List single table or chain by name

chain.go

@@ -193,6 +193,43 @@ func (cc *Conn) ListChains() ([]*Chain, error) {
 	return cc.ListChainsOfTableFamily(TableFamilyUnspecified)
 }
 
+// ListChain returns a single chain configured in the specified table
+func (cc *Conn) ListChain(table *Table, chain string) (*Chain, error) {
+	conn, closer, err := cc.netlinkConn()
+	if err != nil {
+		return nil, err
+	}
+	defer func() { _ = closer() }()
+
+	attrs := []netlink.Attribute{
+		{Type: unix.NFTA_TABLE_NAME, Data: []byte(table.Name + "\x00")},
+		{Type: unix.NFTA_CHAIN_NAME, Data: []byte(chain + "\x00")},
+	}
+	msg := netlink.Message{
+		Header: netlink.Header{
+			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_GETCHAIN),
+			Flags: netlink.Request,
+		},
+		Data: append(extraHeader(uint8(table.Family), 0), cc.marshalAttr(attrs)...),
+	}
+
+	response, err := conn.Execute(msg)
+	if err != nil {
+		return nil, fmt.Errorf("conn.Execute failed: %v", err)
+	}
+
+	if got, want := len(response), 1; got != want {
+		return nil, fmt.Errorf("expected %d response message for chain, got %d", want, got)
+	}
+
+	ch, err := chainFromMsg(response[0])
+	if err != nil {
+		return nil, err
+	}
+
+	return ch, nil
+}
+
 // ListChainsOfTableFamily returns currently configured chains for the specified
 // family in the kernel. It lists all chains ins all tables if family is
 // TableFamilyUnspecified.

nftables_test.go

@@ -1746,6 +1746,160 @@ func TestListChains(t *testing.T) {
 	}
 }
 
+func TestListChainByName(t *testing.T) {
+	conn, newNS := nftest.OpenSystemConn(t, *enableSysTests)
+	defer nftest.CleanupSystemConn(t, newNS)
+	conn.FlushRuleset()
+	defer conn.FlushRuleset()
+
+	table := &nftables.Table{
+		Name:   "chain_test",
+		Family: nftables.TableFamilyIPv4,
+	}
+	tr := conn.AddTable(table)
+
+	c := &nftables.Chain{
+		Name:  "filter",
+		Table: table,
+	}
+	conn.AddChain(c)
+
+	if err := conn.Flush(); err != nil {
+		t.Errorf("conn.Flush() failed: %v", err)
+	}
+
+	cr, err := conn.ListChain(tr, c.Name)
+	if err != nil {
+		t.Fatalf("conn.ListChain() failed: %v", err)
+	}
+
+	if got, want := cr.Name, c.Name; got != want {
+		t.Fatalf("got chain %s, want chain %s", got, want)
+	}
+
+	if got, want := cr.Table.Name, table.Name; got != want {
+		t.Fatalf("got chain table %s, want chain table %s", got, want)
+	}
+}
+
+func TestListChainByNameUsingLasting(t *testing.T) {
+	conn, newNS := nftest.OpenSystemConn(t, *enableSysTests)
+	conn, err := nftables.New(nftables.WithNetNSFd(int(newNS)), nftables.AsLasting())
+	if err != nil {
+		t.Fatalf("nftables.New() failed: %v", err)
+	}
+	defer nftest.CleanupSystemConn(t, newNS)
+	conn.FlushRuleset()
+	defer conn.FlushRuleset()
+
+	table := &nftables.Table{
+		Name:   "chain_test_lasting",
+		Family: nftables.TableFamilyIPv4,
+	}
+	tr := conn.AddTable(table)
+
+	c := &nftables.Chain{
+		Name:  "filter_lasting",
+		Table: table,
+	}
+	conn.AddChain(c)
+
+	if err := conn.Flush(); err != nil {
+		t.Errorf("conn.Flush() failed: %v", err)
+	}
+
+	cr, err := conn.ListChain(tr, c.Name)
+	if err != nil {
+		t.Fatalf("conn.ListChain() failed: %v", err)
+	}
+
+	if got, want := cr.Name, c.Name; got != want {
+		t.Fatalf("got chain %s, want chain %s", got, want)
+	}
+
+	if got, want := cr.Table.Name, table.Name; got != want {
+		t.Fatalf("got chain table %s, want chain table %s", got, want)
+	}
+}
+
+func TestListTableByName(t *testing.T) {
+	conn, newNS := nftest.OpenSystemConn(t, *enableSysTests)
+	defer nftest.CleanupSystemConn(t, newNS)
+	conn.FlushRuleset()
+	defer conn.FlushRuleset()
+
+	table1 := &nftables.Table{
+		Name:   "table_test",
+		Family: nftables.TableFamilyIPv4,
+	}
+	conn.AddTable(table1)
+	table2 := &nftables.Table{
+		Name:   "table_test_inet",
+		Family: nftables.TableFamilyINet,
+	}
+	conn.AddTable(table2)
+	table3 := &nftables.Table{
+		Name:   table1.Name,
+		Family: nftables.TableFamilyINet,
+	}
+	conn.AddTable(table3)
+
+	if err := conn.Flush(); err != nil {
+		t.Errorf("conn.Flush() failed: %v", err)
+	}
+
+	tr, err := conn.ListTable(table1.Name)
+	if err != nil {
+		t.Fatalf("conn.ListTable() failed: %v", err)
+	}
+
+	if got, want := tr.Name, table1.Name; got != want {
+		t.Fatalf("got table %s, want table %s", got, want)
+	}
+
+	// not specifying table family should return family ipv4
+	tr, err = conn.ListTable(table3.Name)
+	if err != nil {
+		t.Fatalf("conn.ListTable() failed: %v", err)
+	}
+	if got, want := tr.Name, table1.Name; got != want {
+		t.Fatalf("got table %s, want table %s", got, want)
+	}
+	if got, want := tr.Family, table1.Family; got != want {
+		t.Fatalf("got table family %v, want table family %v", got, want)
+	}
+
+	// specifying correct INet family
+	tr, err = conn.ListTableOfFamily(table3.Name, nftables.TableFamilyINet)
+	if err != nil {
+		t.Fatalf("conn.ListTable() failed: %v", err)
+	}
+	if got, want := tr.Name, table3.Name; got != want {
+		t.Fatalf("got table %s, want table %s", got, want)
+	}
+	if got, want := tr.Family, table3.Family; got != want {
+		t.Fatalf("got table family %v, want table family %v", got, want)
+	}
+
+	// not specifying correct family should return err since no table in ipv4
+	tr, err = conn.ListTable(table2.Name)
+	if err == nil {
+		t.Fatalf("conn.ListTable() should have failed")
+	}
+
+	// specifying correct INet family
+	tr, err = conn.ListTableOfFamily(table2.Name, nftables.TableFamilyINet)
+	if err != nil {
+		t.Fatalf("conn.ListTable() failed: %v", err)
+	}
+	if got, want := tr.Name, table2.Name; got != want {
+		t.Fatalf("got table %s, want table %s", got, want)
+	}
+	if got, want := tr.Family, table2.Family; got != want {
+		t.Fatalf("got table family %v, want table family %v", got, want)
+	}
+}
+
 func TestAddChain(t *testing.T) {
 	tests := []struct {
 		name  string

