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Could anyone verify if my assumptions are correct?

I think most popular browser(Chrome, Firefox, ...) as a standard send requests with HTTP/1.1 in each request line.

I think whether or not a HTTP/1.1 response is given is determined by the Web server(E.g. a specific version of Apache, Nginx, ...) that hosts the web application. I assume all modern web servers now have HTTP/1.1. If the web server doesn't support HTTP/1.1 I think it will interpret the HTTP/1.1 request as if it was HTTP/1.0 and give a HTTP/1.0 response.

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up vote 1 down vote accepted

Yes, I believe you have the gist of it with one exception:

  1. each request specifies the http protocol level
  2. the webserver decides what to do differantly (if anything) based on a request with up/down level versioning.
  3. HTTP/1.1 is well established and any decent server will support it.

The version matching however is not quite as adaptive as you suggest though. if the client request specifies a MAJOR version that the server does not support, the server responds with

505 HTTP Version Not Supported

in your case, 1.1 and 1.0 share a major version, so (with some exceptions) your assumption is correct, the server will try to respond to a down level request.

for more info on http response codes, see RFC 2616 section 10 and section 3.1

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