From ea13ff2c4aea37623c5ca9c27a0bd1465afce5bd Mon Sep 17 00:00:00 2001
From: Bert Blommers <info@bertblommers.nl>
Date: Sun, 15 Dec 2024 17:06:33 -0100
Subject: [PATCH] DynamoDB: update_item() can now return list of binaries
 (#8401)

---
 moto/dynamodb/models/utilities.py    |  3 +++
 tests/test_dynamodb/test_dynamodb.py | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/moto/dynamodb/models/utilities.py b/moto/dynamodb/models/utilities.py
index 6d4636e787a4..52b97efc4be5 100644
--- a/moto/dynamodb/models/utilities.py
+++ b/moto/dynamodb/models/utilities.py
@@ -1,3 +1,4 @@
+import base64
 import json
 import re
 from typing import Any, Dict, List, Optional
@@ -7,6 +8,8 @@ class DynamoJsonEncoder(json.JSONEncoder):
     def default(self, o: Any) -> Any:
         if hasattr(o, "to_json"):
             return o.to_json()
+        elif isinstance(o, bytes):
+            return base64.b64encode(o).decode("utf-8")
 
 
 def dynamo_json_dump(dynamo_object: Any) -> str:
diff --git a/tests/test_dynamodb/test_dynamodb.py b/tests/test_dynamodb/test_dynamodb.py
index f8b930289ec4..1905c4e8c4fb 100644
--- a/tests/test_dynamodb/test_dynamodb.py
+++ b/tests/test_dynamodb/test_dynamodb.py
@@ -4952,3 +4952,25 @@ def test_query_with_gsi_reverse_paginated():
         {"pri": {"S": "pri_10"}, "alt": {"S": "alt_2"}},
     ]
     assert "LastEvaluatedKey" not in p2
+
+
+@pytest.mark.aws_verified
+@dynamodb_aws_verified()
+def test_update_item_with_list_of_bytes(table_name=None):
+    dynamodb = boto3.resource("dynamodb", region_name="us-east-1")
+    table = dynamodb.Table(table_name)
+
+    b1 = b"\n\x014\x18\xc3\xb0\xf8\xba\x06"
+    b2 = b"\n\x012\x18\xc3\xb0\xf8\xba\x06"
+
+    update = table.update_item(
+        Key={"pk": "clientA"},
+        UpdateExpression="SET #items = :new_items",
+        ExpressionAttributeValues={":new_items": [b1, b2]},
+        ExpressionAttributeNames={"#items": "items"},
+        ReturnValues="UPDATED_NEW",
+    )
+    assert update["Attributes"]["items"] == [Binary(b1), Binary(b2)]
+
+    get = table.get_item(Key={"pk": "clientA"})
+    assert get["Item"] == {"pk": "clientA", "items": [Binary(b1), Binary(b2)]}