HTTP compression in .NET Framework 2.0

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Introduction

This article describes the implementation of a utility class that will allow HTTP requests informing the server (or any appliance in the network between the client and the server) what types of compression it can handle and uncompress the response from the server (if any) without changing the client application.

HTTP compression is very useful when the cost of the connection is high.

The factory pattern of creating WebRequest instances

The WebRequest supplies two methods to create instances:

• CreateDefault - Initializes a new WebRequest instance for the specified URI scheme.
• Create - Initializes a new WebRequest instance for the specified URI scheme.

The WebRequest class uses instances of classes that implement the IWebRequestCreate interface and are registered in the webRequestModules section in the configuration files. The Create method (called by both CreateDefault and Create) returns an initialized instance of a WebRequest descendent class capable of performing a standard request/response transaction for the protocol without needing any protocol-specific fields modified.

On the other hand, the previously created WebRequest derived instances will return WebResponse derived instances that will handle the HTTP response.

Because of the way the factory pattern is implemented, we can change the behavior of already built applications (our applications or even the .NET Framework) to request and handle HTTP compression, changing only the configuration files.

Since in versions 2.0 and above of the .NET framework already support compression, there is no need to supply WebRequestand WebResponse derived class implementations. All that's needed is a class that implements the IWebRequestCreate interface to create the WebRequestderived instance and set it up.

The code

As shown before, to add HTTP compression to our applications, we just have to build three classes:

• CompressibleHttpRequestCreator - implementing the IWebRequestCreate interface.

CompressibleHttpRequestCreator

In order for the applications that use HttpWebRequest and HttpWebResponse to work without any changes, CompressibleHttpRequestCreator.Create has to return a HttpWebRequest instance. Unfortunately, there is no public construtor for HttpWebRequest or publicly accessible implementation of IWebRequestCreate.Create that creates a HttpWebRequest instance, so some reflection will be needed.

The implementation of IWebRequestCreate.Create just creates an instance of HttpWebRequest and sets its HttpWebRequest.AutomaticDecompression to accept all types of compression.

public class CompressibleHttpRequestCreator : IWebRequestCreate
{
    public CompressibleHttpRequestCreator()
    {
    }

    WebRequest IWebRequestCreate.Create(Uri uri)
    {
        HttpWebRequest httpWebRequest = 
            Activator.CreateInstance(typeof(HttpWebRequest),
            BindingFlags.CreateInstance | BindingFlags.Public | 
            BindingFlags.NonPublic | BindingFlags.Instance,
            null, new object[] { uri, null }, null) as HttpWebRequest;

        if (httpWebRequest == null)
        {
            return null;
        }

        httpWebRequest.AutomaticDecompression =DecompressionMethods.GZip | 
            DecompressionMethods.Deflate;

        return httpWebRequest;
    }
}  

Configuration

Now, to add HTTP compression support to any application, all that's needed is to add the corresponding entries to the webRequestModules section in the configuration file.

<configuration>
  <system.net>
    <webRequestModules>
      <remove prefix="http:"/>
      <add prefix="http:" 
            type="Pajocomo.Net.CompressibleHttpRequestCreator, Pajocomo" />
    </webRequestModules>
  </system.net>
</configuration>

History

When I first ported this from .NET 1.1, I completely missed the fact that HttpWebRequest and HttpWebResponse already implemented compression.

Thanks to Bj�rn to point that out to me.