pac

Proxy Auto-Config (PAC) is a mechanism that automatically determines request proxy rules using JavaScript scripts, allowing you to dynamically select a proxy or direct connection based on criteria such as URL, domain name, and IP address.

Rule Syntax

pattern pac://value [filters...]

Parameters	Description	Detailed Documentation
pattern	Expression to match request URLs	Match Pattern Documentation
value	Operation content, supports the following types: • Directory/File Path • Remote URL • Inline/Embedded/Values content	Operation Instruction Documentation
filters	Optional filters, supports matching: • Request URL/Method/Header/Content • Response Status Code/Header	Filter Documentation

Configuration Example

# Embedded PAC Script
``` test.pac
function FindProxyForURL(url, host) {
  // ...
}
```
www.example.com/path pac://{test.pac}

# Values
www.example.com/path1 pac://{test2.pac}

# Local File
www.example.com/path3 pac:///User/xxx/test.pac

# Remote PAC Script
* pac://https://raw.githubusercontent.com/imweb/node-pac/master/test/scripts/normal.pac

Advanced Usage

After proxying a request to an upstream proxy, by default the upstream proxy will use DNS to obtain the server IP address based on the requested domain name before continuing the request. If you want the upstream proxy to continue the request based on a specific IP address and port, you can do this:

www.example.com pac://https://xxx/path/normal.pac 1.1.1.1 enable://proxyHost
www.example.com pac:///User/xxx/test.pac 1.1.1.1:8080 enable://proxyHost

1.1.1.1 Equivalent to host://1.1.1.1

Notes

The pac protocol only applies to the substituted URL (i.e., the Final URL shown in the Overview). If the Final URL is empty, it will take effect on the original request URL.

For example, with the rule:

www.example.com/api www.example.com pac://https://xxx/path/normal.pac

When a request is made to https://www.example.com/api/path, Whistle processes it and changes the URL to https://www.example.com/path (this becomes the Final URL). Although the intention is to apply the PAC script https://xxx/path/normal.pac to https://www.example.com/path, the pac rule only matches the original domain www.example.com/api before substitution. Since the converted Final URL is now www.example.com/path, this rule will not be triggered.

To ensure the rule also applies to the substituted request, you can break it into two separate rules:

www.example.com/api www.example.com  
www.example.com pac://https://xxx/path/normal.pac

This way, the original request is first rewritten by the first rule, generating a new Final URL. Then, the second pac rule matches this new URL.