Revert "refactor: reorganize message handling for better type safety and clar…" (#282)

This reverts commit 9d0f2daddb.

src/mcp/client/session.py

@@ -1,11 +1,12 @@
 from datetime import timedelta
 from typing import Any, Protocol
 
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import AnyUrl, TypeAdapter
 
 import mcp.types as types
 from mcp.shared.context import RequestContext
-from mcp.shared.session import BaseSession, ReadStream, RequestResponder, WriteStream
+from mcp.shared.session import BaseSession, RequestResponder
 from mcp.shared.version import SUPPORTED_PROTOCOL_VERSIONS
 
 
@@ -58,8 +59,8 @@ class ClientSession(
 ):
     def __init__(
         self,
-        read_stream: ReadStream,
+        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        write_stream: WriteStream,
+        write_stream: MemoryObjectSendStream[types.JSONRPCMessage],
         read_timeout_seconds: timedelta | None = None,
         sampling_callback: SamplingFnT | None = None,
         list_roots_callback: ListRootsFnT | None = None,

src/mcp/client/sse.py

@@ -6,16 +6,10 @@ from urllib.parse import urljoin, urlparse
 import anyio
 import httpx
 from anyio.abc import TaskStatus
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from httpx_sse import aconnect_sse
 
 import mcp.types as types
-from mcp.shared.session import (
-    ReadStream,
-    ReadStreamWriter,
-    WriteStream,
-    WriteStreamReader,
-)
-from mcp.types import MessageFrame
 
 logger = logging.getLogger(__name__)
 
@@ -37,11 +31,11 @@ async def sse_client(
     `sse_read_timeout` determines how long (in seconds) the client will wait for a new
     event before disconnecting. All other HTTP operations are controlled by `timeout`.
     """
-    read_stream: ReadStream
+    read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-    read_stream_writer: ReadStreamWriter
+    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
 
-    write_stream: WriteStream
+    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-    write_stream_reader: WriteStreamReader
+    write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
 
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -90,11 +84,8 @@ async def sse_client(
 
                                     case "message":
                                         try:
-                                            message = MessageFrame(
                                             message = types.JSONRPCMessage.model_validate_json(  # noqa: E501
                                                 sse.data
-                                                ),
-                                                raw=sse,
                                             )
                                             logger.debug(
                                                 f"Received server message: {message}"

src/mcp/client/websocket.py

@@ -1,7 +1,7 @@
 import json
 import logging
 from contextlib import asynccontextmanager
-from typing import Any, AsyncGenerator
+from typing import AsyncGenerator
 
 import anyio
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
@@ -10,7 +10,6 @@ from websockets.asyncio.client import connect as ws_connect
 from websockets.typing import Subprotocol
 
 import mcp.types as types
-from mcp.types import MessageFrame
 
 logger = logging.getLogger(__name__)
 
@@ -20,8 +19,8 @@ async def websocket_client(
     url: str,
 ) -> AsyncGenerator[
     tuple[
-        MemoryObjectReceiveStream[MessageFrame[Any] | Exception],
+        MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        MemoryObjectSendStream[MessageFrame[Any]],
+        MemoryObjectSendStream[types.JSONRPCMessage],
     ],
     None,
 ]:
@@ -54,11 +53,7 @@ async def websocket_client(
             async with read_stream_writer:
                 async for raw_text in ws:
                     try:
-                        json_message = types.JSONRPCMessage.model_validate_json(
+                        message = types.JSONRPCMessage.model_validate_json(raw_text)
-                            raw_text
-                        )
-                        # Create MessageFrame with JSON message as root
-                        message = MessageFrame(message=json_message, raw=raw_text)
                         await read_stream_writer.send(message)
                     except ValidationError as exc:
                         # If JSON parse or model validation fails, send the exception
@@ -71,8 +66,8 @@ async def websocket_client(
             """
             async with write_stream_reader:
                 async for message in write_stream_reader:
-                    # Extract the JSON-RPC message from MessageFrame and convert to JSON
+                    # Convert to a dict, then to JSON
-                    msg_dict = message.message.model_dump(
+                    msg_dict = message.model_dump(
                         by_alias=True, mode="json", exclude_none=True
                     )
                     await ws.send(json.dumps(msg_dict))

src/mcp/server/lowlevel/server.py

@@ -74,6 +74,7 @@ from contextlib import AbstractAsyncContextManager, AsyncExitStack, asynccontext
 from typing import Any, AsyncIterator, Generic, TypeVar
 
 import anyio
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import AnyUrl
 
 import mcp.types as types
@@ -83,7 +84,7 @@ from mcp.server.session import ServerSession
 from mcp.server.stdio import stdio_server as stdio_server
 from mcp.shared.context import RequestContext
 from mcp.shared.exceptions import McpError
-from mcp.shared.session import ReadStream, RequestResponder, WriteStream
+from mcp.shared.session import RequestResponder
 
 logger = logging.getLogger(__name__)
 
