On 11/13/2013 9:50 AM, Bill Cole wrote: > On 13 Nov 2013, at 6:39, Stan Hoeppner wrote:
>> Also, note that the carat (^) anchor isn't necessary. The header fields >> you're testing for are in the left most position. Thus no reason to >> left anchor your expression. > > There absolutely ARE reasons to anchor RE's in header_checks: > > 1. Performance. In recent years email has developed a sort of header > cancer: new, often proprietary, and often opaque headers that routinely > have logical lengths of hundreds of characters. Not anchoring a header > check to the start of the header when you only want to check a few > specific headers wastes effort scanning for a match anywhere in a > header, potentially taking hundreds of times longer to confirm a non-match In recent years CPUs have become so blindingly fast it makes no difference. Any excess cycles burned by a non anchored regex were idle cycles anyway. There are good arguments for anchoring expressions, but saving CPU cycles is simply no longer one of them, not for years now. I used to make your argument here, but again, it no longer applies. > 2. Matching unanticipated headers. Except for the very few headers with > tightly defined structure (e.g. Date), *ANY* header could potentially > include any string that would match "(To|From|Cc|Reply-To): " starting > somewhere other than the start of the line. e.g. "Subject: I'm naive > enough to think I want to discard all mail with To: admin@ in a header" This is a stronger argument, though I'm not sure how realistic a scenario this is, with the email address in the subject. A better argument would be that without anchoring the expression would also match headers such as X-Original-To: ad...@example.com Delivered-To: ad...@example.com in which case I'd agree he should anchor. I didn't take these into account previously. -- Stan
