vendor: add d2g/dhcp4server

vendor/golang.org/x/net/ipv4/helper_unix.go

@@ -0,0 +1,50 @@
+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd
+
+package ipv4
+
+import (
+	"net"
+	"reflect"
+)
+
+func (c *genericOpt) sysfd() (int, error) {
+	switch p := c.Conn.(type) {
+	case *net.TCPConn, *net.UDPConn, *net.IPConn:
+		return sysfd(p)
+	}
+	return 0, errInvalidConnType
+}
+
+func (c *dgramOpt) sysfd() (int, error) {
+	switch p := c.PacketConn.(type) {
+	case *net.UDPConn, *net.IPConn:
+		return sysfd(p.(net.Conn))
+	}
+	return 0, errInvalidConnType
+}
+
+func (c *payloadHandler) sysfd() (int, error) {
+	return sysfd(c.PacketConn.(net.Conn))
+}
+
+func (c *packetHandler) sysfd() (int, error) {
+	return sysfd(c.c)
+}
+
+func sysfd(c net.Conn) (int, error) {
+	cv := reflect.ValueOf(c)
+	switch ce := cv.Elem(); ce.Kind() {
+	case reflect.Struct:
+		netfd := ce.FieldByName("conn").FieldByName("fd")
+		switch fe := netfd.Elem(); fe.Kind() {
+		case reflect.Struct:
+			fd := fe.FieldByName("sysfd")
+			return int(fd.Int()), nil
+		}
+	}
+	return 0, errInvalidConnType
+}