refactor(event-handler): Add ResponseBuilder and more docs (#412)

Author: Michael Brewer

aws_lambda_powertools/event_handler/api_gateway.py

@@ -12,14 +12,57 @@
 
 
 class ProxyEventType(Enum):
+    """An enumerations of the supported proxy event types.
+
+    **NOTE:** api_gateway is an alias of http_api_v1"""
+
     http_api_v1 = "APIGatewayProxyEvent"
     http_api_v2 = "APIGatewayProxyEventV2"
     alb_event = "ALBEvent"
     api_gateway = http_api_v1
 
 
 class CORSConfig(object):
-    """CORS Config"""
+    """CORS Config
+
+
+    Examples
+    --------
+
+    Simple cors example using the default permissive cors, not this should only be used during early prototyping
+
+        >>> from aws_lambda_powertools.event_handler.api_gateway import ApiGatewayResolver
+        >>>
+        >>> app = ApiGatewayResolver()
+        >>>
+        >>> @app.get("/my/path", cors=True)
+        >>> def with_cors():
+        >>>      return {"message": "Foo"}
+
+    Using a custom CORSConfig where `with_cors` used the custom provided CORSConfig and `without_cors`
+    do not include any cors headers.
+
+        >>> from aws_lambda_powertools.event_handler.api_gateway import (
+        >>>    ApiGatewayResolver, CORSConfig
+        >>> )
+        >>>
+        >>> cors_config = CORSConfig(
+        >>>    allow_origin="https://wwww.example.com/",
+        >>>    expose_headers=["x-exposed-response-header"],
+        >>>    allow_headers=["x-custom-request-header"],
+        >>>    max_age=100,
+        >>>    allow_credentials=True,
+        >>> )
+        >>> app = ApiGatewayResolver(cors=cors_config)
+        >>>
+        >>> @app.get("/my/path", cors=True)
+        >>> def with_cors():
+        >>>      return {"message": "Foo"}
+        >>>
+        >>> @app.get("/another-one")
+        >>> def without_cors():
+        >>>     return {"message": "Foo"}
+    """
 
     _REQUIRED_HEADERS = ["Authorization", "Content-Type", "X-Amz-Date", "X-Api-Key", "X-Amz-Security-Token"]
 
@@ -55,6 +98,7 @@ def __init__(
         self.allow_credentials = allow_credentials
 
     def to_dict(self) -> Dict[str, str]:
+        """Builds the configured Access-Control http headers"""
         headers = {
             "Access-Control-Allow-Origin": self.allow_origin,
             "Access-Control-Allow-Headers": ",".join(sorted(self.allow_headers)),
@@ -68,7 +112,37 @@ def to_dict(self) -> Dict[str, str]:
         return headers
 
 
+class Response:
+    """Response data class that provides greater control over what is returned from the proxy event"""
+
+    def __init__(
+        self, status_code: int, content_type: Optional[str], body: Union[str, bytes, None], headers: Dict = None
+    ):
+        """
+
+        Parameters
+        ----------
+        status_code: int
+            Http status code, example 200
+        content_type: str
+            Optionally set the Content-Type header, example "application/json". Note this will be merged into any
+            provided http headers
+        body: Union[str, bytes, None]
+            Optionally set the response body. Note: bytes body will be automatically base64 encoded
+        headers: dict
+            Optionally set specific http headers. Setting "Content-Type" hear would override the `content_type` value.
+        """
+        self.status_code = status_code
+        self.body = body
+        self.base64_encoded = False
+        self.headers: Dict = headers or {}
+        if content_type:
+            self.headers.setdefault("Content-Type", content_type)
+
+
 class Route:
+    """Internally used Route Configuration"""
+
     def __init__(
         self, method: str, rule: Any, func: Callable, cors: bool, compress: bool, cache_control: Optional[str]
     ):
@@ -80,68 +154,125 @@ def __init__(
         self.cache_control = cache_control
 
 
-class Response:
-    def __init__(
-        self, status_code: int, content_type: Optional[str], body: Union[str, bytes, None], headers: Dict = None
-    ):
-        self.status_code = status_code
-        self.body = body
-        self.base64_encoded = False
-        self.headers: Dict = headers or {}
-        if content_type:
-            self.headers.setdefault("Content-Type", content_type)
+class ResponseBuilder:
+    """Internally used Response builder"""
 
-    def add_cors(self, cors: CORSConfig):
-        self.headers.update(cors.to_dict())
+    def __init__(self, response: Response, route: Route = None):
+        self.response = response
+        self.route = route
 
-    def add_cache_control(self, cache_control: str):
-        self.headers["Cache-Control"] = cache_control if self.status_code == 200 else "no-cache"
+    def _add_cors(self, cors: CORSConfig):
+        """Update headers to include the configured Access-Control headers"""
+        self.response.headers.update(cors.to_dict())
 
