Dpac is a dynamic proxy auto configuration CGI application. It returns a Javascript proxy configuration dynamically based on the client's IP address.

It's a CGI application, which means it's invoked by a web server. When web browsers send a request for their proxy configuration, dpac looks at the source IP address and responds with a proxy auto configuration file that matches the network and filename specified in a configuration file.

This makes it simple and easy to route traffic to different proxies or a cluster of proxies based on a client's IP address.

For example, you could configure all of the browsers on your network to request the proxy configuration from http://pac.example.com/proxy.pac. You'd then create the files below:

1. The configuration file, ending in ".conf": proxy.pac.conf

This file contains the list of networks that are mapped to the data files that contain your Javascript function, like this:

10.0.0.0/9    proxy1.js
10.128.0.0/9  proxy2.js
*             proxy1.js

The asterisk character ("*") matches all IP addresses. Therefore, it's intended use is as a wildcard, or default, line in the conf file that applies to all clients. It should typically be the last line; since it matches all addresses, every line below it will be ignored (i.e. the first match wins and processing stops).

2. The proxy auto configuration data files referenced in the conf file.

These files should contain the Javascript function "FindProxyForURL" that contains the proxy selection logic you want to return to the browser. Continuing the example above, you'd need to create 2 data files:

proxy1.js:

function FindProxyForURL(url, host)
{
    if (isPlainHostName(host)) {
        return "DIRECT";
    } else if (dnsDomainIs(host, ".example.com")) {
        return "DIRECT";
    } else if (isInNet(host, "10.0.0.0", "255.0.0.0")) {
        return "DIRECT";
    } else if (isInNet(host, "172.16.0.0", "255.240.0.0")) {
        return "DIRECT";
    } else if (isInNet(host, "192.168.0.0", "255.255.0.0")) {
        return "DIRECT";
    } else if (isInNet(host, "127.0.0.0", "255.0.0.0")) {
        return "DIRECT";
    } else if (isInNet(host, myIpAddress(), "255.255.255.255")) {
        return "DIRECT";
    } else {
        return "PROXY proxy1.example.com:3128; PROXY proxy1b.example.com:3128";
    }
}

proxy2.js:

function FindProxyForURL(url, host)
{
    if (isPlainHostName(host)) {
        return "DIRECT";
    } else if (dnsDomainIs(host, ".example.com")) {
        return "DIRECT";
    } else if (isInNet(host, "10.0.0.0", "255.0.0.0")) {
        return "DIRECT";
    } else if (isInNet(host, "172.16.0.0", "255.240.0.0")) {
        return "DIRECT";
    } else if (isInNet(host, "192.168.0.0", "255.255.0.0")) {
        return "DIRECT";
    } else if (isInNet(host, "127.0.0.0", "255.0.0.0")) {
        return "DIRECT";
    } else if (isInNet(host, myIpAddress(), "255.255.255.255")) {
        return "DIRECT";
    } else {
        return "PROXY proxy2.example.com:3128; PROXY proxy2b.example.com:3128";
    }
}

Configure your web server (Apache, NGINX, etc.) to run dpac as a CGI application and copy the files above to the configured directory. Be sure to follow any best practices for security for your web server when configuring it for CGI.

Build the dpac binary if needed (see the Makefile and bin directory) and copy it to your web server's configured CGI directory. Rename dpac to proxy.pac or whatever name matches your proxy auto configuration URL. When run, it will look in its current directory for a filename matching itself with the .conf extension. For example, if dpac is renamed to proxy.pac, it will look in its current directory for a configuration file named proxy.pac.conf.

See the www directory for an example.

Since there are currently no automated tests, check functions and values using a debugger.

From the command line, you can test different conf files by running dpac in a tmp directory:

$ cd dpac-master
$ mkdir tmp
$ cd src
$ make
$ cd ../tmp
$ cp ../www/proxy* .
$ cp ../src/dpac proxy.pac
# edit proxy.pac.conf with values to test
$ REMOTE_ADDR="10.128.2.3" ./proxy.pac