How To: Code a Basic TCP/IP Client & Server Duo in Python

TCP/IP Client / Server Application

Hello! Today's blog post will be about coding a very rudimentary Client and Server application duo, which will communicate by using TCP Sockets.

It is, as illustrated, in principle, just two cans and a string that ties them together. The server will listen for clients and accept incoming data, while the client will, upon startup, check for the server on a predefined port and if found, will enable you to send messages! If not, it will simply exit with an exception.

For a more substantial read about TCP/IP, refer to this Wiki article. It should be sufficient and cover the basics of the model.

Requirements

• Python

Step 1 Server Application

This is going to be our receiving end (no puns, please) of the duet.

#!C:\python27 #Replace with usr/bin/ clause for Linux

import SocketServer #imports the socket server library

class EchoHandler( SocketServer.StreamRequestHandler ): #declares the class
    def handle(self): #installs handler
        input= self.request.recv(1024) #defines request buffer
        print "Input: %r" % ( input, ) #prints data received
        self.request.send("Received: %r" % ( input, ) ) #sends message to client saying..

#.."message received"

server= SocketServer.TCPServer( ("",7000), EchoHandler )#adds listener at port 7000
print "Starting Server..."
server.serve_forever() #enables the server to run forever as long as a client is connected

Simple enough, right?

Step 2 Client Application

Now we will code the application which will enable us to send messages to the server.

#!C:\python27

import socket

class Client( object ): #defines client class
    rbufsize= -1 #sets read buffer
    wbufsize= 0 #sets write buffer
    def __init__( self, address=('localhost',7000) ): #defines initialisation function
        self.server=socket.socket( socket.AF_INET, socket.SOCK_STREAM )#initiates socket by passing address and protocol parameters
        self.server.connect( address ) # connects to set address and port
        self.rfile = self.server.makefile('rb', self.rbufsize) #makes file object for response processing
        self.wfile = self.server.makefile('wb', self.wbufsize) # same as above but for writing/response sending
    def makeRequest( self, text ): # request function which will handle the data transfer
        self.wfile.write( text )
        data= self.rfile.read()
        self.server.close() # closes this instance of the connection
        return data

print "Connecting to Echo Server"
i = 0 #from here to end of file, infinite loop for message sending to server
while (i > -1):
    c= Client()
    response = c.makeRequest(raw_input("Enter something: "))
    print repr(response)
    print "Finished"

And that's it.

End Notes

Fire up the "Server" app first, then launch the client and try sending some data.

If all goes well, you should get the server to print out some received data. Hope you enjoy making these apps!