T.C.P SOCKETS
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. The socket library provides specific classes for handling the common transports as well as a generic interface for handling the rest.
A Simple Server
To write Internet servers, we use the socket function available in socket module to create a socket object. A socket object is then used to call other functions to setup a socket server.
Now call bind(hostname, port) function to specify a port for your service on the given host.
Next, call the accept method of the returned object. This method waits until a client connects to the port you specified, and then returns a connection object that represents the connection to that client.
#!/usr/bin/python #server.py file
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
A Simple Client
Let us write a very simple client program which opens a connection to a given port 12345 and given host. This is very simple to create a socket client using Python’s socket module function.
The socket.connect (hosname, port ) opens a TCP connection to hostnameon the port. Once you have a socket open, you can read from it like any IO object. When done, remember to close it, as you would close a file.
The following code is a very simple client that connects to a given host and port, reads any available data from the socket, and then exits −
#!/usr/bin/python # This is client.py file
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() # Close the socket when done
Now run this server.py in background and then run above client.py to see the result.
# Following would start a server in background.
$ python server.py &
# Once server is started run client as follows:
$ python client.py
This would produce following result −
Got connection from (‘127.0.0.1’, 48437)
Thank you for connecting
Computer Networking 