lntest: add coverage for single hop blinded route query routes

itest/lnd_route_blinding.go

@@ -19,7 +19,8 @@ import (
 // it sets up a nework of Alice - Bob - Carol and creates a mock blinded route
 // that uses Carol as the introduction node (plus dummy hops to cover multiple
 // hops). The test simply asserts that the structure of the route is as
-// expected.
+// expected. It also includes the edge case of a single-hop blinded route,
+// which indicates that the introduction node is the recipient.
 func testQueryBlindedRoutes(ht *lntest.HarnessTest) {
 	var (
 		ctxb = context.Background()
@@ -287,6 +288,42 @@ func testQueryBlindedRoutes(ht *lntest.HarnessTest) {
 	require.NotNil(ht, htlcAttempt.Failure)
 	require.Equal(ht, uint32(2), htlcAttempt.Failure.FailureSourceIndex)
 
+	// Next, we test an edge case where just an introduction node is
+	// included as a "single hop blinded route".
+	introNodeBlinded := &lnrpc.BlindedPayment{
+		BlindedPath: &lnrpc.BlindedPath{
+			IntroductionNode: carol.PubKey[:],
+			BlindingPoint:    blindingBytes,
+			BlindedHops: []*lnrpc.BlindedHop{
+				{
+					// The first hop in the blinded route is
+					// expected to be the introduction node.
+					BlindedNode:   carolBlindedBytes,
+					EncryptedData: encryptedDataCarol,
+				},
+			},
+		},
+		// Fees and expiry are zero for single-hop blinded paths.
+		BaseFeeMsat:    0,
+		TotalCltvDelta: 0,
+	}
+	req = &lnrpc.QueryRoutesRequest{
+		AmtMsat: paymentAmt,
+		BlindedPath: []*lnrpc.BlindedPayment{
+			introNodeBlinded,
+		},
+		FinalCltvDelta: int32(finalDelta),
+	}
+
+	ctxt, cancel = context.WithTimeout(ctxb, defaultTimeout)
+	resp, err = alice.RPC.LN.QueryRoutes(ctxt, req)
+	cancel()
+	require.NoError(ht, err)
+
+	// Assert that we have one route, and two hops: Alice/Bob and Bob/Carol.
+	require.Len(ht, resp.Routes, 1)
+	require.Len(ht, resp.Routes[0].Hops, 2)
+
 	ht.CloseChannel(alice, chanPointAliceBob)
 	ht.CloseChannel(bob, chanPointBobCarol)
 }