Networking - Proxy - PAC File - About PAC Files

A PAC (Proxy Auto-Configuration) file is a JavaScript function that determines whether web browser requests (HTTP, HTTPS, and FTP) go directly to the destination or are forwarded to a web proxy server.

The JavaScript function contained in the PAC file defines the function: 

function FindProxyForURL(url, host) {
  // ...
}

NOTE: Parameters:

  • url: The URL being accessed.
    • The path and query components of https:// URLs are stripped.
      • Different browsers may offer options to override or disable this.
  • host: The hostname extracted from the URL.
    • This is only for convenience; it is the same string as between :// and the first : or / after that.
    • The port number is not included in this parameter; It can be extracted from the URL when necessary.

References

https://developer.mozilla.org/en-US/docs/Web/HTTP/Proxy_servers_and_tunneling/Proxy_Auto-Configuration_PAC_file