[Xerte-dev] Re: example_zipper issue revisited

Fri May 2 12:47:51 BST 2014

Hi Ron,

Yes I've got a few lying around also so it is a bit of an issue...

I've tried that code on 4 servers and 2 worked and two didn't. I haven't checked yet but it's probably either safe_mode being on or zip not being available (both of which we could check for). I've also see a few code samples using 7z, tar etc so it is possible that we could check for these eventualities and use the most appropriate technique...

That being said, i've done some testing and can't seem to get executable detection to work consistently on Windows servers which is where command line zip is most likely to not be available...

Also, i've not tested it but if the user cancelling the zip stops the rest of the php code running then that could be very problematic. We would have to delete files at the start of the code although we may have to change the format of the temporary file. The number at the end is obviously to allow two or more different people to export at the same time but these then get orphaned if the process quits. What we could do is have two numbers with the first calculable, zipper_xx_yyy and then we can delete all the zipper_xx_* except for the xx in use today... or we delete all zipper folders that were created >x hours ago.

I think we first need to get some export routines that work on different systems though as we can't expect everyone can crank their memory limit up to 300Mb...

Regards,

John Smith | Learning Technologist
Room A251, Govan Mbeki Building | School of Health & Life Sciences | Glasgow Caledonian University
Cowcaddens Road | Glasgow | G4 0BA

Please address ALL support requests to hlsblt at gcu.ac.uk where one of the School Learning Technologists will pick up the job. This will ensure that all jobs are completed as promptly as possible.
________________________________________
From: xerte-dev-bounces at lists.nottingham.ac.uk [xerte-dev-bounces at lists.nottingham.ac.uk] On Behalf Of Ron Mitchell [ronm at mitchellmedia.co.uk]
Sent: 02 May 2014 11:59
To: 'For Xerte technical developers'
Subject: [Xerte-dev] Re: example_zipper issue revisited

Hi all
My inclinations is to scream aaaarrrrrgh! Having had what seems like
coincidental support requests but is clearly all part of the same issue so
I've lost track of how long this issue has existed and how widespread it
might be. To explain...

Late yesterday I received a request from one of the HEA projects regarding
two of their students being unable to export their projects. After
investigation it turns out both students have been uploading quite a few
videos as part of their LO's in this case .flv's and so sure enough the
projects weren't exporting and creatining more and more example_zipper files
after each attempt.

One of these particular projects showed 158MB of media via media & quota and
the other 242MB
One had 47 zipper files the other 21 and across all the user folders 200+
zipper files!

I'm a bit concerned how widespread this could be with people unaware of the
issue. I know it's not best practice to upload loads of video direct but
lets be realistic users are going to do this and sometimes with good reason.

John - This server was also set to 128MB memory limit by defauls so I tried
your export.php but that was generating an empty zip download.

I've increased the memory limit to 300MB and with the current 2.1 code and
original export.php the above two projects export ok without leaving
example_zipper files behind.

However I also noticed looking at the folder via ftp as you suggested John,
that if the user cancels the export, even with the memory limit increased,
the example zipper doesn't then get removed. I don't know if this would be
different with develop or if your export.php would only work with develop
John?

But I am wondering if this is a bit of a ticking timebomb for lots of
installations! If anyone has SSH access to their installation(s) try find .
-type f -name 'example_zipper*'

Perhaps the temp file name should have been example_zippo! ;-)

We obviously need to crack this one asap...

Ron

-----Original Message-----
From: xerte-dev-bounces at lists.nottingham.ac.uk
[mailto:xerte-dev-bounces at lists.nottingham.ac.uk] On Behalf Of Smith, John
Sent: 01 May 2014 14:51
To: For Xerte technical developers
Subject: [Xerte-dev] Re: example_zipper issue revisited

Hi Tom,

Yes, definitely, no worries. I'm about to investigate a windows install with
both the original code and this new code to see whether I can get it to run.
Will update you.

