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eTag without Last-Modified - Does this now give Content Negotiation?

Many years ago Content Negotiation *required* a Last-Modified header

     
11:08 pm on Jun 11, 2019 (gmt 0)

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A non-profit, well-maintained website, with Admin that seem to know what they are doing, is sending dynamic pages that include all HTTP/1.1 headers (including a weak eTag) but no Last-Modified nor Expiry.

I'm interested in hearing from Webmasters with current experience on whether they have found the above situation to make any difference to Content Negotiation. I'm no longer a current Webmaster, but certainly my experiments during my years in that role suggested that both Last-Modified, Expiry + Cache-Control headers were essential, even with HTTP/1.1 browsers, in order to keep bandwidth at a minimum & server response at a maximum.

I want to be able to offer accurate help to the site, but do not want to look like a complete prat if, indeed, website interaction has changed so that the Last-Modified header is no longer required and an eTag header is sufficient. So, what is the up-to-date situation?

Further info:

Content Negotiation is a bit of a geeky subject, so here is some brief info for novices.

This old page on WebmasterWorld [webmasterworld.com] gives some basic information on the mechanics of Content Negotiation. It began with the introduction of HTTP/1.0 in May 1996 [w3.org]. That is when browsers & web-servers began to interact with each other, and when (as just one example) the 304 Not Modified Response Header was introduced.

These are selected Response headers for one of the dynamic pages at the site in question:-

$ wget -O /dev/null -S https://www.example.com/way/17236956
--2019-06-11 19:15:05-- https://www.example.com/way/17236956
HTTP request sent, awaiting response...
HTTP/1.1 200 OK
Date: Tue, 11 Jun 2019 18:15:05 GMT
Server: Apache/2.4.29 (Ubuntu)
Cache-Control: max-age=0, private, must-revalidate
Vary: Accept-Language,Accept-Encoding
Content-Language: en
ETag: W/"6b6023e8efd4983110d4097ec2ee5e56"
Status: 200 OK
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8
Length: unspecified [text/html]
Saving to: ‘/dev/null’

…and a static file from the same site which basically makes the point that Apache always sends both HTTP/1.1 + HTTP/1.0 headers:

$ wget -O /dev/null -S https://www.example.com/robots.txt
HTTP request sent, awaiting response...
HTTP/1.1 200 OK
Date: Tue, 11 Jun 2019 18:29:58 GMT
Server: Apache/2.4.29 (Ubuntu)
Last-Modified: Thu, 06 Jun 2019 17:26:06 GMT
ETag: "184-58aab0255d051"
Accept-Ranges: bytes
Content-Length: 388
Vary: Accept-Encoding
Keep-Alive: timeout=5, max=100
Content-Type: text/plain; charset=utf-8
11:32 pm on June 11, 2019 (gmt 0)

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Well, wouldya believe it, only minutes after I post this thread it gets modified to:-

Is there any change to the advice in HTTP/1.1 (rfc2626 June 1999) [w3.org]?

13.3.4 Rules for When to Use Entity Tags and Last-Modified Dates

We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types ought to be used, and for what purposes.

In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity tag and a Last-Modified value.
12:52 am on June 12, 2019 (gmt 0)

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WebmasterWorld Administrator not2easy is a WebmasterWorld Top Contributor of All Time 10+ Year Member Top Contributors Of The Month

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Co-incidence or they're reading over your shoulder?
1:02 am on June 12, 2019 (gmt 0)

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Yeah, but we've only gone from 1996 to 1999. What is the situation in 2019? Has it changed at all (I suspect not)?

PS
I took up your suggestion of a fresh sticky.
5:05 am on June 12, 2019 (gmt 0)

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WebmasterWorld Senior Member tangor is a WebmasterWorld Top Contributor of All Time 10+ Year Member Top Contributors Of The Month

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the more things change, the more they stay the same ...

Until somebody comes up with a reason NOT to include these ... makes sense to keep using them.