[Qgis-user] [QGIS-Developer] Python Implementation of QgsNetworkContentFetcher

Nyall Dawson nyall.dawson at gmail.com
Tue Nov 26 21:35:13 PST 2019 

On Wed, 27 Nov 2019 at 15:26, Denis Rouzaud <denis.rouzaud at gmail.com> wrote:
>
> Thanks Nyall for the precisions.
> I wasn't aware of QgsBlockingNetworkRequest.
>
> So basically, if I don't require authcf, then starting from 3.6 there is no reason to use my python nam, I should use both QgsNetworkContentFetcher and QgsBlockingNetworkRequest. And from 3.10 if require authcfg in QgsNetworkContentFetcher.
> Is this correct?

QgsBlockingNetworkRequest has always supported auth, so you should use
that in 3.6 and above in all situations WHEN you need a blocking
request.

QgsNetworkContentFetcher is async, so definitely prefer to use that
whenever you don't need a blocking request.

I'd say the matrix is something like

QGIS 3.4:

 Blocking:
   With auth: python nam (but be aware that it CAN and DOES crash
crashes if used on the main thread)
   Without auth: python nam (but be aware that it CAN and DOES crash
crashes if used on the main thread)

 Non-blocking:
   With auth:      nothing available off-the-shelf -- roll your own
using raw the qt and QGIS auth api?
   Without auth: QgsNetworkContentFetcher

QGIS 3.6 - 3.8:

 Blocking:
   With auth: QgsBlockingNetworkRequest
   Without auth: QgsBlockingNetworkRequest

 Non-blocking:
   With auth:      nothing available off-the-shelf -- roll your own
using raw the qt and QGIS auth api?
   Without auth: QgsNetworkContentFetcher

QGIS 3.10:

 Blocking:
   With auth: QgsBlockingNetworkRequest
   Without auth: QgsBlockingNetworkRequest

 Non-blocking:
   With auth:      QgsNetworkContentFetcher
   Without auth: QgsNetworkContentFetcher


Nyall



>
> Cheers,
> Denis
>
> Le mer. 27 nov. 2019 à 00:27, Nyall Dawson <nyall.dawson at gmail.com> a écrit :
>>
>> On Wed, 27 Nov 2019 at 00:44, Denis Rouzaud <denis.rouzaud at gmail.com> wrote:
>> >
>> > Hi,
>> >
>> > Jumping late but we use the work from NAM Alessandro did in a couple of locator filters.
>> > https://github.com/opengisch/qgis-swiss-locator/blob/master/swiss_locator/core/network_access_manager.py
>> >
>> > I believe I have done very very few adaptations/fixes to the original work and it works like a charm.
>>
>> Not quite. It works in some circumstances, but it uses an event loop.
>> So if you run it on the main thread, you're potentially doing an
>> effective call to QApplication.processEvents, which can lead to all
>> sorts of crashes. That said, it's generally a safe approach to use for
>> QGIS <= 3.4... just don't use it in any code which relates to
>> rendering!
>>
>> >
>> > I had in mind to bring this as is within QGIS core for some time. The main point being for us the blocking request rather than authcfg.
>>
>> That's EXACTLY what QgsBlockingNetworkRequest is -- please don't
>> re-re-implement this!
>>
>> Nyall
>>
>>
>> >
>> > Denis
>> >
>> > Le mar. 26 nov. 2019 à 15:36, C Hamilton <adenaculture at gmail.com> a écrit :
>> >>
>> >> Thanks everyone. This gives me some good ideas. These are the possible solutions:
>> >>
>> >> 1. Write a python implementation of QgsNetworkContentFetcher or QgsBlockingNetworkRequest. With this I could look at the QGIS version and if it is 3.10 or greater import the core method; otherwise, import the python implementation.
>> >> 2. Use the old Boundless implementation if it still works in QGIS 3.
>> >> 3. Use QgsFileDownloader and save it as a temporary file before processing.
>> >>
>> >> Calvin
>> >>
>> >> On Tue, Nov 26, 2019 at 2:29 AM Alessandro Pasotti <apasotti at gmail.com> wrote:
>> >>>
>> >>>
>> >>>
>> >>> On Tue, Nov 26, 2019 at 8:22 AM Richard Duivenvoorde <rdmailings at duif.net> wrote:
>> >>>>
>> >>>> On 26/11/2019 00.06, Nyall Dawson wrote:
>> >>>>
>> >>>> > There's not. But there's the ex-boundless "networkaccessmanager"
>> >>>> > implementation that supports authcfg, which you can find at
>> >>>> > https://github.com/north-road/qgis-redistricting-plugin/blob/master/redistrict/linz/networkaccessmanager.py
>> >>>> > (and other projects -- as far as I'm aware there's no real upstream
>> >>>> > for this... Alessandro?).
>> >>>>
>> >>>> I used this Boundless thingie for several plugins now (original source
>> >>>> is now pointing/redirecting to planetlabs [0]).
>> >>>
>> >>>
>> >>> Yes, that's the "upstream" but I don't know if that one is maintained anymore.
>> >>>
>> >>> Btw, there is also a specialized class for sync/async downloads that supports authcfg: https://qgis.org/api/classQgsFileDownloader.html#details
>> >>>
>> >>>
>> >>>>
>> >>>>
>> >>>> I think we already discussed several times that it would be good to
>> >>>> incorporate this into a commons lib for QGIS. But if I'm correct the
>> >>>> actual interface was not exactly what some wanted, and if I recall
>> >>>> correct Nyall tried to pull this into c++ but hit some multithreading
>> >>>> issues.
>> >>>>
>> >>>> But as Nyall says: I think this is a great lib to use in a plugin (also
>> >>>> because it used the QgisNetwork-stuff, so you can receive the signals
>> >>>> from it or log the precise urls, like we do in the QGISnetworklogger
>> >>>> plugin [1]
>> >>>>
>> >>>> Regards,
>> >>>>
>> >>>> Richard Duivenvoorde
>> >>>>
>> >>>> [0]
>> >>>> https://github.com/planetfederal/lib-qgis-commons/blob/master/qgiscommons2/network/networkaccessmanager.py
>> >>>> [1] https://github.com/rduivenvoorde/qgisnetworklogger
>> >>>> _______________________________________________
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>> >>>
>> >>>
>> >>>
>> >>> --
>> >>> Alessandro Pasotti
>> >>> w3:   www.itopen.it
>> >>
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