if 20 > l || l > len(b) {
		return n
	}
	if b[0]>>4 != 4 {
		return n
	}
	copy(b, b[l:])
	return n - l
}

func (c *IPConn) readMsg(b, oob []byte) (n, oobn, flags int, addr *IPAddr, err error) {
	var sa syscall.Sockaddr
	n, oobn, flags, sa, err = c.fd.readMsg(b, oob, 0)
	switch sa := sa.(type) {
	case *syscall.SockaddrInet4:
		addr = &IPAddr{IP: sa.Addr[0:]}
	case *syscall.SockaddrInet6:

		if sa.Name != "" {
			addr = &UnixAddr{Name: sa.Name, Net: sotypeToNet(c.fd.sotype)}
		}
	}
	return n, addr, err
}

func (c *UnixConn) readMsg(b, oob []byte) (n, oobn, flags int, addr *UnixAddr, err error) {
	var sa syscall.Sockaddr
	n, oobn, flags, sa, err = c.fd.readMsg(b, oob, readMsgFlags)
	if readMsgFlags == 0 && err == nil && oobn > 0 {
		setReadMsgCloseOnExec(oob[:oobn])
	}

	switch sa := sa.(type) {

				if err = fd.pd.waitRead(fd.isFile); err == nil {
					continue
				}
			}
		}
		err = fd.eofError(n, err)
		return n, err
	}
}

// ReadMsg wraps the recvmsg network call.
func (fd *FD) ReadMsg(p []byte, oob []byte, flags int) (int, int, int, syscall.Sockaddr, error) {
	if err := fd.readLock(); err != nil {
		return 0, 0, 0, nil, err
	}
	defer fd.readUnlock()

			port = from.Port
		}
	}
	if err == nil {
		addr = netip.AddrPortFrom(ip, uint16(port))
	}
	return n, addr, err
}

func (c *UDPConn) readMsg(b, oob []byte) (n, oobn, flags int, addr netip.AddrPort, err error) {
	switch c.fd.family {
	case syscall.AF_INET:
		var sa syscall.SockaddrInet4
		n, oobn, flags, err = c.fd.readMsgInet4(b, oob, 0, &sa)