template: add support for Jinja2 template evaluation

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

moonraker/components/template.py

@@ -0,0 +1,66 @@
+# Template Factory helper
+#
+# Copyright (C) 2021 Eric Callahan <arksine.code@gmail.com>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+from __future__ import annotations
+import logging
+import jinja2
+import json
+
+# Annotation imports
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Dict
+)
+
+if TYPE_CHECKING:
+    from moonraker import Server
+    from confighelper import ConfigHelper
+
+class TemplateFactory:
+    def __init__(self, config: ConfigHelper) -> None:
+        self.server = config.get_server()
+        self.jenv = jinja2.Environment('{%', '%}', '{', '}')
+        self.jenv.add_extension("jinja2.ext.do")
+        self.jenv.filters['fromjson'] = json.loads
+        self.add_environment_global('raise_error', self._raise_error)
+
+    def add_environment_global(self, name: str, value: Any):
+        if name in self.jenv.globals:
+            raise self.server.error(
+                f"Jinja 2 environment already contains global {name}")
+        self.jenv.globals[name] = value
+
+    def _raise_error(self, err_msg: str, err_code: int = 400) -> None:
+        raise self.server.error(err_msg, err_code)
+
+    def create_template(self, source: str) -> JinjaTemplate:
+        return JinjaTemplate(source, self.server, self.jenv)
+
+class JinjaTemplate:
+    def __init__(self,
+                 source: str,
+                 server: Server,
+                 env: jinja2.Environment
+                 ) -> None:
+        self.server = server
+        self.orig_source = source.strip()
+        try:
+            self.template = env.from_string(self.orig_source)
+        except Exception:
+            logging.exception(f"Error creating template from source:\n{source}")
+            raise
+
+    def render(self, context: Dict[str, Any] = {}) -> str:
+        try:
+            return self.template.render(context).strip()
+        except Exception as e:
+            raise self.server.error("Error rendering template") from e
+
+    def __str__(self) -> str:
+        return self.orig_source
+
+def load_component(config: ConfigHelper) -> TemplateFactory:
+    return TemplateFactory(config)

scripts/moonraker-requirements.txt

@@ -11,3 +11,4 @@ paho-mqtt==1.5.1
 pycurl==7.44.1
 zeroconf==0.37.0
 preprocess-cancellation==0.1.6
+jinja2==3.0.3