Writing ASP.NET Plugins

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CKFinder functionality can be extended with server-side plugins. Although the full source code of the CKFinder server connector is available and can be modified in any way desired, a much better way of enhancing the CKFinder connector is to create a plugin.

The main advantages of plugins are:

  • Upgrades are much easier.
  • The plugin code is stored in a single place.
  • Plugins can be easily disabled when they are not needed anymore.

Common use cases:

  • Adding a new server-side command (i.e. fileditor and imageresize plugin).
  • Working with uploaded files (i.e. watermark plugin).
  • Extending information returned by the Init command (i.e. imageresize plugin).

Creating a plugin

Step1: Create plugin folder

Create a directory for your plugin inside of the "plugins" directory (by default CKFinder comes with three plugins: dummy, fileeditor, imagreresize). Let's use "myplugin" as the plugin name and use the same name for our new folder.

Step2: Create JavaScript plugin

Inside of your plugin's folder ("myplugin") create an empty file named plugin.js.
(If your plugin is a pure server side plugin, you may skip that step)

Step3: Create .dll file with your plugin

// Let's skip that step for now

Step4: Enable plugin

  • Copy .dll file with a plugin to the "bin" folder of your application
  • In config.ascx add your plugin to the Plugins list:
Plugins = new string[] {
	// class name, assembly name
	"CKFinder.Plugins.FileSize, CKFinder_FileSize"
};

ASP.NET plugin system

Hooks

CKFinder provides several hooks that can be used to extend the functionality of the CKFinder application. Assigning a function (also known as an event handler) to a hook will cause that function to be called at the appropriate point in the main CKFinder code, to perform whatever additional task(s) the developer thinks would be useful at that point. Each hook can have multiple handlers assigned to it, in which case it will call the functions in the order that they are assigned.

Registering an event handler to a hook is very simple: 

// MyBeforeExecuteCommandEventHandler is our custom event handler (method)
CKFinderEvent.BeforeExecuteCommand += 
       new CKFinder.Connector.CKFinderEvent.Hook( this.MyBeforeExecuteCommandEventHandler );

Available hooks (events)

Hook Since Description
AfterFileUpload 2.0 Executed after successful file upload.
BeforeExecuteCommand 2.0 Executed before a server side command is executed.
InitCommand 2.0 Executed straight before sending the result of the Init command.

Enabling JavaScript plugin

Sometimes a server side plugin might come with a client side (JavaScript) plugin, that should be automatically enabled when the server side plugin is enabled.
The JavascriptPlugins property is a special variable that does that.

To enable a plugin, simply define it's name (to add multiple plugins, separate their names with a comma). 

public string JavascriptPlugins
{
	get { return "myplugin"; }
}

This code is virtually equal to specyfying in config.js: 

config.extraPlugins = 'myplugin';

but the advantage of defining it in a plugin is that it will be enabled only when the server side plugin is also enabled.

Sample plugin: FileSize (adding new server side command - complete example)

Introduction

Probably the best way to learn new things is to write a code, so let's write a plugin that adds a new server side command to the connector. We'll create a command that returns a size of a given file.

If you're unfamiliar with CKFinder architecture, please take a look at Server Side Integration documentation. Alternatively, just bear in mind that CKFinder is an AJAX application and that the connection between the user interface running in a browser and the server connector is simply made of AJAX calls to the connector. Check AJAX calls in Firebug to better understand CKFinder.

The FileSize plugin should provide a new command named "FileSize", in other words, calling: 

/ckfinder/core/connector/aspx/connector.aspx?command=FileSize&type=Files&currentFolder=%2F&fileName=foobar.jpg

(assuming that foobar.jpg exists) should return a valid XML response: 

<Connector resourceType="Files">
<Error number="0"/>
<CurrentFolder path="/" url="/ckfinder/userfiles/files/" acl="255"/>
<FileSize size="5647"/>
</Connector>

The project

Let's create a C# project now to generate a .dll file.

  • Create a new C# project (Class Library).
  • Add reference to CKFinder.dll (right-click "References" in the "Solution Explorer", use "Browse" to select CKFinder.dll from the directory you have saved it).
  • In Project Properties change Assembly name to CKFinder_FileSize and Default namespace to CKFinder.Plugins
  • Rename the default file created by VS (Class1.cs) into FileSize.cs.

