[bug]: httpcore.RemoteProtocolError: Server disconnected without sending a response.

[R0Wi]

Describe the bug
When using the context chat function, I (sometimes) get the Exception: httpcore.RemoteProtocolError: Server disconnected without sending a response.

To Reproduce
Steps to reproduce the behavior:

1. Go to Context Chat in NC frontend
2. Type in a question
3. Click on "Context Chat"

Expected behavior
A clear and concise description of what you expected to happen.

Server logs (if applicable)

{"reqId":"2zSA1egPbXxBNR6l8KVy","level":3,"time":"2025-01-02T19:32:36+00:00","remoteAddr":"","user":"--","app":"no app in context","method":"","url":"--","message":"Unknown error while processing TaskProcessing task","userAgent":"--","version":"30.0.4.1","exception":{"Exception":"RuntimeException","Message":"Error received from Context Chat Backend (ExApp) with status code 500: unknown error","Code":0,"Trace":[{"file":"/var/www/html/custom_apps/context_chat/lib/Service/LangRopeService.php","line":311,"function":"requestToExApp","class":"OCA\\ContextChat\\Service\\LangRopeService","type":"->","args":["/query","POST",{"query":"PROMPT","userId":"usr","useContext":true}]},{"file":"/var/www/html/custom_apps/context_chat/lib/TaskProcessing/ContextChatProvider.php","line":118,"function":"query","class":"OCA\\ContextChat\\Service\\LangRopeService","type":"->","args":["usr","WPROMPT"]},{"file":"/var/www/html/lib/private/TaskProcessing/Manager.php","line":810,"function":"process","class":"OCA\\ContextChat\\TaskProcessing\\ContextChatProvider","type":"->","args":["usr",{"prompt":"PROMPT","scopeType":"none","scopeList":[],"scopeListMeta":"[]"},{"__class__":"Closure"}]},{"file":"/var/www/html/lib/private/TaskProcessing/SynchronousBackgroundJob.php","line":54,"function":"processTask","class":"OC\\TaskProcessing\\Manager","type":"->","args":[{"__class__":"OCP\\TaskProcessing\\Task"},{"__class__":"OCA\\ContextChat\\TaskProcessing\\ContextChatProvider"}]},{"file":"/var/www/html/lib/public/BackgroundJob/Job.php","line":61,"function":"run","class":"OC\\TaskProcessing\\SynchronousBackgroundJob","type":"->","args":[null]},{"file":"/var/www/html/lib/public/BackgroundJob/QueuedJob.php","line":43,"function":"start","class":"OCP\\BackgroundJob\\Job","type":"->","args":[{"__class__":"OC\\BackgroundJob\\JobList"}]},{"file":"/var/www/html/lib/public/BackgroundJob/QueuedJob.php","line":29,"function":"start","class":"OCP\\BackgroundJob\\QueuedJob","type":"->","args":[{"__class__":"OC\\BackgroundJob\\JobList"}]},{"file":"/var/www/html/core/Command/Background/JobWorker.php","line":129,"function":"execute","class":"OCP\\BackgroundJob\\QueuedJob","type":"->","args":[{"__class__":"OC\\BackgroundJob\\JobList"}]},{"file":"/var/www/html/3rdparty/symfony/console/Command/Command.php","line":326,"function":"execute","class":"OC\\Core\\Command\\Background\\JobWorker","type":"->","args":[{"__class__":"Symfony\\Component\\Console\\Input\\ArgvInput"},{"__class__":"Symfony\\Component\\Console\\Output\\ConsoleOutput"}]},{"file":"/var/www/html/core/Command/Base.php","line":161,"function":"run","class":"Symfony\\Component\\Console\\Command\\Command","type":"->","args":[{"__class__":"Symfony\\Component\\Console\\Input\\ArgvInput"},{"__class__":"Symfony\\Component\\Console\\Output\\ConsoleOutput"}]},{"file":"/var/www/html/3rdparty/symfony/console/Application.php","line":1078,"function":"run","class":"OC\\Core\\Command\\Base","type":"->","args":[{"__class__":"Symfony\\Component\\Console\\Input\\ArgvInput"},{"__class__":"Symfony\\Component\\Console\\Output\\ConsoleOutput"}]},{"file":"/var/www/html/3rdparty/symfony/console/Application.php","line":324,"function":"doRunCommand","class":"Symfony\\Component\\Console\\Application","type":"->","args":[{"__class__":"OC\\Core\\Command\\Background\\JobWorker"},{"__class__":"Symfony\\Component\\Console\\Input\\ArgvInput"},{"__class__":"Symfony\\Component\\Console\\Output\\ConsoleOutput"}]},{"file":"/var/www/html/3rdparty/symfony/console/Application.php","line":175,"function":"doRun","class":"Symfony\\Component\\Console\\Application","type":"->","args":[{"__class__":"Symfony\\Component\\Console\\Input\\ArgvInput"},{"__class__":"Symfony\\Component\\Console\\Output\\ConsoleOutput"}]},{"file":"/var/www/html/lib/private/Console/Application.php","line":183,"function":"run","class":"Symfony\\Component\\Console\\Application","type":"->","args":[{"__class__":"Symfony\\Component\\Console\\Input\\ArgvInput"},{"__class__":"Symfony\\Component\\Console\\Output\\ConsoleOutput"}]},{"file":"/var/www/html/console.php","line":87,"function":"run","class":"OC\\Console\\Application","type":"->","args":[{"__class__":"Symfony\\Component\\Console\\Input\\ArgvInput"}]},{"file":"/var/www/html/occ","line":11,"args":["/var/www/html/console.php"],"function":"require_once"}],"File":"/var/www/html/custom_apps/context_chat/lib/Service/LangRopeService.php","Line":166,"message":"Unknown error while processing TaskProcessing task","exception":[],"CustomMessage":"Unknown error while processing TaskProcessing task"},"id":"6776ef57ad2aa"}

