Working with FTP over HTTP, users can retrieve files from an FTP server without setting up and configuring an FTP client.
FTP over HTTP is a type of HTTP traffic going on between a web browser and a proxy, such as the proxy provided by Web Gateway. In most respects, sending an FTP-over-HTTP request is like sending any other HTTP request. The difference is that the requested resource resides on an FTP server rather than an HTTP server. FTP over HTTP traffic is configured in explicit proxy mode.
An FTP-over-HTTP request contains a URL prefixed with ftp:// instead of http://. The HTTP host header value includes port 21 instead of no port number (in which case port 80 is assumed).
The following is an example of an FTP-over-HTTP request that a client sends to Web Gateway at the beginning of the communication.
GET ftp://10.10.80.200/ HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE 8.0) Host: 10.10.80.200:21 Proxy-Connection: Keep-Alive
When Web Gateway receives this request, it recognizes that the requested resource resides on an FTP server, due to the presence of ftp://" and port 21.
Web Gateway then uses native FTP to retrieve the resource from the FTP server. Any FTP response traffic is "translated" on Web Gateway into HTTP terms before passing it on to the client. Sometimes this requires Web Gateway to create an HTML page, so the client can display the results, for example, a listing of FTP directories, in the web browser.
Use of the HTTP proxy port
FTP over HTTP is handled on Web Gateway much like any other HTTP communication with a client. Requests should therefore be sent from the client to the HTTP proxy port on Web Gateway, which is 9090 by default.
There is no need to configure the FTP proxy port, which is 2121 by default, as use of this port is only required if a client sends requests under the native FTP protocol.
Advantages and disadvantages
FTP over HTTP has advantages and disadvantages. Using this method to retrieve files from an FTP server allows users to work with a web browser, which saves them the effort of setting up and configuring an FTP client, such as the open-source Filezilla client.
The major disadvantage of FTP over HTTP is that it does not allow users to upload files. File upload requires the use of native FTP, an FTP client program on the client system, and use of the FTP proxy port on Web Gateway if users choose to send traffic this way.
Another disadvantage of FTP over HTTP is that most web browsers have issues with it.