Risk Disk and Squid

We use RiskDisk at work to see if a company we’re going to do business with is trustworthy, but recently it was complaining HTTP Error 417: Expectation Failed when it tried to do any online lookups.

I tracked this down to it sending Expect: 100-continue in the headers of the request it sent to its server. However, it was going via our web proxy at work, which is Squid. Recently I upgraded Squid to 2.7, and this seems to be the cause of the problems. Squid 2.7 is less forgiving about that particular header (which is apparently an RFC violation on the part of the client).

It’s easily fixed by adding ignore_expect_100 on to your Squid configuration.