{"reqId":"2zSA1egPbXxBNR6l8KVy","level":2,"time":"2025-01-02T19:32:36+00:00","remoteAddr":"","user":"--","app":"no app in context","method":"","url":"--","message":"A TaskProcessing context_chat:context_chat task with id 73 failed with the following message: Error received from Context Chat Backend (ExApp) with status code 500: unknown error","userAgent":"--","version":"30.0.4.1","data":[],"id":"6776ef57ad27f"}

Context Chat Backend logs (if applicable, from the docker container)

id=74 status='STATUS_SCHEDULED' output=None
id=74 status='STATUS_RUNNING' output=None
id=74 status='STATUS_RUNNING' output=None
original traceback: Traceback (most recent call last):
  File "/usr/local/lib/python3.11/dist-packages/httpx/_transports/default.py", line 101, in map_httpcore_exceptions
    yield
  File "/usr/local/lib/python3.11/dist-packages/httpx/_transports/default.py", line 250, in handle_request
    resp = self._pool.handle_request(req)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpcore/_sync/connection_pool.py", line 256, in handle_request
    raise exc from None
  File "/usr/local/lib/python3.11/dist-packages/httpcore/_sync/connection_pool.py", line 236, in handle_request
    response = connection.handle_request(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpcore/_sync/connection.py", line 103, in handle_request
    return self._connection.handle_request(request)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpcore/_sync/http11.py", line 136, in handle_request
    raise exc
  File "/usr/local/lib/python3.11/dist-packages/httpcore/_sync/http11.py", line 106, in handle_request
    ) = self._receive_response_headers(**kwargs)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpcore/_sync/http11.py", line 177, in _receive_response_headers
    event = self._receive_event(timeout=timeout)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpcore/_sync/http11.py", line 231, in _receive_event
    raise RemoteProtocolError(msg)
httpcore.RemoteProtocolError: Server disconnected without sending a response.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/app/context_chat_backend/utils.py", line 94, in exception_wrap
    resconn.send({ 'value': fun(*args, **kwargs), 'error': None })
                            ^^^^^^^^^^^^^^^^^^^^
  File "/app/context_chat_backend/chain/one_shot.py", line 70, in process_context_query
    output = llm.invoke(
             ^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/langchain_core/language_models/llms.py", line 390, in invoke
    self.generate_prompt(
  File "/usr/local/lib/python3.11/dist-packages/langchain_core/language_models/llms.py", line 755, in generate_prompt
    return self.generate(prompt_strings, stop=stop, callbacks=callbacks, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/langchain_core/language_models/llms.py", line 950, in generate
    output = self._generate_helper(
             ^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/langchain_core/language_models/llms.py", line 792, in _generate_helper
    raise e
  File "/usr/local/lib/python3.11/dist-packages/langchain_core/language_models/llms.py", line 779, in _generate_helper
    self._generate(
  File "/usr/local/lib/python3.11/dist-packages/langchain_core/language_models/llms.py", line 1502, in _generate
    self._call(prompt, stop=stop, run_manager=run_manager, **kwargs)
  File "/app/context_chat_backend/models/nc_texttotext.py", line 85, in _call
    i += 1
           