@@ -473,8 +474,8 @@ class Server(Generic[LifespanResultT]):
 
     async def run(
         self,
-        read_stream: ReadStream,
+        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        write_stream: WriteStream,
+        write_stream: MemoryObjectSendStream[types.JSONRPCMessage],
         initialization_options: InitializationOptions,
         # When False, exceptions are returned as messages to the client.
         # When True, exceptions are raised, which will cause the server to shut down

src/mcp/server/models.py

@@ -5,7 +5,9 @@ and tools.
 
 from pydantic import BaseModel
 
-from mcp.types import ServerCapabilities
+from mcp.types import (
+    ServerCapabilities,
+)
 
 
 class InitializationOptions(BaseModel):

src/mcp/server/session.py

@@ -42,15 +42,14 @@ from typing import Any, TypeVar
 
 import anyio
 import anyio.lowlevel
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import AnyUrl
 
 import mcp.types as types
 from mcp.server.models import InitializationOptions
 from mcp.shared.session import (
     BaseSession,
-    ReadStream,
     RequestResponder,
-    WriteStream,
 )
 
 
@@ -77,8 +76,8 @@ class ServerSession(
 
     def __init__(
         self,
-        read_stream: ReadStream,
+        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        write_stream: WriteStream,
+        write_stream: MemoryObjectSendStream[types.JSONRPCMessage],
         init_options: InitializationOptions,
     ) -> None:
         super().__init__(

src/mcp/server/sse.py

@@ -38,6 +38,7 @@ from urllib.parse import quote
 from uuid import UUID, uuid4
 
 import anyio
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import ValidationError
 from sse_starlette import EventSourceResponse
 from starlette.requests import Request
@@ -45,13 +46,6 @@ from starlette.responses import Response
 from starlette.types import Receive, Scope, Send
 
 import mcp.types as types
-from mcp.shared.session import (
-    ReadStream,
-    ReadStreamWriter,
-    WriteStream,
-    WriteStreamReader,
-)
-from mcp.types import MessageFrame
 
 logger = logging.getLogger(__name__)
 
@@ -69,7 +63,9 @@ class SseServerTransport:
     """
 
     _endpoint: str
-    _read_stream_writers: dict[UUID, ReadStreamWriter]
+    _read_stream_writers: dict[
+        UUID, MemoryObjectSendStream[types.JSONRPCMessage | Exception]
+    ]
 
     def __init__(self, endpoint: str) -> None:
         """
@@ -89,11 +85,11 @@ class SseServerTransport:
             raise ValueError("connect_sse can only handle HTTP requests")
 
         logger.debug("Setting up SSE connection")
-        read_stream: ReadStream
+        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-        read_stream_writer: ReadStreamWriter
+        read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
 
-        write_stream: WriteStream
+        write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-        write_stream_reader: WriteStreamReader
+        write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
 
         read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
         write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -176,4 +172,4 @@ class SseServerTransport:
         logger.debug(f"Sending message to writer: {message}")
         response = Response("Accepted", status_code=202)
         await response(scope, receive, send)
-        await writer.send(MessageFrame(message=message, raw=request))
+        await writer.send(message)

src/mcp/server/stdio.py

@@ -24,15 +24,9 @@ from io import TextIOWrapper
 
 import anyio
 import anyio.lowlevel
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 
 import mcp.types as types
-from mcp.shared.session import (
-    ReadStream,
-    ReadStreamWriter,
-    WriteStream,
-    WriteStreamReader,
-)
-from mcp.types import MessageFrame
 
 
 @asynccontextmanager
@@ -53,11 +47,11 @@ async def stdio_server(
     if not stdout:
         stdout = anyio.wrap_file(TextIOWrapper(sys.stdout.buffer, encoding="utf-8"))
 
