lnd: exponential backoff for ProbePayment

Implement retry mechanism with
exponential backoff for ProbePayment.

Add backoff package to handle retries with exponential backoff.
In cln, the default retry time is set to 60 seconds,
so the backoff setting is not made.

lnd/client.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/elementsproject/peerswap/log"
 
+	"github.com/cenkalti/backoff/v4"
 	"github.com/elementsproject/peerswap/lightning"
 	"github.com/elementsproject/peerswap/onchain"
 	"github.com/elementsproject/peerswap/swap"
@@ -380,7 +381,29 @@ func (l *Client) GetPeers() []string {
 // The receiver node aren't able to settle the payment.
 // When the probe is successful, the receiver will return
 // a incorrect_or_unknown_payment_details error to the sender.
-func (l *Client) ProbePayment(scid string, amountMsat uint64) (bool, string, error) {
+func (l *Client) ProbePayment(scid string, amountMsat uint64) (success bool, paymentError string, err error) {
+	// maxRetries is the maximum number of retries for the probePayment.
+	const maxRetries = 5
+	// Set backoff retry to avoid swap failures
+	// due to temporary channel failures such as `TemporaryChannelFailure`
+	err = backoff.Retry(func() error {
+		var innerErr error
+		success, paymentError, innerErr = l.probePayment(scid, amountMsat)
+		if innerErr != nil {
+			return innerErr
+		}
+		if paymentError != "" {
+			return fmt.Errorf("probePayment() %w", errors.New(paymentError))
+		}
+		if !success {
+			return errors.New("probePayment() failed")
+		}
+		return nil
+	}, backoff.WithMaxRetries(backoff.NewExponentialBackOff(), maxRetries))
+	return success, paymentError, err
+}
+
+func (l *Client) probePayment(scid string, amountMsat uint64) (bool, string, error) {
 	chsRes, err := l.lndClient.ListChannels(context.Background(), &lnrpc.ListChannelsRequest{})
 	if err != nil {
 		return false, "", fmt.Errorf("ListChannels() %w", err)