socks in java (opening via socks)

Question

how do i add SOCKS support to my application? and where can i get the libs?

Answer 1

From http://java.sun.com/javase/6/docs/technotes/guides/net/proxies.html

The SOCKS protocol, as defined in RFC 1928, provides a framework for client server applications to safely traverse a firewall both at the TCP and UDP level. In that sense it is a lot more generic than higher level proxies (like HTTP or FTP specific proxies). J2SE 5.0 provides SOCKS support for client TCP sockets.

There are 2 system properties related to SOCKS:

socksProxyHost for the host name of the SOCKS proxy server
socksProxyPort for the port number, the default value being 1080

Note that there is no dot ('.') after the prefix this time. This is for historical reasons and to ensure backward compatibility. Once a SOCKS proxy is specified in this manner, all TCP connections will be attempted through the proxy.

Example:

$ java -DsocksProxyHost=socks.mydomain.com GetURL

Here, during the execution of the code, every outgoing TCP socket will go through the SOCKS proxy server at socks.mydomain.com:1080.

Now, what happens when both a SOCKS proxy and a HTTP proxy are defined? Well the rule is that settings for higher level protocols, like HTTP or FTP, take precedence over SOCKS settings. So, in that particular case, when establishing a HTTP connection, the SOCKS proxy settings will be ignored and the HTTP proxy will be contacted. Let's look at an example:

$ java -Dhttp.proxyHost=webcache.mydomain.com -Dhttp.proxyPort=8080 -DsocksProxyHost=socks.mydomain.com GetURL

Here, an http URL will go through webcache.mydomain.com:8080 because the http settings take precedence. But what about an ftp URL? Since no specific proxy settings were assigned for FTP, and since FTP is on top of TCP, then FTP connections will be attempted through the SOCKS proxy server at socks.mydomsain.com:1080. If an FTP proxy had been specified, then that proxy would have been used instead.