multi: merge DetermineFeePerKw and Estimate

This commit moves `DetermineFeePerKw` into the `Estimate` method on
`FeePreference`. A few callsites previously calling `DetermineFeePerKw`
without the max fee rate is now also temporarily fixed by forcing them
to use `Estimate` with the default sweeper max fee rate.

sweep/walletsweep.go

@@ -27,6 +27,10 @@ var (
 	// ErrNoFeePreference is returned when we attempt to satisfy a sweep
 	// request from a client whom did not specify a fee preference.
 	ErrNoFeePreference = errors.New("no fee preference specified")
+
+	// ErrFeePreferenceConflict is returned when both a fee rate and a conf
+	// target is set for a fee preference.
+	ErrFeePreferenceConflict = errors.New("fee preference conflict")
 )
 
 // FeePreference allows callers to express their time value for inclusion of a
@@ -50,35 +54,70 @@ func (p FeePreference) String() string {
 }
 
 // Estimate returns a fee rate for the given fee preference. It ensures that
-// the fee rate respects the bounds of the relay fee and the specified max fee
-// rates.
-//
-// TODO(yy): add tests.
+// the fee rate respects the bounds of the relay fee and the max fee rates, if
+// specified.
 func (f FeePreference) Estimate(estimator chainfee.Estimator,
 	maxFeeRate chainfee.SatPerKWeight) (chainfee.SatPerKWeight, error) {
 
+	var (
+		feeRate chainfee.SatPerKWeight
+		err     error
+	)
+
+	switch {
+	// Ensure a type of fee preference is specified to prevent using a
+	// default below.
+	case f.FeeRate == 0 && f.ConfTarget == 0:
+		return 0, ErrNoFeePreference
+
+	// If both values are set, then we'll return an error as we require a
+	// strict directive.
+	case f.FeeRate != 0 && f.ConfTarget != 0:
+		return 0, ErrFeePreferenceConflict
+
+	// If the target number of confirmations is set, then we'll use that to
+	// consult our fee estimator for an adequate fee.
+	case f.ConfTarget != 0:
+		feeRate, err = estimator.EstimateFeePerKW((f.ConfTarget))
+		if err != nil {
+			return 0, fmt.Errorf("unable to query fee "+
+				"estimator: %w", err)
+		}
+
+	// If a manual sat/kw fee rate is set, then we'll use that directly.
+	// We'll need to convert it to sat/kw as this is what we use
+	// internally.
+	case f.FeeRate != 0:
+		feeRate = f.FeeRate
+
+		// Because the user can specify 1 sat/vByte on the RPC
+		// interface, which corresponds to 250 sat/kw, we need to bump
+		// that to the minimum "safe" fee rate which is 253 sat/kw.
+		if feeRate == chainfee.AbsoluteFeePerKwFloor {
+			log.Infof("Manual fee rate input of %d sat/kw is "+
+				"too low, using %d sat/kw instead", feeRate,
+				chainfee.FeePerKwFloor)
+
+			feeRate = chainfee.FeePerKwFloor
+		}
+	}
+
 	// Get the relay fee as the min fee rate.
 	minFeeRate := estimator.RelayFeePerKW()
 
-	// Ensure a type of fee preference is specified to prevent using a
-	// default below.
-	if f.FeeRate == 0 && f.ConfTarget == 0 {
-		return 0, ErrNoFeePreference
-	}
-
-	feeRate, err := DetermineFeePerKw(estimator, f)
-	if err != nil {
-		return 0, err
-	}
-
+	// If that bumped fee rate of at least 253 sat/kw is still lower than
+	// the relay fee rate, we return an error to let the user know. Note
+	// that "Relay fee rate" may mean slightly different things depending
+	// on the backend. For bitcoind, it is effectively max(relay fee, min
+	// mempool fee).
 	if feeRate < minFeeRate {
 		return 0, fmt.Errorf("%w: got %v, minimum is %v",
 			ErrFeePreferenceTooLow, feeRate, minFeeRate)
 	}
 
