C# FTP server never receives incoming transfer connection after processing EPRT command

Question

I am building an FTP server that will get images from a camera and store the photos in a local directory. I am having issues grabbing the file from the port given to me. Here is the conversation:

Server(me):"220 Ready!"
Client:"USER Guest"
Server: "331 Username ok, need password"
Client:"PASS "
Server: "230 user logged in"
Client: "PWD"
Server: "257 \"/\""
Client: "EPRT |1|172.22.22.103|58719|
Server:"500 IDK"
Client: "PORT 172,22,22,103,147,237"
Server:"200 Ready for Transport"
Client: "TYPE I"
Server:"200 I understand it is an image file"
Client: "STOR .TEST.RHPRYI"

I found the port by converting the last two numbers to hexadecimal (93,ED) appending them and then converting back to decimal. My final port is 37869. I then create a new TcpClient to use as a download, but my TcpListener never picks up the camera. Also I am not sure my download method is correct.

I got lots of my code from here:
http://www.codeproject.com/Articles/380769/Creating-an-FTP-Server-in-Csharp-with-IPv-Support

Really my question comes down to: How do I get the file being sent by the client as an FTP server in C#?

Here is my code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Net;
using System.Threading;
using System.Net.Sockets;
using System.Drawing;
using Microsoft.VisualBasic;
//Creates a TcpServer that is used to transfer images from the Axis Camera to a directory on a computer
//ftpdmin was chosen as the name because it was supposed to be a replica of a program in c just made in csharp
//However, it was really hard to transfer from c because all of the struct names and functions were nonintuitive
//This program is completely made from internet sources, and there are definitely bugs. For instance it does not implement
// many FTP calls. 


namespace ftpdmin
{
    class Server
    {
    //TCPListener listens to a given IP and port to wait for a connection with the camera

    //Download Listener listens to the port given by the camera in the PORT command, which is the
    //port at which the files needed to be downloaded are stored.

    //Listen thread implements tcpListener. We do not want to be stuck in an infinite loop, but
    //we always want to be listening to the camera. That is why we use another thread.

    //Downlaod thread implements the downloadlistener for the same reason as above

    //File name is the download files name given by the camera in the STOR command.

    //direct is the directory to save the files at on the local computer. It was given in the main
    // method of the console program. See Program.cs

    private TcpListener tcpListener;
    private TcpListener downloadListener;
    private Thread listenThread;
    private Thread downloadThread;
    private string fileName;

    private string direct;

    //Initialize Ip adress and threads
    public Server(string dir)
    {
        direct = dir;
        this.tcpListener = new TcpListener(IPAddress.Parse("172.22.22.104"), 3000);
        this.listenThread = new Thread(new ThreadStart(ListenForClients));
        this.listenThread.Start();
    }

    private void ListenForClients()
    {
        //Start listening
        this.tcpListener.Start();

        while (true)
        {
            //blocks until a client has connected to the server
            TcpClient client = this.tcpListener.AcceptTcpClient();

            //create a thread to handle communication 
            //with connected client
            Thread clientThread = new Thread(new ParameterizedThreadStart(HandleClientComm));
            clientThread.Start(client);
        }
    }

    private void ListenForDownloads()
    {
        this.downloadThread.Start();

        while(true)
        {
            TcpClient downloadClient = this.downloadListener.AcceptTcpClient();
            Thread clientDownloadThread = new Thread(new ParameterizedThreadStart(HandleClientDownload));
            clientDownloadThread.Start(downloadClient);
        }
    }

    private void HandleClientDownload(object downloadClient)
    {
        Console.WriteLine("IM HERE");
        TcpClient downloaderClient = (TcpClient) downloadClient;
        NetworkStream downloadStream = downloaderClient.GetStream();
        StreamWriter downloadWriter = new StreamWriter(downloadStream, Encoding.ASCII);
        StreamReader downloadReader = new StreamReader(downloadStream);
        try
        {
            //Sets up the path to store the file
            string path = Path.Combine(direct, fileName);
            FileStream file = File.Create(path);
            //Implements the method to download a file
            CopyStream(file, downloadStream);
            file.Close();
        }
        catch (Exception e)
        {
            Console.WriteLine("a socket error has occured:" + e);

