Question

I have a device that continually outputs data and I would like to send that data to a client on the same network as it is produced and I’m not finding a good solution. Here is what I’m trying.

Server:

import SocketServer
from subprocess import Popen,PIPE

class Handler(SocketServer.BaseRequestHandler):
    def handle(self):
        if not hasattr(self, 'Proc'):
            self.Proc = Popen('r.sh', stdout=PIPE)
        socket = self.request[1]
        socket.sendto(self.Proc.stdout.readline(),self.client_address)

if __name__ == "__main__":                         
    HOST, PORT = "192.168.1.1", 6001

    server = SocketServer.UDPServer((HOST, PORT), Handler)
    server.serve_forever()

Client:

import socket
data = " ".join(sys.argv[1:])
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(data + "\n", ("192.168.1.1", 6001))
try:
    received = sock.recv(1024)
while True:
    print "Sent:     {}".format(data)
    print "Received: {}".format(received)
    sock.sendto('more' + "\n", ("192.168.1.1", 6001))
    received = sock.recv(1024)
except:
    print "No more messages"

arg[1] for the client is a program that outputs lines of data for several minutes that I need to process as it is created. The problem seems to be that every time the client sends another request, a new Handler object is created, so I loose Proc. How can I stream Proc.stdout?

Edit: The device is a Korebot2, so I have limited access to other python libraries due to space.

Answer 1

Using UDP you get a new “connection” each time you send a datagram, which is the reason you notice that a new object instance is created each time you send something. You’re probably using the wrong kind of protocol here… UDP is used mostly for sending distinct “datagrams”, or when a longer connection is not needed. TCP is also called a “streaming” protocol, and is often used for data that has no fixed end.

Also remember that UDP is not a reliable protocol, if used over a network it is almost guaranteed that you will loose packets.