[client] Add experimental support for userspace routing (#3134)

client/firewall/nftables/manager_linux.go

@@ -318,6 +318,11 @@ func (m *Manager) cleanupNetbirdTables() error {
 	return nil
 }
 
+// SetLogLevel sets the log level for the firewall manager
+func (m *Manager) SetLogLevel(log.Level) {
+	// not supported
+}
+
 // Flush rule/chain/set operations from the buffer
 //
 // Method also get all rules after flush and refreshes handle values in the rulesets

client/firewall/nftables/manager_linux_test.go

@@ -107,7 +107,7 @@ func TestNftablesManager(t *testing.T) {
 			Kind: expr.VerdictAccept,
 		},
 	}
-	require.ElementsMatch(t, rules[0].Exprs, expectedExprs1, "expected the same expressions")
+	compareExprsIgnoringCounters(t, rules[0].Exprs, expectedExprs1)
 
 	ipToAdd, _ := netip.AddrFromSlice(ip)
 	add := ipToAdd.Unmap()
@@ -307,3 +307,18 @@ func TestNftablesManagerCompatibilityWithIptables(t *testing.T) {
 	stdout, stderr = runIptablesSave(t)
 	verifyIptablesOutput(t, stdout, stderr)
 }
+
+func compareExprsIgnoringCounters(t *testing.T, got, want []expr.Any) {
+	t.Helper()
+	require.Equal(t, len(got), len(want), "expression count mismatch")
+
+	for i := range got {
+		if _, isCounter := got[i].(*expr.Counter); isCounter {
+			_, wantIsCounter := want[i].(*expr.Counter)
+			require.True(t, wantIsCounter, "expected Counter at index %d", i)
+			continue
+		}
+
+		require.Equal(t, got[i], want[i], "expression mismatch at index %d", i)
+	}
+}

client/firewall/nftables/router_linux.go

@@ -233,7 +233,13 @@ func (r *router) AddRouteFiltering(
 		UserData: []byte(ruleKey),
 	}
 
-	rule = r.conn.AddRule(rule)
+	// Insert DROP rules at the beginning, append ACCEPT rules at the end
+	if action == firewall.ActionDrop {
+		// TODO: Insert after the established rule
+		rule = r.conn.InsertRule(rule)
+	} else {
+		rule = r.conn.AddRule(rule)
+	}
 
 	log.Tracef("Adding route rule %s", spew.Sdump(rule))
 	if err := r.conn.Flush(); err != nil {