[Zope] accessing session data error

[Michael Dunstan]

Hi Leticia,

The mixture of ``response.write()`` including JavaScript to drive the  
browser to a new location along with writing objects in ZODB all  
within the same transaction can break some of the promises that you'd  
normally expect Zope and a browser to keep.

My guess is that browser is being told to visit ``end`` before the  
transaction started by ``init2`` has finished. Perhaps a conflict  
error is causing that transaction to take longer than you expect.  
Normally this would not trip you up as your browser does not see  
anything until after the transaction has finished. (In this normal  
mode you might see a conflict error rendered in the browser if the  
publication machinery had to give up.)

For your example try breaking up ``init2`` into two scripts. The  
first that writes the session data and then redirects the browser to  
the second. The second then does not touch session data and manages  
all the ``response.write()``s. And remove the unused ``sessionData =  
context.REQUEST.SESSION`` from ``external``.

Cheers
Michael

On 21/06/2005, at 6:20 AM, Leticia Larrosa wrote:

> Hi all:
>
> I think that I found a ZOPE bug. Is really very important for me  
> know what can I do for avoid it. The first 9 steps are to recreate  
> the situation and the other steps are to provoke the error.
>
> Step 1: Crate a folder called "reproducingError" in Zope Interface  
> Manage
>
> Step 2: create a page template called "index_html" in the  
> "reproducingError" folder with the following content:
> "
> <!-- index_html page template -->
> <form name="form1" method="post" action="reproducingError/init">
>   <input type="text" name="user">
>   <input type="submit" name="Submit" value="Submit">
> </form>
> "
>
> Step 3: create a python script called "init" in the  
> "reproducingError" folder with the following content:
> "
> # init script
> sessionData = container.REQUEST.SESSION
> sessionData.set("userId", container.REQUEST.user)
> return context.init2_html()
> "
>
> Step 4: create a page template called "init2_html" in the  
> "reproducingError" folder with the following content:
> "
> <!-- init2_html page template -->
> <a href="init2">passing face 2</a>
> "
>
> Step 5: create a python script called "init2" in the  
> "reproducingError" folder with the following content:
> "
> # init2 script
> request = context.REQUEST
> sessionData = request.SESSION
> sessionData.set('idService', 'testService')
> context.first()
> return context.external(context)
> "
>
> Step 6: create a page template called "first_html" in the  
> "reproducingError" folder with the following content:
> "
> First Response
> "
>
> Step 7: create a python script called "first" in the  
> "reproducingError" folder with the following content:
> "
> # first script
> response = container.REQUEST.RESPONSE
> str = container.first_html()
> response.write(str)
> response.flush()
> "
>
> Step 8: create an external method called "external" in the  
> "reproducingError" folder with the following content, in where the  
> function of the external method is "communicationResponse" and the  
> module is any name that you give to the file:
> "
> # external method
> import time
> def communicationResponse(context):
>     response = context.REQUEST.RESPONSE
>     sessionData = context.REQUEST.SESSION
>     strDetailEnd = "<script>window.location='reproducingError/end'</ 
> script>"
>
>     for item in range(1, 40):
>         time.sleep(3)
>         response.write("Response iteration:" + str(item))
>         response.flush()
>     response.write(strDetailEnd)
>     response.flush()
> "
>
> Step 9: create a python script called "end" in the  
> "reproducingError" folder with the following content:
> "
> # end script
> idService = context.REQUEST.SESSION['idService']
> return "Fin - " + idService
> "
>
> Step 10: open two explorer in wich call the object  
> "reproducingError" (Example: localhost:8080/reproducingError)
>
> Step 11: enter an example text in each one.
>
> Step 12: clink in the link of one of them, and 5 second later clink  
> on the link of the other explorer. The waiting for around 5 second  
> is necesary because with other time interval not allways get the  
> error.
>
> Stpe 13: and wait the "Response iteration"...  Please if the error  
> don't appear in any of the pages, begins at Step 9 again. and try  
> to count to 5 witch other velocity :)
>
> The correct result is:
> "
> Fin - testService
> "
>
> The error is:
> "
> Site Error
> An error was encountered while publishing this resource.
> Error Type: KeyError
> Error Value: 'idService'
> "
> The traceback:
> "
> Traceback (innermost last):
>   Module ZPublisher.Publish, line 101, in publish
>   Module ZPublisher.mapply, line 88, in mapply
>   Module ZPublisher.Publish, line 39, in call_object
>   Module Shared.DC.Scripts.Bindings, line 306, in __call__
>   Module Shared.DC.Scripts.Bindings, line 343, in _bindAndExec
>   Module Products.PythonScripts.PythonScript, line 323, in _exec
>   Module None, line 2, in end
>    - <PythonScript at /approach/reproducingError/end>
>    - Line 2
>   Module AccessControl.ZopeGuards, line 67, in guarded_getitem
>   Module Products.Transience.TransientObject, line 176, in __getitem__
> KeyError: 'idService'
> "
>
> I will appreciate if you try until the error appear, because I not  
> always obtain the error. I thinks that it is bacause the time  
> interval between the two request.
>
> A curious thing is that when I obtain the error, if I wait around  
> 15 second and refresh the page in wich i obtain the error, the  
> correct result appear.. and no errors come.
>
> Sorry for the extended message, but I need any help that you can  
> give me, because this describe error environment imitate a  
> funcionality that I must give in a system very import that i'm doing.
>
> I'm using Zope 2.7.6 for Windows.
>
> Thanks in advanced.
> Leticia
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