-    read_stream: ReadStream
+    read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-    read_stream_writer: ReadStreamWriter
+    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
 
-    write_stream: WriteStream
+    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-    write_stream_reader: WriteStreamReader
+    write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
 
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -72,9 +66,7 @@ async def stdio_server(
                         await read_stream_writer.send(exc)
                         continue
 
-                    await read_stream_writer.send(
+                    await read_stream_writer.send(message)
-                        MessageFrame(message=message, raw=line)
-                    )
         except anyio.ClosedResourceError:
             await anyio.lowlevel.checkpoint()
 
@@ -82,7 +74,6 @@ async def stdio_server(
         try:
             async with write_stream_reader:
                 async for message in write_stream_reader:
-                    # Extract the inner JSONRPCRequest/JSONRPCResponse from MessageFrame
                     json = message.model_dump_json(by_alias=True, exclude_none=True)
                     await stdout.write(json + "\n")
                     await stdout.flush()

src/mcp/server/websocket.py

@@ -2,17 +2,11 @@ import logging
 from contextlib import asynccontextmanager
 
 import anyio
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from starlette.types import Receive, Scope, Send
 from starlette.websockets import WebSocket
 
 import mcp.types as types
-from mcp.shared.session import (
-    ReadStream,
-    ReadStreamWriter,
-    WriteStream,
-    WriteStreamReader,
-)
-from mcp.types import MessageFrame
 
 logger = logging.getLogger(__name__)
 
@@ -27,11 +21,11 @@ async def websocket_server(scope: Scope, receive: Receive, send: Send):
     websocket = WebSocket(scope, receive, send)
     await websocket.accept(subprotocol="mcp")
 
-    read_stream: ReadStream
+    read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-    read_stream_writer: ReadStreamWriter
+    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
 
-    write_stream: WriteStream
+    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-    write_stream_reader: WriteStreamReader
+    write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
 
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -46,9 +40,7 @@ async def websocket_server(scope: Scope, receive: Receive, send: Send):
                         await read_stream_writer.send(exc)
                         continue
 
-                    await read_stream_writer.send(
+                    await read_stream_writer.send(client_message)
-                        MessageFrame(message=client_message, raw=message)
-                    )
         except anyio.ClosedResourceError:
             await websocket.close()
 

src/mcp/shared/memory.py

@@ -11,11 +11,11 @@ from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStre
 
 from mcp.client.session import ClientSession, ListRootsFnT, SamplingFnT
 from mcp.server import Server
-from mcp.types import MessageFrame
+from mcp.types import JSONRPCMessage
 
 MessageStream = tuple[
-    MemoryObjectReceiveStream[MessageFrame | Exception],
+    MemoryObjectReceiveStream[JSONRPCMessage | Exception],
-    MemoryObjectSendStream[MessageFrame],
+    MemoryObjectSendStream[JSONRPCMessage],
 ]
 
 
@@ -32,10 +32,10 @@ async def create_client_server_memory_streams() -> (
     """
     # Create streams for both directions
     server_to_client_send, server_to_client_receive = anyio.create_memory_object_stream[
-        MessageFrame | Exception
+        JSONRPCMessage | Exception
     ](1)
     client_to_server_send, client_to_server_receive = anyio.create_memory_object_stream[
-        MessageFrame | Exception
+        JSONRPCMessage | Exception
     ](1)
 
     client_streams = (server_to_client_receive, client_to_server_send)
@@ -60,9 +60,12 @@ async def create_connected_server_and_client_session(
 ) -> AsyncGenerator[ClientSession, None]:
     """Creates a ClientSession that is connected to a running MCP server."""
     async with create_client_server_memory_streams() as (
-        (client_read, client_write),
+        client_streams,
-        (server_read, server_write),
+        server_streams,
     ):
+        client_read, client_write = client_streams
+        server_read, server_write = server_streams
+
         # Create a cancel scope for the server task
         async with anyio.create_task_group() as tg:
             tg.start_soon(

src/mcp/shared/session.py

@@ -22,18 +22,12 @@ from mcp.types import (
     JSONRPCNotification,
     JSONRPCRequest,
     JSONRPCResponse,
-    MessageFrame,
     RequestParams,
     ServerNotification,
     ServerRequest,
     ServerResult,
 )
 
