Fix SSE server transport to correctly handle leading slashes in session URL

PawitRoy · PawitRoy · commit 451c35afafbb · 2025-04-07T21:31:04.000+07:00
diff --git a/src/mcp/server/sse.py b/src/mcp/server/sse.py
@@ -37,6 +37,7 @@ async def handle_sse(request):
 from urllib.parse import quote
 from uuid import UUID, uuid4
 import os
+import re
 
 import anyio
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
@@ -99,7 +100,7 @@ async def connect_sse(self, scope: Scope, receive: Receive, send: Send):
         session_id = uuid4()
         session_uri = f"{quote(self._endpoint)}?session_id={session_id.hex}"
         # join the base path and endpoint
-        session_full_url = os.path.join(self._base_path, session_uri.replace("$/", ""))
+        session_full_url = os.path.join(self._base_path, re.sub("^/", "", session_uri, 1))
         self._read_stream_writers[session_id] = read_stream_writer
         logger.debug(f"Created new session with ID: {session_id}")
 
