I have a game or for that matter any remote user interface with a server and multiple clients which should communicate via network.
Both client and server should be able to send updates asynchronously.
This seems to be a very natural service definition, which let's grpc manage sessions.
syntax = "proto3";
package mygame;
service Game {
rpc participate(stream ClientRequest) returns (ServerResponse);
}
message ClientRequest {
// Fields for the initial request and further updates
}
message ServerResponse {
// Game updates
}
Implementing the client is trivial (although the following code is obviously incomplete and simplified).
class Client:
def __init__(self):
self.channel = grpc.insecure_channel("localhost:50051")
self.stub = game_pb2_grpc.GameStub(channel)
self.output_queue = queue.Queue()
def output_iter(self):
while True:
client_output_msg = self.output_queue.get()
self.output_queue.task_done()
yield client_output_msg
def do_work(self):
for response in self.stub.participate(self.output_iter()):
print(response) # handle update
with grpc.insecure_channel("localhost:50051") as channel:
client = Client()
client.do_work()
What seems hard is implementing the server without blocking.
class Game(game_pb2_grpc.GameServicer):
def __init__(self):
self.pending_events = queue.Queue()
def participate(self, request_iter, context):
for client_update in request_iter:
print(client_update)
# !!!
# The next bit won't happen if the client has no updates
# !!!
try:
while True:
server_update = self.pending_events.get_nowait()
yield server_update
except queue.Empty:
pass
server = grpc.server(ThreadPoolExecutor(max_workers=100))
game_pb2_grpc.add_GameServicer_to_server(Game(), server)
server.add_insecure_port("[::]:50051")
server.start()
server.wait_for_termination()
As commented in the code, the client won't receive updates if it doesn't constantly send requests.
Maybe a async approach would be better, which might also solve other problems in this design.
PS: This issue has been solved with grpc in go here, however i don't see how to translate this to pythons grpc implementations.
I would be very happy about any help!
I was finally able to get it working using the python asynio api.
The basic idea is to decouple read and write into two coroutines using asyncio.create_task.
For anybody interested, here is a solution.
class Game(game_pb2_grpc.GameServicer):
async def read_client_requests(self, request_iter):
async for client_update in request_iter:
print("Recieved message from client:", client_update, end="")
async def write_server_responses(self, context):
for i in range(15):
await context.write(game_pb2.ServerResponse(dummy_value=str(i)))
await asyncio.sleep(0.5)
async def participate(self, request_iter, context):
read_task = asyncio.create_task(self.read_client_requests(request_iter))
write_task = asyncio.create_task(self.write_server_responses(context))
await read_task
await write_task
async def serve():
server = grpc.aio.server()
game_pb2_grpc.add_GameServicer_to_server(Game(), server)
server.add_insecure_port("[::]:50051")
await server.start()
await server.wait_for_termination()
if __name__ == "__main__":
asyncio.run(serve())
Note that instead of the write coroutine, a yield would also be sufficient.
I have my Tornado client continuously listening to my Tornado server in a loop, as it is mentioned here - http://tornadoweb.org/en/stable/websocket.html#client-side-support. It looks like this:
import tornado.websocket
from tornado import gen
#gen.coroutine
def test():
client = yield tornado.websocket.websocket_connect("ws://localhost:9999/ws")
client.write_message("Hello")
while True:
msg = yield client.read_message()
if msg is None:
break
print msg
client.close()
if __name__ == "__main__":
tornado.ioloop.IOLoop.instance().run_sync(test)
I'm not able to get multiple instances of clients to connect to the server. The second client always waits for the first client process to end before it connects to the server. The server is set up as follows, with reference from Websockets with Tornado: Get access from the "outside" to send messages to clients and Tornado - Listen to multiple clients simultaneously over websockets.
class WSHandler(tornado.websocket.WebSocketHandler):
clients = set()
def open(self):
print 'new connection'
WSHandler.clients.add(self)
def on_message(self, message):
print 'message received %s' % message
# process received message
# pass it to a thread which updates a variable
while True:
output = updated_variable
self.write_message(output)
def on_close(self):
print 'connection closed'
WSHandler.clients.remove(self)
application = tornado.web.Application([(r'/ws', WSHandler),])
if __name__ == "__main__":
http_server = tornado.httpserver.HTTPServer(application)
http_server.listen(9999)
tornado.ioloop.IOLoop.instance().start()
But this has not worked - for some reason even after I have made a successful first connection, the second connection just fails to connect i.e. it does not even get added to the clients set.
