Wrap JSONRPC messages with SessionMessage for metadata support

src/mcp/client/__main__.py

@@ -11,8 +11,8 @@
 from mcp.client.session import ClientSession
 from mcp.client.sse import sse_client
 from mcp.client.stdio import StdioServerParameters, stdio_client
+from mcp.shared.message import SessionMessage
 from mcp.shared.session import RequestResponder
-from mcp.types import JSONRPCMessage
 
 if not sys.warnoptions:
     import warnings
@@ -36,8 +36,8 @@ async def message_handler(
 
 
 async def run_session(
-    read_stream: MemoryObjectReceiveStream[JSONRPCMessage | Exception],
-    write_stream: MemoryObjectSendStream[JSONRPCMessage],
+    read_stream: MemoryObjectReceiveStream[SessionMessage | Exception],
+    write_stream: MemoryObjectSendStream[SessionMessage],
     client_info: types.Implementation | None = None,
 ):
     async with ClientSession(

src/mcp/client/session.py

@@ -7,6 +7,7 @@
 
 import mcp.types as types
 from mcp.shared.context import RequestContext
+from mcp.shared.message import SessionMessage
 from mcp.shared.session import BaseSession, RequestResponder
 from mcp.shared.version import SUPPORTED_PROTOCOL_VERSIONS
 
@@ -92,8 +93,8 @@ class ClientSession(
 ):
     def __init__(
         self,
-        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        write_stream: MemoryObjectSendStream[types.JSONRPCMessage],
+        read_stream: MemoryObjectReceiveStream[SessionMessage | Exception],
+        write_stream: MemoryObjectSendStream[SessionMessage],
         read_timeout_seconds: timedelta | None = None,
         sampling_callback: SamplingFnT | None = None,
         list_roots_callback: ListRootsFnT | None = None,

src/mcp/client/sse.py

@@ -10,6 +10,7 @@
 from httpx_sse import aconnect_sse
 
 import mcp.types as types
+from mcp.shared.message import SessionMessage
 
 logger = logging.getLogger(__name__)
 
@@ -31,11 +32,11 @@ 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: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
+    read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
+    read_stream_writer: MemoryObjectSendStream[SessionMessage | Exception]
 
-    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-    write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
+    write_stream: MemoryObjectSendStream[SessionMessage]
+    write_stream_reader: MemoryObjectReceiveStream[SessionMessage]
 
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -97,7 +98,8 @@ async def sse_reader(
                                             await read_stream_writer.send(exc)
                                             continue
 
-                                        await read_stream_writer.send(message)
+                                        session_message = SessionMessage(message)
+                                        await read_stream_writer.send(session_message)
                                     case _:
                                         logger.warning(
                                             f"Unknown SSE event: {sse.event}"
@@ -111,11 +113,13 @@ async def sse_reader(
                     async def post_writer(endpoint_url: str):
                         try:
                             async with write_stream_reader:
-                                async for message in write_stream_reader:
-                                    logger.debug(f"Sending client message: {message}")
+                                async for session_message in write_stream_reader:
+                                    logger.debug(
+                                        f"Sending client message: {session_message}"
+                                    )
                                     response = await client.post(
                                         endpoint_url,
-                                        json=message.model_dump(
+                                        json=session_message.message.model_dump(
                                             by_alias=True,
                                             mode="json",
                                             exclude_none=True,

src/mcp/client/stdio/__init__.py

@@ -11,6 +11,7 @@
 from pydantic import BaseModel, Field
 
 import mcp.types as types
+from mcp.shared.message import SessionMessage
 
 from .win32 import (
     create_windows_process,
@@ -98,11 +99,11 @@ async def stdio_client(server: StdioServerParameters, errlog: TextIO = sys.stder
     Client transport for stdio: this will connect to a server by spawning a
     process and communicating with it over stdin/stdout.
     """
-    read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
+    read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
+    read_stream_writer: MemoryObjectSendStream[SessionMessage | Exception]
 
-    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-    write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
+    write_stream: MemoryObjectSendStream[SessionMessage]
+    write_stream_reader: MemoryObjectReceiveStream[SessionMessage]
 
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -143,7 +144,8 @@ async def stdout_reader():
                             await read_stream_writer.send(exc)
                             continue
 
-                        await read_stream_writer.send(message)
+                        session_message = SessionMessage(message)
+                        await read_stream_writer.send(session_message)
         except anyio.ClosedResourceError:
             await anyio.lowlevel.checkpoint()
 
