Use signal handle to shut down flask-socketio server - server

Question

I am using macOS Mojave and Python 3.7. In my work, I want to shut down flask-socketio server completely from the signal handler, which is defined as SignalHandler in my code. I noticed that, without the signal handler, the server can be shut down completely with Ctrl-C. However, the signal handler is necessary for my work. I searched online and couldn't find the solution to shut the server down in my case. For your information, I found solutions to shut the server down by "call flask-socketio stop from HTTP or SocketIO handler function", or "shut down a gevent (pywsgi) server gracefully".
The example code is given as below:
import os
import threading
import signal
import requests
from flask import Flask, send_from_directory
from flask_socketio import SocketIO, Namespace
import eventlet
class WebsiteCreator(threading.Thread):
def __init__(self):
super().__init__()
def run(self):
app = Flask(__name__, template_folder="templates",
static_folder="templates/static")
app.config['SECRET_KEY'] = 'Secret!'
socketio = SocketIO(app, engineio_logger=True, logger=True)
# Create a URL route in our application for "/"
#app.route('/')
def test_page():
"""
This function loads the homepage
"""
return send_from_directory(
os.path.join(app.root_path, 'templates'),
"index1.html"
)
#app.route('/stop', methods=['POST'])
def shutdown_server():
"""
This function stops the flask-socketio server
"""
print("Received request to shut down the server.")
socketio.stop() #something wrong here, but don't know how to solve
return "The server has been shut down."
class MyCustomNamespace(Namespace):
def on_connect(self):
print("Client just connected")
def on_disconnect(self):
print("Client just left")
def on_messages(self, data):
print(f"\nReceived data from client: \n {data}\n")
return data
socketio.on_namespace(MyCustomNamespace('/channel_A'))
try:
eventlet.wsgi.server(
eventlet.wrap_ssl(eventlet.listen(("localhost", 8080)),
certfile='server.crt',
keyfile='server.key',
server_side=True), app)
except Exception as e:
print(f"Website is not established due to:\n{e}")
# Terminate code from shell
class SignalHandler(object):
def __init__(self):
pass
def __call__(self, signum, frame):
print("Shutting down the website.")
# Begin 'something' here to shut down the server...
shutdown_server = requests.post("https://localhost:8080/stop", data=None)
print(f"Shut down the server feedback: {shutdown_server}")
# 'Something' ends here
print("The website has been shut down.")
if __name__ == '__main__':
WebsiteCreator().start()
# If the following part is not included, the server can be shut down using Ctrl-C
handler = SignalHandler()
signal.signal(signal.SIGINT, handler)
In the code, I am running the flask-socketio server in a thread. I want to shut the server down by doing some actions in the SignalHandler.
Yet, when I exited the system with Ctrl-C, some exceptions raised:
^C
Shutting down the website.
(23066) accepted ('127.0.0.1', 49720)
Received request to shut down the server.
127.0.0.1 - - [22/Nov/2019 13:08:18] "POST /stop HTTP/1.1" 200 0 0.000365
wsgi exiting
Exception ignored in: <module 'threading' from '/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py'>
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 1308, in _shutdown
lock.acquire()
File "web_app.py", line 74, in __call__
shutdown_server = requests.post("https://localhost:8080/stop", data=None)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/requests/api.py", line 116, in post
return request('post', url, data=data, json=json, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/requests/api.py", line 60, in request
return session.request(method=method, url=url, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/requests/sessions.py", line 533, in request
resp = self.send(prep, **send_kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/requests/sessions.py", line 646, in send
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/hubs/kqueue.py", line 105, in wait
readers.get(fileno, hub.noop).cb(fileno)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/greenthread.py", line 221, in main
result = function(*args, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/wsgi.py", line 818, in process_request
proto.__init__(conn_state, self)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/wsgi.py", line 357, in __init__
self.handle()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/wsgi.py", line 390, in handle
self.handle_one_request()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/wsgi.py", line 419, in handle_one_request
self.raw_requestline = self._read_request_line()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/wsgi.py", line 402, in _read_request_line
return self.rfile.readline(self.server.url_length_limit)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/socket.py", line 589, in readinto
return self._sock.recv_into(b)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/green/ssl.py", line 241, in recv_into
return self._base_recv(nbytes, flags, into=True, buffer_=buffer)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/green/ssl.py", line 256, in _base_recv
read = self.read(nbytes, buffer_)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/green/ssl.py", line 176, in read
super(GreenSSLSocket, self).read, *args, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/eventlet/green/ssl.py", line 150, in _call_trampolining
return func(*a, **kw)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/ssl.py", line 926, in read
raise ValueError("Read on closed or unwrapped SSL socket.")
r = adapter.send(request, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/requests/adapters.py", line 498, in send
ValueError: Read on closed or unwrapped SSL socket.
Removing descriptor: 8
142f38bdaaf34c7e8883e99a766fe310: Unexpected error "Read on closed or unwrapped SSL socket.", closing connection
raise ConnectionError(err, request=request)
requests.exceptions.ConnectionError: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))
Please give me some ideas! Thanks in advance.

Answer 1

This is what I use in my projects, works great using gevent. Make sure you start your server AFTER you init your signal. The signal should be identical, just minus the gevent part.
def shutdown():
print('Shutting down ...')
server.stop(timeout=60)
exit(signal.SIGTERM)
gevent.signal(signal.SIGTERM, shutdown)
gevent.signal(signal.SIGINT, shutdown) #CTRL C
server.serve_forever()