Mike-Ward.Net

HTTP Compression in ASP.NET 2.0

Mads Kristensen writes an excellent blog called .NET Slave. Recently, he posted an article on how easy it is to enable HTTP compression in ASP.NET 2.0 without having to touch IIS. This is a handy thing to have when using hosted services like Go Daddy where you don’t have access to the IIS configuration. I’ve had it bookmarked for some time intending to add it to this site. Well I finally took the plunge and added it.

The code is surprisingly brief and works as advertised. However, I did run into a few issues that the original code did not address. For instance, the built-in web server in Visual Studio 2005 does not seem to work correctly when compression is enabled. Also, some services like Feed Burner do not accept compression even though their request header indicates otherwise. I’ve added a few extra checks to the original code to fix these issues.

using System;  
using System.Web;  
using System.IO.Compression;  
  
public class CompressionModule : IHttpModule  
{  
    const string GZIP = "gzip";  
    const string DEFLATE = "deflate";  
    static string[] exceptions = { "=rss", "=rpc", "localhost" };  
      
    void IHttpModule.Init(HttpApplication context)  
    {  
        context.BeginRequest += BeginRequest;  
    }  
      
    void BeginRequest(object sender, EventArgs e)  
    {  
        try  
        {  
            if (RequestContains(exceptions))  
            {  
                return;  
            }  
              
            HttpApplication app = sender as HttpApplication;  
              
            if (EncodingAccepted(GZIP))  
            {  
                app.Response.Filter = new GZipStream(app.Response.Filter, CompressionMode.Compress);  
                SetEncoding(GZIP);  
            }  
              
            else if (EncodingAccepted(DEFLATE))  
            {  
                app.Response.Filter = new DeflateStream(app.Response.Filter, CompressionMode.Compress);  
                SetEncoding(DEFLATE);  
            }  
        }  
          
        catch (Exception)  
        {  
        // Log it here...  
        }  
    }  
      
    bool RequestContains(string[] values)  
    {  
        string request = HttpContext.Current.Request.Url.AbsoluteUri.ToLowerInvariant();  
          
        foreach (string value in values)  
        {  
            if (request.Contains(value))  
            {  
                return true;  
            }  
        }  
          
        return false;  
    }  
      
    bool EncodingAccepted(string encoding)  
    {  
        string acceptEncoding =   
        HttpContext.Current.Request.Headers["Accept-encoding"] ?? string.Empty;  
          
        return acceptEncoding.Contains(encoding);  
    }  
      
    void SetEncoding(string encoding)  
    {  
        HttpContext.Current.Response.AppendHeader("Content-encoding", encoding);  
    }  
      
    void IHttpModule.Dispose()  
    {  
        // Nothing to dispose;   
    }  
}

Technorati tags: ASP.NET, HTTP, Compression

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