I initially thought the while True would not block the server from receiving and handling more clients, but it does as without it multiple clients are able to connect. How can I send back continuously updated information from my internal thread without using the while True?
Any help would be greatly appreciated!
To write messages to client in a while loop, you can use the yield None inside the loop. This will pause the while loop and then Tornado's IOLoop will be free to accept new connections.
Here's an example:
#gen.coroutine
def on_message(self):
while True:
self.write_message("Hello")
yield None
Thanks for your answer #xyres! I was able to get it to work by starting a thread in the on_message method that handed processing and the while True to a function outside the WSHandler class. I believe this allowed for the method to run outside of Tornado's IOLoop, unblocking new connections.
This is how my server looks now:
def on_message(self, message):
print 'message received %s' % message
sendThread = threading.Thread(target=send, args=(self, message))
sendThread.start()
def send(client, msg):
# process received msg
# pass it to a thread which updates a variable
while True:
output = updated_variable
client.write_message(output)
Where send is a function defined outside the class which does the required computation for me and writes back to client inside thewhile True.
I'm trying to implement a REST client in python that reacts to messages received from the server received through an opened websocket with the concerned server.
Here is the scenario:
client opens a websocket with the server
from time to time, the server sends a message to the client
when the client receives the messages, it gets some information from
the server
The current client I have is able to open the websocket and to receive the message from the server. However, as soon as it receives the messages, it gets the information from the server then terminates while I'd like to keep it listening for other messages that will make it get a new content from the server.
Here is the piece of code I have:
def openWs(serverIp, serverPort):
##ws url setting
wsUrl = "ws://"+serverIp+":"+serverPort+"/websocket"
##open ws
ws = create_connection(wsUrl)
##send user id
print "Sending User ID..."
ws.send("user_1")
print "Sent"
##receiving data on ws
print "Receiving..."
result = ws.recv()
##getting new content
getUrl = "http://"+serverIp+":"+serverPort+"/"+result+"/entries"
getRest(getUrl)
I don't know if using threads is appropriate or not, I'm not expert in that.
If someone could help, it'll be great.
Thanks in advance.
I finished with this code, doing what I'm expecting. Git it from here
import websocket
import thread
import time
def on_message(ws, message):
print message
def on_error(ws, error):
print error
def on_close(ws):
print "### closed ###"
def on_open(ws):
def run(*args):
for i in range(3):
time.sleep(1)
ws.send("Hello %d" % i)
time.sleep(1)
ws.close()
print "thread terminating..."
thread.start_new_thread(run, ())
if __name__ == "__main__":
websocket.enableTrace(True)
ws = websocket.WebSocketApp("ws://localhost:5000/chat",
on_message = on_message,
on_error = on_error,
on_close = on_close)
ws.on_open = on_open
ws.run_forever()
I need to create a class that can receive and store SMTP messages, i.e. E-Mails. To do so, I am using asyncore according to an example posted here. However, asyncore.loop() is blocking so I cannot do anything else in the code.
So I thought of using threads. Here is an example-code that shows what I have in mind:
class MyServer(smtpd.SMTPServer):
# derive from the python server class
def process_message(..):
# overwrite a smtpd.SMTPServer method to be able to handle the received messages
...
self.list_emails.append(this_email)
def get_number_received_emails(self):
"""Return the current number of stored emails"""
return len(self.list_emails)
def start_receiving(self):
"""Start the actual server to listen on port 25"""
self.thread = threading.Thread(target=asyncore.loop)
self.thread.start()
def stop(self):
"""Stop listening now to port 25"""
# close the SMTPserver from itself
self.close()
self.thread.join()
I hope you get the picture. The class MyServer should be able to start and stop listening to port 25 in a non-blocking way, able to be queried for messages while listening (or not). The start method starts the asyncore.loop() listener, which, when a reception of an email occurs, append to an internal list. Similar, the stop method should be able to stop this server, as suggested here.
Despite the fact this code does not work as I expect to (asyncore seems to run forever, even I call the above stop method. The error I raise is catched within stop, but not within the target function containing asyncore.loop()), I am not sure if my approach to the problem is senseful. Any suggestions for fixing the above code or proposing a more solid implementation (without using third party software), are appreciated.