-ReadStream = MemoryObjectReceiveStream[MessageFrame | Exception]
-ReadStreamWriter = MemoryObjectSendStream[MessageFrame | Exception]
-WriteStream = MemoryObjectSendStream[MessageFrame]
-WriteStreamReader = MemoryObjectReceiveStream[MessageFrame]
-
 SendRequestT = TypeVar("SendRequestT", ClientRequest, ServerRequest)
 SendResultT = TypeVar("SendResultT", ClientResult, ServerResult)
 SendNotificationT = TypeVar("SendNotificationT", ClientNotification, ServerNotification)
@@ -171,8 +165,8 @@ class BaseSession(
 
     def __init__(
         self,
-        read_stream: ReadStream,
+        read_stream: MemoryObjectReceiveStream[JSONRPCMessage | Exception],
-        write_stream: WriteStream,
+        write_stream: MemoryObjectSendStream[JSONRPCMessage],
         receive_request_type: type[ReceiveRequestT],
         receive_notification_type: type[ReceiveNotificationT],
         # If none, reading will never time out
@@ -248,9 +242,7 @@ class BaseSession(
 
         # TODO: Support progress callbacks
 
-        await self._write_stream.send(
+        await self._write_stream.send(JSONRPCMessage(jsonrpc_request))
-            MessageFrame(message=JSONRPCMessage(jsonrpc_request), raw=None)
-        )
 
         try:
             with anyio.fail_after(
@@ -286,18 +278,14 @@ class BaseSession(
             **notification.model_dump(by_alias=True, mode="json", exclude_none=True),
         )
 
-        await self._write_stream.send(
+        await self._write_stream.send(JSONRPCMessage(jsonrpc_notification))
-            MessageFrame(message=JSONRPCMessage(jsonrpc_notification), raw=None)
-        )
 
     async def _send_response(
         self, request_id: RequestId, response: SendResultT | ErrorData
     ) -> None:
         if isinstance(response, ErrorData):
             jsonrpc_error = JSONRPCError(jsonrpc="2.0", id=request_id, error=response)
-            await self._write_stream.send(
+            await self._write_stream.send(JSONRPCMessage(jsonrpc_error))
-                MessageFrame(message=JSONRPCMessage(jsonrpc_error), raw=None)
-            )
         else:
             jsonrpc_response = JSONRPCResponse(
                 jsonrpc="2.0",
@@ -306,9 +294,7 @@ class BaseSession(
                     by_alias=True, mode="json", exclude_none=True
                 ),
             )
-            await self._write_stream.send(
+            await self._write_stream.send(JSONRPCMessage(jsonrpc_response))
-                MessageFrame(message=JSONRPCMessage(jsonrpc_response), raw=None)
-            )
 
     async def _receive_loop(self) -> None:
         async with (
@@ -316,13 +302,10 @@ class BaseSession(
             self._write_stream,
             self._incoming_message_stream_writer,
         ):
-            async for raw_message in self._read_stream:
+            async for message in self._read_stream:
-                if isinstance(raw_message, Exception):
+                if isinstance(message, Exception):
-                    await self._incoming_message_stream_writer.send(raw_message)
+                    await self._incoming_message_stream_writer.send(message)
-                    continue
+                elif isinstance(message.root, JSONRPCRequest):
-
-                message = raw_message.message
-                if isinstance(message.root, JSONRPCRequest):
                     validated_request = self._receive_request_type.model_validate(
                         message.root.model_dump(
                             by_alias=True, mode="json", exclude_none=True

