[Qgis-user] QGIS Server and PostgreSQL projects

[User Adminofff]

Hi,

I'm trying to make QGIS Server to serve projects from PostgreSQL 
database on the web.
Could anyone tell me please, is it possible to do that, or I can serve 
only files?

The general workflow should look like this:

1. Operators with QGIS Desktop are connecting to PostgreSQL, and 
create/modify projects in it.
No files are involved. This part works, I was able to save test project 
on one system, and open it on the other.

2. After finishing project creation/modification, Operators send a link 
to it to the consumers/implementors.
The idea is to be able to view the project in a browser on any device. 
No editing is needed, at least at this moment.
I've installed QGIS Server on the same host as PostgreSQL, set 
nginx/related stuff, and tested that it successfully serves file project.
Then I've tried to get the project from database. qgis user, under which 
QGIS server is run, was allowed passwordless connection to PostgreSQL 
via localhost.

Having test URL for file like this
https://domain.com/qgisserver/cgi-bin/qgis_mapserv.fcgi?LAYERS=countries&SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&CRS=EPSG:4326&WIDTH=400&HEIGHT=200&BBOX=-90,-180,90,180&MAP=/home/qgis/projects/world.qgs 


I've replaced file path with naive PostgreSQL URL like this
https://domain.com/qgisserver/cgi-bin/qgis_mapserv.fcgi?LAYERS=countries&SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&CRS=EPSG:4326&WIDTH=400&HEIGHT=200&BBOX=-90,-180,90,180&MAP=postgresql://127.0.0.1:5432?sslmode=disable&dbname=qgis&schema=world&project=world 

But got this error:

<ServerException>
Project file error. For OWS services: please provide a SERVICE and a MAP 
parameter pointing to a valid QGIS project file
</ServerException>

The error says that QGIS Server wants file, no mentions about database.
On other hand, documentation below says that for MAP parameter either 
file path or PostgreSQL URL is needed, so it should work?

https://docs.qgis.org/3.34/en/docs/server_manual/config.html#qgis-server-envvar 

QGIS_PROJECT_FILE
The .qgs or .qgz project file, normally passed as a parameter in the 
query string (with MAP), you can also set it as an environment variable 
(for example by using mod_rewrite Apache module).

**Note that you may also indicate a project stored in PostgreSQL**, e.g. 
postgresql://localhost:5432?sslmode=disable&dbname=mydb&schema=myschema&project=myproject 
or inside a geopackage file, e.g. 
geopackage:/path/to/geopackage/file.gpkg?projectName=myProjectName.


Searching in the Internet for the error above, I've found this bug report
https://github.com/qgis/QGIS/issues/31192

 From which I've got the idea to encode PostgreSQL URL in test URL, but 
it didn't work with the same error as above.
Also, it looks like report author is connecting with QGIS Desktop to 
QGIS Server, not browser, so this is not my case?
Also-also, as I've stuck with nginx for unrelated to QGIS reasons, I 
cannot test proposed there Apache rewrite magic.

I've tried to see if there is anything useful in QGIS Server logs, but 
there are no any related messages in them.
I've set QGIS_SERVER_LOG_PROFILE to true, but that didn't change 
anything. I see my request to QGIS server only in nginx logs, but 
nothing in QGIS Server logs, and no even failed connection attempts in 
PostgreSQL logs.

So, is there any way to have PostreSQL projects served via QGIS Server, 
or I can use only files?
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