Log nested exception for idempotency feature

Author: Michal Ploski

aws_lambda_powertools/utilities/idempotency/base.py

@@ -113,7 +113,9 @@ def _process_idempotency(self):
             record = self._get_idempotency_record()
             return self._handle_for_status(record)
         except Exception as exc:
-            raise IdempotencyPersistenceLayerError("Failed to save in progress record to idempotency store") from exc
+            raise IdempotencyPersistenceLayerError(
+                "Failed to save in progress record to idempotency store", exc
+            ) from exc
 
         return self._get_function_response()
 

aws_lambda_powertools/utilities/idempotency/exceptions.py

@@ -3,49 +3,68 @@
 """
 
 
-class IdempotencyItemAlreadyExistsError(Exception):
+class BaseError(Exception):
+    """
+    Base error class that overwrites the way exception and extra information is printed.
+    See https://github.com/awslabs/aws-lambda-powertools-python/issues/1772
+    """
+
+    def format_msg(self, *args: str) -> str:
+        full_msg = str(args[0])
+        if args[1:]:
+            full_msg += f': ({"".join(str(arg) for arg in args[1:])})'
+        return full_msg
+
+    def __init__(self, *args: str):
+        if args:
+            super().__init__(self.format_msg(*args))
+        else:
+            super().__init__()
+
+
+class IdempotencyItemAlreadyExistsError(BaseError):
     """
     Item attempting to be inserted into persistence store already exists and is not expired
     """
 
 
-class IdempotencyItemNotFoundError(Exception):
+class IdempotencyItemNotFoundError(BaseError):
     """
     Item does not exist in persistence store
     """
 
 
-class IdempotencyAlreadyInProgressError(Exception):
+class IdempotencyAlreadyInProgressError(BaseError):
     """
     Execution with idempotency key is already in progress
     """
 
 
-class IdempotencyInvalidStatusError(Exception):
+class IdempotencyInvalidStatusError(BaseError):
     """
     An invalid status was provided
     """
 
 
-class IdempotencyValidationError(Exception):
+class IdempotencyValidationError(BaseError):
     """
     Payload does not match stored idempotency record
     """
 
 
-class IdempotencyInconsistentStateError(Exception):
+class IdempotencyInconsistentStateError(BaseError):
     """
     State is inconsistent across multiple requests to persistence store
     """
 
 
-class IdempotencyPersistenceLayerError(Exception):
+class IdempotencyPersistenceLayerError(BaseError):
     """
     Unrecoverable error from the data store
     """
 
 
-class IdempotencyKeyError(Exception):
+class IdempotencyKeyError(BaseError):
     """
     Payload does not contain an idempotent key
     """

tests/functional/idempotency/test_idempotency.py

@@ -1070,7 +1070,13 @@ def test_idempotent_lambda_save_inprogress_error(persistence_store: DynamoDBPers
     # GIVEN a miss configured persistence layer
     # like no table was created for the idempotency persistence layer
     stubber = stub.Stubber(persistence_store.table.meta.client)
-    stubber.add_client_error("put_item", "ResourceNotFoundException")
+    service_error_code = "ResourceNotFoundException"
+    service_message = "Custom message"
+    stubber.add_client_error(
+        "put_item",
+        service_error_code,
+        service_message,
+    )
     stubber.activate()
 
     @idempotent(persistence_store=persistence_store)
@@ -1083,9 +1089,14 @@ def lambda_handler(event, context):
         lambda_handler({}, lambda_context)
 
     # THEN idempotent should raise an IdempotencyPersistenceLayerError
+    # AND append downstream exception details
     stubber.assert_no_pending_responses()
     stubber.deactivate()
-    assert "Failed to save in progress record to idempotency store" == e.value.args[0]
+    assert "Failed to save in progress record to idempotency store" in e.value.args[0]
+    assert (
+        f": (An error occurred ({service_error_code}) when calling the PutItem operation: {service_message})"
+        in e.value.args[0]
+    )
 
 
 def test_handler_raise_idempotency_key_error(persistence_store: DynamoDBPersistenceLayer, lambda_context):