fix: clean up SSE session on client disconnect

Varun Sharma · Copilot · Varun Sharma · commit 1fce2fdc6b83 · 2026-03-02T17:16:17.000+05:30
Remove session from _read_stream_writers when a client disconnects from the SSE endpoint. Previously, stale session entries accumulated indefinitely, causing issues after server reloads where old session IDs would still be found in the dict (but with closed streams). Fixes #423 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
diff --git a/src/mcp/server/sse.py b/src/mcp/server/sse.py
@@ -186,6 +186,7 @@ async def response_wrapper(scope: Scope, receive: Receive, send: Send):
                 )
                 await read_stream_writer.aclose()
                 await write_stream_reader.aclose()
+                self._read_stream_writers.pop(session_id, None)
                 logging.debug(f"Client session disconnected {session_id}")
 
             logger.debug("Starting SSE response task")

Original file line number	Diff line number	Diff line change
`@@ -186,6 +186,7 @@ async def response_wrapper(scope: Scope, receive: Receive, send: Send):`
`186`	`186`	`)`
`187`	`187`	`await read_stream_writer.aclose()`
`188`	`188`	`await write_stream_reader.aclose()`
	`189`	`+ self._read_stream_writers.pop(session_id, None)`
`189`	`190`	`logging.debug(f"Client session disconnected {session_id}")`
`190`	`191`
`191`	`192`	`logger.debug("Starting SSE response task")`