The solution provided might not be the most sophisticated solution, but it works reasonable and has been tested.
First of all, the matter with asyncore.loop() is that it blocks until all asyncore channels are closed, as user Wessie pointed out in a comment before. Referring to the smtp example mentioned earlier, it turns out that smtpd.SMTPServer inherits from asyncore.dispatcher (as described on the smtpd documentation), which answers the question of which channel to be closed.
Therefore, the original question can be answered with the following updated example code:
class CustomSMTPServer(smtpd.SMTPServer):
# store the emails in any form inside the custom SMTP server
emails = []
# overwrite the method that is used to process the received
# emails, putting them into self.emails for example
def process_message(self, peer, mailfrom, rcpttos, data):
# email processing
class MyReceiver(object):
def start(self):
"""Start the listening service"""
# here I create an instance of the SMTP server, derived from asyncore.dispatcher
self.smtp = CustomSMTPServer(('0.0.0.0', 25), None)
# and here I also start the asyncore loop, listening for SMTP connection, within a thread
# timeout parameter is important, otherwise code will block 30 seconds after the smtp channel has been closed
self.thread = threading.Thread(target=asyncore.loop,kwargs = {'timeout':1} )
self.thread.start()
def stop(self):
"""Stop listening now to port 25"""
# close the SMTPserver to ensure no channels connect to asyncore
self.smtp.close()
# now it is save to wait for the thread to finish, i.e. for asyncore.loop() to exit
self.thread.join()
# now it finally it is possible to use an instance of this class to check for emails or whatever in a non-blocking way
def count(self):
"""Return the number of emails received"""
return len(self.smtp.emails)
def get(self):
"""Return all emails received so far"""
return self.smtp.emails
....
So in the end, I have a start and a stop method to start and stop listening on port 25 within a non-blocking environment.
Coming from the other question asyncore.loop doesn't terminate when there are no more connections
I think you are slightly over thinking the threading. Using the code from the other question, you can start a new thread that runs the asyncore.loop by the following code snippet:
import threading
loop_thread = threading.Thread(target=asyncore.loop, name="Asyncore Loop")
# If you want to make the thread a daemon
# loop_thread.daemon = True
loop_thread.start()
This will run it in a new thread and will keep going till all asyncore channels are closed.
You should consider using Twisted, instead. http://twistedmatrix.com/trac/browser/trunk/doc/mail/examples/emailserver.tac demonstrates how to set up an SMTP server with a customizable on-delivery hook.
Alex answer is the best but was incomplete for my use case. I wanted to test SMTP as part of a unit test which meant building the fake SMTP server inside my test objects and the server would not terminate the asyncio thread so I had to add a line to set it to a daemon thread to allow the rest of the unit test to complete without blocking waiting for that asyncio thread to join. I also added in complete logging of all email data so that I could assert anything sent through the SMTP.
Here is my fake SMTP class:
class TestingSMTP(smtpd.SMTPServer):
def __init__(self, *args, **kwargs):
super(TestingSMTP, self).__init__(*args, **kwargs)
self.emails = []
def process_message(self, peer, mailfrom, rcpttos, data, **kwargs):
msg = {'peer': peer,
'mailfrom': mailfrom,
'rcpttos': rcpttos,
'data': data}
msg.update(kwargs)
self.emails.append(msg)
class TestingSMTP_Server(object):
def __init__(self):
self.smtp = TestingSMTP(('0.0.0.0', 25), None)
self.thread = threading.Thread()
def start(self):
self.thread = threading.Thread(target=asyncore.loop, kwargs={'timeout': 1})
self.thread.daemon = True
self.thread.start()
def stop(self):
self.smtp.close()
self.thread.join()
def count(self):
return len(self.smtp.emails)
def get(self):
return self.smtp.emails
And here is how it is called by the unittest classes:
smtp_server = TestingSMTP_Server()
smtp_server.start()
# send some emails
assertTrue(smtp_server.count() == 1) # or however many you intended to send
assertEqual(self.smtp_server.get()[0]['mailfrom'], 'first#fromaddress.com')
# stop it when done testing
smtp_server.stop()
In case anyone else needs this fleshed out a bit more, here's what I ended up using. This uses smtpd for the email server and smtpblib for the email client, with Flask as a http server [gist]:
