Internet Magic (Proxy Server) Windows Application

using System;
using System.Text;
using System.Net;
using System.Net.Sockets;
using internet_magic;

namespace internet_magic.Ftp {

///<summary>Relays FTP data between a remote host and a local client.</summary>
internal sealed class FtpDataConnection : Client {
	///<summary>Initializes a new instance of the FtpDataConnection class.</summary>
	public FtpDataConnection() : base() {}
	///<summary>Initializes a new instance of the FtpDataConnection class.</summary>
	///<param name="RemoteAddress">The address on the local FTP client to connect to.</param>
	///<returns>The PORT command string to send to the FTP server.</returns>
	public string ProcessPort(IPEndPoint RemoteAddress) {
		try {
			ListenSocket = new Socket(IPAddress.Any.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
			ListenSocket.Bind(new IPEndPoint(IPAddress.Any, 0));
			ListenSocket.Listen(1);
			ListenSocket.BeginAccept(new AsyncCallback(this.OnPortAccept), ListenSocket);
			ClientSocket = new Socket(RemoteAddress.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
			ClientSocket.BeginConnect(RemoteAddress, new AsyncCallback(this.OnPortConnected), ClientSocket);
            return "PORT " + Listener.GetLocalExternalIP().ToString().Replace('.', ',') + "," + Math.Floor((double)((IPEndPoint)ListenSocket.LocalEndPoint).Port / 256).ToString() + "," + (((IPEndPoint)ListenSocket.LocalEndPoint).Port % 256).ToString() + "\r\n";
		} catch {
			Dispose();
			return "PORT 0,0,0,0,0,0\r\n";
		}
	}
	///<summary>Called when we're connected to the data port on the local FTP client.</summary>
	///<param name="ar">The result of the asynchronous operation.</param>
	private void OnPortConnected(IAsyncResult ar) {
		try {
			ClientSocket.EndConnect(ar);
			StartHandshake();
		} catch {
			Dispose();
		}
	}
	///<summary>Called when there's a connection from the remote FTP server waiting to be accepted.</summary>
	///<param name="ar">The result of the asynchronous operation.</param>
	private void OnPortAccept(IAsyncResult ar) {
		try {
			DestinationSocket = ListenSocket.EndAccept(ar);
			ListenSocket.Close();
			ListenSocket = null;
			StartHandshake();
		} catch {
			Dispose();
		}
	}
	///<summary>Starts relaying data between the remote FTP server and the local FTP client.</summary>
	public override void StartHandshake() {
		if (DestinationSocket != null && ClientSocket != null && DestinationSocket.Connected && ClientSocket.Connected)
			StartRelay();
	}
	///<summary>Gets or sets the Socket that's used to listen for incoming connections.</summary>
	///<value>A Socket that's used to listen for incoming connections.</value>
	private Socket ListenSocket {
		get {
			return m_ListenSocket;
		}
		set {
			if (m_ListenSocket != null)
				m_ListenSocket.Close();
			m_ListenSocket = value;
		}
	}
	///<summary>Gets or sets the parent of this FtpDataConnection.</summary>
	///<value>The FtpClient object that's the parent of this FtpDataConnection object.</value>
	private FtpClient Parent {
		get {
			return m_Parent;
		}
		set {
			m_Parent = value;
		}
	}
	///<summary>Gets or sets a string that stores the reply that has been sent from the remote FTP server.</summary>
	///<value>A string that stores the reply that has been sent from the remote FTP server.</value>
	private string FtpReply {
		get {
			return m_FtpReply;
		}
		set {
			m_FtpReply = value;
		}
	}
	///<summary>Gets or sets a boolean value that indicates whether the FtpDataConnection expects a reply from the remote FTP server or not.</summary>
	///<value>A boolean value that indicates whether the FtpDataConnection expects a reply from the remote FTP server or not.</value>
