staticaddr: exclude close-to-expiry depositis from SelectDeposits

Author: hieblmi

staticaddr/loopin/manager.go

@@ -862,8 +862,30 @@ func (m *Manager) GetAllSwaps(ctx context.Context) ([]*StaticAddressLoopIn,
 // are needed to cover the amount requested without leaving a dust change. It
 // returns an error if the sum of deposits minus dust is less than the requested
 // amount.
-func SelectDeposits(targetAmount btcutil.Amount, deposits []*deposit.Deposit,
-	csvExpiry uint32, blockHeight uint32) ([]*deposit.Deposit, error) {
+func SelectDeposits(targetAmount btcutil.Amount,
+	unfilteredDeposits []*deposit.Deposit, csvExpiry uint32,
+	blockHeight uint32) ([]*deposit.Deposit, error) {
+
+	// Filter out deposits that are too close to expiry to be swapped.
+	var deposits []*deposit.Deposit
+	for _, d := range unfilteredDeposits {
+		depositExpiryHeight := d.ConfirmationHeight + int64(csvExpiry)
+
+		// The htlc expiry height is the current height plus the htlc
+		// cltv delta.
+		htlcExpiryHeight := blockHeight + DefaultLoopInOnChainCltvDelta
+
+		// Ensure that the deposit doesn't expire before the htlc.
+		if depositExpiryHeight < int64(htlcExpiryHeight+
+			DepositHtlcDelta) {
+			log.Debugf("Skipping deposit %s as it expires close "+
+				"to the htlc", d.OutPoint.String())
+
+			continue
+		}
+
+		deposits = append(deposits, d)
+	}
 
 	// Sort the deposits by amount in descending order, then by
 	// blocks-until-expiry in ascending order.

staticaddr/loopin/manager_test.go

@@ -121,6 +121,43 @@ func TestSelectDeposits(t *testing.T) {
 			expected:    []*deposit.Deposit{d3},
 			expectedErr: "",
 		},
+		{
+			name: "prefilter filters deposits close to expiry",
+			deposits: func() []*deposit.Deposit {
+				// dClose expires before
+				// htlcExpiry+DepositHtlcDelta and must be
+				// filtered out. dOK expires exactly at the
+				// threshold and must be eligible.
+				dClose := &deposit.Deposit{
+					Value:              3_000_000,
+					ConfirmationHeight: 3000,
+				}
+				dClose.Hash = chainhash.Hash{5}
+				dClose.Index = 0
+				dOK := &deposit.Deposit{
+					Value:              2_000_000,
+					ConfirmationHeight: 3050,
+				}
+				dOK.Hash = chainhash.Hash{6}
+				dOK.Index = 0
+				return []*deposit.Deposit{dClose, dOK}
+			}(),
+			targetValue: 1_000_000,
+			csvExpiry:   1000,
+			blockHeight: 3000,
+			expected: func() []*deposit.Deposit {
+				// Only dOK should be considered.
+				// dClose is filtered.
+				dOK := &deposit.Deposit{
+					Value:              2_000_000,
+					ConfirmationHeight: 3050,
+				}
+				dOK.Hash = chainhash.Hash{6}
+				dOK.Index = 0
+				return []*deposit.Deposit{dOK}
+			}(),
+			expectedErr: "",
+		},
 	}
 
 	for _, tc := range testCases {