.NET ช่วยอธิบายการเขียนโปรแกรมรับส่งไฟล์ผ่านเครือข่าย ด้วยภาษา C# ผ่าน Socket หน่อยค่ะ

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Text;
using System.Threading;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.Reflection;

class MainClass
{
   public static void Main()
   {
      IPAddress host = IPAddress.Parse("192.168.104.104");
      IPEndPoint hostep = new IPEndPoint(host, 8080);
      Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

      try
      {
         sock.Connect(hostep);
      } catch (SocketException e) {
         Console.WriteLine("Not Connect to host");
         Console.WriteLine(e.ToString());
         sock.Close();
         return;
      }

      try
      {
         sock.Send(Encoding.ASCII.GetBytes("testing"));
      } catch (SocketException e) {
          Console.WriteLine("Problem sending data");
          Console.WriteLine( e.ToString());
          sock.Close();
          return;
      }
      sock.Close();
   }
}

//FILE TRANSFER USING C#.NET SOCKET - SERVER
class FTServerCode
{
    IPEndPoint ipEnd; 
    Socket sock;
    public FTServerCode()
    {
        ipEnd = new IPEndPoint(IPAddress.Any, 5656); 
        //Make IP end point to accept any IP address with port no 5656.
        sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.IP);
        //Here creating new socket object with protocol type and transfer data type
        sock.Bind(ipEnd); 
        //Bind end point with newly created socket.
    }
    public static string receivedPath;
    public static string curMsg = "Stopped";
    public void StartServer()
    {
        try
        {
            curMsg = "Starting...";
            sock.Listen(100);
            /* That socket object can handle maximum 100 client connection at a time & 
            waiting for new client connection /
            curMsg = "Running and waiting to receive file.";
            Socket clientSock = sock.Accept();
            /* When request comes from client that accept it and return 
            new socket object for handle that client. */
            byte[] clientData = new byte[1024 * 5000];
            int receivedBytesLen = clientSock.Receive(clientData);
            curMsg = "Receiving data...";    
            int fileNameLen = BitConverter.ToInt32(clientData, 0); 
            /* I've sent byte array data from client in that format like 
            [file name length in byte][file name] [file data], so need to know 
            first how long the file name is. /
            string fileName = Encoding.ASCII.GetString(clientData, 4, fileNameLen);
            /* Read file name */
            BinaryWriter bWrite = new BinaryWriter(File.Open
		(receivedPath +"/"+ fileName, FileMode.Append)); ; 
            /* Make a Binary stream writer to saving the receiving data from client. /
            bWrite.Write(clientData, 4 + fileNameLen, 
		receivedBytesLen - 4 - fileNameLen);
            /* Read remain data (which is file content) and 
            save it by using binary writer. */
            curMsg = "Saving file...";
            bWrite.Close();
            clientSock.Close(); 
            /* Close binary writer and client socket */
            curMsg = "Received & Saved file; Server Stopped.";
        }
        catch (Exception ex)
        {
            curMsg = "File Receiving error.";
        }
    }
} 

//FILE TRANSFER USING C#.NET SOCKET - CLIENT
class FTClientCode
{
    public static string curMsg = "Idle";
    public static void SendFile(string fileName)
    {
        try
        {
             IPAddress[] ipAddress = Dns.GetHostAddresses("localhost");
             IPEndPoint ipEnd = new IPEndPoint(ipAddress[0], 5656); 
             /* Make IP end point same as Server. */
             Socket clientSock = new Socket(AddressFamily.InterNetwork, 
		SocketType.Stream, ProtocolType.IP);
             /* Make a client socket to send data to server. */
             string filePath = "";
             /* File reading operation. */
             fileName = fileName.Replace("\\", "/");
             while (fileName.IndexOf("/") > -1)
             {
                 filePath += fileName.Substring(0, fileName.IndexOf("/") + 1);
                 fileName = fileName.Substring(fileName.IndexOf("/") + 1);
             }         
             byte[] fileNameByte = Encoding.ASCII.GetBytes(fileName);
             if (fileNameByte.Length > 850 * 1024)
             {
                 curMsg = "File size is more than 850kb, please try with small file.";
                 return;
             }
             curMsg = "Buffering ...";
             byte[] fileData = File.ReadAllBytes(filePath + fileName); 
             /* Read & store file byte data in byte array. */
             byte[] clientData = new byte[4 + fileNameByte.Length + fileData.Length]; 
             /* clientData will store complete bytes which will store file name length, 
             file name & file data. */
             byte[] fileNameLen = BitConverter.GetBytes(fileNameByte.Length);
             /* File name length’s binary data. */
             fileNameLen.CopyTo(clientData, 0);
             fileNameByte.CopyTo(clientData, 4);
             fileData.CopyTo(clientData, 4 + fileNameByte.Length);
             /* copy these bytes to a variable with format line [file name length]
             [file name] [ file content] */
             curMsg = "Connection to server ...";
             clientSock.Connect(ipEnd); 
             /* Trying to connection with server. /
             curMsg = "File sending...";
             clientSock.Send(clientData);
             /* Now connection established, send client data to server. */
             curMsg = "Disconnecting...";
             clientSock.Close(); 
             /* Data send complete now close socket. */
             curMsg = "File transferred.";
        }
        catch (Exception ex)
        {
             if(ex.Message=="No connection could be made because the target machine 
                actively refused it")
                 curMsg="File Sending fail. Because server not running." ;
             else
                 curMsg = "File Sending fail." + ex.Message;
        } 
    }
}