Java Socket Programming behind proxy

Question

I have written a TCP IP socket program which works fine. But my socket program did not work if my server or client is behind proxy. So how to overcome from this type of issue.

Thanks Bapi

Answer 1

Well there's two issues to consider:

1. Behind a proxy; and
2. Behind a firewall.

Firewall tends to be easier: you simply use port 80 (HTTP) or 443 (HTTPS). Proxy is harder because direct network communication tends to be disabled from normal PCs.

This is why you often find people using HTTP and/or SSL as their transport mediums because they bypass these kinds of security issues. You can do push content (with long-lived connections aka Comet techniques) so there's typically no real technical reason not to.

But it's hard to say one way or the other if that's a good idea or not without knowing more about your application and any pertinent requirements.

Answer 2

Proxies usually work at the application level, not at the transport level. Here is some information about Java and proxies.

Answer 3

Depending on the proxy, there may be little that you can do. If the Proxy is designed to block all traffic that it does not directly handle, then you have to either go through the proxy, somehow working with it, or you have to find a way to sneak through the proxy.

For example, many applications are built on top of HTTP precisely because it is commonly allowed through firewalls and is commonly proxy-friendly. Thus, it's a pretty safe way of communicating when you know that you'll be installing the application in environments where proxies may exist.

In your case, it depends on what port(s) your application uses, on whether these ports are commonly handled by a proxy for any existing protocol, on whether or not you're using a standard (commonly known) protocol or have invented your own, and so on.

Is this proxy a transparent proxy? (That is, do web browsers have to be configured to see it, or not?) The kind of proxy it is determines part of how your application needs to work with it. Is the proxy controlled by your organization?

You say you are using port 5018. Just as an experiment, can you try using port 80? Just because you're using port 80 doesn't mean you have to use HTTP. This is worth a try to see if it helps.