget, satPerByte uint32
-	switch {
-	case ctx.IsSet("conf_target") && ctx.IsSet("sat_per_byte"):
-		return fmt.Errorf("either conf_target or sat_per_byte should " +
-			"be set, but not both")
-	case ctx.IsSet("conf_target"):
-		confTarget = uint32(ctx.Uint64("conf_target"))
-	case ctx.IsSet("sat_per_byte"):
-		satPerByte = uint32(ctx.Uint64("sat_per_byte"))
-	}
-
 	client, cleanUp := getWalletClient(ctx)
 	defer cleanUp()
 
 	resp, err := client.BumpFee(context.Background(), &walletrpc.BumpFeeRequest{
 		Outpoint:   protoOutPoint,
-		TargetConf: confTarget,
-		SatPerByte: satPerByte,
+		TargetConf: uint32(ctx.Uint64("conf_target")),
+		SatPerByte: uint32(ctx.Uint64("sat_per_byte")),
+		Force:      ctx.Bool("force"),
 	})
 	if err != nil {
 		return err

cmd/lncli/walletrpc_types.go

@@ -13,6 +13,7 @@ type PendingSweep struct {
 	NextBroadcastHeight uint32   `json:"next_broadcast_height"`
 	RequestedSatPerByte uint32   `json:"requested_sat_per_byte"`
 	RequestedConfTarget uint32   `json:"requested_conf_target"`
+	Force               bool     `json:"force"`
 }
 
 // NewPendingSweepFromProto converts the walletrpc.PendingSweep proto type into
@@ -27,5 +28,6 @@ func NewPendingSweepFromProto(pendingSweep *walletrpc.PendingSweep) *PendingSwee
 		NextBroadcastHeight: pendingSweep.NextBroadcastHeight,
 		RequestedSatPerByte: pendingSweep.RequestedSatPerByte,
 		RequestedConfTarget: pendingSweep.RequestedConfTarget,
+		Force:               pendingSweep.Force,
 	}
 }

lnrpc/walletrpc/walletkit.proto

@@ -197,6 +197,12 @@ message PendingSweep {
 
     // The requested fee rate, expressed in sat/byte, for this output.
     uint32 requested_sat_per_byte = 9 [json_name = "requested_sat_per_byte"];
+
+    /**
+    Whether this input must be force-swept. This means that it is swept even
+    if it has a negative yield.
+    */
+    bool force = 7 [json_name = "force"];
 }
 
 message PendingSweepsRequest {
@@ -221,6 +227,12 @@ message BumpFeeRequest {
     with.
     */
     uint32 sat_per_byte = 3 [json_name = "sat_per_byte"];
+
+    /**
+    Whether this input must be force-swept. This means that it is swept even
+    if it has a negative yield.
+    */
+    bool force = 4 [json_name = "force"];
 }
 
 message BumpFeeResponse {

lnrpc/walletrpc/walletkit_server.go

@@ -416,6 +416,7 @@ func (w *WalletKit) PendingSweeps(ctx context.Context,
 			NextBroadcastHeight: nextBroadcastHeight,
 			RequestedSatPerByte: requestedFeeRate,
 			RequestedConfTarget: requestedFee.ConfTarget,
+			Force:               pendingInput.Params.Force,
 		})
 	}
 
@@ -486,7 +487,8 @@ func (w *WalletKit) BumpFee(ctx context.Context,
 	// being broadcast. If it is not aware of the input however,
 	// lnwallet.ErrNotMine is returned.
 	params := sweep.Params{
-		Fee: feePreference,
+		Fee:   feePreference,
+		Force: in.Force,
 	}
 
 	_, err = w.cfg.Sweeper.UpdateParams(*op, params)

sweep/sweeper.go

@@ -67,11 +67,15 @@ type Params struct {
 	// swept. If a confirmation target is specified, then we'll map it into
 	// a fee rate whenever we attempt to cluster inputs for a sweep.
 	Fee FeePreference
+
+	// Force indicates whether the input should be swept regardless of
+	// whether it is economical to do so.
+	Force bool
 }
 
 // String returns a human readable interpretation of the sweep parameters.
 func (p Params) String() string {
-	return fmt.Sprintf("fee=%v", p.Fee)
+	return fmt.Sprintf("fee=%v, force=%v", p.Fee, p.Force)
 }
 
 // pendingInput is created when an input reaches the main loop for the first
@@ -398,10 +402,10 @@ func (s *UtxoSweeper) SweepInput(input input.Input,
 	}
 
 	log.Infof("Sweep request received: out_point=%v, witness_type=%v, "+
-		"time_lock=%v, amount=%v, fee_preference=%v", input.OutPoint(),
-		input.WitnessType(), input.BlocksToMaturity(),
+		"time_lock=%v, amount=%v, fee_preference=%v, force=%v",
+		input.OutPoint(), input.WitnessType(), input.BlocksToMaturity(),
 		btcutil.Amount(input.SignDesc().Output.Value),
-		params.Fee)
+		params.Fee, params.Force)
 
 	sweeperInput := &sweepInputMessage{
 		input:      input,