channeldb: update QueryPayments to use sequence nr index and paginator

Use the new paginatior strcut for payments. Add some tests which will
specifically test cases on and around the missing index we force in our
test to ensure that we properly handle this case. We also add a sanity
check in the test that checks that we can query when we have no
payments.

channeldb/payments_test.go

@@ -165,18 +165,24 @@ func TestRouteSerialization(t *testing.T) {
 }
 
 // deletePayment removes a payment with paymentHash from the payments database.
-func deletePayment(t *testing.T, db *DB, paymentHash lntypes.Hash) {
+func deletePayment(t *testing.T, db *DB, paymentHash lntypes.Hash, seqNr uint64) {
 	t.Helper()
 
 	err := kvdb.Update(db, func(tx kvdb.RwTx) error {
 		payments := tx.ReadWriteBucket(paymentsRootBucket)
 
+		// Delete the payment bucket.
 		err := payments.DeleteNestedBucket(paymentHash[:])
 		if err != nil {
 			return err
 		}
 
-		return nil
+		key := make([]byte, 8)
+		byteOrder.PutUint64(key, seqNr)
+
+		// Delete the index that references this payment.
+		indexes := tx.ReadWriteBucket(paymentsIndexBucket)
+		return indexes.Delete(key)
 	})
 
 	if err != nil {
@@ -350,6 +356,42 @@ func TestQueryPayments(t *testing.T) {
 			lastIndex:      7,
 			expectedSeqNrs: []uint64{3, 4, 5, 6, 7},
 		},
+		{
+			name: "query payments reverse before index gap",
+			query: PaymentsQuery{
+				IndexOffset:       3,
+				MaxPayments:       7,
+				Reversed:          true,
+				IncludeIncomplete: true,
+			},
+			firstIndex:     1,
+			lastIndex:      1,
+			expectedSeqNrs: []uint64{1},
+		},
+		{
+			name: "query payments reverse on index gap",
+			query: PaymentsQuery{
+				IndexOffset:       2,
+				MaxPayments:       7,
+				Reversed:          true,
+				IncludeIncomplete: true,
+			},
+			firstIndex:     1,
+			lastIndex:      1,
+			expectedSeqNrs: []uint64{1},
+		},
+		{
+			name: "query payments forward on index gap",
+			query: PaymentsQuery{
+				IndexOffset:       2,
+				MaxPayments:       2,
+				Reversed:          false,
+				IncludeIncomplete: true,
+			},
+			firstIndex:     3,
+			lastIndex:      4,
+			expectedSeqNrs: []uint64{3, 4},
+		},
 	}
 
 	for _, tt := range tests {
@@ -358,11 +400,16 @@ func TestQueryPayments(t *testing.T) {
 			t.Parallel()
 
 			db, cleanup, err := makeTestDB()
-			defer cleanup()
-
 			if err != nil {
 				t.Fatalf("unable to init db: %v", err)
 			}
+			defer cleanup()
+
+			// Make a preliminary query to make sure it's ok to
+			// query when we have no payments.
+			resp, err := db.QueryPayments(tt.query)
+			require.NoError(t, err)
+			require.Len(t, resp.Payments, 0)
 
 			// Populate the database with a set of test payments.
 			// We create 6 original payments, deleting the payment
@@ -391,7 +438,13 @@ func TestQueryPayments(t *testing.T) {
 
 				// Immediately delete the payment with index 2.
 				if i == 1 {
-					deletePayment(t, db, info.PaymentHash)
+					pmt, err := pControl.FetchPayment(
+						info.PaymentHash,
+					)
+					require.NoError(t, err)
+
+					deletePayment(t, db, info.PaymentHash,
+						pmt.SequenceNum)
 				}
 
 				// If we are on the last payment entry, add a