policies/expression: use pb_message() for messages instead of returning a tuple

passbook/core/models.py

@@ -13,7 +13,6 @@ from django.utils.translation import gettext_lazy as _
 from guardian.mixins import GuardianUserMixin
 from jinja2 import Undefined
 from jinja2.exceptions import TemplateSyntaxError, UndefinedError
-from jinja2.nativetypes import NativeEnvironment
 from model_utils.managers import InheritanceManager
 from structlog import get_logger
 
@@ -24,7 +23,6 @@ from passbook.lib.models import CreatedUpdatedModel
 from passbook.policies.models import PolicyBindingModel
 
 LOGGER = get_logger()
-NATIVE_ENVIRONMENT = NativeEnvironment()
 
 
 def default_token_duration():
@@ -208,8 +206,11 @@ class PropertyMapping(models.Model):
         self, user: Optional[User], request: Optional[HttpRequest], **kwargs
     ) -> Any:
         """Evaluate `self.expression` using `**kwargs` as Context."""
+        from passbook.policies.expression.evaluator import Evaluator
+
+        evaluator = Evaluator()
         try:
-            expression = NATIVE_ENVIRONMENT.from_string(self.expression)
+            expression = evaluator.env.from_string(self.expression)
         except TemplateSyntaxError as exc:
             raise PropertyMappingExpressionException from exc
         try:
@@ -221,8 +222,11 @@ class PropertyMapping(models.Model):
             raise PropertyMappingExpressionException from exc
 
     def save(self, *args, **kwargs):
+        from passbook.policies.expression.evaluator import Evaluator
+
+        evaluator = Evaluator()
         try:
-            NATIVE_ENVIRONMENT.from_string(self.expression)
+            evaluator.env.from_string(self.expression)
         except TemplateSyntaxError as exc:
             raise ValidationError("Expression Syntax Error") from exc
         return super().save(*args, **kwargs)

passbook/policies/expression/evaluator.py

@@ -1,8 +1,9 @@
 """passbook expression policy evaluator"""
 import re
-from typing import TYPE_CHECKING, Any, Dict, Optional
+from typing import TYPE_CHECKING, Any, Dict, List, Optional
 
 from django.core.exceptions import ValidationError
+from django.http import HttpRequest
 from jinja2 import Undefined
 from jinja2.exceptions import TemplateSyntaxError
 from jinja2.nativetypes import NativeEnvironment
@@ -25,12 +26,32 @@ class Evaluator:
 
     _env: NativeEnvironment
 
+    _context: Dict[str, Any]
+    _messages: List[str]
+
     def __init__(self):
-        self._env = NativeEnvironment()
+        self._env = NativeEnvironment(
+            extensions=["jinja2.ext.do",],
+            trim_blocks=True,
+            lstrip_blocks=True,
+            line_statement_prefix=">",
+        )
         # update passbook/policies/expression/templates/policy/expression/form.html
         # update docs/policies/expression/index.md
         self._env.filters["regex_match"] = Evaluator.jinja2_filter_regex_match
         self._env.filters["regex_replace"] = Evaluator.jinja2_filter_regex_replace
+        self._env.globals["pb_message"] = self.jinja2_func_message
+        self._context = {
+            "pb_is_group_member": Evaluator.jinja2_func_is_group_member,
+            "pb_logger": get_logger(),
+            "requests": Session(),
+        }
+        self._messages = []
+
+    @property
+    def env(self) -> NativeEnvironment:
+        """Access to our custom NativeEnvironment"""
+        return self._env
 
     @staticmethod
     def jinja2_filter_regex_match(value: Any, regex: str) -> bool:
@@ -47,52 +68,57 @@ class Evaluator:
         """Check if `user` is member of group with name `group_name`"""
         return user.groups.filter(name=group_name).exists()
 
-    def _get_expression_context(
-        self, request: PolicyRequest, **kwargs
-    ) -> Dict[str, Any]:
-        """Return dictionary with additional global variables passed to expression"""
+    def jinja2_func_message(self, message: str):
+        """Wrapper to append to messages list, which is returned with PolicyResult"""
+        self._messages.append(message)
+
+    def set_policy_request(self, request: PolicyRequest):
+        """Update context based on policy request (if http request is given, update that too)"""
         # update passbook/policies/expression/templates/policy/expression/form.html
         # update docs/policies/expression/index.md
-        kwargs["pb_is_group_member"] = Evaluator.jinja2_func_is_group_member
-        kwargs["pb_logger"] = get_logger()
-        kwargs["requests"] = Session()
-        kwargs["pb_is_sso_flow"] = request.context.get(PLAN_CONTEXT_SSO, False)
+        self._context["pb_is_sso_flow"] = request.context.get(PLAN_CONTEXT_SSO, False)
+        self._context["request"] = request
         if request.http_request:
-            kwargs["pb_client_ip"] = (
+            self.set_http_request(request.http_request)
+
+    def set_http_request(self, request: HttpRequest):
+        """Update context based on http request"""
+        # update passbook/policies/expression/templates/policy/expression/form.html
+        # update docs/policies/expression/index.md
+        self._context["pb_client_ip"] = (
             get_client_ip(request.http_request) or "255.255.255.255"
         )
+        self._context["request"] = request
         if SESSION_KEY_PLAN in request.http_request.session:
-                kwargs["pb_flow_plan"] = request.http_request.session[SESSION_KEY_PLAN]
-        return kwargs
+            self._context["pb_flow_plan"] = request.http_request.session[
+                SESSION_KEY_PLAN
+            ]
 
