fix(LambdaHandler): remove context option

The LambdaContext paramater for Validator#validate_event calls have bben removed
in order to avoid any tampering with the context object.

BREAKING CHANGE: The context option has been removed.

Author: sleistner

lambda_handlers/__init__.py

@@ -9,11 +9,7 @@
     InternalServerError,
 )
 from lambda_handlers.version import __version__  # noqa
-from lambda_handlers.handlers import (  # noqa
-    HTTPHandler,
-    EventHandler,
-    LambdaHandler,
-)
+from lambda_handlers.handlers import HTTPHandler, EventHandler, LambdaHandler  # noqa
 from lambda_handlers.response import cors_headers, response_builder  # noqa
 from lambda_handlers.formatters import input_format, output_format  # noqa
 from lambda_handlers.validators import jsonschema, marshmallow  # noqa

lambda_handlers/handlers/event_handler.py

@@ -42,7 +42,7 @@ def validator(self) -> Validator:
 
     def before(self, event, context):
         """Event hook called before the handler. It formats and validates `event`."""
-        return self.validate_event(self.format_input(event), context)
+        return self.validate_event(self.format_input(event)), context
 
     def after(self, result):
         """Event method called after the handler. It formats and validates `result`."""

lambda_handlers/handlers/http_handler.py

@@ -4,13 +4,7 @@
 from typing import Any, Dict
 
 from lambda_handlers.types import Headers, APIGatewayProxyResult
-from lambda_handlers.errors import (
-    FormatError,
-    NotFoundError,
-    BadRequestError,
-    ValidationError,
-    ResultValidationError,
-)
+from lambda_handlers.errors import FormatError, NotFoundError, BadRequestError, ValidationError, ResultValidationError
 from lambda_handlers.response import CORSHeaders
 from lambda_handlers.handlers.event_handler import EventHandler
 from lambda_handlers.response.response_builder import (
@@ -96,7 +90,8 @@ def _create_headers(self, headers: Headers) -> Headers:
 
         return headers or None
 
-    def _handle_error(self, error) -> APIGatewayProxyResult:
+    @staticmethod
+    def _handle_error(error) -> APIGatewayProxyResult:
         if isinstance(error, NotFoundError):
             return not_found(error.description)
         if isinstance(error, ResultValidationError):

lambda_handlers/handlers/lambda_handler.py

@@ -1,11 +1,11 @@
 """A base class for AWS Lambda handlers."""
 
 from abc import ABC
-from typing import Any, Dict, Tuple, Callable, Optional
+from typing import Any, Dict, Tuple, NewType, Callable, Optional
 from functools import wraps
 
 Event = Dict[str, Any]
-Context = Dict[str, Any]
+LambdaContext = NewType('LambdaContext', object)
 
 
 class LambdaHandler(ABC):
@@ -17,25 +17,20 @@ class LambdaHandler(ABC):
     def __init__(self, handler: Optional[Callable] = None):
         self._handler = handler
 
-    def __call__(self, handler: Callable):
-        """Decorate `handler`."""
+    def __call__(self, handler: Callable):  # noqa: D102
         @wraps(handler)
         def wrapper(event, context):
             return self._call_handler(handler, event, context)
+
         return wrapper
 
-    def _call_handler(
-        self,
-        handler: Callable,
-        event: Event,
-        context: Context,
-    ) -> Any:
+    def _call_handler(self, handler: Callable, event: Event, context: LambdaContext) -> Any:
         try:
             return self.after(handler(*self.before(event, context)))
         except Exception as exception:
             return self.on_exception(exception)
 
-    def before(self, event: Event, context: Context) -> Tuple[Event, Context]:
+    def before(self, event: Event, context: LambdaContext) -> Tuple[Event, LambdaContext]:
         """Event method to be called just before the handler is executed."""
         return event, context
 

lambda_handlers/handlers/mixins/validation_mixin.py

@@ -13,14 +13,12 @@ def validator(self):
         """Return the validator for events and results."""
         pass
 