-    def compress(self):
-        self.headers["Content-Encoding"] = "gzip"
-        if isinstance(self.body, str):
-            self.body = bytes(self.body, "utf-8")
-        gzip = zlib.compressobj(9, zlib.DEFLATED, zlib.MAX_WBITS | 16)
-        self.body = gzip.compress(self.body) + gzip.flush()
+    def _add_cache_control(self, cache_control: str):
+        """Set the specified cache control headers for 200 http responses. For non-200 `no-cache` is used."""
+        self.response.headers["Cache-Control"] = cache_control if self.response.status_code == 200 else "no-cache"
 
-    def to_dict(self) -> Dict[str, Any]:
-        if isinstance(self.body, bytes):
-            self.base64_encoded = True
-            self.body = base64.b64encode(self.body).decode()
+    def _compress(self):
+        """Compress the response body, but only if `Accept-Encoding` headers includes gzip."""
+        self.response.headers["Content-Encoding"] = "gzip"
+        if isinstance(self.response.body, str):
+            self.response.body = bytes(self.response.body, "utf-8")
+        gzip = zlib.compressobj(9, zlib.DEFLATED, zlib.MAX_WBITS | 16)
+        self.response.body = gzip.compress(self.response.body) + gzip.flush()
+
+    def _route(self, event: BaseProxyEvent, cors: Optional[CORSConfig]):
+        """Optionally handle any of the route's configure response handling"""
+        if self.route is None:
+            return
+        if self.route.cors:
+            self._add_cors(cors or CORSConfig())
+        if self.route.cache_control:
+            self._add_cache_control(self.route.cache_control)
+        if self.route.compress and "gzip" in (event.get_header_value("accept-encoding", "") or ""):
+            self._compress()
+
+    def build(self, event: BaseProxyEvent, cors: CORSConfig = None) -> Dict[str, Any]:
+        """Build the full response dict to be returned by the lambda"""
+        self._route(event, cors)
+
+        if isinstance(self.response.body, bytes):
+            self.response.base64_encoded = True
+            self.response.body = base64.b64encode(self.response.body).decode()
         return {
-            "statusCode": self.status_code,
-            "headers": self.headers,
-            "body": self.body,
-            "isBase64Encoded": self.base64_encoded,
+            "statusCode": self.response.status_code,
+            "headers": self.response.headers,
+            "body": self.response.body,
+            "isBase64Encoded": self.response.base64_encoded,
         }
 
 
 class ApiGatewayResolver:
+    """API Gateway and ALB proxy resolver
+
+    Examples
+    --------
+    Simple example with a custom lambda handler using the Tracer capture_lambda_handler decorator
+
+        >>> from aws_lambda_powertools import Tracer
+        >>> from aws_lambda_powertools.event_handler.api_gateway import (
+        >>>    ApiGatewayResolver
+        >>> )
+        >>>
+        >>> tracer = Tracer()
+        >>> app = ApiGatewayResolver()
+        >>>
+        >>> @app.get("/get-call")
+        >>> def simple_get():
+        >>>      return {"message": "Foo"}
+        >>>
+        >>> @app.post("/post-call")
+        >>> def simple_post():
+        >>>     post_data: dict = app.current_event.json_body
+        >>>     return {"message": post_data["value"]}
+        >>>
+        >>> @tracer.capture_lambda_handler
+        >>> def lambda_handler(event, context):
+        >>>    return app.resolve(event, context)
+
+    """
+
     current_event: BaseProxyEvent
     lambda_context: LambdaContext
 
     def __init__(self, proxy_type: Enum = ProxyEventType.http_api_v1, cors: CORSConfig = None):
+        """
+        Parameters
+        ----------
+        proxy_type: ProxyEventType
+            Proxy request type, defaults to API Gateway V1
+        cors: CORSConfig
+            Optionally configure and enabled CORS. Not each route will need to have to cors=True
+        """
         self._proxy_type = proxy_type
         self._routes: List[Route] = []
         self._cors = cors
         self._cors_methods: Set[str] = {"OPTIONS"}
 
     def get(self, rule: str, cors: bool = False, compress: bool = False, cache_control: str = None):
+        """Get route decorator with GET `method`"""
         return self.route(rule, "GET", cors, compress, cache_control)
 
     def post(self, rule: str, cors: bool = False, compress: bool = False, cache_control: str = None):
+        """Post route decorator with POST `method`"""
         return self.route(rule, "POST", cors, compress, cache_control)
 
     def put(self, rule: str, cors: bool = False, compress: bool = False, cache_control: str = None):
+        """Put route decorator with PUT `method`"""
         return self.route(rule, "PUT", cors, compress, cache_control)
 
     def delete(self, rule: str, cors: bool = False, compress: bool = False, cache_control: str = None):
+        """Delete route decorator with DELETE `method`"""
         return self.route(rule, "DELETE", cors, compress, cache_control)
 
     def patch(self, rule: str, cors: bool = False, compress: bool = False, cache_control: str = None):
+        """Patch route decorator with PATCH `method`"""
         return self.route(rule, "PATCH", cors, compress, cache_control)
 
