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public class ETagAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
filterContext.HttpContext.Response.Filter = new ETagFilter(filterContext.HttpContext.Response, filterContext.RequestContext.HttpContext.Request);
}
}
public class ETagFilter : MemoryStream
{
private HttpResponseBase _response = null;
private HttpRequestBase _request;
private Stream _filter = null;
public ETagFilter(HttpResponseBase response, HttpRequestBase request)
{
_response = response;
_request = request;
_filter = response.Filter;
}
private string GetToken(Stream stream)
{
var checksum = new byte[0];
checksum = MD5.Create().ComputeHash(stream);
return Convert.ToBase64String(checksum, 0, checksum.Length);
}
public override void Write(byte[] buffer, int offset, int count)
{
var data = new byte[count];
Buffer.BlockCopy(buffer, offset, data, 0, count);
var token = GetToken(new MemoryStream(data));
var clientToken = _request.Headers["If-None-Match"];
if (token != clientToken)
{
_response.AddHeader("ETag", token);
_filter.Write(data, 0, count);
}
else
{
_response.SuppressContent = true;
_response.StatusCode = 304;
_response.StatusDescription = "Not Modified";
_response.AddHeader("Content-Length", "0");
}
}
} 
