feat: support rendering message template with Jinja

Add config setting to enable Jinja templates

Signed-off-by: Christopher Arndt <chris@chrisarndt.de>

Dockerfile

@@ -1,5 +1,5 @@
 FROM python:3.11-alpine
-RUN python3 -m pip --no-cache-dir install bleach markdown matrix-nio
+RUN python3 -m pip --no-cache-dir install bleach jinja2 markdown matrix-nio
 ADD matrixchat-notify.py /bin/
 ADD matrixchat-notify-config.json /etc/
 RUN chmod +x /bin/matrixchat-notify.py

README.md

@@ -40,7 +40,7 @@ steps:
 * `allowed_tags` *(default:* [`DEFAULT_ALLOWED_TAGS`]*)*
 
     List or set or string with comma-separated list of HTML tag names. HTML
-    tags not included, will be stripped from the HTML output generated by
+    tags not included will be stripped from the HTML output generated by
     rendering a Markdown message template.
 
     Note that the default list does not include any tags, which allow to load
@@ -64,14 +64,28 @@ steps:
 
     The Matrix homeserver URL.
 
+* `jinja`
+
+    If set to `yes`, `y`, `true`, `t`, `on` or `1`, the message template is
+    rendered with the [Jinja] templating engine (instead of performing simple
+    placeholder substitution). The template context is controlled by the
+    `pass_environment` setting, same as with non-Jinja templates, but
+    placeholders use a different syntax (example: `{{DRONE_REPO}}`), so the
+    `template` setting should be changed to be a valid Jinja2 template string
+    when this is enabled.
+
+    Using this feature requires the `jinja2` Python module to be available
+    (it is installed by default in the plugin's docker image).
+
 * `markdown`
 
-    If set to `yes`, `y`, `true` or `on`, the message resulting from template
-    substtution is considered to be in Markdown format and will be rendered to
-    HTML and sent as a formatted message with `org.matrix.custom.html` format.
+    If set to `yes`, `y`, `true`, `t`, `on` or `1`, the message resulting from
+    template substtution is considered to be in Markdown format and will be
+    rendered to HTML and sent as a formatted message with the format set to
+    `org.matrix.custom.html`.
 
     Using this feature requires the `markdown` and `bleach` Python modules to
-    be available (the plugin's docker image has them installed).
+    be available (they are installed by default in the plugin's docker image).
 
 * `markdown_extensions` *(default:* `admonition, extra, sane_lists, smarty`)
 
@@ -98,9 +112,9 @@ steps:
 
 * `template` *(default:* `${DRONE_BUILD_STATUS}`*)*
 
-    The message template. Valid placeholders of the form `${PLACEHOLDER}` will
-    be substituted with the values of the matching environment variables
-    (subject to filtering according to the `pass_environment` setting).
+    The message template. Valid placeholders (example: `${DRONE_REPO}`) will be
+    substituted with the values of the matching environment variables (subject
+    to filtering according to the `pass_environment` setting).
 
     See this [reference] for environment variables available in drone.io CI
     pipelines.
@@ -114,6 +128,7 @@ steps:
 [`DEFAULT_ALLOWED_TAGS`]: ./matrixchat-notify.py#L34
 [allowed attributes]: https://bleach.readthedocs.io/en/latest/clean.html#allowed-attributes-attributes
 [drone.io]: https://drone.io/
+[jinja]: https://jinja.palletsprojects.com/
 [list of extensions]: https://python-markdown.github.io/extensions/
 [plugin]: https://docs.drone.io/plugins/overview/
 [reference]: https://docs.drone.io/pipeline/environment/reference/

matrixchat-notify.py

@@ -5,6 +5,7 @@ Requires:
 
 * <https://pypi.org/project/matrix-nio>
 * Optional: <https://pypi.org/project/bleach/>
+* Optional: <https://pypi.org/project/Jinja2/>
 * Optional: <https://pypi.org/project/markdown/>
 
 """
@@ -73,6 +74,7 @@ SETTINGS_KEYS = (
     "deviceid",
     "devicename",
     "homeserver",
+    "jinja",
     "markdown",
     "markdown_extensions",
     "pass_environment",
@@ -86,7 +88,7 @@ log = logging.getLogger(PROG)
 
 def tobool(s):
     try:
-        return strtobool(s)
+        return strtobool(str(s))
     except ValueError:
         return False
 
@@ -156,15 +158,15 @@ async def send_notification(config, message):
     await client.close()
 
 
-def render_message(config):
-    pass_environment = config.get("pass_environment", "")
+def get_template_context(config):
+    pass_environment = config.get("pass_environment", [])
 
     if not isinstance(pass_environment, list):
         pass_environment = [pass_environment]
 
     patterns = []
     for value in pass_environment:
-        # expand any comma-separetd names/patterns
+        # expand any comma-separated names/patterns
         if "," in value:
             patterns.extend([p.strip() for p in value.split(",") if p.strip()])
         else:
@@ -176,8 +178,23 @@ def render_message(config):
     for pattern in patterns:
         filtered_names.update(fnmatch.filter(env_names, pattern))
 
-    context = {name: os.environ[name] for name in tuple(filtered_names)}
+    return {name: os.environ[name] for name in tuple(filtered_names)}
+
+
+def render_message(config):
+    context = get_template_context(config)
     template = config.get("template", DEFAULT_TEMPLATE)
+
+    if tobool(config.get("jinja")):
+        try:
+            from jinja2.sandbox import SandboxedEnvironment
+
+            env = SandboxedEnvironment()
+            return env.from_string(template).render(context)
+        except Exception as exc:
+            log.error("Could not render Jinja2 template: %s", exc)
+            return template
+    else:
         return Template(template).safe_substitute(context)