feat: support for local Event invocation type

Author: monroeclinton

samcli/commands/local/lib/local_lambda.py

@@ -96,6 +96,43 @@ def __init__(
         self.container_host_interface = container_host_interface
         self.extra_hosts = extra_hosts
 
+    def get_function(self, function_identifier: str) -> Function:
+        """
+        Get a Lambda function by identifier, raising FunctionNotFound if not found.
+
+        Parameters
+        ----------
+        function_identifier : str
+            Identifier of the Lambda function, it can be logicalID, function name or full path
+
+        Returns
+        -------
+        Function
+            The Lambda function configuration
+
+        Raises
+        ------
+        InvalidFunctionNameException
+            When the function identifier doesn't match AWS Lambda's validation pattern
+        FunctionNotFound
+            When we cannot find a function with the given identifier
+        """
+        # Normalize function identifier from ARN if provided
+        normalized_function_identifier = normalize_sam_function_identifier(function_identifier)
+
+        # Generate the correct configuration based on given inputs
+        function = self.provider.get(normalized_function_identifier)
+
+        if not function:
+            all_function_full_paths = [f.full_path for f in self.provider.get_all()]
+            available_function_message = "{} not found. Possible options in your template: {}".format(
+                function_identifier, all_function_full_paths
+            )
+            LOG.info(available_function_message)
+            raise FunctionNotFound("Unable to find a Function with name '{}'".format(function_identifier))
+
+        return function
+
     def invoke(
         self,
         function_identifier: str,
@@ -138,19 +175,8 @@ def invoke(
         FunctionNotfound
             When we cannot find a function with the given name
         """
-        # Normalize function identifier from ARN if provided
-        normalized_function_identifier = normalize_sam_function_identifier(function_identifier)
-
-        # Generate the correct configuration based on given inputs
-        function = self.provider.get(normalized_function_identifier)
-
-        if not function:
-            all_function_full_paths = [f.full_path for f in self.provider.get_all()]
-            available_function_message = "{} not found. Possible options in your template: {}".format(
-                function_identifier, all_function_full_paths
-            )
-            LOG.info(available_function_message)
-            raise FunctionNotFound("Unable to find a Function with name '{}'".format(function_identifier))
+        # Get the function configuration
+        function = self.get_function(function_identifier)
 
         LOG.debug("Found one Lambda function with name '%s'", function_identifier)
         if function.packagetype == ZIP:

samcli/local/lambda_service/local_lambda_http_service.py

@@ -3,6 +3,7 @@
 import io
 import json
 import logging
+from concurrent.futures import ThreadPoolExecutor
 from datetime import datetime
 from urllib.parse import unquote
 
@@ -11,6 +12,7 @@
 
 from samcli.commands.local.cli_common.durable_context import DurableContext
 from samcli.commands.local.lib.exceptions import TenantIdValidationError, UnsupportedInlineCodeError
+from samcli.lib.utils.invocation_type import EVENT
 from samcli.lib.utils.name_utils import InvalidFunctionNameException, normalize_sam_function_identifier
 from samcli.lib.utils.stream_writer import StreamWriter
 from samcli.local.docker.exceptions import DockerContainerCreationFailedException
@@ -67,6 +69,7 @@ def __init__(self, lambda_runner, port, host, stderr=None, ssl_context=None):
         super().__init__(lambda_runner.is_debugging(), port=port, host=host, ssl_context=ssl_context)
         self.lambda_runner = lambda_runner
         self.stderr = stderr
+        self.executor = ThreadPoolExecutor()
 
     def create(self):
         """
@@ -240,32 +243,36 @@ def _invoke_request_handler(self, function_name):
         # Extract durable execution name from headers
         durable_execution_name = flask_request.headers.get("X-Amz-Durable-Execution-Name")
 
-        stdout_stream_string = io.StringIO()
-        stdout_stream_bytes = io.BytesIO()
-        stdout_stream_writer = StreamWriter(stdout_stream_string, stdout_stream_bytes, auto_flush=True)
+        arguments = {
+            "function_name": function_name,
+            "request_data": request_data,
+            "invocation_type": invocation_type,
+            "durable_execution_name": durable_execution_name,
+            "tenant_id": tenant_id,
+        }
+
+        headers = {"Content-Type": "application/json"}
+
+        if invocation_type == EVENT:
+            # Validate function exists before submitting async task
+            if validation_error := self._validate_function_for_invocation(function_name):
+                return validation_error
+
+            self.executor.submit(self._invoke_async_lambda, **arguments)
+            return self.service_response("", headers, 202)
 
