improv: add support for custom lambda handlers with kwargs #242 (#269)

* improv: support kwargs

* chore: add a comment to not forget about async tracer

aws_lambda_powertools/tracing/tracer.py

@@ -290,7 +290,7 @@ def handler(event, context):
         )
 
         @functools.wraps(lambda_handler)
-        def decorate(event, context):
+        def decorate(event, context, **kwargs):
             with self.provider.in_subsegment(name=f"## {lambda_handler_name}") as subsegment:
                 global is_cold_start
                 if is_cold_start:
@@ -300,7 +300,7 @@ def decorate(event, context):
 
                 try:
                     logger.debug("Calling lambda handler")
-                    response = lambda_handler(event, context)
+                    response = lambda_handler(event, context, **kwargs)
                     logger.debug("Received lambda handler response successfully")
                     self._add_response_as_metadata(
                         method_name=lambda_handler_name,
@@ -487,6 +487,7 @@ async def async_tasks():
             env=os.getenv(constants.TRACER_CAPTURE_ERROR_ENV, "true"), choice=capture_error
         )
 
+        # Maintenance: Need a factory/builder here to simplify this now
         if inspect.iscoroutinefunction(method):
             return self._decorate_async_function(
                 method=method, capture_response=capture_response, capture_error=capture_error, method_name=method_name

tests/functional/test_tracing.py

@@ -34,6 +34,19 @@ def handler(event, context):
     handler({}, {})
 
 
+def test_capture_lambda_handler_with_additional_kwargs(dummy_response):
+    # GIVEN tracer lambda handler decorator is used
+    tracer = Tracer(disabled=True)
+
+    # WHEN a lambda handler signature has additional keyword arguments
+    @tracer.capture_lambda_handler
+    def handler(event, context, my_extra_option=None, **kwargs):
+        return dummy_response
+
+    # THEN tracer should not raise an Exception
+    handler({}, {}, blah="blah")
+
+
 def test_capture_method(dummy_response):
     # GIVEN tracer method decorator is used
     tracer = Tracer(disabled=True)