pool: round default min chan amt to nearest unit

cmd/pool/order.go

@@ -105,31 +105,29 @@ func parseCommonParams(ctx *cli.Context, blockDuration uint32) (*poolrpc.Order,
 	}
 
 	// If the minimum channel amount flag wasn't provided, use a default of
-	// 10%, but make sure it doesn't dip below the minimum allowed.
-	minOrderChanAmt := btcutil.Amount(order.BaseSupplyUnit)
+	// 10% and round to the nearest unit.
 	minChanAmt := btcutil.Amount(ctx.Uint64("min_chan_amt"))
 	if minChanAmt == 0 {
-		minChanAmt = btcutil.Amount(params.Amt) / 10
-		if minChanAmt < minOrderChanAmt {
-			minChanAmt = minOrderChanAmt
-		}
+		minChanAmt = order.RoundToNextSupplyUnit(
+			btcutil.Amount(params.Amt) / 10,
+		).ToSatoshis()
 	}
 
 	// Verify the minimum channel amount flag has been properly set.
 	switch {
-	case minChanAmt%minOrderChanAmt != 0:
+	case minChanAmt%order.BaseSupplyUnit != 0:
 		return nil, fmt.Errorf("minimum channel amount %v must be "+
-			"a multiple of %v", minChanAmt, minOrderChanAmt)
+			"a multiple of %v", minChanAmt, order.BaseSupplyUnit)
 
-	case minChanAmt < minOrderChanAmt:
+	case minChanAmt < order.BaseSupplyUnit:
 		return nil, fmt.Errorf("minimum channel amount %v is below "+
-			"required value of %v", minChanAmt, minOrderChanAmt)
+			"required value of %v", minChanAmt, order.BaseSupplyUnit)
 
 	case minChanAmt > btcutil.Amount(params.Amt):
 		return nil, fmt.Errorf("minimum channel amount %v is above "+
 			"order amount %v", minChanAmt, btcutil.Amount(params.Amt))
 	}
-	params.MinUnitsMatch = uint32(minChanAmt / minOrderChanAmt)
+	params.MinUnitsMatch = uint32(minChanAmt / order.BaseSupplyUnit)
 
 	var err error
 	params.TraderKey, err = parseAccountKey(ctx, args)

order/supplyunit.go

@@ -10,7 +10,7 @@ type SupplyUnit uint64
 const (
 	// BaseSupplyUnit is the smallest channel that can be bought or sold in
 	// the system. These units are expressed in satoshis.
-	BaseSupplyUnit SupplyUnit = 100_000
+	BaseSupplyUnit btcutil.Amount = 100_000
 )
 
 // NewSupplyFromSats calculates the number of supply units that can be bought or
@@ -21,6 +21,12 @@ func NewSupplyFromSats(sats btcutil.Amount) SupplyUnit {
 	return SupplyUnit(uint64(sats) / uint64(BaseSupplyUnit))
 }
 
+// RoundToNextSupplyUnit computes and rounds to the next whole number of supply
+// units from the given amount in satoshis.
+func RoundToNextSupplyUnit(sats btcutil.Amount) SupplyUnit {
+	return SupplyUnit((sats + BaseSupplyUnit - 1) / BaseSupplyUnit)
+}
+
 // ToSatoshis maps a set number of supply units to the corresponding number of
 // satoshis.
 func (s SupplyUnit) ToSatoshis() btcutil.Amount {

order/supplyunit_test.go

@@ -0,0 +1,34 @@
+package order_test
+
+import (
+	"math/rand"
+	"reflect"
+	"testing"
+	"testing/quick"
+
+	"github.com/btcsuite/btcutil"
+	"github.com/lightninglabs/pool/order"
+	"github.com/stretchr/testify/require"
+)
+
+// TestRoundToNextSupplyUnit runs a quick check scenario to ensure the
+// correctness of RoundToNextSupplyUnit.
+func TestRoundToNextSupplyUnit(t *testing.T) {
+	t.Parallel()
+
+	f := func(sats btcutil.Amount) bool {
+		units := order.RoundToNextSupplyUnit(sats)
+		if sats%order.BaseSupplyUnit == 0 {
+			return units == order.NewSupplyFromSats(sats)
+		}
+		return units == order.NewSupplyFromSats(sats)+1
+	}
+
+	cfg := &quick.Config{
+		Values: func(v []reflect.Value, r *rand.Rand) {
+			v[0] = reflect.ValueOf(btcutil.Amount(r.Int63()))
+		},
+	}
+
+	require.NoError(t, quick.Check(f, cfg))
+}