         try:
-            # Normalize function name from ARN if provided
-            normalized_function_name = normalize_sam_function_identifier(function_name)
-
-            invoke_headers = self.lambda_runner.invoke(
-                normalized_function_name,
-                request_data,
-                invocation_type=invocation_type,
-                durable_execution_name=durable_execution_name,
-                tenant_id=tenant_id,
-                stdout=stdout_stream_writer,
-                stderr=self.stderr,
-            )
+            invoke_headers, stdout_stream_string, stdout_stream_bytes = self._invoke_lambda(**arguments)
         except (InvalidFunctionNameException, TenantIdValidationError) as e:
             LOG.error("Validation error: %s", str(e))
             return LambdaErrorResponses.validation_exception(str(e))
         except UnsupportedInvocationType as e:
-            LOG.warning("invocation-type: %s is not supported. RequestResponse is only supported.", invocation_type)
+            LOG.warning(
+                "invocation-type: %s is not supported. Event and RequestResponse are only supported.", invocation_type
+            )
             return LambdaErrorResponses.not_implemented_locally(str(e))
         except FunctionNotFound:
-            LOG.debug("%s was not found to invoke.", normalized_function_name)
-            return LambdaErrorResponses.resource_not_found(normalized_function_name)
+            return self._handle_function_not_found(function_name)
         except UnsupportedInlineCodeError:
             return LambdaErrorResponses.not_implemented_locally(
                 "Inline code is not supported for sam local commands. Please write your code in a separate file."
@@ -278,20 +285,87 @@ def _invoke_request_handler(self, function_name):
         )
 
         # Prepare headers
-        headers = {"Content-Type": "application/json"}
         if invoke_headers and isinstance(invoke_headers, dict):
             headers.update(invoke_headers)
 
         if is_lambda_user_error_response:
             headers["x-amz-function-error"] = "Unhandled"
-            return self.service_response(lambda_response, headers, 200)
-
-        # For async invocations (Event type), return 202
-        if invocation_type == "Event":
-            return self.service_response("", headers, 202)
 
         return self.service_response(lambda_response, headers, 200)
 
+    def _validate_function_for_invocation(self, function_name):
+        """
+        Validates that a function exists and can be invoked.
+
+        Parameters
+        ----------
+        function_name : str
+            Name or ARN of the function to validate
+
+        Returns
+        -------
+        Flask.Response or None
+            Error response if validation fails, None if validation succeeds
+        """
+        try:
+            self.lambda_runner.get_function(function_name)
+            return None
+        except FunctionNotFound:
+            return self._handle_function_not_found(function_name)
+        except InvalidFunctionNameException as e:
+            LOG.error("Validation error: %s", str(e))
+            return LambdaErrorResponses.validation_exception(str(e))
+
+    def _handle_function_not_found(self, function_name):
+        """
+        Handles FunctionNotFound exception by returning appropriate error response.
+
+        Parameters
+        ----------
+        function_name : str
+            Name or ARN of the function that was not found
+
+        Returns
+        -------
+        Flask.Response
+            Error response for function not found
+        """
+        normalized_function_name = normalize_sam_function_identifier(function_name)
+        LOG.debug("%s was not found to invoke.", normalized_function_name)
+        return LambdaErrorResponses.resource_not_found(normalized_function_name)
+
+    def _invoke_async_lambda(self, function_name, **kwargs):
+        """
+        Wrapper for _invoke_lambda that runs in an async context (Event invocation type)
+        """
+        try:
+            self._invoke_lambda(function_name=function_name, **kwargs)
+        except Exception as e:
+            LOG.error("Async invocation failed for function %s: %s", function_name, str(e), exc_info=True)
+
+    def _invoke_lambda(self, function_name, request_data, invocation_type, durable_execution_name, tenant_id):
+        """
+        Invokes a Lambda function and returns the result
+        """
+
+        stdout_stream_string = io.StringIO()
+        stdout_stream_bytes = io.BytesIO()
+        stdout_stream_writer = StreamWriter(stdout_stream_string, stdout_stream_bytes, auto_flush=True)
+
+        normalized_function_name = normalize_sam_function_identifier(function_name)
+
+        invoke_headers = self.lambda_runner.invoke(
+            normalized_function_name,
+            request_data,
+            invocation_type=invocation_type,
+            durable_execution_name=durable_execution_name,
+            tenant_id=tenant_id,
+            stdout=stdout_stream_writer,
+            stderr=self.stderr,
+        )
+
+        return invoke_headers, stdout_stream_string, stdout_stream_bytes
+
     def _get_durable_execution_handler(self, durable_execution_arn):
         """
         Handler for GET /2025-12-01/durable-executions/{DurableExecutionArn}

samcli/local/lambdafn/runtime.py

@@ -13,6 +13,7 @@
 
 from samcli.lib.telemetry.metric import capture_parameter
 from samcli.lib.utils.file_observer import LambdaFunctionObserver
+from samcli.lib.utils.invocation_type import EVENT, REQUEST_RESPONSE
 from samcli.lib.utils.packagetype import ZIP
 from samcli.local.docker.container import Container, ContainerContext
 from samcli.local.docker.container_analyzer import ContainerAnalyzer
@@ -305,9 +306,10 @@ def invoke(
                 )
             else:
                 # Only RequestResponse supported for regular Lambda functions
-                if invocation_type != "RequestResponse":
+                if invocation_type not in [EVENT, REQUEST_RESPONSE]:
                     raise UnsupportedInvocationType(
-                        f"invocation-type: {invocation_type} is not supported. RequestResponse is only supported."
+                        f"invocation-type: {invocation_type} is not supported. "
+                        "Event and RequestResponse are only supported."
                     )
 
                 # The container handles concurrency control internally via its semaphore.