Extract ASGI scope creation into function (Kludex#162)

* 🏗 simplify magnum call function

extract scope and request body creation into a dedicated functions

* 📝 add documentation to create scope function

Author: ediskandarov-cur

mangum/adapter.py

@@ -6,7 +6,7 @@
 from dataclasses import dataclass, InitVar
 from contextlib import ExitStack
 
-from mangum.types import ASGIApp
+from mangum.types import ASGIApp, Scope
 from mangum.protocols.lifespan import LifespanCycle
 from mangum.protocols.http import HTTPCycle
 from mangum.exceptions import ConfigurationError
@@ -91,89 +91,102 @@ def __call__(self, event: dict, context: "LambdaContext") -> dict:
                 )
                 stack.enter_context(lifespan_cycle)
 
-            request_context = event["requestContext"]
-
-            if event.get("multiValueHeaders"):
-                headers = {
-                    k.lower(): ", ".join(v) if isinstance(v, list) else ""
-                    for k, v in event.get("multiValueHeaders", {}).items()
-                }
-            elif event.get("headers"):
-                headers = {k.lower(): v for k, v in event.get("headers", {}).items()}
-            else:
-                headers = {}
-
-            # API Gateway v2
-            if event.get("version") == "2.0":
-                source_ip = request_context["http"]["sourceIp"]
-                path = request_context["http"]["path"]
-                http_method = request_context["http"]["method"]
-                query_string = event.get("rawQueryString", "").encode()
-
-                if event.get("cookies"):
-                    headers["cookie"] = "; ".join(event.get("cookies", []))
-
-            # API Gateway v1 / ELB
-            else:
-                if "elb" in request_context:
-                    # NOTE: trust only the most right side value
-                    source_ip = headers.get("x-forwarded-for", "").split(", ")[-1]
-                else:
-                    source_ip = request_context.get("identity", {}).get("sourceIp")
-
-                path = event["path"]
-                http_method = event["httpMethod"]
-
-                if event.get("multiValueQueryStringParameters"):
-                    query_string = urllib.parse.urlencode(
-                        event.get("multiValueQueryStringParameters", {}), doseq=True
-                    ).encode()
-                elif event.get("queryStringParameters"):
-                    query_string = urllib.parse.urlencode(
-                        event.get("queryStringParameters", {})
-                    ).encode()
-                else:
-                    query_string = b""
-
-            server_name = headers.get("host", "mangum")
-            if ":" not in server_name:
-                server_port = headers.get("x-forwarded-port", 80)
-            else:
-                server_name, server_port = server_name.split(":")  # pragma: no cover
-            server = (server_name, int(server_port))
-            client = (source_ip, 0)
-
-            if not path:  # pragma: no cover
-                path = "/"
-            elif self.api_gateway_base_path:
-                if path.startswith(self.api_gateway_base_path):
-                    path = path[len(self.api_gateway_base_path) :]
-
-            scope = {
-                "type": "http",
-                "http_version": "1.1",
-                "method": http_method,
-                "headers": [[k.encode(), v.encode()] for k, v in headers.items()],
-                "path": urllib.parse.unquote(path),
-                "raw_path": None,
-                "root_path": "",
-                "scheme": headers.get("x-forwarded-proto", "https"),
-                "query_string": query_string,
-                "server": server,
-                "client": client,
-                "asgi": {"version": "3.0"},
-                "aws.event": event,
-                "aws.context": context,
-            }
-
             is_binary = event.get("isBase64Encoded", False)
             initial_body = event.get("body") or b""
             if is_binary:
                 initial_body = base64.b64decode(initial_body)
             elif not isinstance(initial_body, bytes):
                 initial_body = initial_body.encode()
 
+            scope = self._create_scope(event, context)
             http_cycle = HTTPCycle(scope, text_mime_types=self.text_mime_types)
             response = http_cycle(self.app, initial_body)
 
         return response
+
+    def _create_scope(self, event: dict, context: "LambdaContext") -> Scope:
+        """Creates a scope object according to ASGI specification from a Lambda Event.
+
+        https://asgi.readthedocs.io/en/latest/specs/www.html#http-connection-scope
+
+        The event comes from various sources: AWS ALB, AWS API Gateway of different
+        versions and configurations(multivalue header, etc).
+        Thus, some heuristics is applied to guess an event type.
+
+        """
+        request_context = event["requestContext"]
+
+        if event.get("multiValueHeaders"):
+            headers = {
+                k.lower(): ", ".join(v) if isinstance(v, list) else ""
+                for k, v in event.get("multiValueHeaders", {}).items()
+            }
+        elif event.get("headers"):
+            headers = {k.lower(): v for k, v in event.get("headers", {}).items()}
+        else:
+            headers = {}
+
+        # API Gateway v2
+        if event.get("version") == "2.0":
+            source_ip = request_context["http"]["sourceIp"]
+            path = request_context["http"]["path"]
+            http_method = request_context["http"]["method"]
+            query_string = event.get("rawQueryString", "").encode()
+
+            if event.get("cookies"):
+                headers["cookie"] = "; ".join(event.get("cookies", []))
+
+        # API Gateway v1 / ELB
+        else:
+            if "elb" in request_context:
+                # NOTE: trust only the most right side value
+                source_ip = headers.get("x-forwarded-for", "").split(", ")[-1]
+            else:
+                source_ip = request_context.get("identity", {}).get("sourceIp")
+
+            path = event["path"]
+            http_method = event["httpMethod"]
+
+            if event.get("multiValueQueryStringParameters"):
+                query_string = urllib.parse.urlencode(
+                    event.get("multiValueQueryStringParameters", {}), doseq=True
+                ).encode()
+            elif event.get("queryStringParameters"):
+                query_string = urllib.parse.urlencode(
+                    event.get("queryStringParameters", {})
+                ).encode()
+            else:
+                query_string = b""
+
+        server_name = headers.get("host", "mangum")
+        if ":" not in server_name:
+            server_port = headers.get("x-forwarded-port", 80)
+        else:
+            server_name, server_port = server_name.split(":")  # pragma: no cover
+        server = (server_name, int(server_port))
+        client = (source_ip, 0)
+
+        if not path:  # pragma: no cover
+            path = "/"
+        elif self.api_gateway_base_path:
+            if path.startswith(self.api_gateway_base_path):
+                path = path[len(self.api_gateway_base_path) :]
+
+        scope = {
+            "type": "http",
+            "http_version": "1.1",
+            "method": http_method,
+            "headers": [[k.encode(), v.encode()] for k, v in headers.items()],
+            "path": urllib.parse.unquote(path),
+            "raw_path": None,
+            "root_path": "",
+            "scheme": headers.get("x-forwarded-proto", "https"),
+            "query_string": query_string,
+            "server": server,
+            "client": client,
+            "asgi": {"version": "3.0"},
+            "aws.event": event,
+            "aws.context": context,
+        }
+
+        return scope