itest: add test case for policy in route hint

This commit tests that the routing policy of the correct peer (the
policy pointing toward the recipient of an invoice) is included in an
asset invoice.

Author: guggero

itest/litd_custom_channels_test.go

@@ -2890,6 +2890,47 @@ func testCustomChannelsLiquidityEdgeCasesCore(ctx context.Context,
 	)
 
 	logBalance(t.t, nodes, assetID, "after safe asset htlc failure")
+
+	// Another test case: Make sure an asset invoice contains the correct
+	// channel policy. We expect it to be the policy for the direction from
+	// edge node to receiver node. To test this, we first set two different
+	// policies on the channel between Erin and Fabia.
+	resp, err := erin.UpdateChannelPolicy(ctx, &lnrpc.PolicyUpdateRequest{
+		Scope: &lnrpc.PolicyUpdateRequest_ChanPoint{
+			ChanPoint: chanPointEF,
+		},
+		BaseFeeMsat:   31337,
+		FeeRatePpm:    443322,
+		TimeLockDelta: 19,
+	})
+	require.NoError(t.t, err)
+	require.Empty(t.t, resp.FailedUpdates)
+
+	resp, err = fabia.UpdateChannelPolicy(ctx, &lnrpc.PolicyUpdateRequest{
+		Scope: &lnrpc.PolicyUpdateRequest_ChanPoint{
+			ChanPoint: chanPointEF,
+		},
+		BaseFeeMsat:   42069,
+		FeeRatePpm:    223344,
+		TimeLockDelta: 18,
+	})
+	require.NoError(t.t, err)
+	require.Empty(t.t, resp.FailedUpdates)
+
+	// We now create an invoice on Fabia and expect Erin's policy to be used
+	// in the invoice.
+	invoiceResp = createAssetInvoice(t.t, erin, fabia, 100_000, assetID)
+	req, err := erin.DecodePayReq(ctx, &lnrpc.PayReqString{
+		PayReq: invoiceResp.PaymentRequest,
+	})
+	require.NoError(t.t, err)
+
+	require.Len(t.t, req.RouteHints, 1)
+	require.Len(t.t, req.RouteHints[0].HopHints, 1)
+	invoiceHint := req.RouteHints[0].HopHints[0]
+	require.EqualValues(t.t, 31337, invoiceHint.FeeBaseMsat)
+	require.EqualValues(t.t, 443322, invoiceHint.FeeProportionalMillionths)
+	require.EqualValues(t.t, 19, invoiceHint.CltvExpiryDelta)
 }
 
 // testCustomChannelsLiquidityEdgeCases is a test that runs through some