  File "/usr/local/lib/python3.11/dist-packages/nc_py_api/nextcloud.py", line 144, in ocs
    return self._session.ocs(method, path, content=content, json=json, params=params, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/nc_py_api/_session.py", line 207, in ocs
    response = self.adapter.request(
               ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpx/_client.py", line 825, in request
    return self.send(request, auth=auth, follow_redirects=follow_redirects)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpx/_client.py", line 914, in send
    response = self._send_handling_auth(
               ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpx/_client.py", line 942, in _send_handling_auth
    response = self._send_handling_redirects(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpx/_client.py", line 979, in _send_handling_redirects
    response = self._send_single_request(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpx/_client.py", line 1014, in _send_single_request
    response = transport.handle_request(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/httpx/_transports/default.py", line 249, in handle_request
    with map_httpcore_exceptions():
  File "/usr/lib/python3.11/contextlib.py", line 158, in __exit__
    self.gen.throw(typ, value, traceback)
  File "/usr/local/lib/python3.11/dist-packages/httpx/_transports/default.py", line 118, in map_httpcore_exceptions
    raise mapped_exc(message) from exc
httpx.RemoteProtocolError: Server disconnected without sending a response.

TRACE:    172.22.0.8:38990 - ASGI [17] Send {'type': 'http.response.start', 'status': 500, 'headers': '<...>'}
INFO:     172.22.0.8:38990 - "POST /query HTTP/1.1" 500 Internal Server Error
TRACE:    172.22.0.8:38990 - ASGI [17] Send {'type': 'http.response.body', 'body': '<3521 bytes>'}
TRACE:    172.22.0.8:38990 - ASGI [17] Raised exception
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/dist-packages/uvicorn/protocols/http/h11_impl.py", line 403, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/uvicorn/middleware/proxy_headers.py", line 60, in __call__
    return await self.app(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/uvicorn/middleware/message_logger.py", line 84, in __call__
    raise exc from None
  File "/usr/local/lib/python3.11/dist-packages/uvicorn/middleware/message_logger.py", line 80, in __call__
    await self.app(scope, inner_receive, inner_send)
  File "/usr/local/lib/python3.11/dist-packages/fastapi/applications.py", line 1054, in __call__
    await super().__call__(scope, receive, send)
  File "/usr/local/lib/python3.11/dist-packages/starlette/applications.py", line 113, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/usr/local/lib/python3.11/dist-packages/starlette/middleware/errors.py", line 187, in __call__
    raise exc
  File "/usr/local/lib/python3.11/dist-packages/starlette/middleware/errors.py", line 165, in __call__
    await self.app(scope, receive, _send)
  File "/app/context_chat_backend/ocs_utils.py", line 79, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.11/dist-packages/starlette/middleware/exceptions.py", line 62, in __call__
    await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  File "/usr/local/lib/python3.11/dist-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    raise exc
  File "/usr/local/lib/python3.11/dist-packages/starlette/_exception_handler.py", line 42, in wrapped_app
    await app(scope, receive, sender)
  File "/usr/local/lib/python3.11/dist-packages/starlette/routing.py", line 715, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/usr/local/lib/python3.11/dist-packages/starlette/routing.py", line 735, in app
    await route.handle(scope, receive, send)
  File "/usr/local/lib/python3.11/dist-packages/starlette/routing.py", line 288, in handle
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.11/dist-packages/starlette/routing.py", line 76, in app
    await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  File "/usr/local/lib/python3.11/dist-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    raise exc
