Add VercelAIAdapter.dump_messages to convert Pydantic AI messages to Vercel AI messages

pydantic_ai_slim/pydantic_ai/ui/_adapter.py

@@ -143,6 +143,11 @@ def load_messages(cls, messages: Sequence[MessageT]) -> list[ModelMessage]:
         """Transform protocol-specific messages into Pydantic AI messages."""
         raise NotImplementedError
 
+    @classmethod
+    def dump_messages(cls, messages: Sequence[ModelMessage]) -> list[MessageT]:
+        """Transform Pydantic AI messages into protocol-specific messages."""
+        raise NotImplementedError
+
     @abstractmethod
     def build_event_stream(self) -> UIEventStream[RunInputT, EventT, AgentDepsT, OutputDataT]:
         """Build a protocol-specific event stream transformer."""

pydantic_ai_slim/pydantic_ai/ui/vercel_ai/_adapter.py

@@ -2,10 +2,12 @@
 
 from __future__ import annotations
 
+import json
+import uuid
 from collections.abc import Sequence
 from dataclasses import dataclass
 from functools import cached_property
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any, cast
 
 from pydantic import TypeAdapter
 from typing_extensions import assert_never
@@ -15,10 +17,13 @@
     BinaryContent,
     BuiltinToolCallPart,
     BuiltinToolReturnPart,
+    CachePoint,
     DocumentUrl,
     FilePart,
     ImageUrl,
     ModelMessage,
+    ModelRequest,
+    ModelResponse,
     RetryPromptPart,
     SystemPromptPart,
     TextPart,
@@ -35,6 +40,9 @@
 from ._event_stream import VercelAIEventStream
 from .request_types import (
     DataUIPart,
+    DynamicToolInputAvailablePart,
+    DynamicToolOutputAvailablePart,
+    DynamicToolOutputErrorPart,
     DynamicToolUIPart,
     FileUIPart,
     ReasoningUIPart,
@@ -43,10 +51,12 @@
     SourceUrlUIPart,
     StepStartUIPart,
     TextUIPart,
+    ToolInputAvailablePart,
     ToolOutputAvailablePart,
     ToolOutputErrorPart,
     ToolUIPart,
     UIMessage,
+    UIMessagePart,
 )
 from .response_types import BaseChunk
 
@@ -122,7 +132,16 @@ def load_messages(cls, messages: Sequence[UIMessage]) -> list[ModelMessage]:  #
                     if isinstance(part, TextUIPart):
                         builder.add(TextPart(content=part.text))
                     elif isinstance(part, ReasoningUIPart):
-                        builder.add(ThinkingPart(content=part.text))
+                        pydantic_ai_meta = (part.provider_metadata or {}).get('pydantic_ai', {})
+                        builder.add(
+                            ThinkingPart(
+                                content=part.text,
+                                id=pydantic_ai_meta.get('id'),
+                                signature=pydantic_ai_meta.get('signature'),
+                                provider_name=pydantic_ai_meta.get('provider_name'),
+                                provider_details=pydantic_ai_meta.get('provider_details'),
+                            )
+                        )
                     elif isinstance(part, FileUIPart):
                         try:
                             file = BinaryContent.from_data_uri(part.url)
@@ -141,7 +160,20 @@ def load_messages(cls, messages: Sequence[UIMessage]) -> list[ModelMessage]:  #
                             builtin_tool = part.provider_executed
 
                         tool_call_id = part.tool_call_id
-                        args = part.input
+
+                        args: str | dict[str, Any] | None = part.input
+
+                        if isinstance(args, str):
+                            try:
+                                parsed = json.loads(args)
+                                if isinstance(parsed, dict):
+                                    args = cast(dict[str, Any], parsed)
+                            except json.JSONDecodeError:
+                                pass
+                        elif isinstance(args, dict) or args is None:
+                            pass
+                        else:
+                            assert_never(args)
 