src/mcp/types.py

@@ -180,49 +180,6 @@ class JSONRPCMessage(
     pass
 
 
-RawT = TypeVar("RawT")
-
-
-class MessageFrame(BaseModel, Generic[RawT]):
-    """
-    A wrapper around the general message received that contains both the parsed message
-    and the raw message.
-
-    This class serves as an encapsulation for JSON-RPC messages, providing access to
-    both the parsed structure (root) and the original raw data. This design is
-    particularly useful for Server-Sent Events (SSE) consumers who may need to access
-    additional metadata or headers associated with the message.
-
-    The 'root' attribute contains the parsed JSONRPCMessage, which could be a request,
-    notification, response, or error. The 'raw' attribute preserves the original
-    message as received, allowing access to any additional context or metadata that
-    might be lost in parsing.
-
-    This dual representation allows for flexible handling of messages, where consumers
-    can work with the structured data for standard operations, but still have the
-    option to examine or utilize the raw data when needed, such as for debugging,
-    logging, or accessing transport-specific information.
-    """
-
-    message: JSONRPCMessage
-    raw: RawT | None = None
-    model_config = ConfigDict(extra="allow")
-
-    def model_dump(self, *args, **kwargs):
-        """
-        Dumps the model to a dictionary, delegating to the root JSONRPCMessage.
-        This method allows for consistent serialization of the parsed message.
-        """
-        return self.message.model_dump(*args, **kwargs)
-
-    def model_dump_json(self, *args, **kwargs):
-        """
-        Dumps the model to a JSON string, delegating to the root JSONRPCMessage.
-        This method provides a convenient way to serialize the parsed message to JSON.
-        """
-        return self.message.model_dump_json(*args, **kwargs)
-
-
 class EmptyResult(Result):
     """A response that indicates success but carries no data."""
 

tests/client/test_session.py

@@ -1,5 +1,3 @@
-from types import NoneType
-
 import anyio
 import pytest
 
@@ -13,9 +11,9 @@ from mcp.types import (
     InitializeRequest,
     InitializeResult,
     JSONRPCMessage,
+    JSONRPCNotification,
     JSONRPCRequest,
     JSONRPCResponse,
-    MessageFrame,
     ServerCapabilities,
     ServerResult,
 )
@@ -24,10 +22,10 @@ from mcp.types import (
 @pytest.mark.anyio
 async def test_client_session_initialize():
     client_to_server_send, client_to_server_receive = anyio.create_memory_object_stream[
-        MessageFrame[NoneType]
+        JSONRPCMessage
     ](1)
     server_to_client_send, server_to_client_receive = anyio.create_memory_object_stream[
-        MessageFrame[NoneType]
+        JSONRPCMessage
     ](1)
 
     initialized_notification = None
@@ -36,7 +34,7 @@ async def test_client_session_initialize():
         nonlocal initialized_notification
 
         jsonrpc_request = await client_to_server_receive.receive()
-        assert isinstance(jsonrpc_request, MessageFrame)
+        assert isinstance(jsonrpc_request.root, JSONRPCRequest)
         request = ClientRequest.model_validate(
             jsonrpc_request.model_dump(by_alias=True, mode="json", exclude_none=True)
         )
@@ -58,25 +56,21 @@ async def test_client_session_initialize():
         )
 
         async with server_to_client_send:
-            assert isinstance(jsonrpc_request.message.root, JSONRPCRequest)
             await server_to_client_send.send(
-                MessageFrame(
+                JSONRPCMessage(
-                    message=JSONRPCMessage(
                     JSONRPCResponse(
                         jsonrpc="2.0",
-                            id=jsonrpc_request.message.root.id,
+                        id=jsonrpc_request.root.id,
                         result=result.model_dump(
                             by_alias=True, mode="json", exclude_none=True
                         ),
                     )
-                    ),
-                    raw=None,
                 )
             )
             jsonrpc_notification = await client_to_server_receive.receive()
-            assert isinstance(jsonrpc_notification.message, JSONRPCMessage)
+            assert isinstance(jsonrpc_notification.root, JSONRPCNotification)
             initialized_notification = ClientNotification.model_validate(
-                jsonrpc_notification.message.model_dump(
+                jsonrpc_notification.model_dump(
                     by_alias=True, mode="json", exclude_none=True
                 )
             )

tests/issues/test_192_request_id.py

@@ -11,7 +11,6 @@ from mcp.types import (
     JSONRPCMessage,
     JSONRPCNotification,
     JSONRPCRequest,
-    MessageFrame,
     NotificationParams,
 )
 
@@ -65,9 +64,7 @@ async def test_request_id_match() -> None:
             jsonrpc="2.0",
         )
 
-        await client_writer.send(
+        await client_writer.send(JSONRPCMessage(root=init_req))
-            MessageFrame(message=JSONRPCMessage(root=init_req), raw=None)
-        )
         await server_reader.receive()  # Get init response but don't need to check it
 
         # Send initialized notification
@@ -76,27 +73,21 @@ async def test_request_id_match() -> None:
             params=NotificationParams().model_dump(by_alias=True, exclude_none=True),
             jsonrpc="2.0",
         )
-        await client_writer.send(
+        await client_writer.send(JSONRPCMessage(root=initialized_notification))
-            MessageFrame(
-                message=JSONRPCMessage(root=initialized_notification), raw=None
-            )
-        )
 
