On 17Dec15, Paul Vixie allegedly wrote:
> > That the request pipeline order doesn't necesarily match the response
> > pipeline order is particularly unexpected in some protocols (and
> > likely non-compliant), such as HTTP < 2.0
>
> i think this is opaque to the dns-over-http specification. that is, while
> http may under
> its covers do all kinds of asynchronous things
I may not be being very clear or I may misunderstand. As far as
implementation is concerned you are of course correct. As far as the
semantics of the order of responses over HTTP, not so much.
What I was getting at is that a dns-over-http client can pipeline send
request id=1 then request id=2 and get back pipelined response id=2
then response id=1 over a single connection:
Client Server
Request id=1 ---->
Request id=2 ---->
.. time passes
<---- Response id=2
<---- Response id=1
That is, a dns-over-http client has to do more elaborate
request/response matching with id (+query RR) rather than rely on
submit order for matching.
This re-ordering of responses is not allowed in regular HTTP 1.* and
would almost certainly break common HTTP clients that expect pipeline
order to be maintained.
I'm not saying this is good or bad, just saying it's an important
topic for any dns-over-*stream* protocol to discuss. Least surprise
and all that.
Mark.
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