app.py
from flask import Flask, render_template
from smtp_client import send_email
from smtp_server import SMTPServer
app = Flask(__name__)
#app.route('/send_email')
def email():
server = SMTPServer()
server.start()
try:
send_email()
finally:
server.stop()
return 'OK'
#app.route('/')
def index():
return 'Woohoo'
if __name__ == '__main__':
app.run(debug=True, host='0.0.0.0')
smtp_server.py
# smtp_server.py
import smtpd
import asyncore
import threading
class CustomSMTPServer(smtpd.SMTPServer):
def process_message(self, peer, mailfrom, rcpttos, data):
print('Receiving message from:', peer)
print('Message addressed from:', mailfrom)
print('Message addressed to:', rcpttos)
print('Message length:', len(data))
return
class SMTPServer():
def __init__(self):
self.port = 1025
def start(self):
'''Start listening on self.port'''
# create an instance of the SMTP server, derived from asyncore.dispatcher
self.smtp = CustomSMTPServer(('0.0.0.0', self.port), None)
# start the asyncore loop, listening for SMTP connection, within a thread
# timeout parameter is important, otherwise code will block 30 seconds
# after the smtp channel has been closed
kwargs = {'timeout':1, 'use_poll': True}
self.thread = threading.Thread(target=asyncore.loop, kwargs=kwargs)
self.thread.start()
def stop(self):
'''Stop listening to self.port'''
# close the SMTPserver to ensure no channels connect to asyncore
self.smtp.close()
# now it is safe to wait for asyncore.loop() to exit
self.thread.join()
# check for emails in a non-blocking way
def get(self):
'''Return all emails received so far'''
return self.smtp.emails
if __name__ == '__main__':
server = CustomSMTPServer(('0.0.0.0', 1025), None)
asyncore.loop()
smtp_client.py
import smtplib
import email.utils
from email.mime.text import MIMEText
def send_email():
sender='author#example.com'
recipient='6142546977#tmomail.net'
msg = MIMEText('This is the body of the message.')
msg['To'] = email.utils.formataddr(('Recipient', recipient))
msg['From'] = email.utils.formataddr(('Author', 'author#example.com'))
msg['Subject'] = 'Simple test message'
client = smtplib.SMTP('127.0.0.1', 1025)
client.set_debuglevel(True) # show communication with the server
try:
client.sendmail('author#example.com', [recipient], msg.as_string())
finally:
client.quit()
Then start the server with python app.py and in another request simulate a request to /send_email with curl localhost:5000/send_email. Note that to actually send the email (or sms) you'll need to jump through other hoops detailed here: https://blog.codinghorror.com/so-youd-like-to-send-some-email-through-code/.
I wrote a demo about chatting with other clients with pyxmpp2，but when the client is idle for about 5 minutes the server would disconnect with the client,openfire cannot config the timeout,so I decide to send a presence message in 5 minutes ,the problem puzzling me is when to send the prensense message?
import pyxmpp2
class EchoBot(EventHandler, XMPPFeatureHandler):
"""Echo Bot implementation."""
def __init__(self, my_jid, settings):
version_provider = VersionProvider(settings)
self.client = Client(my_jid, [self, version_provider], settings)
#event_handler(AuthorizedEvent)
def handle_authorized(self,event):
presence = Presence(to_jid ="....",stanza_type = "available")
self.client.stream.send(presence)
def run(self):
"""Request client connection and start the main loop."""
self.client.connect()
self.client.run()
def disconnect(self):
""""""
self.client.disconnect()
def keepconnect(self):
presence = Presence(to_jid ="....",stanza_type = "available")
self.client.stream.send(presence)
print "send presence"
....
bot = McloudBot(JID(mcloudbotJID), settings)
try:
bot.run()
t = threading.Thread(target=bot.run())
timer=threading.Timer(5,bot.keepconnect())
t.start()
timer.start()
except KeyboardInterrupt:
bot.disconnect()
but it seems not work...
Check out
http://community.igniterealtime.org/docs/DOC-2053
This details the dissconnect idle property in OF that you can set to a value in milli seconds
Dissconnecting idle clients is something that's important in session based comms. It has more to do with the client closing unexpectedly rather than just neing idle though.
You can implement ping or heartbeat packet sending in your client as you mention above. Maybe check out the pidgin implementation of whitespace IQ requests.
Hope this steers you in the right direction.
James