PAC Functions | FindProxyForURL

All modern browsers support a set of functions explictly made available for use in PAC files. PAC files run within a sandbox and while many standard JavaScript functions may be supported, the sandbox prevents PAC files from being able to perform actions based on the contents of a webpage, nor do they have access to functions that can access a browser user agent, or pull the public IP address of a user.

The Functions

dnsDomainIs
Evaluates hostnames and returns true if hostnames match. Used mainly to match and exception individual hostnames.

// If the hostname matches google.com or www.google.com 
// send direct to the Internet. 
if (dnsDomainIs(host, "google.com") || dnsDomainIs(host, "www.google.com")) 
    return "DIRECT";

shExpMatch
Will attempt to match hostname or URL to a specified shell expression, and returns true if matched.

// Any requests with a hostname ending with the extension .local
// will be sent direct to the Internet.
if (shExpMatch(host, "*.local"))
	return "DIRECT";

// A request for the host vpn.domain.com or any request for a file or folder in the
// location http://abcdomain.com/folder/ will be sent direct to the Internet.
if (shExpMatch(host, "vpn.domain.com") ||
	shExpMatch(url, "http://abcdomain.com/folder/*"))
	return "DIRECT";

isInNet
This function evaluates the IP address of a hostname, and if within a specified subnet returns true. If a hostname is passed the function will resolve the hostname to an IP address.

// If IP of requested website website falls within IP range, send direct to the Internet. 
if (isInNet(dnsResolve(host), "172.16.0.0", "255.240.0.0")) 
	return "DIRECT";

myIpAddress
Returns the IP address of the host machine. However, with the rise of IPv6 and no ability to distinguish between multiple active network adapters, this function should be avoided.

// If the machine requesting a website falls within IP range, 
// send traffic via proxy 10.10.5.1 running on port 8080. 
if (isInNet(myIpAddress(), "10.10.1.0", "255.255.255.0")) 
	return "PROXY 10.10.5.1:8080";

dnsResolve
Resolves a hostname to an IP address. Note that browsers do not perform unique DNS lookups for the same host per function-use – local DNS caching is respected and multiple uses of this function will not have a DNS load or performance impact.

// Example #1 - If IP of the requested host falls within any of the ranges specified, send direct. 
if (isInNet(dnsResolve(host), "10.0.0.0", "255.0.0.0") || 
	isInNet(dnsResolve(host), "172.16.0.0", "255.240.0.0") || 
	isInNet(dnsResolve(host), "192.168.0.0", "255.255.0.0") || 
	isInNet(dnsResolve(host), "127.0.0.0", "255.255.255.0")) 
	return "DIRECT";

// Example #2 - If IP of the requested host falls within any of the ranges specified, send direct. 
resolvedHost = dnsResolve(host);
if (isInNet(resolvedHost, "10.0.0.0", "255.0.0.0") || 
	isInNet(resolvedHost, "172.16.0.0", "255.240.0.0") || 
	isInNet(resolvedHost, "192.168.0.0", "255.255.0.0") || 
	isInNet(resolvedHost, "127.0.0.0", "255.255.255.0")) 
	return "DIRECT";

isPlainHostName
This function will return true if the hostname contains no dots, e.g. http://intranet – useful when applying exceptions for internal websites.

// If user requests plain hostnames, e.g. http://intranet/, // http://webserver-name01/, send direct. 
if (isPlainHostName(host)) 
	return "DIRECT";

localHostOrDomainIs
Evaluates hostname and only returns true if exact hostname match is found.

// If the Host requested is "www" or "www.google.com", send direct. 
if (localHostOrDomainIs(host, "www.google.com")) 
	return "DIRECT";

isResolvable
Attempts to resolve a hostname to an IP address and returns true if successful.

// If the host requested can be resolved by DNS, send via proxy1.example.com. 
if (isResolvable(host)) 
	return "PROXY proxy1.example.com:8080";

dnsDomainLevels
This function returns the number of DNS domain levels (number of dots) in the hostname. Can be used to exception internal websites which use short DNS names, e.g. http://intranet

// If hostname contains any dots, send via proxy1.example.com, otherwise send direct. 
if (dnsDomainLevels(host) > 0) 
	return "PROXY proxy1.example.com:8080"; 
		else return "DIRECT";

weekdayRange
Allows rules to be time based, e.g. only return a proxy during specific days.

// If during the period of Monday to Friday, proxy1.example.com will be returned, otherwise 
// users will go direct for any day outside this period. 
if (weekdayRange("MON", "FRI")) 
	return "PROXY proxy1.example.com:8080"; 
		else return "DIRECT";

dateRange
Allows rules to be time based, e.g. only return a proxy during specific months.

// If during the period of January to March, proxy1.example.com will be returned, otherwise 
// users will go direct for any month outside this period. 
if (dateRange("JAN", "MAR")) 
	return "PROXY proxy1.example.com:8080"; 
		else return "DIRECT";

timeRange
Allows rules to be time based, e.g. only return a proxy during specific hours.

// If during the period 8am to 6pm, proxy1.example.com will be returned, otherwise 
// users will go direct for any time outside this period. 
if (timeRange(8, 18)) 
	return "PROXY proxy1.example.com:8080"; 
		else return "DIRECT";