  File "/usr/local/lib/python3.11/dist-packages/starlette/_exception_handler.py", line 42, in wrapped_app
    await app(scope, receive, sender)
  File "/usr/local/lib/python3.11/dist-packages/starlette/routing.py", line 73, in app
    response = await f(request)
               ^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/fastapi/routing.py", line 301, in app
    raw_response = await run_endpoint_function(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/fastapi/routing.py", line 214, in run_endpoint_function
    return await run_in_threadpool(dependant.call, **values)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/starlette/concurrency.py", line 39, in run_in_threadpool
    return await anyio.to_thread.run_sync(func, *args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/anyio/to_thread.py", line 56, in run_sync
    return await get_async_backend().run_sync_in_worker_thread(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/anyio/_backends/_asyncio.py", line 2505, in run_sync_in_worker_thread
    return await future
           ^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/anyio/_backends/_asyncio.py", line 1005, in run
    result = context.run(func, *args)
             ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/context_chat_backend/controller.py", line 163, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/app/context_chat_backend/controller.py", line 390, in _
    return execute_query(query)
           ^^^^^^^^^^^^^^^^^^^^
  File "/app/context_chat_backend/controller.py", line 379, in execute_query
    return exec_in_proc(target=target, args=args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/context_chat_backend/utils.py", line 117, in exec_in_proc
    raise result['error']
httpx.RemoteProtocolError: Server disconnected without sending a response.
TRACE:    172.22.0.8:38990 - HTTP connection lost

Setup Details (please complete the following information):

• Nextcloud Version: 30.0
• AppAPI Version: 4.0.3
• Context Chat PHP Version 4.0.1
• Context Chat Backend Version 4.0.1
• Nextcloud deployment method: Docker
• Context Chat Backend deployment method: [Docker

Additional context
The issue is not always reproducible. I can only tell that it happens in the /ocs/v1.php/taskprocessing/task/ call. I was able to find a (ugly) workaround by catching the raised exception:

context_chat_backend/context_chat_backend/models/nc_texttotext.py

Line 85 in c70d7d8

response = nc.ocs("GET", f"/ocs/v1.php/taskprocessing/task/{task.id}")

        try:
            task = Response.model_validate(response).task
            print(task)

            i = 0
            # wait for 30 minutes
            while task.status != "STATUS_SUCCESSFUL" and task.status != "STATUS_FAILED" and i < 60 * 6:
                time.sleep(5)
                i += 1
                try:
                    response = nc.ocs("GET", f"/ocs/v1.php/taskprocessing/task/{task.id}")
                except RemoteProtocolError as e:
                    print(e)
                    continue
                task = Response.model_validate(response).task
                print(task)
        except ValidationError as e:
            raise LlmException("Failed to parse Nextcloud TaskProcessing task result") from e

One of the outputs I captured after this adjustment from the backend:

id=80 status='STATUS_SCHEDULED' output=None
id=80 status='STATUS_RUNNING' output=None
TRACE:    172.22.0.8:52810 - HTTP connection lost
id=80 status='STATUS_RUNNING' output=None
id=80 status='STATUS_RUNNING' output=None
Server disconnected without sending a response.
id=80 status='STATUS_RUNNING' output=None
id=80 status='STATUS_RUNNING' output=None
id=80 status='STATUS_SUCCESSFUL' output={'output': ...

You can see that the (temporary) loss of the connection from the chat backend to the NC server (also hosted in Docker) doesn't break the full process. I think that putting some "retry mechanism" in place here makes sense somehow.

I found a similar issue here where they also worked around this by retrying the request.