The whole code will be in a single file (FileSize.cs). For the sake of simplicity, let's take a look at Filesize.cs that just does exactly what we need: 

namespace CKFinder.Connector.CommandHandlers
{
  // Since we want to send a XML response, we'll extend the XmlCommandHandlerBase class
  public class FileSizeCommandHandler : XmlCommandHandlerBase
  {
    public FileSizeCommandHandler() : base() {}

    // (5) The buildXml method is used to construct an XML response
    protected override void BuildXml()
    {
      string fileName = Request["FileName"];
      string filePath = System.IO.Path.Combine( this.CurrentFolder.ServerPath, fileName );

      long fileSize = new System.IO.FileInfo( filePath ).Length;

      // (6) Adding a <FileSize> element to the XML response.
      XmlNode oFileSize = XmlUtil.AppendElement( this.ConnectorNode, "FileSize" );
      XmlUtil.SetAttribute( oFileSize, "size", fileSize.ToString() );
    }
  }
}

namespace CKFinder.Plugins
{
  public class FileSize : CKFinder.CKFinderPlugin
  {
    public string JavascriptPlugins
    {
      get { return "myplugin"; }
    }

    public void Init( CKFinder.Connector.CKFinderEvent CKFinderEvent )
    {
      // (1) Register our custom BeforeExecuteCommand event handler (MyBeforeExecuteCommandEventHandler function).
      CKFinderEvent.BeforeExecuteCommand += 
            new CKFinder.Connector.CKFinderEvent.Hook( this.MyBeforeExecuteCommandEventHandler );
    }

    // (2) Our event handler
    protected void MyBeforeExecuteCommandEventHandler( object sender, CKFinder.Connector.CKFinderEventArgs args )
    {
      String command = (String)args.data[0];

      // (3) Register the "FileSize" command
      if ( command == "FileSize" )
      {
        HttpResponse Response = (HttpResponse)args.data[1];

        // (4) Our custom class (FileSizeCommandHandler) will do the rest
        CKFinder.Connector.CommandHandlers.CommandHandlerBase commandHandler =
          new CKFinder.Connector.CommandHandlers.FileSizeCommandHandler();

        // The sendResponse method is defined in XmlCommandHandlerBase, it creates 
        // a basic XML response and calls the buildXml()method 
        commandHandler.SendResponse( Response );
      }
    }
  }
}

Step1: Register an event handler

CKFinderEvent.BeforeExecuteCommand += 
       new CKFinder.Connector.CKFinderEvent.Hook( this.MyBeforeExecuteCommandEventHandler );

Step2: Create an event handler

protected void MyBeforeExecuteCommandEventHandler( object sender, CKFinder.Connector.CKFinderEventArgs args )

Step3: Register the "FileSize" command

The BeforeExecuteCommand hook is used to define your own server side command 

if ( command == "FileSize" )
// ...

Step4: Create a class to send the XML response

If your plugin returns an XML response, you'll usually just extend the XmlCommandHandlerBase class to reduce the amount of code to write, however it is not a requirement. 

public class FileSizeCommandHandler : XmlCommandHandlerBase

Step5: Create the buildXml method

In the MyBeforeExecuteCommandEventHandler method we have called sendResponse. The sendResponse method is defined in XmlCommandHandlerBase class, it creates a basic XML response and calls the buildXml method, which we need to define. 

protected override void BuildXml()
// ...

Step6: Construct the XML response

The main task of the buildXml method is to construct an XML response, so we're doing it below: 

XmlNode oFileSize = XmlUtil.AppendElement( this.ConnectorNode, "FileSize" );
XmlUtil.SetAttribute( oFileSize, "size", fileSize.ToString() );

Full source code

FileSize.cs

The full source code of a plugin with all necessary security checks: (save the code as FileSize.cs in your C# project) 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Web;
using System.Web.UI;
using CKFinder;

namespace CKFinder.Connector.CommandHandlers
{
	// Since we will send a XML response, we'll extend the XmlCommandHandlerBase class
	public class FileSizeCommandHandler : XmlCommandHandlerBase
	{
		public FileSizeCommandHandler() : base(){}

