I created a text file as a custom welcome message ...
The retrieval of a file does not involve calling requests.get() to retrieve the URL via http which is where the issue occurs.
...
So for example, to create a lists specific english language welcome template for the list.example.com list you could just put the template in var/templates/lists/list.example.com/en/list:user:notice:welcome.txt or to make it sitewide, in var/templates/site/en/list:user:notice:welcome.txt
Thank you, that is indeed useful info, and as the site-owner I'll use it. But it's of no help to a list-owner who wants to create a custom template, because they have to use Postorius.
So, I'm thinking (in broad brush strokes) that if I'm stuck with this "http glitch" I could write a script to:
- extract the text of the custom message from the database,
- write that message text to a file
- update the templates.uri entries to replace the http://localhost... with file:///path/to/file
- cron the script to run every few minutes.
It screams of utter clunk I know...