backwards compatibility - Is HTTP/1.0 still in use?

Question

Say one is to write an HTTP server/client, how important is it to support HTTP/1.0? Is it still used anywhere nowdays?

Edit: I'm less concerned with the usefullness/importance of HTTP/1.0, rather the amount of software that actually uses it for non-internal (unit testing being internal use, for example) purposes in the real world (browsers, robots, smartphones/stupidphones, etc...).

Answer 1

As of 2016, you would think that the prominence would decline even more since 1.1 was introduced in 1999 so this is about 17 years.

I checked 7,727,198 lines of logs to see what percent I get of HTTP/1.0 and HTTP/1.1:

 Protocol    Counts      Percent
--------------------------------
HTTP/0.9            0     0.00%
HTTP/1.0    1,636,187    21.17%   (all)
HTTP/1.0       15,415     0.20%   (without the obvious robots)
HTTP/1.1    6,091,011    78.83%
HTTP/2              0     0.00%

From what I can see, most of the HTTP/1.0 are from robots. So I tried to remove entries that were obviously from such (i.e. Agent including the word robot, bot, slurp, etc.)

So it looks like the amount of end users still stuck with HTTP/1.0 is very limited today (0.2%). However, if you want to let robots check out your websites, you may need/want to keep HTTP/1.0 operational. Most will anyway include the Host: ... header even though they advertise their connection as an HTTP/1.0 protocol.

Also, the differences between HTTP/1.0 and HTTP/1.1 is very blurry in terms of implementation. Most people are happily mixing both. I would not worry too much about still accepting/handling HTTP/1.0 requests.

On another server I am starting to see HTTP/2.0 requests that look like this (got 2427 and I see 34,161,268 HTTP/1.0 and HTTP/1.1 requests, so 0.007%):

PRI * HTTP/2.0