Add WithSockOptions to modify netlink socket options (#277)

conn.go

@@ -37,16 +37,20 @@ type Conn struct {
 	TestDial nltest.Func // for testing only; passed to nltest.Dial
 	NetNS    int         // fd referencing the network namespace netlink will interact with.
 
-	lasting  bool       // establish a lasting connection to be used across multiple netlink operations.
+	lasting     bool       // establish a lasting connection to be used across multiple netlink operations.
-	mu       sync.Mutex // protects the following state
+	mu          sync.Mutex // protects the following state
-	messages []netlink.Message
+	messages    []netlink.Message
-	err      error
+	err         error
-	nlconn   *netlink.Conn // netlink socket using NETLINK_NETFILTER protocol.
+	nlconn      *netlink.Conn // netlink socket using NETLINK_NETFILTER protocol.
+	sockOptions []SockOption
 }
 
 // ConnOption is an option to change the behavior of the nftables Conn returned by Open.
 type ConnOption func(*Conn)
 
+// SockOption is an option to change the behavior of the netlink socket used by the nftables Conn.
+type SockOption func(*netlink.Conn) error
+
 // New returns a netlink connection for querying and modifying nftables. Some
 // aspects of the new netlink connection can be configured using the options
 // WithNetNSFd, WithTestDial, and AsLasting.
@@ -101,6 +105,14 @@ func WithTestDial(f nltest.Func) ConnOption {
 	}
 }
 
+// WithSockOptions sets the specified socket options when creating a new netlink
+// connection.
+func WithSockOptions(opts ...SockOption) ConnOption {
+	return func(cc *Conn) {
+		cc.sockOptions = append(cc.sockOptions, opts...)
+	}
+}
+
 // netlinkCloser is returned by netlinkConn(UnderLock) and must be called after
 // being done with the returned netlink connection in order to properly close
 // this connection, if necessary.
@@ -284,11 +296,28 @@ func (cc *Conn) FlushRuleset() {
 }
 
 func (cc *Conn) dialNetlink() (*netlink.Conn, error) {
+	var (
+		conn *netlink.Conn
+		err  error
+	)
+
 	if cc.TestDial != nil {
-		return nltest.Dial(cc.TestDial), nil
+		conn = nltest.Dial(cc.TestDial)
+	} else {
+		conn, err = netlink.Dial(unix.NETLINK_NETFILTER, &netlink.Config{NetNS: cc.NetNS})
 	}
 
-	return netlink.Dial(unix.NETLINK_NETFILTER, &netlink.Config{NetNS: cc.NetNS})
+	if err != nil {
+		return nil, err
+	}
+
+	for _, opt := range cc.sockOptions {
+		if err := opt(conn); err != nil {
+			return nil, err
+		}
+	}
+
+	return conn, nil
 }
 
 func (cc *Conn) setErr(err error) {