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/golang.zx2c4.com/wireguard/wgctrl/client.go

@@ -0,0 +1,101 @@
+package wgctrl
+
+import (
+	"errors"
+	"os"
+
+	"golang.zx2c4.com/wireguard/wgctrl/internal/wginternal"
+	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
+)
+
+// Expose an identical interface to the underlying packages.
+var _ wginternal.Client = &Client{}
+
+// A Client provides access to WireGuard device information.
+type Client struct {
+	// Seamlessly use different wginternal.Client implementations to provide an
+	// interface similar to wg(8).
+	cs []wginternal.Client
+}
+
+// New creates a new Client.
+func New() (*Client, error) {
+	cs, err := newClients()
+	if err != nil {
+		return nil, err
+	}
+
+	return &Client{
+		cs: cs,
+	}, nil
+}
+
+// Close releases resources used by a Client.
+func (c *Client) Close() error {
+	for _, wgc := range c.cs {
+		if err := wgc.Close(); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Devices retrieves all WireGuard devices on this system.
+func (c *Client) Devices() ([]*wgtypes.Device, error) {
+	var out []*wgtypes.Device
+	for _, wgc := range c.cs {
+		devs, err := wgc.Devices()
+		if err != nil {
+			return nil, err
+		}
+
+		out = append(out, devs...)
+	}
+
+	return out, nil
+}
+
+// Device retrieves a WireGuard device by its interface name.
+//
+// If the device specified by name does not exist or is not a WireGuard device,
+// an error is returned which can be checked using `errors.Is(err, os.ErrNotExist)`.
+func (c *Client) Device(name string) (*wgtypes.Device, error) {
+	for _, wgc := range c.cs {
+		d, err := wgc.Device(name)
+		switch {
+		case err == nil:
+			return d, nil
+		case errors.Is(err, os.ErrNotExist):
+			continue
+		default:
+			return nil, err
+		}
+	}
+
+	return nil, os.ErrNotExist
+}
+
+// ConfigureDevice configures a WireGuard device by its interface name.
+//
+// Because the zero value of some Go types may be significant to WireGuard for
+// Config fields, only fields which are not nil will be applied when
+// configuring a device.
+//
+// If the device specified by name does not exist or is not a WireGuard device,
+// an error is returned which can be checked using `errors.Is(err, os.ErrNotExist)`.
+func (c *Client) ConfigureDevice(name string, cfg wgtypes.Config) error {
+	for _, wgc := range c.cs {
+		err := wgc.ConfigureDevice(name, cfg)
+		switch {
+		case err == nil:
+			return nil
+		case errors.Is(err, os.ErrNotExist):
+			continue
+		default:
+			return err
+		}
+	}
+
+	return os.ErrNotExist
+}