loopd: filter unavailable deposits in ListUnspentDeposits

ListUnspentRaw returns the unspent wallet view of the
backing lnd wallet. It might be that deposits show up
there that are actually not spendable because they
already have been used but not yet spent by the server.
We filter out such deposits in ListUnspentDeposits.

loopd/swapclient_server.go

@@ -1546,9 +1546,65 @@ func (s *swapClientServer) ListUnspentDeposits(ctx context.Context,
 		return nil, err
 	}
 
-	// Prepare the list response.
+	// ListUnspentRaw returns the unspent wallet view of the backing lnd
+	// wallet. It might be that deposits show up there that are actually
+	// not spendable because they already have been used but not yet spent
+	// by the server. We filter out such deposits here.
+	var (
+		outpoints []string
+		isUnspent = make(map[wire.OutPoint]struct{})
+	)
+
+	// Keep track of confirmed outpoints that we need to check against our
+	// database.
+	confirmedToCheck := make(map[wire.OutPoint]struct{})
+
+	for _, utxo := range utxos {
+		if utxo.Confirmations < deposit.MinConfs {
+			// Unconfirmed deposits are always available.
+			isUnspent[utxo.OutPoint] = struct{}{}
+		} else {
+			// Confirmed deposits need to be checked.
+			outpoints = append(outpoints, utxo.OutPoint.String())
+			confirmedToCheck[utxo.OutPoint] = struct{}{}
+		}
+	}
+
+	// Check the spent status of the deposits by looking at their states.
+	deposits, err := s.depositManager.DepositsForOutpoints(ctx, outpoints)
+	if err != nil {
+		return nil, err
+	}
+	for _, d := range deposits {
+		// A nil deposit means we don't have a record for it. We'll
+		// handle this case after the loop.
+		if d == nil {
+			continue
+		}
+
+		// If the deposit is in the "Deposited" state, it's available.
+		if d.IsInState(deposit.Deposited) {
+			isUnspent[d.OutPoint] = struct{}{}
+		}
+
+		// We have a record for this deposit, so we no longer need to
+		// check it.
+		delete(confirmedToCheck, d.OutPoint)
+	}
+
+	// Any remaining outpoints in confirmedToCheck are ones that lnd knows
+	// about but we don't. These are new, unspent deposits.
+	for op := range confirmedToCheck {
+		isUnspent[op] = struct{}{}
+	}
+
+	// Prepare the list of unspent deposits for the rpc response.
 	var respUtxos []*looprpc.Utxo
 	for _, u := range utxos {
+		if _, ok := isUnspent[u.OutPoint]; !ok {
+			continue
+		}
+
 		utxo := &looprpc.Utxo{
 			StaticAddress: staticAddress.String(),
 			AmountSat:     int64(u.Value),