How to Determine if FTP Directory Exists

Question

I wrote the following code to detect if a directory exists. The `DirectoryExists` method accepts either a fully qualified or relative path. ``` public bool DirectoryExists(string directory) { try { FtpWebRequest request = GetRequest(directory); request.Method = WebRequestMethods.Ftp.ListDirectory; using (FtpWebResponse response = request.GetResponse() as FtpWebResponse) using (StreamReader sr = new StreamReader(response.GetResponseStream(), System.Text.Encoding.ASCII)) { sr.ReadToEnd(); } return true; } catch { } return false; } protected FtpWebRequest GetRequest(string filename = "") { FtpWebRequest request = WebRequest.Create(_host.GetUrl(filename)) as FtpWebRequest; request.Credentials = new NetworkCredential(Username, Password); request.Proxy = null; request.KeepAlive = false; return request; } ``` Note: `_host.GetUrl(filename)` returns the fully qualified path of the specified directory or filename. In my case, this is `ftp://www.mydomain.com/Articles/controls/precisely-defining-…

Accepted Answer

FTP servers reply with a 550 message when you ask for a non existing directory/file. This 550 is translated to an exception in .NET.

Regarding the code you presented I don't see the reason to use a StreamReader in production. A simple modification is the following:

```
public bool DirectoryExists(string directory)
{
  try
  {
    FtpWebRequest request = GetRequest(directory);
    request.Method = WebRequestMethods.Ftp.ListDirectory;
    return request.GetResponse() != null;
  }
  catch
  {
    return false;
  }
}
```

I kept the exception handling as is (missing) but I suggest you to work on it as there are many and different cases to catch that are not related to ftp responses.

request.GetResponse() will generate an exception if the directory does not exist.

I tried it with the following paths for true returns:

- ftp://ftp.mozilla.org/

- ftp://ftp.mozilla.org/pub/

- ftp://ftp.mozilla.org/pub/data/

- ftp://ftp.mozilla.org/pub/data/bloat-reports/

The last one is an existing but empty directory

ftp://ftp.mozilla.org/pub/data/bloat-reports2/ returns false

There is a big but regarding trailing / in paths.

mozilla.org is a zero byte length file under pub directory

ftp://ftp.mozilla.org/pub/mozilla.org returns true

ftp://ftp.mozilla.org/pub/mozilla.org/ returned false and then true ?????

This behavior looks like with what you described. You can easily reproduce it on a browser. I suggest you to do the same with your own paths and check the contents of the directories. In case you do have empty files, remove them or replace their contents with a space, and finally check your code to ensure that you will not create new files or recreate them with zero byte length.

I hope that this helps.

UPDATE

No news, bad news! I assume that nothing of the above helped you. Maybe by going one level up in your path will solve the problem. The idea is to get a list of the parent directory and check it for the child name. If the parent path is valid it should always return non empty string. The code is the following:

```
static bool DirectoryExists(string directory)
{
    try
    {
        directory = GetRequest(directory);
        string
            parent = directory.Substring(0, directory.TrimEnd('/').LastIndexOf('/') + 1),
            child = directory.Substring(directory.TrimEnd('/').LastIndexOf('/') + 1).TrimEnd('/');
        FtpWebRequest request = GetRequest(parent);
        request.Method = WebRequestMethods.Ftp.ListDirectory;
        using (FtpWebResponse response = request.GetResponse() as FtpWebResponse)
        {
            if (response == null)
                return false;
            string data = new StreamReader(response.GetResponseStream(), true).ReadToEnd();
            return data.IndexOf(child, StringComparison.InvariantCultureIgnoreCase) >= 0;
        }
    }
    catch
    {
        return false;
    }
}
```

As you can see there is no need to worry about trailing slashes.

Warning: The code will not cover the case of a subdirectory and a filename with same names under the same path.

How to Determine if FTP Directory Exists

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