What is a PAC agent?

Hi everyone, I am an author who specializes in web proxy knowledge. Today, let's explore the difference between PAC proxies and global proxy servers. I don't know if you have heard of PAC proxies?

PAC proxy, the full name is "Proxy Auto-Config", that is, proxy auto-configuration. It is an intelligent way of selecting proxies that can be accessed according to specific rules to select the appropriate proxy server.

As good as the server is, you can't rely on it for everything. For example, if you are in a company intranet, sometimes you need to access external websites. At this time, you may need to use a PAC proxy. the PAC file will define some rules, such as when you visit the intranet site, direct access; and when you visit the site of the external network, access through the proxy server forwarding.

What is the difference between a PAC proxy and a global proxy server?

Global Proxy Server, or Proxy Server as we know it. Each browser has a global setting, and with the global proxy turned on, all requests are forwarded through the proxy server.

So what exactly is the difference between a PAC proxy and a global proxy server? Actually, the main differences are in usage scenarios and configuration flexibility.

Differences in usage scenarios

PAC proxies are mainly used in specific network environments, such as company intranets. In this case, accessing external websites needs to be realized through a proxy server. While global proxy servers are generally used for individual users. When you need to hide your real IP address or access outside resources, you can set your browser to global proxy mode.

Differences in configuration flexibility

Of course, there are some tricks to using PAC agents. You can define multiple rules in a PAC file, or even use JavaScript to dynamically generate rules. This way, you can choose different proxies based on different needs, such as time, URL matching rules, and so on. This flexibility makes PAC proxies work very well in some special cases.

In contrast, the configuration of a global proxy server is relatively simple. All you need to do is set the address and port number of the proxy server, and then enable global mode. However, due to the relatively simple configuration, the use of global proxy servers is also relatively limited.

A little code example

Next, let's take a look at how to use a PAC proxy in a web page. I'll share a simple example for your reference.

function FindProxyForURL(url, host) {
// Return different proxies based on conditions
if (shExpMatch(url, "http://example.com/*")) {
return "PROXY proxy1.example.com:8080";
}

if (shExpMatch(url, "http://www.example.com/*")) {
return "PROXY proxy2.example.com:8080";
}

// Direct access by default
return "DIRECT".
}

The above code is a simple example of a PAC file. In it, we choose different proxy servers according to the URL we access. When accessing a URL starting with "http://example.com/", we use "proxy1.example.com:8080″ as the proxy server; while when accessing a URL starting with "http://http://example.com/", we use "proxy2.example.com:8080″ as the proxy server; and when accessing a URL starting with "http://http://example.com/", we use "proxy2.example.com:8080″ as the proxy server. /www.example.com/", we use "proxy2.example.com:8080″ as the proxy server; in other cases, we access it directly.

write at the end

Through the introduction of this article, we understand the difference between PAC Proxy and Global Proxy Server. PAC Proxy is suitable for specific network environments with high configuration flexibility, while Global Proxy Server is suitable for simple setup for general users. I hope this article is helpful, thanks for reading!