Shantanu's Blog

Database Consultant

March 26, 2015

 

Managing sockets using python

Here is an example to understand how to open port and get the data from client machines.

This script will open the port 400007 on the server and start listening.
When a client sends data, it simply prints it. And it will also send the same data packet back to the client with the word "Echo =>" appended at the beginning.

from socket import *
myHost = ''
myPort = 40007

sockobj = socket(AF_INET, SOCK_STREAM)
sockobj.bind((myHost, myPort))
sockobj.listen(5)

while True:
    connection, address = sockobj.accept()
    print('Server connected by', address)
    while True:
        data = connection.recv(1024)
        print data
        if not data: break
        connection.send(b'Echo=>' + data)
    connection.close()

The client should also have python installed and it the OS can be Windows or Linux.
The following script will send data to the server mentioned above.
The host, port and message can also be supplied through command line.

import sys
from socket import *

serverHost = '23.21.167.60'
serverPort = 50007
message = [b'Hello network world by shantanu from Windows PC']

if len(sys.argv) > 1:      
    serverHost = sys.argv[1]
    if len(sys.argv) > 2:
        message = (x.encode() for x in sys.argv[2:]) 

sockobj = socket(AF_INET, SOCK_STREAM)
sockobj.connect((serverHost, serverPort))

for line in message:
    sockobj.send(line)
    data = sockobj.recv(1024)
    print('Client received:', data)
   
sockobj.close()

It creates a TCP/IP socket and then connects to the server/ port mentioned.
The object (remember this is python!) is supplied each line through send method.
The response received from the server is simply printed next to "Client Received:"

_____

The server does not handle simultaneous requests. Instead it lines up a queue of 5 clients using the following line....
sockobj.listen(5)
If the server gets more than 5 requsets, it simply denies them with an error. So we need a better solution that will handle multiple concurrent connections.

import os, time, sys
from socket import *
myHost = ''
myPort = 50007

sockobj = socket(AF_INET, SOCK_STREAM)
sockobj.bind((myHost, myPort))
sockobj.listen(5)

def now():
    return time.ctime(time.time())

activeChildren = []
def reapChildren():
        while activeChildren:
            pid, stat = os.waitpid(0, os.WNOHANG)
            if not pid: break
            activeChildren.remove(pid)

def handleClient(connection):
    time.sleep(5)
    while True:
        data = connection.recv(1024)
        if not data: break
        reply = 'Echo=>%s at %s' % (data, now())
        connection.send(reply.encode())
    connection.close()
    os._exit(0)

def dispatcher():
    while True:
        connection, address = sockobj.accept()
        print('Server connected by', address)
        print('at', now())
        reapChildren()
        childPid = os.fork()
        if childPid == 0:
            handleClient(connection)
        else:
            activeChildren.append(childPid)

dispatcher()

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