Question

I am having trouble with my static content being cached on the client (by static I mean js,css,jpeg,gif, etc). (and by client I mean its my development machine most of the time).

As a result, page is either throwing a script error, or not displaying correctly. I am not a Rails developer but I read a few books about it back in time. One thing I remember well is that it appends some magic version number to the end of the included file, so it becomes

<script src="~/Scripts/Invoice.js?201112091712" type="text/javascript"></script>

and if you modify that content file it generates a new version number, so it generates a different include statement, as a result, client thinks it is a new content, and it loads it without checking its cache.

Does asp.net-mvc 3 & IIS 7 support this, or do you know any tools that mimic this behaviour?

Thanks, Hazım

Answer 1

I have this done already in one of my projects, feel free to use my helpers if you like them :

public static class VersionedContentExtensions
{
    public static MvcHtmlString VersionedScript(this HtmlHelper html, string file)
    {
        return VersionedContent(html, "<script src=\"{0}\" type=\"text/javascript\"></script>", file);                     
    }

    public static MvcHtmlString VersionedStyle(this HtmlHelper html, string file)
    {
        return VersionedContent(html, "<link href=\"{0}\" rel=\"stylesheet\" type=\"text/css\">", file);
    }

    private static MvcHtmlString VersionedContent(this HtmlHelper html, string template, string file)
    {
        string hash = HttpContext.Current.Application["VersionedContentHash_" + file] as string;
        if (hash == null)
        {
            string filename = HttpContext.Current.Server.MapPath(file);
            hash = GetMD5HashFromFile(filename);
            HttpContext.Current.Application["VersionedContentHash_" + file] = hash;
        }

        return MvcHtmlString.Create(string.Format(template, file + "?v=" + hash));
    }

    private static string GetMD5HashFromFile(string fileName)
    {
        FileStream file = new FileStream(fileName, FileMode.Open);
        MD5 md5 = new MD5CryptoServiceProvider();
        byte[] retVal = md5.ComputeHash(file);
        file.Close();

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < retVal.Length; i++)
        {
            sb.Append(retVal[i].ToString("x2"));
        }
        return sb.ToString();
    }
}

use them like this :

@Html.VersionedScript("/Scripts/sccat.core.js")