fix(runtime): send bytes in events as base64 instead of a repr string

src/bedrock_agentcore/runtime/utils.py

@@ -1,5 +1,6 @@
 """Bedrock AgentCore runtime utilities for object conversion and serialization."""
 
+import base64
 from dataclasses import asdict, is_dataclass
 from typing import Any
 
@@ -10,13 +11,14 @@ def convert_complex_objects(obj: Any, _depth: int = 0) -> Any:
     if _depth > 50:
         return f"<too_deep:{type(obj).__name__}>"
 
-    # Handle Pydantic models (like AIMessage)
+    # Handle Pydantic models (like AIMessage). The dump can still hold bytes or
+    # sets, so it is converted too.
     if hasattr(obj, "model_dump"):
-        return obj.model_dump()
+        return convert_complex_objects(obj.model_dump(), _depth + 1)
 
-    # Handle dataclasses (like AgentResult)
+    # Handle dataclasses (like AgentResult), converting the dump for the same reason
     elif is_dataclass(obj):
-        return asdict(obj)
+        return convert_complex_objects(asdict(obj), _depth + 1)
 
     # Handle dictionaries recursively
     elif isinstance(obj, dict):
@@ -30,6 +32,10 @@ def convert_complex_objects(obj: Any, _depth: int = 0) -> Any:
     elif isinstance(obj, set):
         return [convert_complex_objects(item, _depth + 1) for item in obj]
 
+    # Handle binary data (base64, since JSON has no bytes type)
+    elif isinstance(obj, (bytes, bytearray)):
+        return base64.b64encode(obj).decode("ascii")
+
     # Return primitives as-is
     else:
         return obj

tests/bedrock_agentcore/runtime/test_app.py

@@ -1059,6 +1059,14 @@ def test_convert_to_sse_json_serializable_data(self):
             parsed_data = json.loads(json_part)
             assert parsed_data == test_data
 
+    def test_convert_to_sse_streams_bytes_as_json_object(self):
+        """An event holding bytes must arrive as a JSON object, not a string of its repr (#659)."""
+        app = BedrockAgentCoreApp()
+
+        sse_string = app._convert_to_sse({"result": {"redactedContent": b"abc"}}).decode("utf-8")
+
+        assert json.loads(sse_string[6:-2]) == {"result": {"redactedContent": "YWJj"}}
+
     def test_convert_to_sse_non_serializable_object(self):
         """Test that non-JSON-serializable objects trigger error handling."""
         app = BedrockAgentCoreApp()

tests/bedrock_agentcore/runtime/test_utils.py

@@ -1,5 +1,6 @@
 """Tests for Bedrock AgentCore runtime utilities."""
 
+import json
 from dataclasses import dataclass
 from typing import List, Optional
 
@@ -178,6 +179,33 @@ def test_sets(self):
         assert "b" in result
         assert "c" in result
 
+    def test_bytes_become_base64_anywhere_in_the_tree(self):
+        """Bytes must end up JSON-serializable, including inside dataclasses and Pydantic models."""
+
+        @dataclass
+        class Block:
+            data: bytes
+
+        class Blob(BaseModel):
+            data: bytes
+
+        event = {
+            "raw": b"abc",
+            "buffer": bytearray(b"\x00\xff"),
+            "dataclass": Block(data=b"abc"),
+            "pydantic": Blob(data=b"abc"),
+        }
+
+        result = convert_complex_objects(event)
+
+        assert result == {
+            "raw": "YWJj",
+            "buffer": "AP8=",
+            "dataclass": {"data": "YWJj"},
+            "pydantic": {"data": "YWJj"},
+        }
+        json.dumps(result)
+
     def test_nested_sets_with_complex_objects(self):
         """Test sets containing hashable objects (complex objects can't be in sets)."""