Network Programming

• Network applications are everywhere. 

• Any time you browse the Web, send an email message, or pop up an X window, you are using a network application.

• Python provides two levels of access to network services.

•  At a low level, you can access the basic socket support in the underlying operating system,which allows you to implement clients and servers for both connection-oriented and connection-less protocols.
• Python also has libraries that provide higher-level access to specific application-level network protocols, such as FTP, HTTP, and so on.

• understanding on most famous concept in Networking - Socket Programming.

What is Socket ?

• Sockets are the endpoints of a bidirectional communications channel. 

• Sockets may communicate within a process, between processes on the same machine, or between processes on different continents.

• Sockets may be implemented over a number of different channel types: Unix domain sockets, TCP, UDP, and so on. 

Client:

import socket               

# Import socket module

s = socket.socket( )         

# Create a socket object

host = socket.gethostname( ) 

# Get local machine name

port = 12345                

# Reserve a port for your service

s.connect((host, port))

print s.recv(1024)

s.close  

Client example2:

 import socket

clientsocket=socket.socket(socket.AF_INET, socket.SOCK_STREAM)

clientsocket.connect(('localhost', 8089))

clientsocket.send('hello')

Client example3:

import socket

import sys

# Create a TCP/IP socket

sock=socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Connect the socket to the port where the server is listening

server_address = ('localhost', 9999)

print >>sys.stderr, 'connecting to %s port %s' % server_address

sock.connect(server_address)

try:

    

    # Send data

    message = 'This is the message.  It will be repeated.'

    print >>sys.stderr, 'sending "%s"' % message

    sock.sendall(message)

    # Look for the response

    amount_received = 0

    amount_expected = len(message)

    

    while amount_received < amount_expected:

        data = sock.recv(16)

        amount_received += len(data)

        print >>sys.stderr, 'received "%s"' % data

finally:

    print >>sys.stderr, 'closing socket'

    sock.close( )

Server :

import socket               

# Import socket module

s = socket.socket( )         

# Create a socket object

host = socket.gethostname( ) 

# Get local machine name

port = 12345                

# Reserve a port for your service.

s.bind((host, port))        

# Bind to the port

s.listen(5)                 

# Now wait for client connection.

while True:

   c, addr = s.accept()     

# Establish connection with client.

   print 'Got connection from', addr

   c.send('Thank you for connecting')

   c.close()                

# Close the connection

Server example2:

import socket

serversocket=socket.socket(socket.AF_INET, socket.SOCK_STREAM)

serversocket.bind(('localhost', 8089))

serversocket.listen(5) 

# become a server socket, maximum 5 connections

while True:

    connection, address = serversocket.accept()

    buf = connection.recv(64)

    if len(buf) > 0:

        print buf

        break

Server Example3:

import socket

import sys

# Create a TCP/IP socket

sock=socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Bind the socket to the port

server_address = ('localhost', 9999)

print >>sys.stderr, 'starting up on %s port %s' % server_address

sock.bind(server_address)

# Listen for incoming connections

sock.listen(1)

while True:

    # Wait for a connection

    print >>sys.stderr, 'waiting for a connection'

    connection, client_address = sock.accept()

    try:

        print >>sys.stderr, 'connection from', client_address

        # Receive the data in small chunks and retransmit it

        while True:

            data = connection.recv(16)

            print >>sys.stderr, 'received "%s"' % data

            if data:

                print >>sys.stderr, 'sending data back to the client'

                connection.sendall(data)

            else:

                print >>sys.stderr, 'no more data from', client_address

                break

            

    finally:

        # Clean up the connection

        connection.close( )

Connecting to server:

example:

import socket
ip = socket.gethostbyname('www.google.com')
print ip

example:

import socket 

import sys 

try:

    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

    print "Socket successfully created"

except socket.error as err:

    print "socket creation failed with error %s" %(err)

# default port for socket

port = 80

try:

    host_ip = socket.gethostbyname('www.google.com')

except socket.gaierror:

    # this means could not resolve the host

    print "there was an error resolving the host"

    sys.exit()

# connecting to the server

s.connect((host_ip,port))

print "the socket has successfully connected to google \

on port == %s" %(host_ip)

Server:

# first of all import the socket library
import socket              

# next create a socket object
s = socket.socket()        
print "Socket successfully created"

# reserve a port on your computer in our
# case it is 12345 but it can be anything
port = 12345              

# Next bind to the port
# we have not typed any ip in the ip field
# instead we have inputted an empty string
# this makes the server listen to requests
# coming from other computers on the network
s.bind(('', port))      
print "socket binded to %s" %(port)

# put the socket into listening mode
s.listen(5)    
print "socket is listening"          

# a forever loop until we interrupt it or
# an error occurs
while True:
   # Establish connection with client.
   c, addr = s.accept()    
   print 'Got connection from', addr

   # send a thank you message to the client.
   c.send('Thank you for connecting')
   # Close the connection with the client
   c.close()              

Client:

# Import socket module
import socket              

# Create a socket object
s = socket.socket()        

# Define the port on which you want to connect
port = 12345              

# connect to the server on local computer
s.connect(('127.0.0.1', port))

# receive data from the server
print s.recv(1024)
# close the connection
s.close()