         # Send ping request with custom ID
         ping_request = JSONRPCRequest(
             id=custom_request_id, method="ping", params={}, jsonrpc="2.0"
         )
 
-        await client_writer.send(
+        await client_writer.send(JSONRPCMessage(root=ping_request))
-            MessageFrame(message=JSONRPCMessage(root=ping_request), raw=None)
-        )
 
         # Read response
         response = await server_reader.receive()
 
         # Verify response ID matches request ID
         assert (
-            response.message.root.id == custom_request_id
+            response.root.id == custom_request_id
         ), "Response ID should match request ID"
 
         # Cancel server task

tests/server/test_lifespan.py

@@ -17,7 +17,6 @@ from mcp.types import (
     JSONRPCMessage,
     JSONRPCNotification,
     JSONRPCRequest,
-    MessageFrame,
 )
 
 
@@ -65,7 +64,7 @@ async def test_lowlevel_server_lifespan():
                 send_stream2,
                 InitializationOptions(
                     server_name="test",
-                    server_version="1.0.0",
+                    server_version="0.1.0",
                     capabilities=server.get_capabilities(
                         notification_options=NotificationOptions(),
                         experimental_capabilities={},
@@ -83,51 +82,42 @@ async def test_lowlevel_server_lifespan():
             clientInfo=Implementation(name="test-client", version="0.1.0"),
         )
         await send_stream1.send(
-            MessageFrame(
+            JSONRPCMessage(
-                message=JSONRPCMessage(
                 root=JSONRPCRequest(
                     jsonrpc="2.0",
                     id=1,
                     method="initialize",
                     params=TypeAdapter(InitializeRequestParams).dump_python(params),
                 )
-                ),
-                raw=None,
             )
         )
         response = await receive_stream2.receive()
 
         # Send initialized notification
         await send_stream1.send(
-            MessageFrame(
+            JSONRPCMessage(
-                message=JSONRPCMessage(
                 root=JSONRPCNotification(
                     jsonrpc="2.0",
                     method="notifications/initialized",
                 )
-                ),
-                raw=None,
             )
         )
 
         # Call the tool to verify lifespan context
         await send_stream1.send(
-            MessageFrame(
+            JSONRPCMessage(
-                message=JSONRPCMessage(
                 root=JSONRPCRequest(
                     jsonrpc="2.0",
                     id=2,
                     method="tools/call",
                     params={"name": "check_lifespan", "arguments": {}},
                 )
-                ),
-                raw=None,
             )
         )
 
         # Get response and verify
         response = await receive_stream2.receive()
-        assert response.message.root.result["content"][0]["text"] == "true"
+        assert response.root.result["content"][0]["text"] == "true"
 
         # Cancel server task
         tg.cancel_scope.cancel()
@@ -188,51 +178,42 @@ async def test_fastmcp_server_lifespan():
             clientInfo=Implementation(name="test-client", version="0.1.0"),
         )
         await send_stream1.send(
-            MessageFrame(
+            JSONRPCMessage(
-                message=JSONRPCMessage(
                 root=JSONRPCRequest(
                     jsonrpc="2.0",
                     id=1,
                     method="initialize",
                     params=TypeAdapter(InitializeRequestParams).dump_python(params),
                 )
-                ),
-                raw=None,
             )
         )
         response = await receive_stream2.receive()
 
         # Send initialized notification
         await send_stream1.send(
-            MessageFrame(
+            JSONRPCMessage(
-                message=JSONRPCMessage(
                 root=JSONRPCNotification(
                     jsonrpc="2.0",
                     method="notifications/initialized",
                 )
-                ),
-                raw=None,
             )
         )
 
         # Call the tool to verify lifespan context
         await send_stream1.send(
-            MessageFrame(
+            JSONRPCMessage(
-                message=JSONRPCMessage(
                 root=JSONRPCRequest(
                     jsonrpc="2.0",
                     id=2,
                     method="tools/call",
                     params={"name": "check_lifespan", "arguments": {}},
                 )
-                ),
-                raw=None,
             )
         )
 
         # Get response and verify
         response = await receive_stream2.receive()
-        assert response.message.root.result["content"][0]["text"] == "true"
+        assert response.root.result["content"][0]["text"] == "true"
 