	internal bool ExpectsReply {
		get {
			return m_ExpectsReply;
		}
		set {
			m_ExpectsReply = value;
		}
	}
	///<summary>Called when the proxy server processes a PASV command.</summary>
	///<param name="Parent">The parent FtpClient object.</param>
	public void ProcessPasv(FtpClient Parent) {
		this.Parent = Parent;
		ExpectsReply = true;
	}
	///<summary>Called when the FtpClient receives a reply on the PASV command from the server.</summary>
	///<param name="Input">The received reply.</param>
	///<returns>True if the input has been processed successfully, false otherwise.</returns>
	internal bool ProcessPasvReplyRecv(string Input) {
		FtpReply += Input;
		if (FtpClient.IsValidReply(FtpReply)) {
			ExpectsReply = false;
			ProcessPasvReply(FtpReply);
			FtpReply = "";
			return true;
		}
		return false;
	}
	///<summary>Processes a PASV reply from the server.</summary>
	///<param name="Reply">The reply to process.</param>
	private void ProcessPasvReply(string Reply) {
		try {
			IPEndPoint ConnectTo = ParsePasvIP(Reply);
			DestinationSocket = new Socket(ConnectTo.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
			DestinationSocket.BeginConnect(ConnectTo, new AsyncCallback(this.OnPasvConnected), DestinationSocket);
		} catch {
			Dispose();
		}
	}
	///<summary>Parses a PASV reply into an instance of the IPEndPoint class.</summary>
	///<param name="Reply">The reply to parse into an IPEndPoint.</param>
	///<returns>An instance of the IPEndPoint class when successful, null otherwise.</returns>
	private IPEndPoint ParsePasvIP(string Reply) {
		int StartIndex, StopIndex;
		string IPString;
		StartIndex = Reply.IndexOf("(");
		if (StartIndex == -1) {
			return null;
		} else {
			StopIndex = Reply.IndexOf(")", StartIndex);
			if (StopIndex == -1)
				return null;
			else
				IPString = Reply.Substring(StartIndex + 1, StopIndex - StartIndex - 1);
		}
		string [] Parts = IPString.Split(',');
		if (Parts.Length == 6)
			return new IPEndPoint(IPAddress.Parse(String.Join(".", Parts, 0, 4)), int.Parse(Parts[4]) * 256 + int.Parse(Parts[5]));
		else
			return null;
	}
	///<summary>Called when we're connected to the data port of the remote FTP server.</summary>
	///<param name="ar">The result of the asynchronous operation.</param>
	private void OnPasvConnected(IAsyncResult ar) {
		try {
			DestinationSocket.EndConnect(ar);
			ListenSocket = new Socket(IPAddress.Any.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
			ListenSocket.Bind(new IPEndPoint(IPAddress.Any, 0));
			ListenSocket.Listen(1);
			ListenSocket.BeginAccept(new AsyncCallback(this.OnPasvAccept), ListenSocket);
            Parent.SendCommand("227 Entering Passive Mode (" + Listener.GetLocalInternalIP().ToString().Replace('.', ',') + "," + Math.Floor((double)((IPEndPoint)ListenSocket.LocalEndPoint).Port / 256).ToString() + "," + (((IPEndPoint)ListenSocket.LocalEndPoint).Port % 256).ToString() + ").\r\n");
		} catch {
			Dispose();
		}
	}
	///<summary>Called when there's a connection from the local FTP client waiting to be accepted.</summary>
	///<param name="ar">The result of the asynchronous operation.</param>
	private void OnPasvAccept(IAsyncResult ar) {
		try {
			ClientSocket = ListenSocket.EndAccept(ar);
			StartHandshake();
		} catch {
			Dispose();
		}
	}
	// private variables
	/// <summary>Holds the value of the ListenSocket property.</summary>
	private Socket m_ListenSocket;
	/// <summary>Holds the value of the Parent property.</summary>
	private FtpClient m_Parent;
	/// <summary>Holds the value of the FtpReply property.</summary>
	private string m_FtpReply = "";
	/// <summary>Holds the value of the ExpectsReply property.</summary>
	private bool m_ExpectsReply = false;
}

}