c# - FTP File Upload with HTTP Proxy

Question

Is there a way to upload a file to a FTP server when behind an HTTP proxy ?

It seems that uploading a file is not supported behind an HTTP Proxy using .Net Webclient. (http://msdn.microsoft.com/en-us/library/system.net.ftpwebrequest.proxy.aspx).

If there is no workaround ? If not, do you know a good and free FTP library I can use ?

Edit: Unfortunately, I don't have any FTP proxy to connect to.

Answer 1

In active FTP mode, the server initiates a data connection to the client. If the client is behind an HTTP proxy, this obviously won't work. In passive FTP mode it is the client who initiates both the initial and the data connections. Since HTTP proxies can tunnel arbitrary outgoing TCP connections (using the CONNECT method), it should be possible to access an FTP server in passive mode via an HTTP proxy.

The FtpWebRequest seems to support passive mode. However, I don't understand why file download and directory listings are supported, whereas file upload, which also uses the same data connection, is not.

Have you confirmed that FtpWebRequest configured for passive mode does not work via an HTTP proxy through which directory listings/file download work just fine?