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How to use Managed Code (C#) to create an FTP Home Directory Provider that is based on the Remote Client IP Address

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I recently had an interesting scenario that was presented to me by a customer: they had a business requirement where they needed to give the same username and password to a group of people, but they didn't want any two people to be able to see anyone else's files. This seemed like an unusual business requirement to me; the whole point of keeping users separate is one of the reasons why we added user isolation to the FTP service.

With that in mind, my first suggestion was - of course - to rethink their business requirement, assign different usernames and passwords to everyone, and use FTP user isolation. But that wasn't going to work for them; their business requirement for giving out the same username and password could not be avoided. So I said that I would get back to them, and I spent the next few days experimenting with a few ideas.

One of my early ideas that seemed somewhat promising was to write a custom home directory provider that dynamically created unique home directories that were based on the session IDs for the individual FTP sessions, and the provider would use those directories to isolate the users. That seemed like a good idea, but when I analyzed the results I quickly saw that it wasn't going to work; as each user logged in, they would get a new session ID, and they wouldn't see their files from their last session. On top of that, the FTP server would rapidly start to collect a large number of session-based directories, with no garbage collection. So it was back to the drawing board for me.

After some discussions with the customer, we reasoned that the best suggestion for their particular environment was to leverage some of the code that I had written for my session-based home directory provider in order to create home directory provider that dynamically created home directories that are based on the remote IP of the FTP client.

I have to stress, however, that this solution will not work in all situations. For example:

  • If multiple FTP clients are accessing your FTP server through the same firewall, their remote IP might appear to be the same.
  • If an FTP client is moving between geographic locations, such as traveling with a laptop, then the remote IP address will change, and the client will not see their files from their previous session.

That being said, the customer felt that those limitations were acceptable for their environment, so I created a home directory provider that dynamically created home directories that were based on the remote IP address of their FTP clients. I agree that it's not a perfect solution, but their business requirement made this scenario considerably difficult to work around.

Note: I wrote and tested the steps in this blog using both Visual Studio 2010 and Visual Studio 2008; if you use an different version of Visual Studio, some of the version-specific steps may need to be changed.

In This Blog

Prerequisites

The following items are required to complete the procedures in this blog:

  1. The following version of IIS must be installed on your Windows computer, and the Internet Information Services (IIS) Manager must also be installed:

    • IIS 7.0 must be installed on Windows Server 2008
    • IIS 7.5 must be installed on Windows Server 2008 R2 or Windows 7

  2. The new FTP 7.5 service must be installed. To install FTP 7.5, follow the instructions in the following topic:

  3. You must have FTP publishing enabled for a site. To create a new FTP site, follow the instructions in the following topic:

  4. Set the content permissions to allow access for the COM+ process identity that handles extensibility:

    • Open a command prompt.

    • Type the following command:

       ICACLS "%SystemDrive%\inetpub\ftproot" /Grant "Network Service":M /T

      Where "%SystemDrive%\inetpub\ftproot" is the home directory for your FTP site.

    • Close the command prompt.

    Note: This last step is necessary for the custom home directory provider to create the isolation directories.

Step 1: Set up the Project Environment

In this step, you will create a project in Microsoft Visual Studio for the demo provider.

  1. Open Visual Studio 2008 or Visual Studio 2010.
  2. Click the File menu, then New, then Project.
  3. In the New Projectdialog box:
    • Choose Visual C# as the project type.
    • Choose Class Library as the template.
    • Type FtpRemoteIPHomeDirectory as the name of the project.
    • Click OK.
  4. When the project opens, add a reference path to the FTP extensibility library:
    • Click Project, and then click FtpRemoteIPHomeDirectory Properties.
    • Click the Reference Paths tab.
    • Enter the path to the FTP extensibility assembly for your version of Windows, where C: is your operating system drive.
      • For Windows Server 2008 and Windows Vista:
        • C:\Windows\assembly\GAC_MSIL\Microsoft.Web.FtpServer\7.5.0.0__31bf3856ad364e35
      • For 32-bit Windows 7 and Windows Server 2008 R2:
        • C:\Program Files\Reference Assemblies\Microsoft\IIS
      • For 64-bit Windows 7 and Windows Server 2008 R2:
        • C:\Program Files (x86)\Reference Assemblies\Microsoft\IIS
    • Click Add Folder.
  5. Add a strong name key to the project:
    • Click Project, and then click FtpRemoteIPHomeDirectory Properties.
    • Click the Signing tab.
    • Check the Sign the assembly check box.
    • Choose <New...> from the strong key name drop-down box.
    • Enter FtpRemoteIPHomeDirectoryKey for the key file name.
    • If desired, enter a password for the key file; otherwise, clear the Protect my key file with a password check box.
    • Click OK.
  6. Note: FTP 7.5 Extensibility does not support the .NET Framework 4.0; if you are using Visual Studio 2010, or you have changed your default framework version, you may need to change the framework version for this project. To do so, use the following steps:
    • Click Project, and then click FtpRemoteIPHomeDirectory Properties.
    • Click the Application tab.
    • Choose .NET Framework 3.5 in the Target framework drop-down menu.
    • Save, close, and re-open the project.
  7. Optional: You can add a custom build event to add the DLL automatically to the Global Assembly Cache (GAC) on your development computer:

    • Click Project, and then click FtpRemoteIPHomeDirectory Properties.

