Fix clean up sse disconnect event (not upgrade lib)

src/mcp/server/sse.py

@@ -145,7 +145,12 @@ async def sse_writer():
 
         async with anyio.create_task_group() as tg:
 
-            async def response_wrapper(scope: Scope, receive: Receive, send: Send):
+            async def response_wrapper(
+                scope: Scope,
+                receive: Receive,
+                send: Send,
+                transport: SseServerTransport,
+            ):
                 """
                 The EventSourceResponse returning signals a client close / disconnect.
                 In this case we close our side of the streams to signal the client that
@@ -156,10 +161,13 @@ async def response_wrapper(scope: Scope, receive: Receive, send: Send):
                 )(scope, receive, send)
                 await read_stream_writer.aclose()
                 await write_stream_reader.aclose()
+                await read_stream.aclose()
+                await write_stream.aclose()
+                transport._read_stream_writers.pop(session_id)
                 logging.debug(f"Client session disconnected {session_id}")
 
             logger.debug("Starting SSE response task")
-            tg.start_soon(response_wrapper, scope, receive, send)
+            tg.start_soon(response_wrapper, scope, receive, send, self)
 
             logger.debug("Yielding read and write streams")
             yield (read_stream, write_stream)

tests/server/test_sse_disconnect.py

@@ -0,0 +1,53 @@
+import asyncio
+from uuid import UUID
+
+import pytest
+from starlette.types import Message, Scope
+
+from mcp.server.sse import SseServerTransport
+
+
+@pytest.mark.anyio
+async def test_sse_disconnect_handle():
+    transport = SseServerTransport(endpoint="/sse")
+    # Create a minimal ASGI scope for an HTTP GET request
+    scope: Scope = {
+        "type": "http",
+        "method": "GET",
+        "path": "/sse",
+        "headers": [],
+    }
+    send_disconnect = False
+
+    # Dummy receive and send functions
+    async def receive() -> dict:
+        nonlocal send_disconnect
+        if not send_disconnect:
+            send_disconnect = True
+            return {"type": "http.request"}
+        else:
+            return {"type": "http.disconnect"}
+
+    async def send(message: Message) -> None:
+        await asyncio.sleep(0)
+
+    # Run the connect_sse context manager
+    async with transport.connect_sse(scope, receive, send) as (
+        read_stream,
+        write_stream,
+    ):
+        # Assert that streams are provided
+        assert read_stream is not None
+        assert write_stream is not None
+
+        # There should be exactly one session
+        assert len(transport._read_stream_writers) == 1
+        # Check that the session key is a UUID
+        session_id = next(iter(transport._read_stream_writers.keys()))
+        assert isinstance(session_id, UUID)
+
+    # Check that the session_id should be clean up
+    assert session_id not in transport._read_stream_writers
+
+    # After context exits, session should be cleaned up
+    assert len(transport._read_stream_writers) == 0