WPAD: Chrome vs Firefox

A short post about a silly issue I hit with WPAD in Chrome, Firefox and IE.

I wanted to use something like:

if (isInNet(myIpAddress(), "172.29.0.0", "255.255.0.0")) { return proxy_no; }
return proxy_yes;

Meaning: if you’re in VLAN 172.29.0.0, don’t apply the proxy; otherwise do.

It works perfectly in IE and Firefox, but not in Chrome 🙁

I contacted Google to understand why. It’s a bug: https://code.google.com/p/chromium/issues/detail?id=267101

The issue has been open for a long time.

Google suggested a workaround: use isInNetEx:

if (isInNetEx(myIpAddress(), "172.29.0.0", "255.255.0.0")) { return proxy_no; }
return proxy_yes;

Great — it works in Chrome now! But then it no longer works at all in Firefox…

The only solution I found was to make sure Firefox never enters the isInNetEx(myIpAddress() loop (to avoid crashing), and explicitly declare all possible cases.

Example:

if (isInNet(myIpAddress(), "172.28.0.0", "255.255.0.0")) { return proxy_yes; }
if (isInNet(myIpAddress(), "172.29.0.0", "255.255.0.0")) { return proxy_no; }

if (isInNetEx(myIpAddress(), "172.28.0.0", "255.255.0.0")) { return proxy_yes; }
if (isInNetEx(myIpAddress(), "172.29.0.0", "255.255.0.0")) { return proxy_no; }

In short: you must declare isInNet(myIpAddress() for all your VLANs like this. Firefox will always stop at the first match.