How do I get root url using ASP not ASP.net

Classic ASP had a Request.ServerVariables collection that contained all server and environment details. Here's what the classic ASP version of the example .NET code looks like:

function getSiteRootUrl()
    dim siteRootUrl, protocol, hostname, port

    if Request.ServerVariables("HTTPS") = "off" then
        protocol = "http"
    else
        protocol = "https"
    end if
    siteRootUrl = protocol & "://"

    hostname = Request.ServerVariables("HTTP_HOST")
    siteRootUrl = siteRootUrl & hostname        

    port = Request.ServerVariables("SERVER_PORT")
    if port <> 80 and port <> 443 then
        siteRootUrl = siteRootUrl & ":" & port
    end if

    getSiteRootUrl = siteRootUrl
end function