René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"MCP server in the HTTP Streamable mode broken","articleBody":"Starting from v1.12.0 (checked with v1.12.0 and v1.12.1) any request to the MCP server in the HTTP Streamable mode produces an error:\n\n```plaintext\nINFO:     127.0.0.1:32926 - \"POST /mcp/ HTTP/1.1\" 307 Temporary Redirect\n[07/23/25 16:34:18] INFO     Processing request of type ListToolsRequest                                        server.py:625\nINFO:     127.0.0.1:32926 - \"POST /mcp HTTP/1.1\" 200 OK\n                    INFO     Terminating session: None                                                 streamable_http.py:630\n                    ERROR    Error in message router                                                   streamable_http.py:880\n                             ╭────────────────── Traceback (most recent call last) ──────────────────╮                       \n                             │ /usr/local/lib/python3.12/site-packages/mcp/server/streamable_http.py │                       \n                             │ :831 in message_router                                                │                       \n                             │                                                                       │                       \n                             │   828 │   │   │   # Create a message router that distributes messages │                       \n                             │   829 │   │   │   async def message_router():                         │                       \n                             │   830 │   │   │   │   try:                                            │                       \n                             │ ❱ 831 │   │   │   │   │   async for session_message in write_stream_r │                       \n                             │   832 │   │   │   │   │   │   # Determine which request stream(s) sho │                       \n                             │   833 │   │   │   │   │   │   message = session_message.message       │                       \n                             │   834 │   │   │   │   │   │   target_request_id = None                │                       \n                             │                                                                       │                       \n                             │ /usr/local/lib/python3.12/site-packages/anyio/abc/_streams.py:35 in   │                       \n                             │ __anext__                                                             │                       \n                             │                                                                       │                       \n                             │    32 │                                                               │                       \n                             │    33 │   async def __anext__(self) -\u003e T_co:                          │                       \n                             │    34 │   │   try:                                                    │                       \n                             │ ❱  35 │   │   │   return await self.receive()                         │                       \n                             │    36 │   │   except EndOfStream:                                     │                       \n                             │    37 │   │   │   raise StopAsyncIteration                            │                       \n                             │    38                                                                 │                       \n                             │                                                                       │                       \n                             │ /usr/local/lib/python3.12/site-packages/anyio/streams/memory.py:111   │                       \n                             │ in receive                                                            │                       \n                             │                                                                       │                       \n                             │   108 │   async def receive(self) -\u003e T_co:                            │                       \n                             │   109 │   │   await checkpoint()                                      │                       \n                             │   110 │   │   try:                                                    │                       \n                             │ ❱ 111 │   │   │   return self.receive_nowait()                        │                       \n                             │   112 │   │   except WouldBlock:                                      │                       \n                             │   113 │   │   │   # Add ourselves in the queue                        │                       \n                             │   114 │   │   │   receive_event = Event()                             │                       \n                             │                                                                       │                       \n                             │ /usr/local/lib/python3.12/site-packages/anyio/streams/memory.py:93 in │                       \n                             │ receive_nowait                                                        │                       \n                             │                                                                       │                       \n                             │    90 │   │                                                           │                       \n                             │    91 │   │   \"\"\"                                                     │                       \n                             │    92 │   │   if self._closed:                                        │                       \n                             │ ❱  93 │   │   │   raise ClosedResourceError                           │                       \n                             │    94 │   │                                                           │                       \n                             │    95 │   │   if self._state.waiting_senders:                         │                       \n                             │    96 │   │   │   # Get the item from the next sender                 │                       \n                             ╰───────────────────────────────────────────────────────────────────────╯                       \n                             ClosedResourceError\n```\n\nRollback to 1.11.0 fix the issue.","author":{"url":"https://github.com/akolotov","@type":"Person","name":"akolotov"},"datePublished":"2025-07-23T16:54:13.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":20},"url":"https://github.com/1190/python-sdk/issues/1190"}