SSH tunnel with port forwarding allows per port TCP/UDP traffic to be 
"forwarded" from one end to the tunnel to the other and appear like it was 
initiated from the remote end of tunnel. For example all traffic send to 
port 5000 on the local machine can be forwarded to a remote machine, on port
25000 and will appear to any client on the remote side as if it was locally 
coming from port 25000

SOCKS is a type of proxy server that works at the TCP level. It usually sits
on port 1080 and forward TCP traffic from there. Because it works at the TCP 
level (contrary to classical HTTP proxies), it can be coupled to SSH tunnels
to create very convenient firewall passthrough and geo-locked services unlocking. 
This tunneling is not a all-or-nothing tunnel an allow each TCP request to be 
selectively forwarding or not

You must first either use a public SOCKS server or create your own SOCKS/SSH
pair in which case you must have a local SOCKS server, a local SSH client and 
a remote SSH server. On Linux, openssh does everything, one local instance with 
dynamic port forwarding (-D) and a remote instance to a friend's network does 
the job. On Windows, you can use Bitvise Client & Server. There is plenty of 
internet litterature on SOCKS/SSH that explain the concept much better than 
anything I could write :-)

    HTTP request ------> SOCKS client ------||-----> SOCKS server ------> www.google.com
    >www.google.com	     >some.socks.com    ||       >www.google.com      >5000
    >5000                >1080              ||       >5000                (from some.socks.com)
	
	HTTP request ------> SOCKS client ----> SOCKS relay  (encrypted)   SOCKS server -----> www.google.com
    >www.google.com	     >192.168.0.1       >SSH client  -----||----> >SSH server          5000
    >5000                >1080              >some.ssh.com     ||      >www.google.com
	                                        >23               ||      >5000 (from some.ssh.com)

One thing to notice with SOCKS5 is the lack of proper authentication mechanism
which means that if you have a username/password, they will be sent in clear
to the server. SOCKS4 does not require authentication. That's why I prefer
to have a local SOCKS server that creates a SSH tunnel to a remote end but this 
means you must have a SSH remote end.

To use socks proxy to your HTTP requests, simply passed a hash named "socks" 
to SimpleAsyncHTTP::new or Async::HTTP::new with the following content. See 
also IO::Socket::Socks)
	
	my $http = Slim::Networking::SimpleAsyncHTTP->new(
		sub { # succes CB },
		sub { # error CB }, 
		{	
			socks => {
				ProxyAddr => '192.168.0.1'
				ProxyPort => 1080,
				Username => 'user',
				Password => 'password',
			}	
		}  
	);
		
	$http->get("http://www.google.com")

	- or -
	
	my $http = Slim::Networking::Async::HTTP->new( { 
				socks => {
					ProxyAddr => '192.168.0.1'
						ProxyPort => 1080,
						Username => 'user',
						Password => 'password',
						}
				}	
	);
	$http ->send_request( {
				'request'     => HTTP::Request->new( GET => "http://www.google.com" ),
				'onHeaders'   => sub { },
				'onError'     => sub { },
				'passthrough' => [ $p1, $p2 ],
				}
	);	

Note that Username and Password are optional. SOCKS version is set to 5 if they 
are set and to 4 otherwise. ProxyPort can be omitted and will be set to 1080.

If 'socks' hash is set but ProxyAddr is missing, a regular SimpleAsync or Async 
call will be made