                         if builtin_tool:
                             call_part = BuiltinToolCallPart(tool_name=tool_name, tool_call_id=tool_call_id, args=args)
@@ -197,3 +229,207 @@ def load_messages(cls, messages: Sequence[UIMessage]) -> list[ModelMessage]:  #
                 assert_never(msg.role)
 
         return builder.messages
+
+    @staticmethod
+    def _dump_request_message(msg: ModelRequest) -> tuple[list[UIMessagePart], list[UIMessagePart]]:
+        """Convert a ModelRequest into a UIMessage."""
+        system_ui_parts: list[UIMessagePart] = []
+        user_ui_parts: list[UIMessagePart] = []
+
+        for part in msg.parts:
+            if isinstance(part, SystemPromptPart):
+                system_ui_parts.append(TextUIPart(text=part.content, state='done'))
+            elif isinstance(part, UserPromptPart):
+                user_ui_parts.extend(_convert_user_prompt_part(part))
+            elif isinstance(part, ToolReturnPart):
+                # Tool returns are merged into the tool call in the assistant message
+                pass
+            elif isinstance(part, RetryPromptPart):
+                if part.tool_name:
+                    # Tool-related retries are handled when processing ToolCallPart in ModelResponse
+                    pass
+                else:
+                    # Non-tool retries (e.g., output validation errors) become user text
+                    user_ui_parts.append(TextUIPart(text=part.model_response(), state='done'))
+            else:
+                assert_never(part)
+
+        return system_ui_parts, user_ui_parts
+
+    @staticmethod
+    def _dump_response_message(  # noqa: C901
+        msg: ModelResponse,
+        tool_results: dict[str, ToolReturnPart | RetryPromptPart],
+    ) -> list[UIMessagePart]:
+        """Convert a ModelResponse into a UIMessage."""
+        ui_parts: list[UIMessagePart] = []
+
+        # For builtin tools, returns can be in the same ModelResponse as calls
+        local_builtin_returns: dict[str, BuiltinToolReturnPart] = {
+            part.tool_call_id: part for part in msg.parts if isinstance(part, BuiltinToolReturnPart)
+        }
+
+        for part in msg.parts:
+            if isinstance(part, BuiltinToolReturnPart):
+                continue
+            elif isinstance(part, TextPart):
+                # Combine consecutive text parts
+                if ui_parts and isinstance(ui_parts[-1], TextUIPart):
+                    ui_parts[-1].text += part.content
+                else:
+                    ui_parts.append(TextUIPart(text=part.content, state='done'))
+            elif isinstance(part, ThinkingPart):
+                thinking_metadata: dict[str, Any] = {}
+                if part.id is not None:
+                    thinking_metadata['id'] = part.id
+                if part.signature is not None:
+                    thinking_metadata['signature'] = part.signature
+                if part.provider_name is not None:
+                    thinking_metadata['provider_name'] = part.provider_name
+                if part.provider_details is not None:
+                    thinking_metadata['provider_details'] = part.provider_details
+
+                provider_metadata = {'pydantic_ai': thinking_metadata} if thinking_metadata else None
+                ui_parts.append(ReasoningUIPart(text=part.content, state='done', provider_metadata=provider_metadata))
+            elif isinstance(part, FilePart):
+                ui_parts.append(
+                    FileUIPart(
+                        url=part.content.data_uri,
+                        media_type=part.content.media_type,
+                    )
+                )
+            elif isinstance(part, BuiltinToolCallPart):
+                call_provider_metadata = (
+                    {'pydantic_ai': {'provider_name': part.provider_name}} if part.provider_name else None
+                )
+
+                if builtin_return := local_builtin_returns.get(part.tool_call_id):
+                    content = builtin_return.model_response_str()
+                    ui_parts.append(
+                        ToolOutputAvailablePart(
+                            type=f'tool-{part.tool_name}',
+                            tool_call_id=part.tool_call_id,
+                            input=part.args_as_json_str(),
+                            output=content,
+                            state='output-available',
+                            provider_executed=True,
+                            call_provider_metadata=call_provider_metadata,
+                        )
+                    )
+                else:
+                    ui_parts.append(
+                        ToolInputAvailablePart(
+                            type=f'tool-{part.tool_name}',
+                            tool_call_id=part.tool_call_id,
+                            input=part.args_as_json_str(),
+                            state='input-available',
+                            provider_executed=True,
+                            call_provider_metadata=call_provider_metadata,
+                        )
+                    )
+            elif isinstance(part, ToolCallPart):
+                tool_result = tool_results.get(part.tool_call_id)
+
+                if isinstance(tool_result, ToolReturnPart):