@@ -152,8 +154,10 @@ async def stdin_writer():
 
         try:
             async with write_stream_reader:
-                async for message in write_stream_reader:
-                    json = message.model_dump_json(by_alias=True, exclude_none=True)
+                async for session_message in write_stream_reader:
+                    json = session_message.message.model_dump_json(
+                        by_alias=True, exclude_none=True
+                    )
                     await process.stdin.send(
                         (json + "\n").encode(
                             encoding=server.encoding,

src/mcp/client/streamable_http.py

@@ -15,6 +15,7 @@
 import httpx
 from httpx_sse import EventSource, aconnect_sse
 
+from mcp.shared.message import SessionMessage
 from mcp.types import (
     ErrorData,
     JSONRPCError,
@@ -52,10 +53,10 @@ async def streamablehttp_client(
     """
 
     read_stream_writer, read_stream = anyio.create_memory_object_stream[
-        JSONRPCMessage | Exception
+        SessionMessage | Exception
     ](0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream[
-        JSONRPCMessage
+        SessionMessage
     ](0)
 
     async def get_stream():
@@ -86,7 +87,8 @@ async def get_stream():
                         try:
                             message = JSONRPCMessage.model_validate_json(sse.data)
                             logger.debug(f"GET message: {message}")
-                            await read_stream_writer.send(message)
+                            session_message = SessionMessage(message)
+                            await read_stream_writer.send(session_message)
                         except Exception as exc:
                             logger.error(f"Error parsing GET message: {exc}")
                             await read_stream_writer.send(exc)
@@ -100,7 +102,8 @@ async def post_writer(client: httpx.AsyncClient):
         nonlocal session_id
         try:
             async with write_stream_reader:
-                async for message in write_stream_reader:
+                async for session_message in write_stream_reader:
+                    message = session_message.message
                     # Add session ID to headers if we have one
                     post_headers = request_headers.copy()
                     if session_id:
@@ -141,9 +144,10 @@ async def post_writer(client: httpx.AsyncClient):
                                         message="Session terminated",
                                     ),
                                 )
-                                await read_stream_writer.send(
+                                session_message = SessionMessage(
                                     JSONRPCMessage(jsonrpc_error)
                                 )
+                                await read_stream_writer.send(session_message)
                                 continue
                         response.raise_for_status()
 
@@ -163,7 +167,8 @@ async def post_writer(client: httpx.AsyncClient):
                                 json_message = JSONRPCMessage.model_validate_json(
                                     content
                                 )
-                                await read_stream_writer.send(json_message)
+                                session_message = SessionMessage(json_message)
+                                await read_stream_writer.send(session_message)
                             except Exception as exc:
                                 logger.error(f"Error parsing JSON response: {exc}")
                                 await read_stream_writer.send(exc)
@@ -175,11 +180,15 @@ async def post_writer(client: httpx.AsyncClient):
                                 async for sse in event_source.aiter_sse():
                                     if sse.event == "message":
                                         try:
-                                            await read_stream_writer.send(
+                                            message = (
                                                 JSONRPCMessage.model_validate_json(
                                                     sse.data
                                                 )
                                             )
+                                            session_message = SessionMessage(message)
+                                            await read_stream_writer.send(
+                                                session_message
+                                            )
                                         except Exception as exc:
                                             logger.exception("Error parsing message")
                                             await read_stream_writer.send(exc)

src/mcp/client/websocket.py

@@ -10,6 +10,7 @@
 from websockets.typing import Subprotocol
 
 import mcp.types as types
+from mcp.shared.message import SessionMessage
 
 logger = logging.getLogger(__name__)
 
@@ -19,8 +20,8 @@ async def websocket_client(
     url: str,
 ) -> AsyncGenerator[
     tuple[
-        MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        MemoryObjectSendStream[types.JSONRPCMessage],
+        MemoryObjectReceiveStream[SessionMessage | Exception],
+        MemoryObjectSendStream[SessionMessage],
     ],
     None,
 ]:
@@ -39,10 +40,10 @@ async def websocket_client(
     # Create two in-memory streams:
     # - One for incoming messages (read_stream, written by ws_reader)
     # - One for outgoing messages (write_stream, read by ws_writer)
-    read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
-    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-    write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
+    read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
+    read_stream_writer: MemoryObjectSendStream[SessionMessage | Exception]
+    write_stream: MemoryObjectSendStream[SessionMessage]
+    write_stream_reader: MemoryObjectReceiveStream[SessionMessage]
 
