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

This reverts commit 9d0f2daddb.

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_writer: ReadStreamWriter
+    read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
+    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
 
-    write_stream: WriteStream
-    write_stream_reader: WriteStreamReader
+    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
+    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(
-                        MessageFrame(message=message, raw=line)
-                    )
+                    await read_stream_writer.send(message)
         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()