HTTP proxies are proxy servers that work via the HTTP protocol. They permit various protocols to be tunnelled over HTTP via the CONNECT method. This is often useful if the desired protocol (such as FTP) is not permitted to pass through a particular firewall. Instead, it could be tunnelled via an HTTP proxy.
HTTP proxies can only make connections to other servers - they are unable to listen on a port for incoming requests (which SOCKS servers can do). This means that active (or PORT) mode in FTP and FTPS cannot be used with HTTP proxies.
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