         # Cancel server task
         tg.cancel_scope.cancel()

tests/server/test_session.py

@@ -9,7 +9,7 @@ from mcp.server.session import ServerSession
 from mcp.types import (
     ClientNotification,
     InitializedNotification,
-    MessageFrame,
+    JSONRPCMessage,
     PromptsCapability,
     ResourcesCapability,
     ServerCapabilities,
@@ -19,10 +19,10 @@ from mcp.types import (
 @pytest.mark.anyio
 async def test_server_session_initialize():
     server_to_client_send, server_to_client_receive = anyio.create_memory_object_stream[
-        MessageFrame[None]
+        JSONRPCMessage
     ](1)
     client_to_server_send, client_to_server_receive = anyio.create_memory_object_stream[
-        MessageFrame[None]
+        JSONRPCMessage
     ](1)
 
     async def run_client(client: ClientSession):

tests/server/test_stdio.py

@@ -4,7 +4,7 @@ import anyio
 import pytest
 
 from mcp.server.stdio import stdio_server
-from mcp.types import JSONRPCMessage, JSONRPCRequest, JSONRPCResponse, MessageFrame
+from mcp.types import JSONRPCMessage, JSONRPCRequest, JSONRPCResponse
 
 
 @pytest.mark.anyio
@@ -13,8 +13,8 @@ async def test_stdio_server():
     stdout = io.StringIO()
 
     messages = [
-        JSONRPCRequest(jsonrpc="2.0", id=1, method="ping"),
+        JSONRPCMessage(root=JSONRPCRequest(jsonrpc="2.0", id=1, method="ping")),
-        JSONRPCResponse(jsonrpc="2.0", id=2, result={}),
+        JSONRPCMessage(root=JSONRPCResponse(jsonrpc="2.0", id=2, result={})),
     ]
 
     for message in messages:
@@ -35,29 +35,17 @@ async def test_stdio_server():
 
         # Verify received messages
         assert len(received_messages) == 2
-        assert isinstance(received_messages[0].message, JSONRPCMessage)
+        assert received_messages[0] == JSONRPCMessage(
-        assert isinstance(received_messages[0].message.root, JSONRPCRequest)
+            root=JSONRPCRequest(jsonrpc="2.0", id=1, method="ping")
-        assert received_messages[0].message.root.id == 1
+        )
-        assert received_messages[0].message.root.method == "ping"
+        assert received_messages[1] == JSONRPCMessage(
-
+            root=JSONRPCResponse(jsonrpc="2.0", id=2, result={})
-        assert isinstance(received_messages[1].message, JSONRPCMessage)
+        )
-        assert isinstance(received_messages[1].message.root, JSONRPCResponse)
-        assert received_messages[1].message.root.id == 2
 
         # Test sending responses from the server
         responses = [
-            MessageFrame(
+            JSONRPCMessage(root=JSONRPCRequest(jsonrpc="2.0", id=3, method="ping")),
-                message=JSONRPCMessage(
+            JSONRPCMessage(root=JSONRPCResponse(jsonrpc="2.0", id=4, result={})),
-                    root=JSONRPCRequest(jsonrpc="2.0", id=3, method="ping")
-                ),
-                raw=None,
-            ),
-            MessageFrame(
-                message=JSONRPCMessage(
-                    root=JSONRPCResponse(jsonrpc="2.0", id=4, result={})
-                ),
-                raw=None,
-            ),
         ]
 
         async with write_stream:
@@ -68,10 +56,13 @@ async def test_stdio_server():
     output_lines = stdout.readlines()
     assert len(output_lines) == 2
 
-    # Parse and verify the JSON responses directly
+    received_responses = [
-    request_json = JSONRPCRequest.model_validate_json(output_lines[0].strip())
+        JSONRPCMessage.model_validate_json(line.strip()) for line in output_lines
-    response_json = JSONRPCResponse.model_validate_json(output_lines[1].strip())
+    ]
-
+    assert len(received_responses) == 2
-    assert request_json.id == 3
+    assert received_responses[0] == JSONRPCMessage(
-    assert request_json.method == "ping"
+        root=JSONRPCRequest(jsonrpc="2.0", id=3, method="ping")
-    assert response_json.id == 4
+    )
+    assert received_responses[1] == JSONRPCMessage(
+        root=JSONRPCResponse(jsonrpc="2.0", id=4, result={})
+    )