iOS NetworkExtension let tunFd =

iOS进行VPN链接获取tunfd ， iOS15无法正常创建连接，14正常！
用以下方法获取：

//获取tunFd
    func getTunFd() ->Int32?
    {
        if #available(iOS 15, *) {
        var buf = [CChar](repeating: 0, count: Int(IFNAMSIZ))
        let utunPrefix = "utun".utf8CString.dropLast()
        return (0...1024).first { (_ fd: Int32) -> Bool in
        var len = socklen_t(buf.count)
        return getsockopt(fd, 2, 2, &buf, &len) == 0 && buf.starts(with: utunPrefix)
        }
        } else {
        return self.packetFlow.value(forKeyPath: "socket.fileDescriptor") as? Int32
        }
    }

参考感谢：https://blog.csdn.net/qq_26359763/article/details/118331747