https://www.cnblogs.com/bibi-feiniaoyuan/p/socket_two.html

socket通信传输的字节是什么内容，客户端和服务端要知道这个字节是文件，是字符串还是其他？应该设计一个协定。例如在内容字节前面插入一个字节表示内容形式，0代表字符串，1代表文件......

private void button1_Click(object sender, EventArgs e)
{
    Socket socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
    IPAddress ip = IPAddress.Parse("192.169.11.87");
    IPEndPoint endPoint = new IPEndPoint(ip, 5000);
    socket.Connect(endPoint);

    string msg = "消息来了";
    byte[] buffer = Encoding.UTF8.GetBytes(msg);
    //如何在buffer前面加一个字节呢，可以使用集合
    List<byte> bufferList = new List<byte>();
    bufferList.Add(0);
    bufferList.AddRange(buffer);
    byte[] newBuffer = bufferList.ToArray();
    socket.Send(newBuffer);
}

private void button1_Click(object sender, EventArgs e)
{
    Socket socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
    IPAddress ip = IPAddress.Parse("192.169.11.87");
    IPEndPoint endPoint = new IPEndPoint(ip, 5000);
    socket.Connect(endPoint);
   
    string path = string.Empty;
    using (FileStream fsRead = new FileStream(path, FileMode.Open, FileAccess.Read))
    {
        byte[] buffer = new byte[1024 * 1024 * 5];
        int r = fsRead.Read(buffer, 0, buffer.Length);
        List<byte> newBuffer = new List<byte>();
        newBuffer.Add(1);
        newBuffer.AddRange(buffer);
        // 是r+1
        socket.Send(newBuffer.ToArray(), 0, r+1, SocketFlags.None);
    }
   
}