The auto-magical HTTP module that does the job is presented below. You need to register it in your Web.config file.
/// <summary>
/// Provides HTTP compression support for CDN services when
/// ASP.NET website is used as origin.
/// </summary>
public sealed class CdnHttpCompressionModule : IHttpModule
{
public void Init(HttpApplication context)
{
context.PreRequestHandlerExecute += Context_PreRequestHandlerExecute;
}
public void Dispose()
{
}
void Context_PreRequestHandlerExecute(object sender, EventArgs e)
{
var application = (HttpApplication)sender;
var request = application.Request;
var response = application.Response;
// ---------------------------------------------------------------------
bool allowed = false;
string via = request.Headers["Via"];
if (!string.IsNullOrEmpty(via))
{
if (via.Contains(".cloudfront.net"))
{
// Amazon CloudFront
allowed = true;
}
// HINT: You can extend with other criterias for other CDN providers.
}
if (!allowed)
return;
// ---------------------------------------------------------------------
try
{
if (request["HTTP_X_MICROSOFTAJAX"] != null)
return;
}
catch (HttpRequestValidationException)
{
}
// ---------------------------------------------------------------------
string acceptEncoding = request.Headers["Accept-Encoding"];
if (string.IsNullOrEmpty(acceptEncoding))
return;
string fileExtension = request.CurrentExecutionFilePathExtension;
if (fileExtension == null)
fileExtension = string.Empty;
fileExtension = fileExtension.ToLowerInvariant();
switch (fileExtension)
{
case "":
case ".js":
case ".htm":
case ".html":
case ".css":
case ".txt":
case ".ico":
break;
default:
return;
}
acceptEncoding = acceptEncoding.ToLowerInvariant();
string newContentEncoding = null;
if (acceptEncoding.Contains("gzip"))
{
// gzip
response.Filter = new GZipStream(response.Filter, CompressionMode.Compress);
newContentEncoding = "gzip";
}
else if (acceptEncoding.Contains("deflate"))
{
// deflate
response.Filter = new DeflateStream(response.Filter, CompressionMode.Compress);
newContentEncoding = "deflate";
}
if (newContentEncoding != null)
{
response.AppendHeader("Content-Encoding", newContentEncoding);
response.Cache.VaryByHeaders["Accept-Encoding"] = true;
}
}
}
The module is designed to work with IIS 7.0 or higher in integrated pipeline mode (Azure Websites have exactly this out of the box). That is the most widespread configuration, so generally it just works once you attach it. Please note that the module should be the first one in a list of modules.
Web.config registration sample:
<configuration>
<system.webServer>
<modules runAllManagedModulesForAllRequests="true">
<add name="CdnHttpCompressionModule" preCondition="managedHandler" type="YourWebsite.Modules.CdnHttpCompressionModule, YourWebsite" />
<!-- You may have other modules here -->
</modules>
<system.webServer>
</configuration>
