Add jinja fromjson custom filter to notification template handling

[delenamalan]

Add a custom Jinja2 filter, fromjson, to convert a JSON string to JSON - which can then be used by Jinja.

This is useful for formatting notifications based on JSON API responses.

If the API route you're watching returns a JSON list, for example, you could format a notification like this:

<ul>
{% for item in current_snapshot|fromson %}
  <li>{{ item.title}}: {{ item.price }}</li>
{% endfor %}
</ul>

[dgtlmoon]

Can you give some (any) information here? whats your use case exactly?

any examples??

[delenamalan]

@dgtlmoon sure, I added a description and example to the PR description now.

The PR is still in draft because I'd still like to add a test and update the docs.

[nmbgeek]

This would be very helpful. I am currently having to use jinja macros to very crudely parse json returned by jq.

[dgtlmoon]

Few things

• whats the security risk with this? anyone can make json.loads run.. https://software.codidact.com/posts/284628 maybe it has some bug and can be exploited?
• It needs a test added
• UI should be updated with a note to say that its possible
• Needs exception handling (what happens if it doesnt actually get JSON data? what should it output? or just throw error in the UI?)
• Needs handling for large strings to avoid DoS

Maybe do something automatic like, if the document begins with { and ends with } then add json_snapshot as a token in the notification settings.... or only actually process json_snapshot if its in the notification body