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -59,7 +60,8 @@ async def ws_reader():
                 async for raw_text in ws:
                     try:
                         message = types.JSONRPCMessage.model_validate_json(raw_text)
-                        await read_stream_writer.send(message)
+                        session_message = SessionMessage(message)
+                        await read_stream_writer.send(session_message)
                     except ValidationError as exc:
                         # If JSON parse or model validation fails, send the exception
                         await read_stream_writer.send(exc)
@@ -70,9 +72,9 @@ async def ws_writer():
             sends them to the server.
             """
             async with write_stream_reader:
-                async for message in write_stream_reader:
+                async for session_message in write_stream_reader:
                     # Convert to a dict, then to JSON
-                    msg_dict = message.model_dump(
+                    msg_dict = session_message.message.model_dump(
                         by_alias=True, mode="json", exclude_none=True
                     )
                     await ws.send(json.dumps(msg_dict))

src/mcp/server/lowlevel/server.py

@@ -84,6 +84,7 @@ async def main():
 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.message import SessionMessage
 from mcp.shared.session import RequestResponder
 
 logger = logging.getLogger(__name__)
@@ -471,8 +472,8 @@ async def handler(req: types.CompleteRequest):
 
     async def run(
         self,
-        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        write_stream: MemoryObjectSendStream[types.JSONRPCMessage],
+        read_stream: MemoryObjectReceiveStream[SessionMessage | Exception],
+        write_stream: MemoryObjectSendStream[SessionMessage],
         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/session.py

@@ -47,6 +47,7 @@ async def handle_list_prompts(ctx: RequestContext) -> list[types.Prompt]:
 
 import mcp.types as types
 from mcp.server.models import InitializationOptions
+from mcp.shared.message import SessionMessage
 from mcp.shared.session import (
     BaseSession,
     RequestResponder,
@@ -82,8 +83,8 @@ class ServerSession(
 
     def __init__(
         self,
-        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        write_stream: MemoryObjectSendStream[types.JSONRPCMessage],
+        read_stream: MemoryObjectReceiveStream[SessionMessage | Exception],
+        write_stream: MemoryObjectSendStream[SessionMessage],
         init_options: InitializationOptions,
         stateless: bool = False,
     ) -> None:

src/mcp/server/sse.py

@@ -46,6 +46,7 @@ async def handle_sse(request):
 from starlette.types import Receive, Scope, Send
 
 import mcp.types as types
+from mcp.shared.message import SessionMessage
 
 logger = logging.getLogger(__name__)
 
@@ -63,9 +64,7 @@ class SseServerTransport:
     """
 
     _endpoint: str
-    _read_stream_writers: dict[
-        UUID, MemoryObjectSendStream[types.JSONRPCMessage | Exception]
-    ]
+    _read_stream_writers: dict[UUID, MemoryObjectSendStream[SessionMessage | Exception]]
 
     def __init__(self, endpoint: str) -> None:
         """
@@ -85,11 +84,11 @@ async def connect_sse(self, scope: Scope, receive: Receive, send: Send):
             raise ValueError("connect_sse can only handle HTTP requests")
 
         logger.debug("Setting up SSE connection")
-        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-        read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
+        read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
+        read_stream_writer: MemoryObjectSendStream[SessionMessage | Exception]
 
-        write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-        write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
+        write_stream: MemoryObjectSendStream[SessionMessage]
+        write_stream_reader: MemoryObjectReceiveStream[SessionMessage]
 
         read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
         write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -109,12 +108,12 @@ async def sse_writer():
                 await sse_stream_writer.send({"event": "endpoint", "data": session_uri})
                 logger.debug(f"Sent endpoint event: {session_uri}")
 
-                async for message in write_stream_reader:
-                    logger.debug(f"Sending message via SSE: {message}")
+                async for session_message in write_stream_reader:
+                    logger.debug(f"Sending message via SSE: {session_message}")
                     await sse_stream_writer.send(
                         {
                             "event": "message",
-                            "data": message.model_dump_json(
+                            "data": session_message.message.model_dump_json(
                                 by_alias=True, exclude_none=True
                             ),
                         }
@@ -169,7 +168,8 @@ async def handle_post_message(
             await writer.send(err)
             return
 
-        logger.debug(f"Sending message to writer: {message}")
+        session_message = SessionMessage(message)
+        logger.debug(f"Sending session message to writer: {session_message}")
         response = Response("Accepted", status_code=202)
         await response(scope, receive, send)
-        await writer.send(message)
+        await writer.send(session_message)