Is there any legitimate use for UA string sniffing vs feature detection? And what could a search engine possibly do that's so bleeding edge it doesn't work in all browsers?
> Warning: A number of older versions of browsers including Chrome, Safari, and UC browser are incompatible with the new None attribute and may ignore or restrict the cookie.
This caveat meant that UA sniffing was the only reliable means of setting cookies that were guaranteed to work properly.
This had nothing to do with feature detection, so the usual suggestions simply won’t work.
You don't get that sort of speed without heavy optimisation. In fact I'd be amazed if www.google.com isn't the most heavily optimised page on the internet. So it's not at all surprising to me that they optimise based on what browser is asking.
basically you can send slightly less data by only sending the relevant layout/js code etc. with the first request instead of sending some variation which then the browser selects/branches one
most likely a terrible optimization for most sides maybe not google search due to how much it's called
but then Google is (as far as I remember) also the company which has tried to push the removal of UA strings (by fixating all UA strings to the same string, or at least a small set of strings)... so quite ironic
But then you will also be incompetent to do it right with UA sniffing, which is even harder and require more maintenance to keep the list up-to-date.
That's the obtuse thought process on how you get the garbage google just showed us.
UA sniffing should be a last resort but there have been times where browsers have claimed to support something but had hard to detect bugs and the cleanest way to handle it was to pretend the feature detection failed on those older browsers.
This is increasingly rare – the last time I had to do it was for Internet Explorer – but I would not take a bet that nobody will ever have a need for it again.
As an example, I recently had to deal with an exception to a TLS 1.2 requirement because while almost all of our traffic is from modern user agents, there was a group of blind users with braille displays using Android KitKat which defaults to only supporting a maximum of TLS 1.1 and “go buy an expensive new device” isn’t an appropriate response even though you might be entirely comfortable saying that random internet crawlers getting an error is okay.
You either support older TLS or you don't. Do not try to fine tune it to one known audience. You just locked everyone that is not in the sample you just whitelisted(!) out of your service. But you don't know about them, so no harm? If you think one use case for tls1.1 is OK for one use case, just accept you support it.
Same for every thing else. Every time you use UA sniff, you are doing it wrong. not matter how smart you think you are. You are not. It's just a momentary feel good because you are oblivious to everything else. Just like you felt good when you blocked tls1.1 before knowing of those blind users. Now you felt good allowing those blind users because you still don't know about another group that you might learn tomorrow or never, because you are blocking them :)
Now extrapolate your arrogant incopetence to your entire user base. How many people do you think you are screwing over that didn't bother to complain and instead just moved away?