Generating meaningful names from a url

@YaronNaveh

A common programming task is to extract some meaningful name from a url.
One example is saving the contents of a url to a file name on disk - we need to have the name for the file.
Bellow there is a c# method that I have written that extracts this name + the results it produces on a few urls.

http://www.myServer.com/Services/Sanity.asmx?WSDL - Sanity
http://www.myServer.com/Services/Sanity.asmx?wsdl=1&xsd=2 - Sanity
http://www.myServer.com/Services/Sanity12345678901234567890123456789012345678901234567890123456789012.asmx - Sanity1234567890123456789012345678901234567
http://www.myServer.com/Services/Sanity.asmx - Sanity
http://www.myServer.com/Services/Sanity/ - Sanity
http://www.myServer.com/Services/Sanity - Sanity
http://www.myServer.com/Services/Sanity?wsdl - Sanity_wsdl
http://www.myServer.com/Services/Sanity/?wsdl - Sanity

public static string GetSuggestedNameFromUrl(string url, string defaultValue)
{
  const int MaxChars = 50;

  string res = Path.GetFileNameWithoutExtension(url);

  //check if there is no file name, i.e. just folder name + query string
  if (String.IsNullOrEmpty(res) || IsNameOnlyQueryString(res))
  {
    res = Path.GetDirectoryName(url);
    res = Path.GetFileName(res);

    if (String.IsNullOrEmpty(res))
       res = defaultValue;
  }

  res = ReplaceInvalidCharacters(res);

  if (res.Length > MaxChars)
     res = res.Substring(0, MaxChars);

  return res;
}


private static string ReplaceInvalidCharacters(string res)
{
  return Regex.Replace(res, @"[^\w]", "_", RegexOptions.Singleline);
}


private static bool IsNameOnlyQueryString(string res)
{
  return !String.IsNullOrEmpty(res) && res[0]=='?';
}

@YaronNaveh

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