refactor: rewrite cfg.go

utils/net.go

@@ -0,0 +1,53 @@
+package utils
+
+import (
+	"net"
+
+	"github.com/go-errors/errors"
+)
+
+func getLocalIP() (net.IP, error) {
+	conn, err := net.Dial("udp", "1.0.0.1:53")
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	host, _, err := net.SplitHostPort(conn.LocalAddr().String())
+	if err != nil {
+		return nil, errors.Wrap(err, 0)
+	}
+	ip := net.ParseIP(host)
+	if ip == nil {
+		return nil, errors.Errorf("failed to parse IP address %q", host)
+	}
+	return ip, nil
+}
+
+func FindDefaultAdapter() (*net.Interface, error) {
+	localIP, err := getLocalIP()
+	if err != nil {
+		return nil, errors.WrapPrefix(err, "failed to get local address", 0)
+	}
+
+	iflist, err := net.Interfaces()
+	if err != nil {
+		return nil, errors.WrapPrefix(err, "failed to get interface list", 0)
+	}
+	for _, iface := range iflist {
+		addrs, err := iface.Addrs()
+		if err != nil {
+			continue
+		}
+		for _, addr := range addrs {
+			ipnet, ok := addr.(*net.IPNet)
+			if !ok {
+				continue
+			}
+			if localIP.Equal(ipnet.IP) {
+				return &iface, nil
+			}
+		}
+	}
+	return nil, errors.New("failed to find default adapter")
+}