asked on

C# SFTP program hangs under task scheduler

I have a C# program that grabs a file each day off an SFTP server. It was running fine for months. It is run as a scheduled task under Task Scheduler. Over the past couple of weeks the task is left hanging when normally it runs in under a minute. I am beginning to wonder if perhaps when this code tries to connect to the SFTP it fails and gets stuck. Does this seem plausible? What else would cause the scheduled task to just hang? If I terminate the task and run it manually the transfer goes right through.

try
{
// Connect
sftpClient = new Renci.SshNet.SftpClient("bolagna.sandwich.io", "my_sftp", "password");
sftpClient.Connect();

// List the contents of a given folder and loop through them
var dirContents = sftpClient.ListDirectory("./upload").ToArray();
foreach (var entry in dirContents)
{

// Check to see if the base filename of the remote file contains "hm_orders_"
if (entry.Name.Contains("hm_orders_"))
{

Do Work

}

gr8gonzo

It could be there's some kind of prompt and the task doesn't know how to handle it. It's hard to tell, but I would suggest doing two things:

First, wrap everything all in a try/catch block so you can log any exceptions that happen:

BEFORE:

<a bunch of code>

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AFTER:

try
{
  <a bunch of code>
}
catch(Exception ex)
{
  System.IO.File.AppendAllText(@"C:\Temp\yourappname.log", String.Format("{0} :: {1}\n", DateTime.Now.ToString("o"), ex.Message));
}

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Second, in case it's not an exception (which I would expect would crash the job rather than hang it), try writing the code's progress to a log.

BEFORE:

<major code line 1>
<minor code line 2>
<minor code line 3>
<major code line 4>
<minor code line 5>

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AFTER:

System.IO.File.AppendAllText(@"C:\Temp\yourappname.log", String.Format("{0} :: {1}\n", DateTime.Now.ToString("o"), "Before major code line 1"));
<major code line 1>
<minor code line 2>
<minor code line 3>
System.IO.File.AppendAllText(@"C:\Temp\yourappname.log", String.Format("{0} :: {1}\n", DateTime.Now.ToString("o"), "Before major code line 4"));
<major code line 4>
<minor code line 5>

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Then run the app via the task scheduler and check out that log file and see where the code manages to reach before it hangs. If it doesn't generate a log at all, it could be some issue with the startup/execution of the app, but again, I would expect that to fail rather than hang.

ste5an

Well, you need to look at the documentation of your used library, how to catch errors.

I have always only used WinSCP .NET without any troubles.

And for your actual code: There are different levels, where I would use separate methods, thus separate error handling. E.g., something like this:

using Renci.SshNet;

private bool Connect(string hostNameOrIP, string userName, string password, out SftpClient sftpClient)
{
    try
    {
        sftpClient = new SftpClient(hostNameOrIP, userName, password);
        sftpClient.Connect();
        return true;
    }
    catch (Exception exception)
    {
        // TODO: Log error.
        return false;
    }
}


private bool ListDirectory(SftpClient sftpClient, string directory, out useCorrectDataType directoryContent)
{
    try
    {
        directoryContent = sftpClient.ListDirectory(directory).ToArray();
        return true;
    }
    catch (Exception exception)
    {
        // TODO: Log error.
        return false;
    }
}

private bool ProcessFile(useCorrectDataType directoryEntry)
{
    try
    {
        // Process entry.
        return true;
    }
    catch (Exception exception)
    {
        // TODO: Log error.
        return false;
    }
}


SftpClient sftpClient = null;
useCorrectDataType directoryContent = null;
if Connect("bolagna.sandwich.io", "my_sftp", "password", out sftpClient)
{
    if ListDirectory(sftClient, "./upload", out directoryContent)
    {
        foreach (useCorrectDataType directoryEntry in directoryContent)
        {
            if (directoryEntry.Name.Contains("hm_orders_"))
            {
                ProcessFile(directoryEntry)
            }
        }
    }
}

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Depending on your used SSH library, the directory parameter for the list method does already take a pattern. Then you don't need the if.