static string GetContentDispositionAttribute (string l, string name)
{
int idx = l.IndexOf (name + "=\"");
if (idx < 0)
return null;
int begin = idx + name.Length + "=\"".Length;
int end = l.IndexOf ('"', begin);
if (end < 0)
return null;
if (begin == end)
return "";
return l.Substring (begin, end - begin);
}