    • Click the Build Events tab.

    • Enter the appropriate commands in the Post-build event command linedialog box, depending on your version of Visual Studio:

      • If you are using Visual Studio 2010:

        net stop ftpsvc
        call "%VS100COMNTOOLS%\vsvars32.bat">null
        gacutil.exe /if "$(TargetPath)"
        net start ftpsvc

      • If you are using Visual Studio 2008:

        net stop ftpsvc
        call "%VS90COMNTOOLS%\vsvars32.bat">null
        gacutil.exe /if "$(TargetPath)"
        net start ftpsvc

      Note: You need to be logged in as an administrator in order to restart the FTP service and add the dll to the Global Assembly Cache.

  8. Save the project.

Step 2: Create the Extensibility Class

In this step, you will implement the extensibility interfaces for the demo provider.

  1. Add the necessary references to the project:
    • Click Project, and then click Add Reference...
    • On the .NET tab, click Microsoft.Web.FtpServer.
    • Click OK.
  2. Add the code for the authentication class:

    • In Solution Explorer, double-click the Class1.cs file.

    • Remove the existing code.

    • Paste the following code into the editor:

       using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.IO;
using Microsoft.Web.FtpServer;

public class FtpRemoteIPHomeDirectory :
    BaseProvider,
    IFtpHomeDirectoryProvider,
    IFtpLogProvider
{
    // Create a dictionary object that will contain
    // session IDs and remote IP addresses.
    private static Dictionary<string, string> _sessionList = null;

    // Store the path to the default FTP folder.
    private static string _defaultDirectory = string.Empty;

    // Override the default initialization method.
    protected override void Initialize(StringDictionary config)
    {
        // Test if the session dictionary has been created.
        if (_sessionList == null)
        {
            // Create the session dictionary.
            _sessionList = new Dictionary<string, string>();
        }
        // Retrieve the default directory path from configuration.
        _defaultDirectory = config["defaultDirectory"];
        // Test for the default home directory (Required).
        if (string.IsNullOrEmpty(_defaultDirectory))
        {
            throw new ArgumentException(
              "Missing default directory path in configuration.");
        }
    }

    // Define the home directory provider method.
    string IFtpHomeDirectoryProvider.GetUserHomeDirectoryData(
        string sessionId,
        string siteName,
        string userName)
    {
        // Create a string with the folder name.
        string _sessionDirectory = String.Format(
            @"{0}\{1}", _defaultDirectory,
            _sessionList[sessionId]);
        try
        {
            // Test if the folder already exists.
            if (!Directory.Exists(_sessionDirectory))
            {
                // Create the physical folder. Note: NETWORK SERVICE
                // needs write permissions to the default folder in
                // order to create each remote IP's home directory.
                Directory.CreateDirectory(_sessionDirectory);
            }
        }
        catch (Exception ex)
        {
            throw ex;
        }
        // Return the path to the session folder.
        return _sessionDirectory;
    }
    // Define the log provider method.
    public void Log(FtpLogEntry logEntry)
    {
        // Test if the USER command was entered.
        if (logEntry.Command.Equals(
            "USER",
            StringComparison.InvariantCultureIgnoreCase))
        {
            // Reformat the remote IP address.
            string _remoteIp = logEntry.RemoteIPAddress
                .Replace(':', '-')
                .Replace('.', '-');
            // Add the remote IP address to the session dictionary.
            _sessionList.Add(logEntry.SessionId, _remoteIp);
        }
        // Test if the command channel was closed (end of session).
        if (logEntry.Command.Equals(
            "CommandChannelClosed",
            StringComparison.InvariantCultureIgnoreCase))
        {
            // Remove the closed session from the dictionary.
            _sessionList.Remove(logEntry.SessionId);
        }
    }
}
  3. Save and compile the project.

