Transparent local proxy to many proxies

Question

In Firefox is add-on FoxyProxy, which makes possible use many proxy with filtering URLs. I need it for any browser, but in many of them it is only possible to set one proxy server. I need a transparent local proxy, which may filters URLs and forwards traffic to other proxies. I've heard about Squid, but I haven't found information about it. It is possible to set it in Linux (and how)?

Answer 1

Most browsers that support Javascript also support Netscape-style proxy autoconfiguration (PAC) files (I'm not aware of a JavaScript-capable browser released this century that doesn't). PAC files contain JavaScript code that is executed to determine what proxy (if any) to use for each request.

function FindProxyForURL(url, host) {
    if (shExpMatch(host, "*.example.com")) {
        return "DIRECT";
    } else if (shExpMatch(host, "somewhere.else")) {
        return "PROXY someproxy:8080";
    } else {
        return "PROXY default-proxy.example.com:3128";
    }
}

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To have a single setting for browsers and other applications that don't support Javascript, you'll need a proxy that supports per-URL parent proxies.

Squid is one possibility, it's a caching proxy designed for high loads and with many features. See Squid selects parent depending on requested URL? for examples of how to set up per-URL parent proxies.

Wwwoffle is another possibility. This proxy is strongly oriented towards having an offline cache, and caches more aggressively than is allowed by the HTTP standards, which is a problem with some sites. Parent proxies can be specified per-URL with wildcard patterns (the default configuration files contains commented-out examples).

Answer 2

The answer here is going to be to set your single value to a proxy server of your own so that all traffic hits it. This can be a system wide setting.

As for setting up your own proxy server, yes squid is the best option I know of and yes it can be setup and run on a Linux machine. It is best run on a gateway/router machine, but you can run it on your personal machine for use locally as well. There are lots of guides available for how to configure it. They cover a wide range of possible uses, you should search specifically for whatever kind of configuration you want to accomplish.