     def route(self, rule: str, method: str, cors: bool = False, compress: bool = False, cache_control: str = None):
+        """Route decorator includes parameter `method`"""
+
         def register_resolver(func: Callable):
             self._routes.append(Route(method, self._compile_regex(rule), func, cors, compress, cache_control))
             if cors:
@@ -151,60 +282,87 @@ def register_resolver(func: Callable):
         return register_resolver
 
     def resolve(self, event, context) -> Dict[str, Any]:
-        self.current_event = self._to_data_class(event)
-        self.lambda_context = context
-        route, response = self._find_route(self.current_event.http_method.upper(), self.current_event.path)
-        if route is None:  # No matching route was found
-            return response.to_dict()
+        """Resolves the response based on the provide event and decorator routes
 
-        if route.cors:
-            response.add_cors(self._cors or CORSConfig())
-        if route.cache_control:
-            response.add_cache_control(route.cache_control)
-        if route.compress and "gzip" in (self.current_event.get_header_value("accept-encoding") or ""):
-            response.compress()
+        Parameters
+        ----------
+        event: Dict[str, Any]
+            Event
+        context: LambdaContext
+            Lambda context
+        Returns
+        -------
+        dict
+            Returns the dict response
+        """
+        self.current_event = self._to_proxy_event(event)
+        self.lambda_context = context
+        return self._resolve().build(self.current_event, self._cors)
 
-        return response.to_dict()
+    def __call__(self, event, context) -> Any:
+        return self.resolve(event, context)
 
     @staticmethod
     def _compile_regex(rule: str):
+        """Precompile regex pattern"""
         rule_regex: str = re.sub(r"(<\w+>)", r"(?P\1.+)", rule)
         return re.compile("^{}$".format(rule_regex))
 
-    def _to_data_class(self, event: Dict) -> BaseProxyEvent:
+    def _to_proxy_event(self, event: Dict) -> BaseProxyEvent:
+        """Convert the event dict to the corresponding data class"""
         if self._proxy_type == ProxyEventType.http_api_v1:
             return APIGatewayProxyEvent(event)
         if self._proxy_type == ProxyEventType.http_api_v2:
             return APIGatewayProxyEventV2(event)
         return ALBEvent(event)
 
-    def _find_route(self, method: str, path: str) -> Tuple[Optional[Route], Response]:
+    def _resolve(self) -> ResponseBuilder:
+        """Resolves the response or return the not found response"""
+        method = self.current_event.http_method.upper()
+        path = self.current_event.path
         for route in self._routes:
             if method != route.method:
                 continue
             match: Optional[re.Match] = route.rule.match(path)
             if match:
                 return self._call_route(route, match.groupdict())
 
+        return self._not_found(method, path)
+
+    def _not_found(self, method: str, path: str) -> ResponseBuilder:
+        """Called when no matching route was found and includes support for the cors preflight response"""
         headers = {}
         if self._cors:
             headers.update(self._cors.to_dict())
+
             if method == "OPTIONS":  # Preflight
                 headers["Access-Control-Allow-Methods"] = ",".join(sorted(self._cors_methods))
-                return None, Response(status_code=204, content_type=None, body=None, headers=headers)
+                return ResponseBuilder(Response(status_code=204, content_type=None, headers=headers, body=None))
 
-        return None, Response(
-            status_code=404,
-            content_type="application/json",
-            body=json.dumps({"message": f"No route found for '{method}.{path}'"}),
-            headers=headers,
+        return ResponseBuilder(
+            Response(
+                status_code=404,
+                content_type="application/json",
+                headers=headers,
+                body=json.dumps({"message": f"No route found for '{method}.{path}'"}),
+            )
         )
 
-    def _call_route(self, route: Route, args: Dict[str, str]) -> Tuple[Route, Response]:
-        return route, self._to_response(route.func(**args))
+    def _call_route(self, route: Route, args: Dict[str, str]) -> ResponseBuilder:
+        """Actually call the matching route with any provided keyword arguments."""
+        return ResponseBuilder(self._to_response(route.func(**args)), route)
 
     @staticmethod
     def _to_response(result: Union[Tuple[int, str, Union[bytes, str]], Dict, Response]) -> Response:
+        """Convert the route's result to a Response
+
+         3 main result types are supported:
+
+        - Tuple[int, str, bytes] and Tuple[int, str, str]: status code, content-type and body (str|bytes)
+        - Dict[str, Any]: Rest api response with just the Dict to json stringify and content-type is set to
+          application/json
+        - Response: returned as is, and allows for more flexibility
+        """
         if isinstance(result, Response):
             return result
         elif isinstance(result, dict):
@@ -215,6 +373,3 @@ def _to_response(result: Union[Tuple[int, str, Union[bytes, str]], Dict, Respons
             )
         else:  # Tuple[int, str, Union[bytes, str]]
             return Response(*result)
-
-    def __call__(self, event, context) -> Any:
-        return self.resolve(event, context)