How to Work with TCP Sockets in Python

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How to Work with TCP Sockets in Python

A network/internet socket is anend-point of interposing communication across a computer network. In Python,the library has a module called socket which offers a low-level networkinginterface, it’s common across various programming languages since it usesOS-level system calls. When you create a socket, use a function called asocket. It accepts family, type, and prototype arguments. Creating a TCP-socket,for the family, you must use a socket.AF_INET or socket.AF_INET6 and for thetype you must use socket.SOCK_STREAM.

Example for Python socket

import socket

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

Main methods to create Python socket objects

· bind() – specific for server sockets.

· listen() – specific for server sockets.

· accept() – specific for server sockets.

· connect() – client sockets.

· send() – both server and client sockets.

· recv() – both server and client sockets.

For instance, echo server from documentation

import socket

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

s.bind((‘localhost’, 50000))

s.listen(1)

conn, addr = s.accept()

while 1:

data =conn.recv(1024)

if not data:

break

conn.sendall(data)

conn.close()

To create a server socket, bindit to localhost and 50000 port, and start listening for incoming connections.To accept an incoming connection call as accept(), this method will block untila new client connects. When it’s happening, will create a new socket andreturns it together with the client’s address. Then, an infinite loop readsdata from the socket in batches of 1 KB using method recv() till it returns ablank string. Next, it sends all incoming data back usinga method called sendall() which inside repeatedly calls send(). Next, to that,it just closes the client’s connection.

A client-side code looks simply

Here instead of bind() andlisten() methods it calls only the connect() method and directly sends data tothe server. Then it receives 1 KB back, closes the socket then writes thereceived data. Each socket method is blocking. For instance, when it reads froma socket or prints to it the program can’t do anything. The possible solutionis to delegate working with clients to separate process/threads, creating anyprocess and swap contexts between them is not a cheap operation. To solve thisissue, there is a so-called asynchronous way of working with sockets. The mainidea is to maintain the socket’s state to an OS and check the program whenthere is something to read from the socket or when it is ready for writing.

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