Question 1

Does the tester support IPv6? How can I test isInNetEx and IPv6 subnets?

Accepted Answer

Yes, this simulator fully supports modern IPv6 PAC extensions with a 128-bit BigInt sandbox engine:

① 128-bit CIDR Prefix Matching:
Native support for isInNetEx(host, "fc00::/7"), isInNetEx(host, "2001:db8::/32"), and any standard IPv6 CIDR prefix.

② IPv6 Target URLs & Hostnames:
You can test bracketed IPv6 literals directly (e.g. https://[fc00::1]/service or http://[2001:db8::1]:8080/), which the sandbox automatically evaluates.

③ Dual-Stack Client Simulation (myIpAddressEx):
Configure mock client IPv6 addresses in the "Mock Environment & DNS" tab for scripts invoking myIpAddressEx().

④ Mock DNS IPv6 Mapping:
Map intranet domain names directly to IPv6 addresses (e.g. internal.svc 2001:db8::100) to test domain-to-IPv6 routing pipelines without touching real DNS.

Question 2

Why do we need a dedicated PAC Tester & Debugger?

Accepted Answer

When testing a PAC file directly in operating systems or browsers (Chrome, Edge, macOS), execution is a complete black box:

① Silent Failures: If a syntax error or exception occurs, the browser silently falls back to DIRECT connection with zero console warnings.
② Aggressive Caching: Browsers cache PAC evaluations for minutes, making rule verification frustrating.
③ Hidden Rule Matches: With dozens of rules, it is difficult to see which condition intercepted a given domain.

This in-browser simulator exposes execution traces, matched conditions, and millisecond timers directly.

Question 3

How does Single URL Trace help identify shadowed rules (Dead Code)?

Accepted Answer

FindProxyForURL executes top-down and short-circuits on the first matching return statement.

If an overly broad rule (such as a wildcard *.internal) is placed above a specific rule, the subsequent rule is shadowed (Dead Code).

The Trace timeline displays:
① The sequential invocation of PAC helpers (dnsDomainIs, isInNetEx, isPlainHostName).
② Evaluated arguments and Boolean outcomes.
③ Exactly which line triggered the return statement.

Question 4

Why is Batch Regression Testing critical before enterprise deployment?

Accepted Answer

Enterprise networks rely on dozens of interconnected systems (GitLab, Jira, cloud services, internal VPCs, APIs).

When an IT administrator adds a new proxy rule, the primary concern is unintended side effects breaking access to existing services.

Batch Testing enables:
① Maintaining a regression suite of 20~50 representative URLs.
② Running one-click simulation in milliseconds after script changes.
③ Reviewing pass/fail status filters and exporting CSV audit reports.

Question 5

How do Mock Client IP and DNS mapping work in this simulator?

Accepted Answer

Many corporate PAC rules route traffic conditionally based on where the client is located:
e.g. If myIpAddress() is on the 10.x LAN, connect DIRECT; if on a remote public IP, route through a secure proxy.

The Mock Context tab lets you:
① Assign simulated client IPv4 and IPv6 addresses.
② Configure custom static DNS resolutions for intranet hostnames.
This enables testing multi-site routing logic without touching your physical network settings.

Question 6

Why does my PAC evaluate to SOCKS5 in the tester, but fails in the browser?

Accepted Answer

A PAC file only instructs the browser where to connect (e.g. "SOCKS5 127.0.0.1:1080").

If browsing fails in practice, common causes include:
① The proxy daemon (Clash, v2ray, SSH tunnel) is not listening on that port.
② Local firewall rules block local socket connections.
③ Client protocol mismatch.
Using failover fallback chains (e.g. "SOCKS5 127.0.0.1:1080; DIRECT") prevents total disconnection during proxy outages.

Question 7

How can I identify performance bottlenecks like dnsResolve blocking?

Accepted Answer

In PAC files, excessive calls to dnsResolve() or isResolvable() create severe latency because DNS lookups run synchronously before HTTP requests can proceed.

Best practices:
① Favor zero-cost string checks (isPlainHostName, dnsDomainIs).
② Use isInNetEx for IPv6/IPv4 CIDR prefix checks.
③ Monitor executionTimeMs in the trace; evaluations taking >5ms indicate excessive synchronous operations.

PAC Tester & Simulator

Frequently Asked Questions7 Q&As