table.go

@@ -112,6 +112,25 @@ func (cc *Conn) FlushTable(t *Table) {
 	})
 }
 
+// ListTable returns table found for the specified name. Searches for
+// the table under IPv4 family. As per nft man page: "When no address
+// family is specified, ip is used by default."
+func (cc *Conn) ListTable(name string) (*Table, error) {
+	return cc.ListTableOfFamily(name, TableFamilyIPv4)
+}
+
+// ListTableOfFamily returns table found for the specified name and table family
+func (cc *Conn) ListTableOfFamily(name string, family TableFamily) (*Table, error) {
+	t, err := cc.listTablesOfNameAndFamily(name, family)
+	if err != nil {
+		return nil, err
+	}
+	if got, want := len(t), 1; got != want {
+		return nil, fmt.Errorf("expected table count %d, got %d", want, got)
+	}
+	return t[0], nil
+}
+
 // ListTables returns currently configured tables in the kernel
 func (cc *Conn) ListTables() ([]*Table, error) {
 	return cc.ListTablesOfFamily(TableFamilyUnspecified)
@@ -120,18 +139,31 @@ func (cc *Conn) ListTables() ([]*Table, error) {
 // ListTablesOfFamily returns currently configured tables for the specified table family
 // in the kernel. It lists all tables if family is TableFamilyUnspecified.
 func (cc *Conn) ListTablesOfFamily(family TableFamily) ([]*Table, error) {
+	return cc.listTablesOfNameAndFamily("", family)
+}
+
+func (cc *Conn) listTablesOfNameAndFamily(name string, family TableFamily) ([]*Table, error) {
 	conn, closer, err := cc.netlinkConn()
 	if err != nil {
 		return nil, err
 	}
 	defer func() { _ = closer() }()
 
+	data := extraHeader(uint8(family), 0)
+	flags := netlink.Request | netlink.Dump
+	if name != "" {
+		data = append(data, cc.marshalAttr([]netlink.Attribute{
+			{Type: unix.NFTA_TABLE_NAME, Data: []byte(name + "\x00")},
+		})...)
+		flags = netlink.Request
+	}
+
 	msg := netlink.Message{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_GETTABLE),
-			Flags: netlink.Request | netlink.Dump,
+			Flags: flags,
 		},
-		Data: extraHeader(uint8(family), 0),
+		Data: data,
 	}
 
 	response, err := conn.Execute(msg)