Building a Simple File download server using C# Samples and examples

The .NET framework provides two namespaces, System.Net and System.Net.Sockets for network programming. The classes and methods of these namespaces help us to write programs, which can communicate across the network. The most widely used protocol TCP is used for stream-based communication. The System.Net.Sockets.Socket is an important class from the System.Net.Sockets namespace. A Socket instance has a local and a remote end-point associated with it. The local end-point contains the connection information for the current socket instance. To create a network server for TCP/IP streaming, you start by creating a TcpListener object to listen to the TCP/IP port you've chosen. On the client side; the client would instantiate a TcpClient class, which represents a TCP/IP client connection to a host.

Demonstrated here is a simple FileServer class which acts as a file download server for clients. A parallel Client class is also presented which asks for the file download at a specified location. Basically; the server reads out the file content using a FileStream object and writes the content out to the Socket using a NetworkStream. The client reads out from the Socket and writes the content out to a FileStream connected to a local file on its side. The communication between the server and client is synchronous. For simplicity; the server is made to handle one request at a time. Also the FileServer always gives the same file to it's clients (hardcoded).


//the Server class
using System;
using System.IO;
using System.Net;
using System.Net.Sockets;

public class FileServer
{
    static string hostName = "127.0.0.1";
    static int port = 65000; //if this port is not available on your machine; pick up some other
    IPAddress localAddr = IPAddress.Parse(hostName);

    public void Start()
    {            
        TcpListener tcpListner = new TcpListener(localAddr, port);
        tcpListner.Start(); //start listening to client request
        for (; ; ) //infinite loop
        {
            //blocks until a client request comes
            Socket socket = tcpListner.AcceptSocket(); 
            if (socket.Connected)
            {
                //Delegate to the SendFileToClient method
                SendFileToClient(socket);
                socket.Close();
            }
        }
    }

    void SendFileToClient(Socket socket)
    {
        NetworkStream netStream = new NetworkStream(socket);
        StreamWriter writer = new StreamWriter(netStream);
        //make sure the specified file exists on your server machine
        FileStream fileStream = File.Open(@"D:\csharp.txt", FileMode.Open, FileAccess.Read, FileShare.Read);
        StreamReader reader = new StreamReader(fileStream);
        string strReadLine = null;
        do
        {
            strReadLine = reader.ReadLine();
            if(strReadLine!= null) writer.WriteLine(strReadLine);
            writer.Flush(); //make sure content is flushed and reaches the client
        } while (strReadLine != null); //exit when nothing more to read
        writer.Close();
    }
}

//the Client class
using System;
using System.IO;
using System.Net;
using System.Net.Sockets;

public class Client
{
    //modify the host name if you are running the server in a different machine
    static string hostName = "127.0.0.1"; 
    static int port = 65000;

    public void FetchFileFromServer()
    {
        TcpClient client = new TcpClient(hostName, port);
        if (client.Connected)
        {
            NetworkStream netStream = client.GetStream();
            StreamReader reader = new StreamReader(netStream);
            string strReadLine = null;
            //note: make sure that the file location/ name is different than the server's location
            //if you are running the server and client on the same machine
            FileStream fileStream =
                File.Open(@"C:\csharp.txt", FileMode.OpenOrCreate, FileAccess.Write, FileShare.None);
            StreamWriter writer = new StreamWriter(fileStream);
            do
            {
                strReadLine = reader.ReadLine();                    
                if (strReadLine != null)
                    writer.WriteLine(strReadLine);
            } while (strReadLine != null);  //exit when there is nothing to receive              
            writer.Close();
            netStream.Close();
        }
    }
}

Here is some test code if you want to run the Server and client on the same machine:


            new Thread(new ThreadStart(new FileServer().Start)).Start();
            Thread client = new Thread(new ThreadStart(new Client().FetchFileFromServer));
            client.Start();
            client.Join();
            //the Server Thread keeps running

If you run the above code you will have a copy of the file csharp.txt in D: drive "downloaded" to the C: drive.

Building a Simple File download server using C#

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