-    def evaluate(self, expression_source: str, request: PolicyRequest) -> PolicyResult:
-        """Parse and evaluate expression.
-        If the Expression evaluates to a list with 2 items, the first is used as passing bool and
-        the second as messages.
-        If the Expression evaluates to a truthy-object, it is used as passing bool."""
+    def evaluate(self, expression_source: str) -> PolicyResult:
+        """Parse and evaluate expression. Policy is expected to return a truthy object.
+        Messages can be added using 'do pb_message()'."""
         try:
-            expression = self._env.from_string(expression_source)
+            expression = self._env.from_string(expression_source.lstrip().rstrip())
         except TemplateSyntaxError as exc:
             return PolicyResult(False, str(exc))
         try:
-            result: Optional[Any] = expression.render(
-                request=request, **self._get_expression_context(request)
-            )
+            result: Optional[Any] = expression.render(self._context)
+        except Exception as exc:  # pylint: disable=broad-except
+            LOGGER.warning("Expression error", exc=exc)
+            return PolicyResult(False, str(exc))
+        else:
+            policy_result = PolicyResult(False)
+            policy_result.messages = tuple(self._messages)
             if isinstance(result, Undefined):
                 LOGGER.warning(
                     "Expression policy returned undefined",
                     src=expression_source,
-                    req=request,
+                    req=self._context,
                 )
-                return PolicyResult(False)
-            if isinstance(result, (list, tuple)) and len(result) == 2:
-                return PolicyResult(*result)
+                policy_result.passing = False
             if result:
-                return PolicyResult(bool(result))
-            return PolicyResult(False)
-        except Exception as exc:  # pylint: disable=broad-except
-            LOGGER.warning("Expression error", exc=exc)
-            return PolicyResult(False, str(exc))
+                policy_result.passing = bool(result)
+            return policy_result
 
     def validate(self, expression: str):
         """Validate expression's syntax, raise ValidationError if Syntax is invalid"""

passbook/policies/expression/models.py

@@ -16,7 +16,9 @@ class ExpressionPolicy(Policy):
 
     def passes(self, request: PolicyRequest) -> PolicyResult:
         """Evaluate and render expression. Returns PolicyResult(false) on error."""
-        return Evaluator().evaluate(self.expression, request)
+        evaluator = Evaluator()
+        evaluator.set_policy_request(request)
+        return evaluator.evaluate(self.expression)
 
     def save(self, *args, **kwargs):
         Evaluator().validate(self.expression)

passbook/policies/expression/tests/test_evaluator.py

@@ -17,13 +17,15 @@ class TestEvaluator(TestCase):
         """test simple value expression"""
         template = "True"
         evaluator = Evaluator()
-        self.assertEqual(evaluator.evaluate(template, self.request).passing, True)
+        evaluator.set_policy_request(self.request)
+        self.assertEqual(evaluator.evaluate(template).passing, True)
 
     def test_messages(self):
         """test expression with message return"""
-        template = "False, 'some message'"
+        template = '{% do pb_message("some message") %}False'
         evaluator = Evaluator()
-        result = evaluator.evaluate(template, self.request)
+        evaluator.set_policy_request(self.request)
+        result = evaluator.evaluate(template)
         self.assertEqual(result.passing, False)
         self.assertEqual(result.messages, ("some message",))
 
@@ -31,7 +33,8 @@ class TestEvaluator(TestCase):
         """test invalid syntax"""
         template = "{%"
         evaluator = Evaluator()
-        result = evaluator.evaluate(template, self.request)
+        evaluator.set_policy_request(self.request)
+        result = evaluator.evaluate(template)
         self.assertEqual(result.passing, False)
         self.assertEqual(result.messages, ("tag name expected",))
 
@@ -39,7 +42,8 @@ class TestEvaluator(TestCase):
         """test undefined result"""
         template = "{{ foo.bar }}"
         evaluator = Evaluator()
-        result = evaluator.evaluate(template, self.request)
+        evaluator.set_policy_request(self.request)
+        result = evaluator.evaluate(template)
         self.assertEqual(result.passing, False)
         self.assertEqual(result.messages, ("'foo' is undefined",))