-	// If the estimated fee rate is above the maximum allowed fee rate,
-	// default to the max fee rate.
-	if feeRate > maxFeeRate {
+	// If a maxFeeRate is specified and the estimated fee rate is above the
+	// maximum allowed fee rate, default to the max fee rate.
+	if maxFeeRate != 0 && feeRate > maxFeeRate {
 		log.Warnf("Estimated fee rate %v exceeds max allowed fee "+
 			"rate %v, using max fee rate instead", feeRate,
 			maxFeeRate)
@@ -89,80 +128,6 @@ func (f FeePreference) Estimate(estimator chainfee.Estimator,
 	return feeRate, nil
 }
 
-// DetermineFeePerKw will determine the fee in sat/kw that should be paid given
-// an estimator, a confirmation target, and a manual value for sat/byte. A
-// value is chosen based on the two free parameters as one, or both of them can
-// be zero.
-//
-// TODO(yy): move it into the above `Estimate`.
-func DetermineFeePerKw(feeEstimator chainfee.Estimator,
-	feePref FeePreference) (chainfee.SatPerKWeight, error) {
-
-	switch {
-	// If both values are set, then we'll return an error as we require a
-	// strict directive.
-	case feePref.FeeRate != 0 && feePref.ConfTarget != 0:
-		return 0, fmt.Errorf("only FeeRate or ConfTarget should " +
-			"be set for FeePreferences")
-
-	// If the target number of confirmations is set, then we'll use that to
-	// consult our fee estimator for an adequate fee.
-	case feePref.ConfTarget != 0:
-		feePerKw, err := feeEstimator.EstimateFeePerKW(
-			uint32(feePref.ConfTarget),
-		)
-		if err != nil {
-			return 0, fmt.Errorf("unable to query fee "+
-				"estimator: %v", err)
-		}
-
-		return feePerKw, nil
-
-	// If a manual sat/byte fee rate is set, then we'll use that directly.
-	// We'll need to convert it to sat/kw as this is what we use
-	// internally.
-	case feePref.FeeRate != 0:
-		feePerKW := feePref.FeeRate
-
-		// Because the user can specify 1 sat/vByte on the RPC
-		// interface, which corresponds to 250 sat/kw, we need to bump
-		// that to the minimum "safe" fee rate which is 253 sat/kw.
-		if feePerKW == chainfee.AbsoluteFeePerKwFloor {
-			log.Infof("Manual fee rate input of %d sat/kw is "+
-				"too low, using %d sat/kw instead", feePerKW,
-				chainfee.FeePerKwFloor)
-			feePerKW = chainfee.FeePerKwFloor
-		}
-
-		// If that bumped fee rate of at least 253 sat/kw is still lower
-		// than the relay fee rate, we return an error to let the user
-		// know. Note that "Relay fee rate" may mean slightly different
-		// things depending on the backend. For bitcoind, it is
-		// effectively max(relay fee, min mempool fee).
-		minFeePerKW := feeEstimator.RelayFeePerKW()
-		if feePerKW < minFeePerKW {
-			return 0, fmt.Errorf("manual fee rate input of %d "+
-				"sat/kw is too low to be accepted into the "+
-				"mempool or relayed to the network", feePerKW)
-		}
-
-		return feePerKW, nil
-
-	// Otherwise, we'll attempt a relaxed confirmation target for the
-	// transaction
-	default:
-		feePerKw, err := feeEstimator.EstimateFeePerKW(
-			defaultNumBlocksEstimate,
-		)
-		if err != nil {
-			return 0, fmt.Errorf("unable to query fee estimator: "+
-				"%v", err)
-		}
-
-		return feePerKw, nil
-	}
-}
-
 // UtxoSource is an interface that allows a caller to access a source of UTXOs
 // to use when crafting sweep transactions.
 type UtxoSource interface {