Regards,

John Smith | Learning Technologist
Room A251, Govan Mbeki Building | School of Health & Life Sciences | Glasgow
Caledonian University Cowcaddens Road | Glasgow | G4 0BA

Please address ALL support requests to hlsblt at gcu.ac.uk where one of the
School Learning Technologists will pick up the job. This will ensure that
all jobs are completed as promptly as possible.
________________________________________
From: xerte-dev-bounces at lists.nottingham.ac.uk
[xerte-dev-bounces at lists.nottingham.ac.uk] On Behalf Of Tom Reijnders
[reijnders at tor.nl]
Sent: 01 May 2014 14:46
To: For Xerte technical developers
Subject: [Xerte-dev] Re: example_zipper issue revisited

I will look into this, but I don't have much time at the moment. Perhaps
topnight. Otherwise, it'll have to be next week.

Tom

Smith, John schreef op 1-5-2014 15:38:
> Well. Preliminary testing looks good with my new code but i haven't tested
on Windows yet - would be interested in getting Tom's take on all of this...
>
> I just added loads of videos via ftp (upload limit set to 7M on this
> server) and checked the memory limit and it is
>
> memory_limit    90M     90M
>
> and with each video being used on a page then i've just successfully
downloaded a 316Mb archive zip without any problems (it took several minutes
too so the script didn't timeout) and was able to play the videos contained
within... and this is just a cheap Dreamhost shared server, nothing fancy...
>
> On to Windoze...
>
> Regards,
>
> John Smith | Learning Technologist
> Room A251, Govan Mbeki Building | School of Health & Life Sciences |
> Glasgow Caledonian University Cowcaddens Road | Glasgow | G4 0BA
>
> Please address ALL support requests to hlsblt at gcu.ac.uk where one of the
School Learning Technologists will pick up the job. This will ensure that
all jobs are completed as promptly as possible.
> ________________________________________
> From: xerte-dev-bounces at lists.nottingham.ac.uk
> [xerte-dev-bounces at lists.nottingham.ac.uk] On Behalf Of Ron Mitchell
> [ronm at mitchellmedia.co.uk]
> Sent: 01 May 2014 10:58
> To: 'For Xerte technical developers'
> Subject: [Xerte-dev] Re: example_zipper issue revisited
>
> Hi John
> the problem is when I originally raised this issue on 8th April it
> coincided with discovering loads of these un-removed example_zipper
> files on the sandpit install. At that time I also mentioned the
> separate session issue as a reason I hadn't updated to a newer
> revision and I think you mentioned that you thought Tom had fixed this
> zipper issue in a later revision. So once we'd identified the cause of
> the session issue (or at least Julian's attempt at fixing his FF issue) I
updated the sandpit code as well as other servers.
> Now I've been using the 2.1 branch for this rather than develop so I'm
> not sure if Tom's fix is in develop but not 2.1 but I think the code
> is the same at the moment.
>
> In short although I've been using a 62MB file from a project a user
> was unable to export, previously there were loads of these zipper
> files in loads of different user/project folders and there are
> probably quite a few again now prior to my changing the memory limit.
>
> I could try resetting the memory_limit back on my own server and test
> again but my previous tests with the 62MB file certainly weren't
> crashing the server. Let me know if you think its worth testing with
> larger files and the default 128MB limit or if your and David's later
> responses have ruled that out as being worthwhile?
>
> I know Tom said last night that he was going to revisit his fix for
> this so would be good to hear back from Tom once he's done that.
>
> Cheers
> Ron
>
> -----Original Message-----
> From: xerte-dev-bounces at lists.nottingham.ac.uk
> [mailto:xerte-dev-bounces at lists.nottingham.ac.uk] On Behalf Of Smith,
> John
> Sent: 01 May 2014 09:57
> To: For Xerte technical developers
> Subject: [Xerte-dev] Re: example_zipper issue revisited
>
> Hi Ron,
>
> Have been thinking about your issue and just wondering whether you
> might have inadvertently chosen the worst file size possible for the
