upstream Node-based cloud export service offline in export demo; switch to Ruby-based service for now

[jywarren]

Following up on #716, @sashadev-sky noted the following demo wasn't working:

https://publiclab.github.io/Leaflet.DistortableImage/examples/export

@jywarren updated export.html but can't make it work.. also seeing it doesn't work in our gh-pages either so perhaps it never worked? The POST req to //34.74.118.242/api/v2/export/ times out in both scenarios. Going to say fixing that part is out of scope for this PR because i have no idea what is wrong! Just made sure here that we aren't using ajax anymore, etc.

Note I tested the startExport function updates on my own gh-pages page https://sasha.mapknitter.org/examples/select.html so I know its not any src code changes.

Where did this url come from ? //34.74.118.242/api/v2/export/

https://34.74.118.242/api/v2/export/ is our node-based export service. There is another in production on https://mapknitter.org as you can see here:

https://github.com/publiclab/mapknitter/blob/92e73e634550d6ec0e3f1e475d062fe967d54c9a/app/assets/javascripts/mapknitter/Map.js#L661-L676

It uses the Ruby-based cloud exporter at https://export.mapknitter.org, which is online. Let's use this until the Node-based service is back online.

Thanks!!!

[jywarren]

I checked! Switching to https://export.mapknitter.org seems to work, although the way we handle the response is very different; in the export demo we currently:

window.location = statusUrl;

so we'll have to change that too.

[jywarren]

In fact, it returns /id/1600207027/status.json, not an image location. We can look at the MapKnitter implementation to see how this can be parsed and repeatedly accessed until an image is ready, and then display it.

[jywarren]

OK, using GitPod i was able to try this out and it works all right - we'd have to parse the response using code like this:

https://github.com/publiclab/mapknitter/blob/92e73e634550d6ec0e3f1e475d062fe967d54c9a/app/assets/javascripts/mapknitter/Map.js#L678-L717