Description:

I am building a Python application using Socket.IO and Eventlet to handle WebSocket communication. The server is designed to process events emitted by clients, including sending HTTP GET requests to an external API. However, I encounter the following error when attempting to make the API call:

maximum recursion depth exceeded while calling a Python object

Context:

• Tech Stack:

  • Socket.IO Server: python-socketio
  • Asynchronous Framework: eventlet
  • HTTP Requests: urllib3

• Environment:

  • Python version: (e.g., Python 3.8.10)
  • Operating System: Linux

• What I am trying to do:

  • Start a Socket.IO server with Eventlet.
  • Handle a WebSocket event (process_data) where I send a GET request to an external API (mock example provided below).
  • Process the API response and send the result back to the client.

• What happens:

  • When the process_data event is triggered, and the API request is made, I get the maximum recursion depth exceeded while calling a Python object error.
  • The same API call works perfectly when tested outside the Eventlet environment.

Code Snippet:

Here’s the relevant portion of my server code:

import socketio
import eventlet
from eventlet import monkey_patch
import urllib3
import json
import logging

 Monkey patch for Eventlet
monkey_patch()

 Logging setup
logging.basicConfig(level=logging.DEBUG)
logger = logging.getLogger(__name__)

 Initialize Socket.IO server
sio = socketio.Server(cors_allowed_origins="*")
app = socketio.WSGIApp(sio)

@sio.on('process_data')
def handle_process_data(sid, data):
    payload = data.get('payload')
    if not payload:
        sio.emit('error', {"message": "Payload is missing."}, to=sid)
        return

    logger.info(f"Payload received: {payload}")
    
     Call the external API to process the payload
    api_result = call_external_api(payload)
    if api_result:
        sio.emit('api_result', {"result": api_result}, to=sid)
    else:
        sio.emit('error', {"message": "Failed to process the data. Please try again."}, to=sid)

def call_external_api(payload):
    """ Call an external API using urllib3 """
    url = f"https://api.example.com/process?data={payload}"
    http = urllib3.PoolManager(cert_reqs='CERT_NONE')   SSL disabled for testing
    headers = {"Authorization": "Bearer test-api-key"}

    try:
        logger.info(f"Sending request to API with payload: {payload}")
        response = http.request('GET', url, headers=headers, timeout=10)
        if response.status == 200:
            return json.loads(response.data.decode('utf-8')).get("result", "Unknown Result")
        else:
            logger.error(f"API Error: {response.status} - {response.data.decode('utf-8')}")
            return None
    except Exception as e:
        logger.error(f"Error calling API: {e}")
        return None

What I Have Tried:

1. Testing the API Outside the Eventlet Environment:

   • The same API request using urllib3 works perfectly in a standalone script without Eventlet.

2. Disabling SSL Verification:

   • Added cert_reqs='CERT_NONE' in urllib3.PoolManager() to disable SSL verification during the API call.

3. Switching to Requests Library:

   • I initially used the requests library, but I encountered the same recursion error. I switched to urllib3 for better compatibility with Eventlet, but the issue persists.

4. Debugging the Call Stack:

   • I added logging to trace the function calls and identify potential recursive loops. The issue seems to originate from the interaction between Eventlet and the HTTP request handling.

5. Limiting Monkey Patching:

   • Modified the monkey_patch() call to exclude networking modules (e.g., monkey_patch(socket=False)), but it caused other parts of the application to fail.

What I Need Help With:

1. Understanding the Cause:

   • Why does the recursion depth error occur when making an HTTP request in the Eventlet environment?

2. Finding a Solution:

   • What is the best way to handle HTTP requests (e.g., using urllib3 or requests) in an Eventlet-based Socket.IO server?

3. Alternatives:

   • Should I switch from Eventlet to another async framework (e.g., Gevent)? If so, how would that affect compatibility with Socket.IO?

Additional Notes:

• The recursion issue seems tied to the Eventlet environment, as the same HTTP request logic works outside of it.
• I would prefer to keep Eventlet unless there is no viable solution.

Thank you in advance for your help!