On 12/21/2011 08:59 PM, Jarred Nicholls wrote:
On Wed, Dec 21, 2011 at 1:34 PM, Olli Pettay <[email protected]
<mailto:[email protected]>> wrote:
On 12/21/2011 05:59 PM, Jarred Nicholls wrote:
On Wed, Dec 21, 2011 at 10:47 AM, Anne van Kesteren
<[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>> wrote:
On Wed, 21 Dec 2011 16:25:33 +0100, Jarred Nicholls
<[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>> wrote:
1. The spec says the timeout should fire after the specified
number of
milliseconds has elapsed since the start of the request. I
presume this means literally that, with no bearing on
whether or
not data is coming over the wire?
Right.
2. Given we have progress events, we can determine that
data is
coming
over the wire and react accordingly (though in an ugly
fashion,
semantically). E.g., the author can disable the timeout or
increase the timeout. Is that use case possible? In other
words, should setting the timeout value during an active
request
reset the timer? Or should the
timer always be basing its elapsed time on the start
time of the
request + the specified timeout value (an absolute point
in the
future)? I
understand the language in the spec is saying the
latter, but
perhaps could use emphasis that the timeout value can be
changed
mid-request.
http://dvcs.w3.org/hg/xhr/rev/____2ffc908d998f
<http://dvcs.w3.org/hg/xhr/rev/__2ffc908d998f>
<http://dvcs.w3.org/hg/xhr/__rev/2ffc908d998f
<http://dvcs.w3.org/hg/xhr/rev/2ffc908d998f>>
Brilliant, no doubts about it now ;)
Furthermore, if the timeout value is set to a value > 0
but less
than the original value, and the elapsed time is past the
(start_time + timeout), do we fire the timeout or do we
effectively disable it?
The specification says "has passed" which seems reasonably
clear to
me. I.e. you fire it.
Cool, agreed.
3. Since network stacks typically operate w/ timeouts
based on data
coming over the wire, what about a different timeout
attribute
that fires a timeout event when data has stalled, e.g.,
dataTimeout? I think this type of timeout would be more
desirable by authors to have control over for
async requests, since today it's kludgey to try and simulate
that with
timers/progress events + abort(). Whereas with the
overall request
timeout, library authors already simulate that easily with
timers + abort() in the async context. For sync requests in
worker contexts, I can see a dataTimeout as being heavily
desired over a simple request timeout.
So if you receive no octet for dataTimeout milliseconds you
get the
timeout event and the request terminates? Sounds reasonable.
Correct. Same timeout exception/event shared with the request
timeout
attribute, and similar setter/getter steps; just having that
separate
criteria for triggering it.
Is there really need for dataTimeout? You could easily use progress
events and .timeout to achieve similar functionality.
This was the reason why I originally asked that .timeout can be set
also when XHR is active.
xhr.onprogress = function() {
this.timeout += 250;
}
Then why have timeout at all? Your workaround for a native dataTimeout
is analogous to using a setTimeout + xhr.abort() to simulate the request
timeout.
I can tell you why I believe we should have dataTimeout in addition to
timeout:
1. Clean code, which is better for authors and the web platform. To
achieve the same results as a native dataTimeout, your snippet would
need to be amended to maintain the time of the start of the request
and calculate the difference between that and the time the progress
event fired + your timeout value:
xhr.timeout = ((new Date()).getTime() - requestStart) + myTimeout;
A dataTimeout is a buffered timer that's reset on each octet of data
that's received; a sliding window of elapsed time before timing out.
Every time the above snippet is calculated, it becomes more and
more erroneous; the margin of error increases because of time delays
of JS events being dispatched, etc.
2. Synchronous requests in worker contexts have no way to simulate this
behavior, for request timeouts nor for data timeouts. Most of the
network stacks in browsers have a default data timeout (e.g. 10
seconds) but allowing the author to override that timeout has value
I'd think. With that said... synchronous requests? What are those? :)
Ah, sync XHR in workers is a good case.
So dataTimeout would fire if no data has been received in the
dataTimeout period? And receiving some data would basically restart the
timer?
(timeout is being implemented in Gecko)
Awesome!
-Olli
--
Anne van Kesteren
http://annevankesteren.nl/
Thanks,
Jarred