        }
    }

    private void HandleClientComm(object client)
    {
        //A Server is TCP has to respond to a bunch of commands from the client. The first thing it
        //does when it connects is send code 220 which says it is good to continue.
        TcpClient tcpClient = (TcpClient)client;
        NetworkStream clientStream = tcpClient.GetStream();
        StreamWriter writer = new StreamWriter(clientStream, Encoding.ASCII);
        StreamReader reader=new StreamReader(clientStream);
        writer.WriteLine("220 Ready!");
        writer.Flush();
        string command=reader.ReadLine().ToUpperInvariant();
        int downloadPort=0;
        string ipOfDownload="";
        Console.WriteLine(command);
      while(!command.Equals("QUIT"))
      {
          //USER comes with the username given to the client. Here I do not check if the cameras username
          //is the same as the username in the program. I just give the command 331 which means continue.
        if(command.Contains("USER"))
        {
            writer.WriteLine("331 Username ok, need password");
            writer.Flush();
        }
        //PASS is the same as username. I do not check the passwords, I just give 230 which continues the FTP.
        else if(command.Contains("PASS"))
        {
            writer.WriteLine("230 User Logged In");
            writer.Flush();
        }
        //PWD is Print working directory. I send 257 to say I have a PWD, and I send / because that is what is saved
        // in the camera. I am not actually going to save files at this directory, I just want to continue.
        else if(command.Contains("PWD"))
        {
            writer.WriteLine("257 \"/\"");
            writer.Flush();
        }
        //This is an important command. The client is sending an IP where it wants to do file transfers. It comes in a 
        //Weird format so all this function is doing is allowing me store Ip as "172.22.22.103" instead of "PORT 172,22,22,103"
        //Also there is a port listed at the end, but it is given in 2 numbers. The conversion to one port number is done by
        //changing the two numbers to hexadecimal, appending them, and then transforming them back to decimal.
        else if(command.Contains("PORT"))
        {
            string portPart1 = "";
            string portPart2 = "";
            Console.WriteLine(command);
            int numberOfCommas=0;
            int i=0;
            bool notPort=true;
            bool isNotPortPart2=true;
            while(i<command.Length && notPort)
            {
               if(command[i].Equals(','))
               {
                   if(numberOfCommas==3)
                   {
                       notPort=false;
                   }
                   else
                   {
                       ipOfDownload+=".";
                       numberOfCommas++;
                   }
               }
               else if(Information.IsNumeric(command[i]))
               {
                   ipOfDownload+=command[i];
               }
               i++;
           }
           while(i<command.Length && isNotPortPart2)
           {
               if(Information.IsNumeric(command[i]))
               {
                   portPart1+=command[i];
               }
               else
               {
                   isNotPortPart2=false;
               }
               i++;
           }
         while(i<command.Length)
         {
             portPart2+=command[i];
             i++;
         }
            Console.WriteLine("IP=" +ipOfDownload);
            Console.WriteLine("PortPart1="+portPart1);
            Console.WriteLine("PortPart2="+portPart2);
            int portPart1int = int.Parse(portPart1);
            int portPart2int = int.Parse(portPart2);
            string portPart1Hex = portPart1int.ToString("X");
            string portPart2Hex = portPart2int.ToString("X");
            string downloadPortHex = portPart1Hex + portPart2Hex;
            downloadPort = Convert.ToInt32(downloadPortHex, 16);
            Console.WriteLine("PortPart1Hex=" + portPart1Hex);
            Console.WriteLine("PortPart2Hex=" + portPart2Hex);
            Console.WriteLine("FinalPort: " + downloadPort);
            this.downloadListener = new TcpListener(IPAddress.Parse(ipOfDownload), downloadPort);
            this.downloadThread = new Thread(new ThreadStart(ListenForDownloads));
            writer.WriteLine("200 Ready for Transport");
            writer.Flush();
     }
    //The client sends TYPE I for image. usually an ftp would switchto binary mode because that is the only way
    //a file can be transferred cleanly.
     else if(command.Contains("TYPE"))
     {
         writer.WriteLine("200 I understand it is an image file");
         writer.Flush();
     }
   //This command gives the name of the file being transferred. I substring to get rid of
   //The STOR . that comes before the file name
     else if(command.Contains("STOR"))
     {
         fileName = command.Substring(6);
         Console.WriteLine(fileName);
     }
    //For all other commands sent by the client, I send 500 which means I'm not implementing those commands.
     else
     {
            writer.WriteLine("500 IDK");
            writer.Flush();
     }
          command=reader.ReadLine().ToUpperInvariant();
          Console.WriteLine(command);
    }    
      writer.WriteLine("221 BYE");
      writer.Flush();
      tcpClient.Close();
    }

    private static long CopyStream(Stream input, Stream output, int bufferSize)
    {
        byte[] buffer = new byte[bufferSize];
        int count = 0;
        long total = 0;

        while ((count = input.Read(buffer, 0, buffer.Length)) > 0)
        {
            output.Write(buffer, 0, count);
            total += count;
        }

        return total;
    }

    private static long CopyStreamAscii(Stream input, Stream output, int bufferSize)
    {
        char[] buffer = new char[bufferSize];
        int count = 0;
        long total = 0;

        using (StreamReader rdr = new StreamReader(input))
        {
            using (StreamWriter wtr = new StreamWriter(output, Encoding.ASCII))
            {
                while ((count = rdr.Read(buffer, 0, buffer.Length)) > 0)
                {
                    wtr.Write(buffer, 0, count);
                    total += count;
                }
            }
        }

        return total;
    }

    private long CopyStream(Stream input, Stream output)
    {
        //if (_transferType == "I")
        //{
            return CopyStream(input, output, 4096);
        //}
        //else
        //{
         //   return CopyStreamAscii(input, output, 4096);
        //}
    }
}

Answer 1

By the ERTP (or PORT) command, the client tells your server where the client is listening for incoming transfer connections to be initiated by the server. Instead you start listening too. So both parties are listening and nothing can happen.

So instead of TcpListener, you need to create TcpClient and actively connect.

See RFC 2428.

What you have implemented resembles passive mode (EPSV or PASV command), while the client is using an active mode.

---

Anyway you should better use an existing implementation of FTP server instead of trying to implement your own.