migrate to golang.zx2c4.com/wireguard/wgctrl (#239)

* migrate to golang.zx2c4.com/wireguard/wgctrl

This commit introduces the usage of wgctrl.
It avoids the usage of exec calls of the wg command
and parsing the output of `wg show`.

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* vendor wgctrl

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* apply suggestions from code review

Remove wireguard.Enpoint struct and use net.UDPAddr for the resolved
endpoint and addr string (dnsanme:port) if a DN was supplied.

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* pkg/*: use wireguard.Enpoint

This commit introduces the wireguard.Enpoint struct.
It encapsulates a DN name with port and a net.UPDAddr.
The fields are private and only accessible over exported Methods
to avoid accidental modification.

Also iptables.GetProtocol is improved to avoid ipv4 rules being applied
by `ip6tables`.

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* pkg/wireguard/conf_test.go: add tests for Endpoint

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* cmd/kg/main.go: validate port range

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* add suggestions from review

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* pkg/mesh/mesh.go: use Equal func

Implement an Equal func for Enpoint and use it instead of comparing
strings.

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* cmd/kgctl/main.go: check port range

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* vendor

Signed-off-by: leonnicolas <leonloechner@gmx.de>

vendor/github.com/mdlayher/genetlink/family_linux.go

@@ -0,0 +1,146 @@
+//+build linux
+
+package genetlink
+
+import (
+	"errors"
+	"fmt"
+	"math"
+
+	"github.com/mdlayher/netlink"
+	"github.com/mdlayher/netlink/nlenc"
+	"golang.org/x/sys/unix"
+)
+
+// errInvalidFamilyVersion is returned when a family's version is greater
+// than an 8-bit integer.
+var errInvalidFamilyVersion = errors.New("invalid family version attribute")
+
+// getFamily retrieves a generic netlink family with the specified name.
+func (c *Conn) getFamily(name string) (Family, error) {
+	b, err := netlink.MarshalAttributes([]netlink.Attribute{{
+		Type: unix.CTRL_ATTR_FAMILY_NAME,
+		Data: nlenc.Bytes(name),
+	}})
+	if err != nil {
+		return Family{}, err
+	}
+
+	req := Message{
+		Header: Header{
+			Command: unix.CTRL_CMD_GETFAMILY,
+			// TODO(mdlayher): grab nlctrl version?
+			Version: 1,
+		},
+		Data: b,
+	}
+
+	msgs, err := c.Execute(req, unix.GENL_ID_CTRL, netlink.Request)
+	if err != nil {
+		return Family{}, err
+	}
+
+	// TODO(mdlayher): consider interpreting generic netlink header values
+
+	families, err := buildFamilies(msgs)
+	if err != nil {
+		return Family{}, err
+	}
+	if len(families) != 1 {
+		// If this were to ever happen, netlink must be in a state where
+		// its answers cannot be trusted
+		panic(fmt.Sprintf("netlink returned multiple families for name: %q", name))
+	}
+
+	return families[0], nil
+}
+
+// listFamilies retrieves all registered generic netlink families.
+func (c *Conn) listFamilies() ([]Family, error) {
+	req := Message{
+		Header: Header{
+			Command: unix.CTRL_CMD_GETFAMILY,
+			// TODO(mdlayher): grab nlctrl version?
+			Version: 1,
+		},
+	}
+
+	flags := netlink.Request | netlink.Dump
+	msgs, err := c.Execute(req, unix.GENL_ID_CTRL, flags)
+	if err != nil {
+		return nil, err
+	}
+
+	return buildFamilies(msgs)
+}
+
+// buildFamilies builds a slice of Families by parsing attributes from the
+// input Messages.
+func buildFamilies(msgs []Message) ([]Family, error) {
+	families := make([]Family, 0, len(msgs))
+	for _, m := range msgs {
+		var f Family
+		if err := (&f).parseAttributes(m.Data); err != nil {
+			return nil, err
+		}
+
+		families = append(families, f)
+	}
+
+	return families, nil
+}
+
+// parseAttributes decodes netlink attributes into a Family's fields.
+func (f *Family) parseAttributes(b []byte) error {
+	ad, err := netlink.NewAttributeDecoder(b)
+	if err != nil {
+		return err
+	}
+
+	for ad.Next() {
+		switch ad.Type() {
+		case unix.CTRL_ATTR_FAMILY_ID:
+			f.ID = ad.Uint16()
+		case unix.CTRL_ATTR_FAMILY_NAME:
+			f.Name = ad.String()
+		case unix.CTRL_ATTR_VERSION:
+			v := ad.Uint32()
+			if v > math.MaxUint8 {
+				return errInvalidFamilyVersion
+			}
+
+			f.Version = uint8(v)
+		case unix.CTRL_ATTR_MCAST_GROUPS:
+			ad.Nested(func(nad *netlink.AttributeDecoder) error {
+				f.Groups = parseMulticastGroups(nad)
+				return nil
+			})
+		}
+	}
+
+	return ad.Err()
+}
+
+// parseMulticastGroups parses an array of multicast group nested attributes
+// into a slice of MulticastGroups.
+func parseMulticastGroups(ad *netlink.AttributeDecoder) []MulticastGroup {
+	groups := make([]MulticastGroup, 0, ad.Len())
+	for ad.Next() {
+		ad.Nested(func(nad *netlink.AttributeDecoder) error {
+			var g MulticastGroup
+			for nad.Next() {
+				switch nad.Type() {
+				case unix.CTRL_ATTR_MCAST_GRP_NAME:
+					g.Name = nad.String()
+				case unix.CTRL_ATTR_MCAST_GRP_ID:
+					g.ID = nad.Uint32()
+				}
+			}
+
+			groups = append(groups, g)
+			return nil
+		})
+	}
+
+	return groups
+}