Automatic Reconnection

Settings

• Config.SslSessionLength - Number of FTP responses after which we automatically reconnect to the FTP server. Only honored for SSL connections, and ignored for plaintext FTP connections. Required to fix an IOException edge case on FTPS connections. Set it to 0 to disable automatic reconnection. Default: 750.

How does automatic reconnection work?

At various intervals, we need to reconnect to the FTP server automatically.

• The FTP server has disconnected us in-between a file transfer, so we need to reconnect and resume the file transfer.
• We predict that the FTPS connection will get corrupted due to OS bugs, so to prevent this, we preemptively disconnect and reconnect on our own.

FTP Server disconnects midway

This happens during upload and download, and is handled within UploadFileInternal (sync/async) and DownloadFileInternal (sync/async).

These functions detect if the FTP connection was lost and automatically try to reconnect and resume the transfer.

It is always enabled and does not require configuration as such.

FTP Connection gets corrupted

This is only needed and enabled for FTPS/SSL connections and not for plaintext FTP.

We noticed that the underlying SSL stream gets "corrupted" (goes into a unrecoverable state) after around 900 FTP responses are received from the server. So we developed this system to bypass this limitation: we count the FTP responses received, and then pre-emptively disconnect and reconnect to the FTP server.

It is always enabled and does not require configuration as such. But you can modify its behavior using the setting Config.SslSessionLength (docs above).