How to catch a FtpWebResponse exception in C#

Question

I am building an FTP utility class in C#. In the case that a WebException is thrown on a call to FtpWebRequest.GetResponse(), in my case the exception is thrown for the requested file not existing on the remote server the FtpWebResponse variable is out of scope.

But even if I declare the variable outside the try..catch block I get a compile error saying "Use of unassigned local variable 'response'", but as far as I can tell there is no way to assign it until you assign the response via the FtpWebRequest.GetResponse() method.

Can someone please advise, or am I missing something obvious?

Thanks!

Here is my current method:

private void Download(string ftpServer, string ftpPath, string ftpFileName, string localPath, 
                           string localFileName, string ftpUserID, string ftpPassword)
    {
        FtpWebRequest reqFTP;
        FtpWebResponse response;
        try
        {
            reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://"
               + ftpServer + "/" + ftpPath + "/" + ftpFileName));
            reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
            reqFTP.UseBinary = true;
            reqFTP.Credentials = new NetworkCredential(ftpUserID,
                                                       ftpPassword);

            /* HERE IS WHERE THE EXCEPTION IS THROWN FOR FILE NOT AVAILABLE*/
            response = (FtpWebResponse)reqFTP.GetResponse();
            Stream ftpStream = response.GetResponseStream();


            FileStream outputStream = new FileStream(localPath + "\\" +
               localFileName, FileMode.Create);

            long cl = response.ContentLength;
            int bufferSize = 2048;
            int readCount;
            byte[] buffer = new byte[bufferSize];

            readCount = ftpStream.Read(buffer, 0, bufferSize);
            while (readCount > 0)
            {
                outputStream.Write(buffer, 0, readCount);
                readCount = ftpStream.Read(buffer, 0, bufferSize);
            }

            ftpStream.Close();
            outputStream.Close();
            response.Close();
        }
        catch (WebException webex)
        {
            /*HERE THE response VARIABLE IS UNASSIGNED*/
            if (response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable) { 
                //do something
            }
        }

score 6 · Accepted Answer · answered Mar 11 '10 at 10:29

6

As generic way to solve this, just assign null to the response first and then check in the catch block if it is null.

    FtpWebResponse response = null;
    try
    {
...
    }
    catch (WebException webex)
    {
        if ((response != null) && (response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable)) { 
            //do something
        }
    }

However, in this specific case, you have all the properties you need on the WebException instance (including the server response)!

answered Mar 11 '10 at 10:29

Lucero

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jeez, i didn't even try that. Thanks for both tips! I looked at the WebExceptionStatus and wasn't sure if there was a type defined specifically for 'file not found'. I will look into that more but the null should do it. – jaywon Mar 11 '10 at 10:38
This solves the unassigned local variable problem, but doesn't help catching the exception because 'response' will still be null when the error happens. Check this question for the correct solution: http://stackoverflow.com/questions/347897/how-to-check-if-file-exists-on-ftp-before-ftpwebrequest – Marc Apr 21 '10 at 06:08
Marc, note that I was addressing both the problem in general as well as the specific case with the `WebException` - see the bottom paragraph (which is the same solution in short as the one provided in your link). – Lucero Apr 21 '10 at 08:57
Ups you're right, sorry I must have missed that part. However when I see code then I prefer reading code and obviously the given code doesn't catch the exception. Maybe you should add a comment to the code itself. – Marc Apr 21 '10 at 14:20

score 2 · Answer 2 · edited May 23 '17 at 12:13

2

The correct solution to the problem can be found in this question here:
How to check if file exists on FTP before FtpWebRequest

In short:
Your 'response' variable will always be null because of the error. You need to test the FtpWebResponse from 'webex.Response' (cast it) to get the StatusCode.

edited May 23 '17 at 12:13

Community

1
1

answered Apr 21 '10 at 06:11

Marc

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You're right, however the code in your answer is misleading as it doesn't help catching the file unavailable exception. – Marc Apr 21 '10 at 14:21

score 1 · Answer 3 · answered Mar 11 '10 at 10:29

1

Well you could always assign a variable:

FtpWebRequest reqFTP = null;
FtpWebResponse response = null;

answered Mar 11 '10 at 10:29

Darin Dimitrov

1,023,142
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How to catch a FtpWebResponse exception in C#

3 Answers3