Weird “Access Denied” - behaviour in read-only mode

Question

In a sharepoint project I save data to a list.

When the Administrator sets the database to ReadOnly, I want to capture the Exception that occurs when trying to write to that list and prevent the system from writing into the list for an hour. This is the code:

 public bool ReadOnlyDb
        {
            get
            {
                HttpSessionState session = HttpContext.Current.Session;
                if (session != null)
                {
                    return session["READONLY"] != null && ((DateTime) session["READONLY"]) > DateTime.Now.AddHours(-1);
                } else
                {
                    return false;
                }
            }
        }



      if (!ReadOnlyDb)
        {
            SPSecurity.RunWithElevatedPrivileges(delegate()
                {
                    using (SPSite site = new SPSite(SPContext.Current.Web.Site.ID))
                    {
                        try
                        {              
                            SPWeb web = site.OpenWeb();
                            web.AllowUnsafeUpdates = true;
                            SPList logList = web.Lists["Log"];

                            SPListItem addableItem = logList.AddItem();
                            addableItem["Title"] = message;
                            addableItem.Update();
                            web.AllowUnsafeUpdates = false;
                            web.Dispose();
                        }
                        catch (Exception ex)
                        {
                            System.Diagnostics.Debug.WriteLine("Log to List DISABLED für Session. (READONLY?)");
                            System.Diagnostics.Debug.WriteLine(ex);

                            HttpSessionState session = HttpContext.Current.Session;
                            if (session != null)
                            {
                                session["READONLY"] = DateTime.Now;
                            }
                        }
                    }
                });
        }
    }

The code works as expected. The exception is thrown in read-only mode and the session-variable "READONLY" is set.

But when the Exception is thrown (as expected) I get a sharepoint "access denied" - message ("sign in as a different user?"). When I reload that page, the session variable is set correctly, so the last line of my method is run.

Also there is no exception thrown in visual studio. Where am I missing something?

Answer 1

When you're trying to catch AccessDenied to handle it yourselves you should set SPSecurity.CatchAccessDeniedException to false:

bool originalCatchValue = SPSecurity.CatchAccessDeniedException;
SPSecurity.CatchAccessDeniedException = false;
try
{
   // details omitted
}
finally
{
   SPSecurity.CatchAccessDeniedException = originalCatchValue;
}