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/internal/wguser/client.go

@@ -0,0 +1,99 @@
+package wguser
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"golang.zx2c4.com/wireguard/wgctrl/internal/wginternal"
+	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
+)
+
+var _ wginternal.Client = &Client{}
+
+// A Client provides access to userspace WireGuard device information.
+type Client struct {
+	dial func(device string) (net.Conn, error)
+	find func() ([]string, error)
+}
+
+// New creates a new Client.
+func New() (*Client, error) {
+	return &Client{
+		// Operating system-specific functions which can identify and connect
+		// to userspace WireGuard devices. These functions can also be
+		// overridden for tests.
+		dial: dial,
+		find: find,
+	}, nil
+}
+
+// Close implements wginternal.Client.
+func (c *Client) Close() error { return nil }
+
+// Devices implements wginternal.Client.
+func (c *Client) Devices() ([]*wgtypes.Device, error) {
+	devices, err := c.find()
+	if err != nil {
+		return nil, err
+	}
+
+	var wgds []*wgtypes.Device
+	for _, d := range devices {
+		wgd, err := c.getDevice(d)
+		if err != nil {
+			return nil, err
+		}
+
+		wgds = append(wgds, wgd)
+	}
+
+	return wgds, nil
+}
+
+// Device implements wginternal.Client.
+func (c *Client) Device(name string) (*wgtypes.Device, error) {
+	devices, err := c.find()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, d := range devices {
+		if name != deviceName(d) {
+			continue
+		}
+
+		return c.getDevice(d)
+	}
+
+	return nil, os.ErrNotExist
+}
+
+// ConfigureDevice implements wginternal.Client.
+func (c *Client) ConfigureDevice(name string, cfg wgtypes.Config) error {
+	devices, err := c.find()
+	if err != nil {
+		return err
+	}
+
+	for _, d := range devices {
+		if name != deviceName(d) {
+			continue
+		}
+
+		return c.configureDevice(d, cfg)
+	}
+
+	return os.ErrNotExist
+}
+
+// deviceName infers a device name from an absolute file path with extension.
+func deviceName(sock string) string {
+	return strings.TrimSuffix(filepath.Base(sock), filepath.Ext(sock))
+}
+
+func panicf(format string, a ...interface{}) {
+	panic(fmt.Sprintf(format, a...))
+}