-    def validate_event(self, event, context):
+    def validate_event(self, event):
         """Validate the event with `self.validator`, return event and context."""
         if self.validator:
-            transformed_event, transformed_context = self.validator.validate_event(event, context)
+            transformed_event = self.validator.validate_event(event)
             event.update(transformed_event)
-            if context is not None:
-                context.update(transformed_context)
-        return event, context
+        return event
 
     def validate_result(self, result: Dict[str, Any]) -> Dict[str, Any]:
         """Validate and return the result with `self.validator`."""

lambda_handlers/handlers/tests/test_lambda_handler.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from lambda_handlers.handlers.lambda_handler import Context, LambdaHandler
+from lambda_handlers.handlers.lambda_handler import LambdaContext, LambdaHandler
 
 Event = Dict[str, Any]
 
@@ -14,7 +14,7 @@ def __init__(self, message: str, event: Event):
 
 
 class CallOrderAwareHandler(LambdaHandler):
-    def before(self, event: Event, context: Context) -> Tuple[Event, Context]:
+    def before(self, event: Event, context: LambdaContext) -> Tuple[Event, LambdaContext]:
         event['route'].append('before')
         return super().before(event, context)
 

lambda_handlers/response/response_builder.py

@@ -4,13 +4,7 @@
 from typing import Any, Union
 
 from lambda_handlers.types import APIGatewayProxyResult
-from lambda_handlers.errors import (
-    LambdaError,
-    NotFoundError,
-    ForbiddenError,
-    BadRequestError,
-    InternalServerError,
-)
+from lambda_handlers.errors import LambdaError, NotFoundError, ForbiddenError, BadRequestError, InternalServerError
 
 
 def ok(result: Any) -> APIGatewayProxyResult:

lambda_handlers/validators/http/http_marshmallow_validator.py

@@ -1,9 +1,7 @@
 """A AWS HTTP event validator that uses Marshmallow."""
 
 from lambda_handlers.validators.http.http_validator import HttpValidator
-from lambda_handlers.validators.marshmallow_validator import (
-    MarshmallowValidator,
-)
+from lambda_handlers.validators.marshmallow_validator import MarshmallowValidator
 
 
 class HttpMarshmallowValidator(MarshmallowValidator, HttpValidator):

lambda_handlers/validators/http/tests/test_http_jsonschema_validator.py

@@ -2,9 +2,7 @@
 
 from lambda_handlers.validators.http.http_validator import HttpValidator
 from lambda_handlers.validators.jsonschema_validator import JSONSchemaValidator
-from lambda_handlers.validators.http.http_jsonschema_validator import (
-    HttpJSONSchemaValidator,
-)
+from lambda_handlers.validators.http.http_jsonschema_validator import HttpJSONSchemaValidator
 
 
 @pytest.fixture(scope='session')

lambda_handlers/validators/http/tests/test_http_marshmallow_validator.py

@@ -3,12 +3,8 @@
 
 from lambda_handlers.errors import EventValidationError
 from lambda_handlers.validators.http.http_validator import HttpValidator
-from lambda_handlers.validators.marshmallow_validator import (
-    MarshmallowValidator,
-)
-from lambda_handlers.validators.http.http_marshmallow_validator import (
-    HttpMarshmallowValidator,
-)
+from lambda_handlers.validators.marshmallow_validator import MarshmallowValidator
+from lambda_handlers.validators.http.http_marshmallow_validator import HttpMarshmallowValidator
 
 
 class TestHttpMarshmallowSchemaValidator:
@@ -39,19 +35,16 @@ def test_validate_valid_request(self, subject):
                 'accountable': True,
             },
         }
-        context = {}
-        assert subject.validate_event(event, context)
+        assert subject.validate_event(event)
 
     def test_validate_invalid_request(self, subject):
         event = {
             'pathParameters': {
                 'user_name': True,
             },
         }
-        context = {}
-
         with pytest.raises(EventValidationError) as error:
-            subject.validate_event(event, context)
+            subject.validate_event(event)
 
         nested_errors = error.value.description
         assert isinstance(nested_errors, list)