fix: add typecheck to lambda wrapper (#533)

* check if event is a dict before getting

* early exit in is_legacy_lambda_step_function

Author: avedmala

Diff for: datadog_lambda/tracing.py

@@ -411,7 +411,10 @@ def is_legacy_lambda_step_function(event):
     """
     Check if the event is a step function that called a legacy lambda
     """
-    event = event.get("Payload", {})
+    if not isinstance(event, dict) or "Payload" not in event:
+        return False
+
+    event = event.get("Payload")
     return "Execution" in event and "StateMachine" in event and "State" in event
 
 

Diff for: tests/test_tracing.py

@@ -678,6 +678,9 @@ def test_is_legacy_lambda_step_function(self):
         }
         self.assertFalse(is_legacy_lambda_step_function(sf_event))
 
+        other_event = ["foo", "bar"]
+        self.assertFalse(is_legacy_lambda_step_function(other_event))
+
 
 class TestXRayContextConversion(unittest.TestCase):
     def test_convert_xray_trace_id(self):