Thanks for the detailed explanation.
What is the idea?
Let's say there are 30 persons in a lecture. Every person is a user of the
my website. But the pages of the presentation should not be presented all
at once. A new page becomes visible at the moment I give it free. Therefore
every client should ask once a second if there is a new page. But it would
be a lot of traffic if every user gets the actual page once every second.
Therefore I want to control whether a page should reload or not.
Now I have tried a very simple version of "mytime":
def mytime():
jetzt=str(request.now)[:19]
if jetzt[18]!="0":
response.status = 304
return dict(jetzt=jetzt)
This function shows every 10 secondes the actual time for 1 second. This is
not the solution I am looking for: the last time value should stay for 9
seconds - but during these 9 seconds the field is empty.
I think it is a step in the right direction.
2014-08-07 21:10 GMT+02:00 Niphlod <[email protected]>:
> technically LOAD uses a GET, so returning the correct cache headers with a
> correct status **should** (read, every browser has its own implementation)
> avoid "fragment" (i.e. web2py component) refreshes. But if you return the
> same Etag with a 200 response with a content, the browser WILL replace it
> (you did anyhow request a refresh with an ajax call AND you're returning a
> content, it will be shameful to discard it). If you return a 304 with no
> content than the fragment shouldn't be replaced.
> This, however, is the theory. In practice, javascript has NO ACCESS to the
> etag (or cache) informations the browser has, so ajax doesn't work EXACTLY
> as normal browser GETs. You may even get around it, but then you'll be
> facing various browser implementations of it....
>
> BTW, there is plenty of docs around the interwebs, such as
> http://juristr.com/blog/2013/06/caching-jquery-ajax-and-other-ie-fun/
>
> What do you need this for ? isn't zillion times easier just to cache the
> response and send it ?
>
>
> On Thursday, August 7, 2014 7:19:40 PM UTC+2, mweissen wrote:
>
>> Thank you for this information. Shall I use a jquery.ajax-call or can I
>> use the LOAD-helper?
>>
>>
>> 2014-08-07 11:24 GMT+02:00 Niphlod <[email protected]>:
>>
>> if you trigger an ajax request, if it's a GET (an idempotent method) you
>>> may avoid reloading the page and get back a 304....................but it's
>>> not handled automatically by web2py unless the content is static.
>>>
>>>
>>> On Thursday, August 7, 2014 7:52:30 AM UTC+2, mweissen wrote:
>>>>
>>>> Dave told me that my explanation was not clear. Let me try it in other
>>>> words. What I want is a program which periodically reloads a page (I think
>>>> using LOAD is the best way), but only if I allow it.
>>>>
>>>> My idea was that the header parts "Last-Modified" and/or "ETag" could
>>>> do the job. Therefore I wrote the program in two steps:
>>>>
>>>> (1) A controller without any response header modification. It shows the
>>>> actual time and reloads once a second - everything is fine.
>>>>
>>>> The functions:
>>>>
>>>> def mytime():
>>>> jetzt=str(request.now)[:19]
>>>> return dict(jetzt=jetzt)
>>>>
>>>> def init():
>>>> return dict()
>>>>
>>>> -------------------------
>>>>
>>>> The views:
>>>>
>>>> mytime.load:
>>>> {{=jetzt}}
>>>>
>>>> init.html:
>>>> {{extend 'layout.html'}}
>>>> {{=LOAD(f="mytime.load", ajax=True, timeout=1000, times="infinity")}}
>>>>
>>>>
>>>>
>>>> (2) Now I want to simulate an unchanged page. Anthony wrote on
>>>> http://stackoverflow.com/questions/14515313/how-to-modify-
>>>> web2py-download-function-to-return-304-not-modified-in-case-the how to
>>>> change the header. I add the response.headers-lines with a *constant
>>>> *"Last-Modified"
>>>> time and/or a *constant *"ETag" (I think every value is allowed here).
>>>> My hope has been that these modifications *would prevent a reload* of
>>>> the page. If this would be correct I would always see the same time. But it
>>>> did not work, regardless of the header modifications the page reloads again
>>>> once a second.
>>>>
>>>> def mytime():
>>>> jetzt=str(request.now)[:19]
>>>> mtime = "Mi, 06 Aug 2014 08:11:00 GMT" # always the same time!
>>>>
>>>> *response.headers['Last-Modified'] = mtime*
>>>>
>>>> * response.headers['Pragma'] = 'cache' response.headers['Cache-*
>>>> *Control'] = 'private' response.headers['ETag'] = "123" # any
>>>> value, constant*
>>>> return dict(jetzt=jetzt)
>>>>
>>>>
>>>> My primary problem is: the LOAD helper (or an other command?) asks the
>>>> server periodically if there is a new content - and the server should
>>>> reload the page under program control.
>>>>
>>>> Is it possible to solve it using the response headers?
>>>>
>>>> The purpose of the request.now call is only to show whether the page
>>>> reloads or not.
>>>>
>>>> Regards, Martin
>>>>
>>>> -
>>>>
>>>
>>
>> --
> Resources:
> - http://web2py.com
> - http://web2py.com/book (Documentation)
> - http://github.com/web2py/web2py (Source code)
> - https://code.google.com/p/web2py/issues/list (Report Issues)
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- http://github.com/web2py/web2py (Source code)
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