ASP.NET MVC URL auto-resolution in CSS files

Question

In normal WebForms scenario, any root-relative URLs (e.g. ~/folder/file.txt) inside CSS files such as:

.form { background-image: url(~/Content/I         


        

Answer 1

If you're trying to parse the ~/ out of any file, including text files, javascript, etc, you can write a handler that assigns a filter to it and you can use that to search for those paths... for example...

public class StringParsingFilter : MemoryStream {

    public Stream OriginalStream {
        get { return this.m_OriginalStream; }
        set { this.m_OriginalStream = value; }
    }
    private System.IO.Stream m_OriginalStream;

    public StringParsingFilter() : base() {
        this.m_OriginalStream = null;
    }

    public override void Flush() {
        this.m_OriginalStream.Flush();
    }

    public override void Write(byte[] buffer, int offset, int count) {

        //otherwise, parse for the correct content
        string value = System.Text.Encoding.Default.GetString(buffer);
        string contentType = HttpContext.Current.Response.ContentType;

        //Do any parsing here
        ...

        //write the new bytes to the stream
        byte[] bytes = System.Text.Encoding.Default.GetBytes(value);
        this.m_OriginalStream.Write(bytes, offset, count + (bytes.Length - buffer.Length));

    }

}

And you'll write a custom handler to know when to assign this filter... like the following...

 public class FilterControlModule : IHttpModule {

    public void Init(HttpApplication context) {
        HttpApplication oAppContext = context;
        oAppContext.BeginRequest += new EventHandler(_HandleSettingFilter);                        
    }

    private void _HandleSettingFilter(object sender, EventArgs e) {

        //You might check the file at this part to make sure
        //it is a file type you want to parse
        //if (!CurrentFile.isStyleSheet()) { return; }
        ...

        //assign the new filter
        StringParsingFilter filter = new StringParsingFilter();
        filter.OriginalStream = HttpContext.Current.Response.Filter;
        HttpContext.Current.Response.Filter = (Stream)filter;

    }

}

It may have actually been easier just to say "look up IHttpModules" but this is some code that I've used to parse files for paths other than ASP.net files.

You'll also have to change some things in your IIS settings to allow the files to be parsed by setting the ASP.net ISAPI to be a wildcard for all of the files that get handled. You can see more at this website, if you're using IIS6 that is...

You can also use this to modify any file types so you could assign some filters for images, some for javascript or stylesheets or ... really anything...