PAC-K003 · ex-functions-not-portable

IPv6 extension functions (isInNetEx, dnsResolveEx, myIpAddressEx)

medium · Compatibility across engines

The Ex functions come from Microsoft's IPv6 extensions to the PAC format. Chromium and WinHTTP implement them; Firefox does not. On an engine without them the call throws and the request is treated as a script failure.

Why it matters

isInNetEx, dnsResolveEx, myIpAddressEx, isResolvableEx, sortIpAddressList and getClientVersion are not part of the original PAC function set. Microsoft defined them for IPv6 support; Chromium added implementations; Firefox has declined to. A PAC that calls them unconditionally fails on Firefox with a ReferenceError (silent DIRECT). If they are needed, guard the call with typeof isInNetEx === "function" and provide a fallback path.

How to fix

Prefer the portable v1 functions; if an Ex function is required, guard it with typeof checks and provide a fallback branch.

Examples

function FindProxyForURL(url, host) {
  if (isInNetEx(host, "fd00::/8")) {
    return "DIRECT";
  }
  return "PROXY proxy.corp.example:8080";
}

function FindProxyForURL(url, host) {
  if (typeof isInNetEx === "function" && isInNetEx(host, "fd00::/8")) {
    return "DIRECT";
  }
  if (shExpMatch(host, "fd*:*")) {
    return "DIRECT";
  }
  return "PROXY proxy.corp.example:8080";
}

Engine behaviour

Source: code = read in the engine's source, doc = vendor documentation, lab = observed in a lab run, expert = practitioner knowledge, not yet verified.

Related rules

• FindProxyForURLEx entry point PAC-K004
• isInNet called with an IPv6 address PAC-K014
• Call to a function that is not defined PAC-E005

References

• https://learn.microsoft.com/en-us/windows/win32/winhttp/ipv6-extensions-to-navigator-auto-config-file-format
• https://source.chromium.org/chromium/chromium/src/+/main:services/proxy_resolver/pac_js_library.h