uMap allows to use remote URL as data sources, but those URLs
are not always CORS open, so this is why there is this "ajax-proxy"
feature, where the URL is passed to the backend.
Additionally, there is a caching feature, which duration is configurable
through frontend settings. Valid values are: disabled, 5 min, 1 hour,
1 day.
Initially, I wanted this to be totally handled by Nginx, but I never
found a wayt to set the proxy_cache_valid value from a query string.
Since then, at least in OSM France servers, the ajax-proxy is still
handled by a Django view, which then opens the remote URL and transfert
the data. This is not optimal. And I suppose this is what is causing
hicups on the OSM France servers lately.
This PR provides a mix option, where python deals with validating the
URL and parsing the TTL parameter, and then it passes the hand to
nginx which will serve the remote content.
So, roughtly:
- the client calls /ajax-proxy/?url=xxx&ttl=300
- python will validate the URL (not internal calls…)
- if UMAP_SENDFILE_HEADER is set, then the python returns an empty
response with the path /proxy/http://url plus it will set the
cache ttl through the header X-Accel-Expires
- this /proxy/ location is then handled by nginx
