Programmatically determine why SecureFTPConnection.Connect() has failed with ControlChannelIOException

Question

I have a .NET application that uses edtFTPnet/PRO to round-robin check a number of different FTP servers, search for files, and if any are found meeting certain criteria, download the files to a local folder.

The app is controlled by information that is entered into a database table by a human.

The human sometimes enters information incorrectly, such as perhaps misspelling a hostname.  When this happens, the SecureFTPConnection's Connect() method fails and raises a ControlChannelIOException with the message "An I/O exception occurred.".

Is there any way to programmatically determine more precisely what the issue is, such as DNS name resolution error?

Thanks!

Answer 1

There are a few different scenarios:

Exception	Cause
FormatException	The user supplies something that looks like an IP address, but which is invalid (e.g. 299.0.0.0).
ArgumentOutOfRangeException	Hostname is longer than 255 characters.
SocketException	Error while connecting to DNS server or to target server
ArgumentException	Hostname could not be resolved
ControlChannelIOException	Error while communicating with server (after connection)
SSHAuthenticationException	SFTP/SCP authentication failed
FTPAuthenticationException	FTP/FTPS authentication failed