Note: If you did not use the optional steps to register the assemblies in the GAC, you will need to manually copy the assemblies to your IIS 7 computer and add the assemblies to the GAC using the Gacutil.exe tool. For more information, see the following topic on the Microsoft MSDN Web site:

Global Assembly Cache Tool (Gacutil.exe)

Step 3: Add the Demo Provider to FTP

In this step, you will add your provider to the global list of custom providers for your FTP service, configure your provider's settings, and enable your provider for an FTP site.

Adding your Provider to FTP

  1. Determine the assembly information for your extensibility provider:
    • In Windows Explorer, open your "C:\Windows\assembly" path, where C: is your operating system drive.
    • Locate the FtpRemoteIPHomeDirectory assembly.
    • Right-click the assembly, and then click Properties.
    • Copy the Culture value; for example: Neutral.
    • Copy the Version number; for example: 1.0.0.0.
    • Copy the Public Key Token value; for example: 426f62526f636b73.
    • Click Cancel.
  2. Add the extensibility provider to the global list of FTP authentication providers:
    • Open the Internet Information Services (IIS) Manager.
    • Click your computer name in the Connections pane.
    • Double-click FTP Authentication in the main window.
    • Click Custom Providers... in the Actions pane.
    • Click Register.
    • Enter FtpRemoteIPHomeDirectory for the provider Name.
    • Click Managed Provider (.NET) .
    • Enter the assembly information for the extensibility provider using the information that you copied earlier. For example:
      FtpRemoteIPHomeDirectory,FtpRemoteIPHomeDirectory,version=1.0.0.0,Culture=neutral,PublicKeyToken=426f62526f636b73
    • Click OK.
    • Clear the FtpRemoteIPHomeDirectory check box in the providers list.
    • Click OK.

Note: If you prefer, you could use the command line to add the provider to FTP by using syntax like the following example:

cd %SystemRoot%\System32\Inetsrv appcmd.exe set config -section:system.ftpServer/providerDefinitions /+"[name='FtpRemoteIPHomeDirectory',type='FtpRemoteIPHomeDirectory,FtpRemoteIPHomeDirectory,version=1.0.0.0,Culture=neutral,PublicKeyToken=426f62526f636b73']" /commit:apphost

Configuring your Provider's Settings

At the moment there is no user interface that allows you to configure properties for a custom home directory provider, so you will have to use the following command line:

cd %SystemRoot%\System32\Inetsrv appcmd.exe set config -section:system.ftpServer/providerDefinitions /+"activation.[name='FtpRemoteIPHomeDirectory']" /commit:apphost appcmd.exe set config -section:system.ftpServer/providerDefinitions /+"activation.[name='FtpRemoteIPHomeDirectory'].[key='defaultDirectory',value='C:\Inetpub\ftproot']" /commit:apphost

Note: The highlighted area contains the value that you need to update with the root directory of your FTP site.

Enabling your Provider for an FTP site

At the moment there is no user interface that allows you to enable a custom home directory provider for an FTP site, so you will have to use the following command line:

cd %SystemRoot%\System32\Inetsrv appcmd.exe set config -section:system.applicationHost/sites /+"[name='My FTP Site'].ftpServer.customFeatures.providers.[name='FtpRemoteIPHomeDirectory']" /commit:apphost appcmd.exe set config -section:system.applicationHost/sites /"[name='My FTP Site'].ftpServer.userIsolation.mode:Custom" /commit:apphost

Note: The highlighted areas contain the name of the FTP site where you want to enable the custom home directory provider.

Summary

In this blog I showed you how to:

  • Create a project in Visual Studio 2010 or Visual Studio 2008 for a custom FTP home directory provider.
  • Implement the extensibility interface for custom FTP home directories.
  • Add a custom home directory provider to your FTP service.

When users connect to your FTP site, the FTP service will create a directory that is based on their remote IP address, and it will drop their session in the corresponding folder for their remote IP address. They will not be able to change to the root directory, or a directory for a different remote IP address.

For example, if the root directory for your FTP site is "C:\Inetpub\ftproot" and a client connects to your FTP site from 192.168.0.100, the FTP home directory provider will create a folder that is named "C:\Inetpub\ftproot\192-168-0-100", and the FTP client's sessions will be isolated in that directory; the FTP client will not be able to change directory to "C:\Inetpub\ftproot" or the home directory for another remote IP.

Once again, there are limitations to this approach, and I agree that it's not a perfect solution in all scenarios; but this provider works as expected when you have to use the same username and password for all of your FTP clients, and you know that your FTP clients will use unique remote IP addresses.

Comments

  • Anonymous
    December 21, 2011
    Hi Robert, Thanks for these excellent articles on extensibility. Is there a way that we can use .NET 4.0 to create these extension classes. Thanks

  • Anonymous
    October 01, 2013
    Can the path returned be a network path i.e. \machineshareusername