Re: Questions about stream state transitions

[Shigeki Ohtsu <[e-mail]>]

Thanks for answers, they are very helpful for me.

Following comments, I've update the table in

http://html5.ohtsu.org/HTTP2_Stream_State.pdf

Please review this if it is correct and I've also submitted a new PR of

https://github.com/http2/http2-spec/pull/179

which is related in receiving PUSH_PROMISE shown in the table as marked (*2)

Please review it too.

Regards,

(2013/07/18 1:24), Martin Thomson wrote:
> This is really valuable work.
>
> I'm going to create a ticket to cover addressing these points:
> https://github.com/http2/http2-spec/issues/175
>
> That one, I'll mark as editorial, but I'll also create a couple of
> extra issues (below).
>
> On 17 July 2013 05:39, Shigeki Ohtsu <[e-mail]> wrote:
>> Hi,
>>
>> The stream state is newly introduced in the draft-04. For my understandings,
>> I've just wrote a table diagram for the stream states transition to cover
>>   all scenarios in the case of sending and receiving frames.
>>
>> The table is listed in
>>
>> http://html5.ohtsu.org/HTTP2_Stream_State.pdf
>
> Note that, in general, you will see a great deal of symmetry between
> the two tables.  If it is a PROTOCOL_ERROR to receive, then it will be
> a MUST NOT for send, aside from the boundary cases where races can
> occur.
>
>> In writing this, I have the folowing five questions which are painted gray in
>> the table field.
>>
>> (1) Receiving RST_STREAM in "idle"
>> Is it a stream error with PROTOCOL_ERROR or falled into "closed" state?
>
> I believe that the right approach is to treat this as a *connection*
> error of type PROTOCOL_ERROR.  Otherwise, an endpoint can be required
> to maintain too much extra state.
> -> https://github.com/http2/http2-spec/issues/176
>
>> (2) Receivng PRIRORITY and WINDOW_UPDATE in "half closed(local)"
>> They are not necessary. So is it to be an error or ignored?
>
> Both can be received in this state.  If you just sent END_STREAM, then
> it would not be unexpected to receive either frame shortly thereafter.
>   Ignoring them seems safe (providing that you apply the usual DoS
> heuristics).
>
>> (3) Sending PRIORITY in "half closed(remote)"
>> No description about this case is in the draft. Is it prohibited?
>
> No need to send it, but it's impossible to force compliance (see above answer).
>
>> (4) Receiving RST_STREAM in "closed"
>> The draft says that " An endpoint that sends a RST_STREAM frame MUST ignore
>> frames that it receives on closed streams after it has sent a RST_STREAM frame."
>>
>> Is this ignored always in the closed state or only in the case
>> after RST_STREAM sent?
>
> If you send RST_STREAM, then receiving RST_STREAM should be OK.  In my
> opinion, an implementation could choose to use RST_STREAM as a signal
> that they can stop ignoring frames on that streams (and transition to
> a  hard connection-level PROTOCOL_ERROR for any other frames that
> appear).
>
> If a stream is closed, either because both peers sent END_STREAM, or
> you *received* RST_STREAM, receiving RST_STREAM is a PROTOCOL_ERROR.
> That, we should clarify.
>
>> (5) Receiving PUSH_PROMISE in "closed"
>> The draft says that 'An endpoint might receive a PUSH_PROMISE frame after
>> it sends RST_STREAM. PUSH_PROMISE causes a stream to become "reserved".'
>>
>> The same question above.
>> Is PUSH_PROMISE always leads the associted stream to be reserved(remote)
>> in the closed state? Or is it limited in the case after RST_STREAM was sent?
>
> This is only valid if you send RST_STREAM.  If you reach "closed" in
> any other way, the remote peer is aware of the close and should not be
> sending junk.  In this case, perhaps we need to escalate the error to
> a connection one, so that we can avoid the need to worry about the
> promised stream.
>
> That might be a general principle that can be applied to invalid
> PUSH_PROMISE frames, lest we end up with streams that are sort-of
> promised, but not promised in any valid way.
> -> https://github.com/http2/http2-spec/issues/177
>
>> If any missings or mistakes are found in the table, I'm very glad to have feedbacks.
>
> I think that you have the PUSH_PROMISE a little wrong, depending on
> which stream that you are talking about.
>
> The stream that you are using here is the *promised* stream.  But the
> frame header for PUSH_PROMISE includes the *associated* stream.
> Perhaps you need to add another column for the effect that
> PUSH_PROMISE has on the associated stream.
>