+                    content = tool_result.model_response_str()
+                    ui_parts.append(
+                        DynamicToolOutputAvailablePart(
+                            tool_name=part.tool_name,
+                            tool_call_id=part.tool_call_id,
+                            input=part.args_as_json_str(),
+                            output=content,
+                            state='output-available',
+                        )
+                    )
+                elif isinstance(tool_result, RetryPromptPart):
+                    error_text = tool_result.model_response()
+                    ui_parts.append(
+                        DynamicToolOutputErrorPart(
+                            tool_name=part.tool_name,
+                            tool_call_id=part.tool_call_id,
+                            input=part.args_as_json_str(),
+                            error_text=error_text,
+                            state='output-error',
+                        )
+                    )
+                else:
+                    ui_parts.append(
+                        DynamicToolInputAvailablePart(
+                            tool_name=part.tool_name,
+                            tool_call_id=part.tool_call_id,
+                            input=part.args_as_json_str(),
+                            state='input-available',
+                        )
+                    )
+            else:
+                assert_never(part)
+
+        return ui_parts
+
+    @classmethod
+    def dump_messages(
+        cls,
+        messages: Sequence[ModelMessage],
+    ) -> list[UIMessage]:
+        """Transform Pydantic AI messages into Vercel AI messages.
+
+        Args:
+            messages: A sequence of ModelMessage objects to convert
+
+        Returns:
+            A list of UIMessage objects in Vercel AI format
+        """
+        tool_results: dict[str, ToolReturnPart | RetryPromptPart] = {}
+
+        for msg in messages:
+            if isinstance(msg, ModelRequest):
+                for part in msg.parts:
+                    if isinstance(part, ToolReturnPart):
+                        tool_results[part.tool_call_id] = part
+                    elif isinstance(part, RetryPromptPart) and part.tool_name:
+                        tool_results[part.tool_call_id] = part
+
+        result: list[UIMessage] = []
+
+        for msg in messages:
+            if isinstance(msg, ModelRequest):
+                system_ui_parts, user_ui_parts = cls._dump_request_message(msg)
+                if system_ui_parts:
+                    result.append(UIMessage(id=str(uuid.uuid4()), role='system', parts=system_ui_parts))
+
+                if user_ui_parts:
+                    result.append(UIMessage(id=str(uuid.uuid4()), role='user', parts=user_ui_parts))
+
+            elif isinstance(  # pragma: no branch
+                msg, ModelResponse
+            ):
+                ui_parts: list[UIMessagePart] = cls._dump_response_message(msg, tool_results)
+                if ui_parts:  # pragma: no branch
+                    result.append(UIMessage(id=str(uuid.uuid4()), role='assistant', parts=ui_parts))
+            else:
+                assert_never(msg)
+
+        return result
+
+
+def _convert_user_prompt_part(part: UserPromptPart) -> list[UIMessagePart]:
+    """Convert a UserPromptPart to a list of UI message parts."""
+    ui_parts: list[UIMessagePart] = []
+
+    if isinstance(part.content, str):
+        ui_parts.append(TextUIPart(text=part.content, state='done'))
+    else:
+        for item in part.content:
+            if isinstance(item, str):
+                ui_parts.append(TextUIPart(text=item, state='done'))
+            elif isinstance(item, BinaryContent):
+                ui_parts.append(FileUIPart(url=item.data_uri, media_type=item.media_type))
+            elif isinstance(item, ImageUrl | AudioUrl | VideoUrl | DocumentUrl):
+                ui_parts.append(FileUIPart(url=item.url, media_type=item.media_type))
+            elif isinstance(item, CachePoint):
+                # CachePoint is metadata for prompt caching, skip for UI conversion
+                pass
+            else:
+                assert_never(item)
+
+    return ui_parts

tests/test_ui.py

@@ -87,6 +87,10 @@ class DummyUIAdapter(UIAdapter[DummyUIRunInput, ModelMessage, str, AgentDepsT, O
     def build_run_input(cls, body: bytes) -> DummyUIRunInput:
         return DummyUIRunInput.model_validate_json(body)
 
+    @classmethod
+    def dump_messages(cls, messages: Sequence[ModelMessage]) -> list[ModelMessage]:
+        return list(messages)
+
     @classmethod
     def load_messages(cls, messages: Sequence[ModelMessage]) -> list[ModelMessage]:
         return list(messages)
@@ -676,3 +680,12 @@ async def send(data: MutableMapping[str, Any]) -> None:
             {'type': 'http.response.body', 'body': b'', 'more_body': False},
         ]
     )
+
+
+def test_dummy_adapter_dump_messages():
+    """Test that DummyUIAdapter.dump_messages returns messages as-is."""
+    from pydantic_ai.messages import UserPromptPart
+
+    messages = [ModelRequest(parts=[UserPromptPart(content='Hello')])]
+    result = DummyUIAdapter.dump_messages(messages)
+    assert result == messages