Add jinja fromjson custom filter

changedetectionio/filters.py

@@ -0,0 +1,6 @@
+import json
+
+def fromjson(value):
+    if value is None or not value:
+        return ""
+    return json.loads(value)

changedetectionio/forms.py

@@ -32,6 +32,7 @@ from changedetectionio import html_tools, content_fetchers
 from changedetectionio.notification import (
     valid_notification_formats,
 )
+from changedetectionio.filters import fromjson
 
 from wtforms.fields import FormField
 
@@ -246,6 +247,7 @@ class ValidateJinja2Template(object):
 
         try:
             jinja2_env = ImmutableSandboxedEnvironment(loader=BaseLoader)
+            jinja2_env.filters['fromjson'] = fromjson
             jinja2_env.globals.update(notification.valid_tokens)
             jinja2_env.from_string(joined_data).render()
         except TemplateSyntaxError as e:

changedetectionio/safe_jinja.py

@@ -8,11 +8,14 @@ import jinja2.sandbox
 import typing as t
 import os
 
+from changedetectionio.filters import fromjson
+
 JINJA2_MAX_RETURN_PAYLOAD_SIZE = 1024 * int(os.getenv("JINJA2_MAX_RETURN_PAYLOAD_SIZE_KB", 1024 * 10))
 
 
 def render(template_str, **args: t.Any) -> str:
     jinja2_env = jinja2.sandbox.ImmutableSandboxedEnvironment(extensions=['jinja2_time.TimeExtension'])
+    jinja2_env.filters['fromjson'] = fromjson
     output = jinja2_env.from_string(template_str).render(args)
     return output[:JINJA2_MAX_RETURN_PAYLOAD_SIZE]