System.Uri is your friend here. This has many helpful utilities on it, but the one you want is GetLeftPart:

 string url = "http://www.website.com/default.aspx?utm_source=twitter&utm_medium=social-media";
 Uri uri = new Uri(url);
 Console.WriteLine(uri.GetLeftPart(UriPartial.Path));

This gives the output: http://www.website.com/default.aspx

[The Uri class does require the protocol, http://, to be specified]

GetLeftPart basicallys says "get the left part of the uri up to the part I specify". This can be Scheme (just the http:// bit), Authority (the www.website.com part), Path (the /default.aspx) or Query (the querystring).

Assuming you are on an aspx web page, you can then use Response.Redirect(newUrl) to redirect the caller.

Hope that helps

I'm guessing that you want to do this because you want your users to see pretty looking URLs. The only way to get the client to "change" the URL in its address bar is to send it to a new location - i.e. you need to redirect them.

Are the query string parameters going to affect the output of your page? If so, you'll have to look at how to maintain state between requests (session variables, cookies, etc.) because your query string parameters will be lost as soon as you redirect to a page without them.

There are a few ways you can do this globally (in order of preference):

• If you have direct control over your server environment then a configurable server module like ISAPI_ReWrite or IIS 7.0 URL Rewrite Module is a great approach.
• A custom IHttpModule is a nice, reusable roll-your-own approach.
• You can also do this in the global.asax as you suggest

You should only use the 301 response code if the resource has indeed moved permanently. Again, this depends on whether your application needs to use the query string parameters. If you use a permanent redirect a browser (that respects the 301 response code) will skip loading a URL like *.../default.aspx?utm_source=twitter&utm_medium=social-media* and load .../default.aspx - you'll never even know about the query string parameters.

Finally, you can use POST method requests. This gives you clean URLs and lets you pass parameters in, but will only work with <form> elements or requests you create using JavaScript.

This may look a little better.

    string rawUrl = String.Concat(this.GetApplicationUrl(), Request.RawUrl);

    if (rawUrl.Contains("/post/"))
    {
        bool hasQueryStrings = Request.QueryString.Keys.Count > 1;

        if (hasQueryStrings)
        {
            Uri uri = new Uri(rawUrl);
            rawUrl = uri.GetLeftPart(UriPartial.Path);

            HtmlLink canonical = new HtmlLink();
            canonical.Href = rawUrl;
            canonical.Attributes["rel"] = "canonical";
            Page.Header.Controls.Add(canonical);
        }
    }

Followed by a function to properly fetch the application URL.

Works perfectly.

Take a look at the UriBuilder class. You can create one with a url string, and the object will then parse this url and let you access just the elements you desire.