Where do I catch and handle maxAllowedContentLength exceeded in IIS7?

Question

I have an aspx page where I’m allowing a user to upload a file and I want to cap the max file upload size to be 10MB. IIS7, .NET 3.5. I have the following configured in my

Answer 1

The simplest method is to handle it in the OnError method of page itself.

I think this works only in .NET 4.0, since the WebEventCode property is documented as NEW in .NET 4.0.

protected override void OnError(EventArgs e)
{
    Exception err = Server.GetLastError();
    if (err is HttpException)
    {
        if ((err as HttpException).WebEventCode == 3004)
        {
            Context.Items["error"] = "File exceeded maximum allowed length.";
            Server.Transfer( Context.Request.Url.LocalPath );
            return;
        }
    }
    base.OnError(e);
}

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);
    if (!IsPostBack)
    {
        string error = Context.Items["error"] as string;
        if (!string.IsNullOrEmpty( error ))
            showErrorMessage( error );
    }
}

What I did was:

• get the last error with Server.GetLastError
• check that it's a "Maximum request length exceeded." error (WebEventCode == 3004).
• added a value to Context.Items collections to flag the request as an error
• transfer the request back to the page itself with Server.Transfer(Context.Request.Url.LocalPath)
• the page's OnLoad method checks for the error flag and displays a message if present

This ensures the error is handled entirely on the requested page, and the page is capable of reporting errors.

Also note that while the browser will eventually receive a proper response, the browser may take its time uploading the entire request before it handles the server's response and displays it. This behavior is probably defined as part of the server/browser interaction in the HTTP protocol, so probably not much can be done about that.