List tables (#16)

list tables function

table.go

@@ -15,23 +15,30 @@
 package nftables
 
 import (
+	"fmt"
+
 	"github.com/mdlayher/netlink"
 	"golang.org/x/sys/unix"
 )
 
+var tableHeaderType = netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_NEWTABLE)
+
 // TableFamily specifies the address family for this table.
 type TableFamily byte
 
 // Possible TableFamily values.
 const (
-	TableFamilyIPv4 TableFamily = unix.AF_INET
-	TableFamilyIPv6 TableFamily = unix.AF_INET6
+	TableFamilyIPv4   TableFamily = unix.AF_INET
+	TableFamilyIPv6   TableFamily = unix.AF_INET6
+	TableFamilyBridge TableFamily = unix.AF_BRIDGE
 )
 
 // A Table contains Chains. See also
 // https://wiki.nftables.org/wiki-nftables/index.php/Configuring_tables
 type Table struct {
-	Name   string
+	Name   string // NFTA_TABLE_NAME
+	Use    uint32 // NFTA_TABLE_USE (Number of chains in table)
+	Flags  uint32 // NFTA_TABLE_FLAGS
 	Family TableFamily
 }
 
@@ -66,3 +73,65 @@ func (cc *Conn) AddTable(t *Table) *Table {
 	})
 	return t
 }
+
+// ListTables returns currently configured tables in the kernel
+func (cc *Conn) ListTables() ([]*Table, error) {
+	conn, err := cc.dialNetlink()
+	if err != nil {
+		return nil, err
+	}
+
+	defer conn.Close()
+
+	msg := netlink.Message{
+		Header: netlink.Header{
+			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_GETTABLE),
+			Flags: netlink.Request | netlink.Dump,
+		},
+		Data: extraHeader(uint8(unix.AF_UNSPEC), 0),
+	}
+
+	response, err := conn.Execute(msg)
+	if err != nil {
+		return nil, err
+	}
+
+	var tables []*Table
+	for _, m := range response {
+		t, err := tableFromMsg(m)
+		if err != nil {
+			return nil, err
+		}
+
+		tables = append(tables, t)
+	}
+
+	return tables, nil
+}
+
+func tableFromMsg(msg netlink.Message) (*Table, error) {
+	if got, want := msg.Header.Type, tableHeaderType; got != want {
+		return nil, fmt.Errorf("unexpected header type: got %v, want %v", got, want)
+	}
+
+	var t Table
+	t.Family = TableFamily(msg.Data[0])
+
+	ad, err := netlink.NewAttributeDecoder(msg.Data[4:])
+	if err != nil {
+		return nil, err
+	}
+
+	for ad.Next() {
+		switch ad.Type() {
+		case unix.NFTA_TABLE_NAME:
+			t.Name = ad.String()
+		case unix.NFTA_TABLE_USE:
+			t.Use = ad.Uint32()
+		case unix.NFTA_TABLE_FLAGS:
+			t.Flags = ad.Uint32()
+		}
+	}
+
+	return &t, nil
+}