> video with 128Mb memory available to PHP. Let me explain (and this is
> entirely hypothetical)...
>
> The zipper creates a blank object (<0.1Mb memory used) The library
> loads all the other files individually and zips them into the object
> (0Mb -> compressed size of all js/html is perhaps around 1-2Mb or
> under) The library then loads the mp4 (now it has the object = 2Mb and
> the video = 62Mb in
> memory) It adds it to the zip object but it's also still in memory
> (mp4 doesn't compress at all so we have 2 + 62 + 62 =126Mb which is
> less than
> 128Mb) It then closes the connection to the mp4 and destroys the
> object (memory now = 64Mb for the zip)
>
> I'm wondering whether a 64 Mb or slightly bigger will cause you to be
> able to crash that server too. Is that something you could try?
>
> Regards,
>
> John Smith | Learning Technologist
> Room A251, Govan Mbeki Building | School of Health & Life Sciences |
> Glasgow Caledonian University Cowcaddens Road | Glasgow | G4 0BA
>
> Please address ALL support requests to hlsblt at gcu.ac.uk where one of
> the School Learning Technologists will pick up the job. This will
> ensure that all jobs are completed as promptly as possible.
> ________________________________________
> From: xerte-dev-bounces at lists.nottingham.ac.uk
> [xerte-dev-bounces at lists.nottingham.ac.uk] On Behalf Of Ron Mitchell
> [ronm at mitchellmedia.co.uk]
> Sent: 01 May 2014 09:09
> To: 'For Xerte technical developers'
> Subject: [Xerte-dev] Re: example_zipper issue revisited
>
> Hi John
> I was just going to test your export code on a server where I don't
> have access to change php settings so the memory limit is fixed at
> 128MB. I know what David means that ideally we want cross platform
> code but as you say there are inevitably different
> solutions/restrictions for some e.g. no control over memory limit. In
> fact the upload limit on this particular shared server is set at the
> default 2MB so I had to upload the test 62MB mp4 via ftp. However I'm
> now confused further because this is the same XOT code as the other
> servers I was using for testing so I expected the export to fail when
> testing before replacing the export code with yours and yet it didn't
> fail and I was able to download the zip which didn't contain any
example_zipper files.
>
> I'm glad you're able to reproduce the issue but not sure how a server
> with 128MB memory limit is able to export ok without a change of code
> or memory limit :-(
>
>
>
> -----Original Message-----
> From: xerte-dev-bounces at lists.nottingham.ac.uk
> [mailto:xerte-dev-bounces at lists.nottingham.ac.uk] On Behalf Of Smith,
> John
> Sent: 01 May 2014 08:38
> To: xerte-dev at lists.nottingham.ac.uk
> Subject: [Xerte-dev] Re: example_zipper issue revisited
>
> All i know Dave is that, with the commented code uncommented, my
> system couldn't download a 56Mb an 79Mb zip but with this code 79Mb
> came down no problem.
>
> We may have to use what we have access to on different systems. There
> may be a similar way to pipe the result into windows or we fall back
> to the old code and crank the memory requirements up yo 300Mb which
> not everyone can most likely do anyway...
>
> Regards
>
> John Smith
> Learning Technologist
> School of Health and Life Sciences
>
> Sent from Samsung Galaxy SII
>
>
>
> David Goodwin <david at palepurple.co.uk> wrote:
>
>
>
> <snip>
> Uses the unix command zip and pipes the stream back into PHP in 8192
> chunks
>
> <snip>
> Also, might not work on Windows...
>
> So therefore it's not worth using?
>
>
> Technically there is no benefit to doing the fread(....) over a
> fpassthru(...) fpassthru does something like 8192 chunks internally.
>
>
> David.
>
> --
> --
> Pale Purple Ltd
> http://www.palepurple.co.uk @PalePurpleLtd
> 0845 0046746 / 07792 380669
> "Bespoke web and mobile application development"
>
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--
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TOR Informatica
Chopinlaan 27
5242HM Rosmalen
Tel: 073 5226191
Fax: 073 5226196

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