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Hi Brion,
thanks for your quick answer!
On 25/09/10 00:27, Brion Vibber wrote:
> Hi David! I've actually been peeking at this extension as I'd like to use
> something like this to generate scannable QR codes with Android software
> download links for other projects. :)
Yeah, I was really astonished that there wasn't already a qrcode extension.
>> 1. QrCodes are generated for pages that do not have or transclude a
>> {{#qrcode:}} function call, in this case properties [2,3,4].
>
> I haven't fully traced out the execution, but I do notice a few things in
> the code that look suspicious.
>
> It looks like you're naming the destination file based on the wiki page that
> has the {{#qrcode}} in it by pulling $wgTitle:
>
> // Use this page's title as part of the filename (Also regenerates
> qrcodes when the label changes).
> $this->_dstFileName = 'QR-'.$wgTitle->getDBKey().$append.'.png';
>
> This might be the cause of some of your problems here... background jobs may
> run re-parses of other seemingly unconnected wiki pages during a request,
> and other fun things where $wgTitle isn't what you expect, and that might be
> one cause of it triggering with an unexpected title. You may find that it's
> more reliable to use $parser->getTitle(), which should definitely return the
> title for the page being actively parsed.
Ok, I'll try that one then, or not, as you suggest below.
> More generally, using the calling page's title means that you can't easily
> put multiple codes on a single page, and the same code used on different
> pages will get copied unnecessarily.
Well you can use multiple codes on a single page, as demonstrated on the
Sandbox [a] and made possible by the $append variable, but you're
certainly right about the latter part.
> I'd recommend naming the file using a hash of the properties used to
> generate the image, instead of naming it for the using page. This will make
> your code a bit more independent of where it gets called from, and will let
> you both put multiple code images on one page and let common images be
> shared among multiple pages.
Will do that too then.
> One potential problem is garbage collection: a code that gets generated and
> used, then removed and not used again will still have been loaded into the
> system. This is an existing problem with things like the texvc math system,
> but is a bit more visible here because the images appear in the local
> uploads area within the wiki. (However they'll be deletable by admins, so
> not too awful!)
Having them uploaded was one of the main reasons I saved the images and
don't just return a url to the src attribute of an image tag. But I
guess you could have a bot run over it or I suppose there's a hook
triggered on deleting a page which would allow to also delete qrcodes
embedded into/linked to it.
>> 6. Looking at the database, the mixup hypothesis is confirmed:
> It's possible that the internal uploading process interferes with global
> parsing state when it generates and saves the description page for the wiki;
> if so, fixing that may require jumping through some interesting hoops. :)
Well then let's hope that the $parser->getTitle() alternative solves the
problem.
David
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