Socket programming is a way of connecting two nodes on a network to communicate with each other. One socket(node) listens on a particular port at an IP, while other socket reaches out to the other to form a connection. Server forms the listener socket while client reaches out to the server.
They are the real backbones behind web browsing. In simpler terms there is a server and a client.
Socket programming is started by importing the socket library and making a simple socket.
import socket s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
Here we made a socket instance and passed it two parameters. The first parameter is AF_INET and the second one is SOCK_STREAM. AF_INET refers to the address family ipv4. The SOCK_STREAM means connection oriented TCP protocol.
Now we can connect to a server using this socket.
Connecting to a server:
Note that if any error occurs during the creation of a socket then a socket.error is thrown and we can only connect to a server by knowing it’s ip. You can find the ip of the server by using this :
$ ping www.google.com
You can also find the ip using python:
import socket ip = socket.gethostbyname('www.google.com') print ip
Here is an example of a script for connecting to Google
Socket successfully created the socket has successfully connected to google on port == 188.8.131.52
- First of all we made a socket.
- Then we resolved google’s ip and lastly we connected to google.
- Now we need to know how can we send some data through a socket.
- For sending data the socket library has a sendall function. This function allows you to send data to a server to which the socket is connected and server can also send data to the client using this function.
A simple server-client program :
A server has a bind() method which binds it to a specific ip and port so that it can listen to incoming requests on that ip and port.A server has a listen() method which puts the server into listen mode. This allows the server to listen to incoming connections. And last a server has an accept() and close() method. The accept method initiates a connection with the client and the close method closes the connection with the client.
- First of all we import socket which is necessary.
- Then we made a socket object and reserved a port on our pc.
- After that we binded our server to the specified port. Passing an empty string means that the server can listen to incoming connections from other computers as well. If we would have passed 127.0.0.1 then it would have listened to only those calls made within the local computer.
- After that we put the server into listen mode.5 here means that 5 connections are kept waiting if the server is busy and if a 6th socket trys to connect then the connection is refused.
- At last we make a while loop and start to accept all incoming connections and close those connections after a thank you message to all connected sockets.
Now we need something with which a server can interact. We could tenet to the server like this just to know that our server is working. Type these commands in the terminal:
# start the server $ python server.py
# keep the above terminal open
# now open another terminal and type:
$ telnet localhost 12345
# in the server.py terminal you will see # this output: Socket successfully created socket binded to 12345 socket is listening Got connection from ('127.0.0.1', 52617)
# In the telnet terminal you will get this: Trying ::1... Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. Thank you for connectingConnection closed by foreign host.
This output shows that our server is working.
Now for the client side:
- First of all we make a socket object.
- Then we connect to localhost on port 12345 (the port on which our server runs) and lastly we receive data from the server and close the connection.
- Now save this file as client.py and run it from the terminal after starting the server script.
# start the server: $ python server.py Socket successfully created socket binded to 12345 socket is listening Got connection from ('127.0.0.1', 52617)
# start the client: $ python client.py Thank you for connecting
Reference : Python Socket Programming
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