Re: SYN_REPLY

I'm about as clear as mud about what we're actually talking about now :)

-=R


On Tue, Feb 26, 2013 at 7:49 PM, William Chan (陈智昌)
<willchan@chromium.org>wrote:

> On Tue, Feb 26, 2013 at 7:37 PM, Amos Jeffries <squid3@treenet.co.nz>wrote:
>
>> On 27/02/2013 2:19 p.m., William Chan (陈智昌) wrote:
>>
>>> On Tue, Feb 26, 2013 at 4:15 PM, Martin Thomson <
>>> martin.thomson@gmail.com <mailto:martin.thomson@gmail.**com<martin.thomson@gmail.com>>>
>>> wrote:
>>>
>>>     On 25 February 2013 20:42, William Chan (陈智昌)
>>>     <willchan@chromium.org <mailto:willchan@chromium.org>**> wrote:
>>>     > Fully agreed it's more general. I think that unless we go all
>>>     the way with
>>>     > ditching SYN_STREAM too (which I disagree with), then I think
>>>     it's a net
>>>     > loss (primarily due to more difficulty in grokking the spec) to
>>>     save a frame
>>>     > type value and combine SYN_REPLY and HEADERS into one.
>>>
>>>     I'm interested in what you feel SYN_STREAM provides that you can't
>>> get
>>>     with HEADERS.
>>>
>>>     I don't care either way about whether the priority is in the message
>>>     or not.  So, in the interests of saving those few bytes, that's a
>>>     feature that could be retained (or even moved to HEADERS).
>>>
>>>
>>> I'm not completely clear here on the stated proposal, so I'll just
>>> reclarify my position here. I think that the priority should be
>>> communicated in the same frame which starts the stream, whether that frame
>>> be called SYN_STREAM or HEADERS. I'm not sure if it makes sense to continue
>>> including the priority information for followup headers, that may arrive in
>>> a HEADERS frame. I'm leaning towards saying it does not.
>>>
>>>
>>>     The only other thing is the UNIDIRECTIONAL flag.  This flag is
>>>     currently redundant: all streams sent by the client are
>>> bidirectional,
>>>     and all streams from the server are unidirectional without exception.
>>>
>>>
>>> I think in the normal HTTP use case, yes. But when you view HTTP/2 as a
>>> transport layer for other protocols, then I think it might be reasonable to
>>> have the server initiate a bidirectional stream. Currently there's no
>>> binding for that in the web platform, but you could imagine it (register an
>>> event handler for server initiated streams, rather than relying on hanging
>>> GETs / client initiated WebSockets). I don't feel strongly here due to not
>>> having a concrete use case.
>>>
>>>
>>>     As I said in another mail, I'm not sure that SYN_STREAM/SYN_REPLY
>>>     actually help with understanding the spec.  On the contrary, I think
>>>     that they lead to false impressions about how streams start.  They
>>>     imply negotiation, which is far from the case.
>>>
>>>
>>> Intriguing. I did not read the read the earlier email and that was my
>>> bad. I think I have a bias because it's always been called SYN_STREAM and
>>> SYN_REPLY and that's how I conceptualize it. I'm willing to say that my
>>> conceptions on the naming might be very biased and maybe should be
>>> discounted.
>>>
>>> In summary, here's my current position:
>>> * the first frame for a stream should include its priority (to be clear,
>>> I don't view the PUSH_PROMISE as belonging to the promised new stream, but
>>> to the associated stream)
>>> * it feels weird to me for subsequent frames on the stream that include
>>> the header name/value block to also include the priority. i don't like the
>>> tight coupling of that.
>>>
>>
>> I do like it and from earlier readings I'm not alone in that. Priority
>> needs to be adaptable within the duration of the stream _in total_.
>> Ignoring the idea one end adjusting priority dynamically.... client can
>> still name its priority based on objects importance for whatever its user
>> is doing, and server claim a higher/lower relative priority based on its
>> own knowledge of the web site/service resource. There is no contradictions
>> there and adjusting the priority preference after input from both ends
>> should not be allowed to affect the traffic flow in any major way - at
>> worst some resources may get slower response time because they initially
>> claimed lower priority and raising it was rejected by the assigning
>> algorithm.
>
>
> Just to be clear, I am very open to reprioritization, and in fact do want
> to experiment with it in HTTP/2. I'm just saying that I feel that it's
> weird to couple it to whatever frame carries the header name/value block.
> I'm trying to work through my head the implications here. I think it means
> that *if* I want to send a follow up HEADERS frame, I'd have to remember
> the priority of the stream, whereas today I calculate it once based off the
> resource type and forget it. Not a huge deal, bookkeeping's easy and the
> extra state is cheap. But it seems nice not to require it.
>
>
>>
>>
>>  * i feel less strongly about the naming of SYN_STREAM+SYN_REPLY vs
>>> HEADERS, after what Martin wrote. i fully admit my mental bias here.
>>>
>>
>> When there are two features largely duplicating the same things bias is
>> expected. :-)
>>
>> Amos
>>
>>
>