Autodetect Active/Passive FTP Clients

Question

Is it possible to autodetect active or passive mode on the connected ftp client. If so, how?

Answer 1

Finding whether the server allows passive or active mode is a bit tricky.

To detect whether passive mode is possible, we have to improvise a bit. One possible way to do this with Rebex FTP:

1. Make sure passive mode is enabled
2. Lower the timeout from the default value of 60 seconds to something like 5 (or even leave it at 60 if detection speed is not an issue for you)
3. Initiate a TransferProgress event handler
4. Try calling GetList or GetNameList (preferably on a folder with few files) 4.
   • If the event handler is called at least once with state of FtpTransferState.Downloading, consider passive mode possible
   • If you get an FtpException with the Status set to Timeout, consider passive mode not impossible
   • If you get an FtpException with the Status set to ConnectFailure, consider passive mode not impossible
   • If you get other result, another error occured

Anyway, this seems rather complicated, so I added it into our list of possible future enhancements.

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