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MCP Streamable-HTTP client errors #21

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MCP Streamable-HTTP client errors#21
@jeffbrl

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@jeffbrl
jeffbrl
opened on Nov 19, 2025

Thank you for the great video and code. This is the best resource I've found on the interwebs.

I noticed this behavior on WSL2 and Windows 11. Client gets an answer along with many traceback messages.

client

python .\client-streamable-http.py
Exception ignored in: <async_generator object HTTP11ConnectionByteStream.__aiter__ at 0x000001DB103C8A40>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\connection_pool.py", line 404, in __aiter__
    yield part
RuntimeError: async generator ignored GeneratorExit
Exception ignored in: <coroutine object HTTP11ConnectionByteStream.aclose at 0x000001DB103BACE0>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 348, in aclose
    await self._connection._response_closed()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 239, in _response_closed
    async with self._state_lock:
               ^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_synchronization.py", line 77, in __aenter__
    await self._anyio_lock.acquire()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 1808, in acquire
    await AsyncIOBackend.cancel_shielded_checkpoint()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2364, in cancel_shielded_checkpoint
    with CancelScope(shield=True):
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 459, in __exit__
    raise RuntimeError(
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
Exception ignored in: <async_generator object HTTP11ConnectionByteStream.__aiter__ at 0x000001DB103CA140>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\connection_pool.py", line 404, in __aiter__
    yield part
RuntimeError: async generator ignored GeneratorExit
Available tools:
  - add: Add two numbers together
Exception ignored in: <coroutine object HTTP11ConnectionByteStream.aclose at 0x000001DB11794580>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 348, in aclose
    await self._connection._response_closed()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 239, in _response_closed
    async with self._state_lock:
               ^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_synchronization.py", line 77, in __aenter__
    await self._anyio_lock.acquire()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 1808, in acquire
    await AsyncIOBackend.cancel_shielded_checkpoint()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2364, in cancel_shielded_checkpoint
    with CancelScope(shield=True):
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 459, in __exit__
    raise RuntimeError(
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
Exception ignored in: <async_generator object HTTP11ConnectionByteStream.__aiter__ at 0x000001DB1038A340>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\connection_pool.py", line 404, in __aiter__
    yield part
RuntimeError: async generator ignored GeneratorExit
2 + 3 = 5
Exception ignored in: <coroutine object HTTP11ConnectionByteStream.aclose at 0x000001DB103B9EE0>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 348, in aclose
    await self._connection._response_closed()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 239, in _response_closed
    async with self._state_lock:
               ^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_synchronization.py", line 77, in __aenter__
    await self._anyio_lock.acquire()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 1808, in acquire
    await AsyncIOBackend.cancel_shielded_checkpoint()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2364, in cancel_shielded_checkpoint
    with CancelScope(shield=True):
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 458, in __exit__
    if current_task() is not self._host_task:
       ^^^^^^^^^^^^^^
RuntimeError: no running event loop

server

python .\server.py
Running server with Streamable HTTP transport
INFO:     Started server process [10104]
INFO:     Waiting for application startup.
[11/19/25 16:06:27] INFO     StreamableHTTP session manager started                       streamable_http_manager.py:112
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8057 (Press CTRL+C to quit)
INFO:     127.0.0.1:61023 - "POST /mcp HTTP/1.1" 307 Temporary Redirect
INFO:     127.0.0.1:61023 - "POST /mcp/ HTTP/1.1" 200 OK
INFO:     127.0.0.1:61026 - "POST /mcp HTTP/1.1" 307 Temporary Redirect
INFO:     127.0.0.1:61026 - "POST /mcp/ HTTP/1.1" 202 Accepted
INFO:     127.0.0.1:61028 - "POST /mcp HTTP/1.1" 307 Temporary Redirect
INFO:     127.0.0.1:61028 - "POST /mcp/ HTTP/1.1" 200 OK
[11/19/25 16:06:33] INFO     Processing request of type ListToolsRequest                                   server.py:619
INFO:     127.0.0.1:61030 - "POST /mcp HTTP/1.1" 307 Temporary Redirect
INFO:     127.0.0.1:61030 - "POST /mcp/ HTTP/1.1" 200 OK
                    INFO     Processing request of type CallToolRequest

I found the redirects odd. I changed the URL in the client to include a trailing / but that introduced other traceback errors.

client

python .\client-streamable-http.py
Exception ignored in: <async_generator object HTTP11ConnectionByteStream.__aiter__ at 0x000001B6E300BB40>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\connection_pool.py", line 404, in __aiter__
    yield part
RuntimeError: async generator ignored GeneratorExit
Exception ignored in: <coroutine object HTTP11ConnectionByteStream.aclose at 0x000001B6E303AC00>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 348, in aclose
    await self._connection._response_closed()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 239, in _response_closed
    async with self._state_lock:
               ^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_synchronization.py", line 77, in __aenter__
    await self._anyio_lock.acquire()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 1808, in acquire
    await AsyncIOBackend.cancel_shielded_checkpoint()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2364, in cancel_shielded_checkpoint
    with CancelScope(shield=True):
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 459, in __exit__
    raise RuntimeError(
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
Exception ignored in: <async_generator object HTTP11ConnectionByteStream.__aiter__ at 0x000001B6E3052A40>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\connection_pool.py", line 404, in __aiter__
    yield part
RuntimeError: async generator ignored GeneratorExit
Available tools:
  - add: Add two numbers together
Exception ignored in: <async_generator object HTTP11ConnectionByteStream.__aiter__ at 0x000001B6E3053240>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\connection_pool.py", line 404, in __aiter__
    yield part
RuntimeError: async generator ignored GeneratorExit
2 + 3 = 5
Exception ignored in: <coroutine object HTTP11ConnectionByteStream.aclose at 0x000001B6E303BAE0>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 348, in aclose
    await self._connection._response_closed()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 239, in _response_closed
    async with self._state_lock:
               ^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_synchronization.py", line 77, in __aenter__
    await self._anyio_lock.acquire()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 1808, in acquire
    await AsyncIOBackend.cancel_shielded_checkpoint()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2364, in cancel_shielded_checkpoint
    with CancelScope(shield=True):
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 458, in __exit__
    if current_task() is not self._host_task:
       ^^^^^^^^^^^^^^
RuntimeError: no running event loop
Exception ignored in: <coroutine object HTTP11ConnectionByteStream.aclose at 0x000001B6E305D700>
Traceback (most recent call last):
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 348, in aclose
    await self._connection._response_closed()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_async\http11.py", line 239, in _response_closed
    async with self._state_lock:
               ^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\httpcore\_synchronization.py", line 77, in __aenter__
    await self._anyio_lock.acquire()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 1808, in acquire
    await AsyncIOBackend.cancel_shielded_checkpoint()
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2364, in cancel_shielded_checkpoint
    with CancelScope(shield=True):
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Documents\development\ai-cookbook\mcp\crash-course\venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 458, in __exit__
    if current_task() is not self._host_task:
       ^^^^^^^^^^^^^^
RuntimeError: no running event loop

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