		// (5) The buildXml method is used to construct an XML response
		protected override void BuildXml()
		{
			if ( !this.CurrentFolder.CheckAcl( AccessControlRules.FileView ) )
			{
				ConnectorException.Throw( Errors.Unauthorized );
			}

			string fileName = Request["FileName"];

			if ( !Connector.CheckFileName( fileName ) || Config.Current.CheckIsHiddenFile( fileName ) )
			{
				ConnectorException.Throw( Errors.InvalidRequest );
				return;
			}

			if ( !this.CurrentFolder.ResourceTypeInfo.CheckExtension( System.IO.Path.GetExtension( fileName ) ) )
			{
				ConnectorException.Throw( Errors.InvalidRequest );
				return;
			}

			string filePath = System.IO.Path.Combine( this.CurrentFolder.ServerPath, fileName );

			if ( !System.IO.File.Exists( filePath ) )
				ConnectorException.Throw( Errors.FileNotFound );

			try
			{
				long fileSize = new System.IO.FileInfo( filePath ).Length;

				// (6) Adding a <FileSize> element to the XML response.
				XmlNode oFileSize = XmlUtil.AppendElement( this.ConnectorNode, "FileSize" );
				XmlUtil.SetAttribute( oFileSize, "size", fileSize.ToString() );
			}
			catch ( OutOfMemoryException )
			{
				ConnectorException.Throw( Errors.InvalidName );
			}
			catch ( System.UnauthorizedAccessException )
			{
				ConnectorException.Throw( Errors.AccessDenied );
			}
			catch ( System.Security.SecurityException )
			{
				ConnectorException.Throw( Errors.AccessDenied );
			}
			catch ( System.ArgumentException )
			{
				ConnectorException.Throw( Errors.FileNotFound );
			}
			catch ( System.IO.PathTooLongException )
			{
				ConnectorException.Throw( Errors.FileNotFound );
			}
			catch ( Exception )
			{
				ConnectorException.Throw( Errors.Unknown );
			}
		}
	}
}

namespace CKFinder.Plugins
{
	public class FileSize : CKFinder.CKFinderPlugin
	{
		// (Optional) Register a javascript plugin named "myplugin"
		public string JavascriptPlugins
		{
			get { return "myplugin"; }
		}

		public void Init( CKFinder.Connector.CKFinderEvent CKFinderEvent )
		{
			// (1) Register our custom BeforeExecuteCommand event 
                        //     handler (MyBeforeExecuteCommandEventHandler function).
			CKFinderEvent.BeforeExecuteCommand += 
                             new CKFinder.Connector.CKFinderEvent.Hook( this.MyBeforeExecuteCommandEventHandler );
		}

		// (2) Our event handler
		protected void MyBeforeExecuteCommandEventHandler( object sender, CKFinder.Connector.CKFinderEventArgs args )
		{
			String command = (String)args.data[0];

			// (3) Register the "FileSize" command
			if ( command == "FileSize" )
			{
				HttpResponse Response = (HttpResponse)args.data[1];

				// (4) Our custom class (FileSizeCommandHandler) will do the rest
				CKFinder.Connector.CommandHandlers.CommandHandlerBase commandHandler =
					new CKFinder.Connector.CommandHandlers.FileSizeCommandHandler();

				// The sendResponse method is defined in XmlCommandHandlerBase, it creates 
				// a basic XML response and calls the buildXml()method 
				commandHandler.SendResponse( Response );
			}
		}
	}
}
plugin.js

.. and the client side (JavaScript) plugin that will call the FileSize command: (save the code as plugin.js in "plugins/myplugin" folder) 

CKFinder.addPlugin( 'myplugin', function( api ) {
	api.addFileContextMenuOption( { label : 'File Size', command : "FileSize" } , function( api, file )
	{
		api.connector.sendCommand( 'FileSize', { fileName : api.getSelectedFile().name }, function( xml )
		{
			if ( xml.checkError() )
				return;

			var size = xml.selectSingleNode( 'Connector/FileSize/@size' );
			api.openMsgDialog( "", "The exact size of a file is: " + size.value + " bytes");
		} );
	});
});

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