ASP.NET has no knowledge of this. You would need to query IIS for the default document list.
The reason for this is that IIS will look in your web folder for the first matching file in the IIS default document list then hand off to the matching ISAPI extension for that file type (by extension) in the script mappings.
To obtain the default document list you can do the following (using the Default Website as an example where the IIS Number = 1):
using System;
using System.DirectoryServices;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
using (DirectoryEntry w3svc =
new DirectoryEntry("IIS://Localhost/W3SVC/1/root"))
{
string[] defaultDocs =
w3svc.Properties["DefaultDoc"].Value.ToString().Split(',');
}
}
}
}
It would then be a case of iterating the defaultDocs array to see which file exists in the folder, the first match is the default document. For example:
// Call me using: string doc = GetDefaultDocument("/");
public string GetDefaultDocument(string serverPath)
{
using (DirectoryEntry w3svc =
new DirectoryEntry("IIS://Localhost/W3SVC/1/root"))
{
string[] defaultDocs =
w3svc.Properties["DefaultDoc"].Value.ToString().Split(',');
string path = Server.MapPath(serverPath);
foreach (string docName in defaultDocs)
{
if(File.Exists(Path.Combine(path, docName)))
{
Console.WriteLine("Default Doc is: " + docName);
return docName;
}
}
// No matching default document found
return null;
}
}
Sadly this won't work if you're in a partial trust ASP.NET environment (for example shared hosting).