網絡喚醒原理淺析(Wake On LAN)

之前我的一篇文章《網絡喚醒全攻略(Wake On Lan)》介紹過如何設置遠程喚醒電腦，着重於使用，這篇主要從原理方面解析一下當中的奧妙；

原理

將喚醒魔術包發送的被喚醒機器的網卡上，魔術包指AMD公司開發的喚醒數據包，具有遠程喚醒的網卡都支持這個標准，用16進制表示如下：

6對“FF”前綴+16次重復MAC地址,舉個例子假如我的網卡MAC地址是：AA:BB:CC:DD:EE:FF:11
那么魔術包就是:

0xFFFFFFFFFFAABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11

但是傳送的時候必須封包成二進制格式才可以傳送，簡單來說，我們抽2個區段分析：
FFFFFFFFFFF 轉成： 11111111 11111111 11111111 11111111 11111111 11111111

AABBCCDDEEFF11 轉成：‭10101010 10111011 11001100 11011101 11101110 11111111 00010001‬

那么封包后就是把每個字節連接在一起：

11111111 11111111 11111111 11111111 11111111  11111111 10101010 10111011 11001100 11011101 11101110 11111111 00010001‬
……..10101010 10111011 11001100 11011101 11101110 11111111 00010001‬（第16次）

開發實現

關鍵代碼（Java）:

	private String Wake(String name, String host, String mac, int port) {
        try {
            byte[] macBytes = getMacBytes(mac);//轉成字節類型
            byte[] bytes = new byte[6 + 16 * macBytes.length];
            for (int i = 0; i < 6; i++) {
                bytes[i] = (byte) 0xff;
            }
            for (int i = 6; i < bytes.length; i += macBytes.length) {
                System.arraycopy(macBytes, 0, bytes, i, macBytes.length); //放入16個MAC地址
            }
            InetAddress address = InetAddress.getByName(host);
            DatagramPacket packet = new DatagramPacket(bytes, bytes.length, address, port);
            DatagramSocket socket = new DatagramSocket();
            socket.send(packet);
            socket.close();
            return "wol_package_sent_success";
        } catch (Exception e) {
            return "wol_package_sent_fail";
        }
    }

private static byte[] getMacBytes(String mac) throws IllegalArgumentException {
        byte[] bytes = new byte[6];
        String[] hex = mac.split("(\\:|\\-)");
        if (hex.length != 6) {
            throw new IllegalArgumentException("Invalid MAC address.");
        }
        try {
            for (int i = 0; i < 6; i++) {
                bytes[i] = (byte) Integer.parseInt(hex[i], 16);
            }
        } catch (NumberFormatException e) {
            throw new IllegalArgumentException("Invalid hex digit in MAC address.");
        }
        return bytes;
    }

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