WIP 12 vpn: add gateway support

Author: pymq

vpn/routes/vpn_hostnet_integration_test.go

@@ -270,7 +270,7 @@ func snapshotNet(t *testing.T) string {
 	}
 	section("ip rule", cmdOut(t, "ip", "rule", "show"))
 	section("route main", cmdOut(t, "ip", "-4", "route", "show"))
-	section("route awl-table", cmdOut(t, "ip", "-4", "route", "show", "table", strconv.Itoa(tableID)))
+	section("route awl-table", routeTableDump(t, tableID))
 	section("iptables filter", cmdOut(t, "iptables", "-S"))
 	section("iptables nat", cmdOut(t, "iptables", "-t", "nat", "-S"))
 	return b.String()
@@ -340,8 +340,28 @@ func mustCmd(t *testing.T, name string, args ...string) {
 
 func cmdOut(t *testing.T, name string, args ...string) string {
 	t.Helper()
-	out, err := exec.Command(name, args...).Output()
-	require.NoErrorf(t, err, "%s %s", name, strings.Join(args, " "))
+	// CombinedOutput (not Output) so a failing command surfaces its stderr
+	// diagnostic in the test log instead of a bare "exit status N". On success
+	// these commands print nothing to stderr, so the captured value is unchanged.
+	out, err := exec.Command(name, args...).CombinedOutput()
+	require.NoErrorf(t, err, "%s %s: %s", name, strings.Join(args, " "), out)
+	return string(out)
+}
+
+// routeTableDump returns the routes in the given table, tolerating the
+// "table does not exist" case. Newer iproute2/kernels (e.g. Ubuntu 24.04) make
+// `ip route show table <id>` fail with exit 2 ("FIB table does not exist") when
+// the table has never held a route, whereas older versions returned empty with
+// exit 0. Both mean the same thing here — an empty table — so normalise to "".
+func routeTableDump(t *testing.T, table int) string {
+	t.Helper()
+	out, err := exec.Command("ip", "-4", "route", "show", "table", strconv.Itoa(table)).CombinedOutput()
+	if err != nil {
+		if strings.Contains(string(out), "does not exist") {
+			return ""
+		}
+		require.NoErrorf(t, err, "ip -4 route show table %d: %s", table, out)
+	}
 	return string(out)
 }