Question

I need to compare the first 5 bytes of a UDP packet to two definitions, and act on them accordingly if it matches one. However, how should I represent the Hex for this since this obviously won’t/isn’t working?

The commented lines are the original way I was doing it, but not very efficient.

private static void HandleQuery(Socket socket, EndPoint Remote)
{
    byte[] A2S_INFO_REQUEST = StringToByteArray("\xFF\xFF\xFF\xFF\x54");
    byte[] A2S_PLAYER = StringToByteArray("\xFF\xFF\xFF\xFF\x55");

    byte[] data = new byte[1400];
    int recv = socket.ReceiveFrom(data, ref Remote);

    // A2S_INFO QUERY
    //if (recv == 25 && data[4] == 84)
    if (CompareByteArray(A2S_INFO_REQUEST, data, 5))
    {
        ReplyInfoQuery(socket, Remote);
    }

    // A2S_PLAYER QUERY
    //if (recv == 9)
    if (CompareByteArray(A2S_PLAYER, data, 5))
    {
        ReplyPlayerQuery(socket, Remote);
    }
}

private static byte[] StringToByteArray(String hex)
{
    int NumberChars = hex.Length;
    byte[] bytes = new byte[NumberChars / 2];
    for (int i = 0; i < NumberChars; i += 2)
    bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
    return bytes;
}

private static bool CompareByteArray(byte[] a1, byte[] a2, int len)
{
    for (int i = 0; i < len; i++)
    {
        if (a1[i] != a2[i])
        {
            return false;
        }
    }

    return true;
}

Answer 1

You can fill a byte array easier:

//byte[] A2S_PLAYER = StringToByteArray("\xFF\xFF\xFF\xFF\x55");
byte[] A2S_PLAYER = new byte[] {0xFF, 0xFF, 0xFF, 0xFF, 0x55} ;