ASP.NET MVC3 App Using plupload to Upload Directly to Amazon S3

UPDATE 8/15/2011:
I can't recommend using this for large files (video files). It's very unreliable. Web size image files and normal email attachment sized files would probably do fine. What I ended up doing to get around it was creating a web app on AppHarbor (which runs on EC2) that I upload the files to and it saves them to S3. Since the AppHarbor app is on a different domain you are still limited to Flash and Silverlight support but you do gain file chunking which brings back some reliability. Alternatively to AppHarbor you could setup your own server on Amazon as well.

I created a working example of using plupload to upload files directly to Amazon S3 and threw it on github, since the .NET examples I found on the web we're incomplete or broken.
https://github.com/crdeutsch/MVC3PluploadToAmazonS3

The files that are being uploaded do not even touch your web server. They are posted directly to Amazon. At the moment plupload only supports the Flash and Silverlight plugins as far as I can tell.

The AmazonS3Helper.cs library originated from Cary Abramoff off of this plupload forum thread.

I've made some changed based on iwasrobbed's excellent Ruby on Rails example.

Usage

Upload the crossdomain.xml found in the root of the site to your Amazon S3 Bucket.

<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
<allow-access-from domain="*" secure="false" />
</cross-domain-policy>

Modify the settings in HomeController.cs to use your Amazan credentials and set your S3 bucket.

public ActionResult Index()
{
 string acl = "private";
 string bucket = "YOUR S3 BUCKET NAME";
 string accessKeyId = "YOUR AMAZON ACCESS KEY ID";
 string secret = "YOUR AMAZON SECRET ACCESS KEY";
 string policy = AmazonS3Helper.ConstructPolicy(bucket, DateTime.UtcNow.Add(new TimeSpan(0, 10, 0, 0)), acl, accessKeyId);
 string signature = AmazonS3Helper.CreateSignature(policy, secret);

 var model = new PluploadAmazonS3Model()
 {
  AWSAccessKeyId = accessKeyId,
  Policy = policy,
  Signature = signature,
  Bucket = bucket,
  Acl = acl
 };

 return View(model);
}

On the View side you could just use Razor to dump the Model variables directly into your javascript, but I decided to use hidden form variables instead in case you want to move the javascript to its own file where embedding Razor syntax won't work.

Hope this saves somebody else some time!