Properly validate serialized messages with BinaryContent by decoding base64 (#1513)

Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com>

Author: DouweM

pydantic_ai_slim/pydantic_ai/messages.py

@@ -589,7 +589,7 @@ def new_event_body():
 """Any message sent to or returned by a model."""
 
 ModelMessagesTypeAdapter = pydantic.TypeAdapter(
-    list[ModelMessage], config=pydantic.ConfigDict(defer_build=True, ser_json_bytes='base64')
+    list[ModelMessage], config=pydantic.ConfigDict(defer_build=True, ser_json_bytes='base64', val_json_bytes='base64')
 )
 """Pydantic [`TypeAdapter`][pydantic.type_adapter.TypeAdapter] for (de)serializing messages."""
 

tests/test_agent.py

@@ -15,6 +15,7 @@
 from pydantic_ai.messages import (
     BinaryContent,
     ModelMessage,
+    ModelMessagesTypeAdapter,
     ModelRequest,
     ModelResponse,
     ModelResponsePart,
@@ -1675,8 +1676,11 @@ def validate_output(ctx: RunContext[None], o: Any) -> Any:  # pragma: no cover
 def test_binary_content_all_messages_json():
     agent = Agent('test')
 
-    result = agent.run_sync(['Hello', BinaryContent(data=b'Hello', media_type='text/plain')])
-    assert json.loads(result.all_messages_json()) == snapshot(
+    content = BinaryContent(data=b'Hello', media_type='text/plain')
+    result = agent.run_sync(['Hello', content])
+
+    serialized = result.all_messages_json()
+    assert json.loads(serialized) == snapshot(
         [
             {
                 'parts': [
@@ -1698,6 +1702,10 @@ def test_binary_content_all_messages_json():
         ]
     )
 
+    # We also need to be able to round trip the serialized messages.
+    messages = ModelMessagesTypeAdapter.validate_json(serialized)
+    assert messages == result.all_messages()
+
 
 def test_instructions_raise_error_when_system_prompt_is_set():
     agent = Agent('test', instructions='An instructions!')