Hello (1)

Learning Outcomes

1. Understand the concept of networking and sockets in Python
2. Demonstrate knowledge on how to use sockets in a body of work

Socket Programming (1)

What is Socket Programming?

• An abstract principle whereby two programs can share a data stream
• Commonly done using an Application Programming Interface (API)
  • uses different protocols available in the internet TCP/IP stack
• Sockets are used to exploit the capabilities of an operating system to interact with the network
• Network sockets are used to establish a connection between processes on the same machines, or different ones
• A socket address is composed of two things:
  1. an IP address
  2. a port number
• Sockets consist of two primary properties, controlling how they send data:
  1. Address Family
  2. Socket Type

Socket Programming (2)

Address Family

• This controls the Open Systems Interconnection (OSI) network layer protocol that is used
• There are three address families in Python:

Socket Programming (3)

Socket Type

• There are two socket types in Python:
  1. SOCK_DGRAM
     • used for User Datagram Protocol (UDP)
     • it does not require a transmission handshake or other setup
     • offers lower reliability of delivery
     • UDP messages may be delivered out of order, more than once, or not at all
     • commonly used for protocols where order is less important or multicasting
  2. SOCK_STREAM
     • used for Transmission Control Protocol (TCP)
     • ensures each message is delivered exactly once, and in the correct order
     • applications that deliver large amounts of data (such as HTTP) use TCP

Using Sockets in Python (1)

• A socket will be specified by:
  • a machine’s IP address
  • a port it is listening to
  • a protocol it uses
• Sockets in Python used a module known as socket

import socket

• Creating a socket is done by using the function socket() from the module
• The general syntax for the socket() function is the following:

x = socket.socket(socket_family, socket_type, protocol=0)

• The syntax above shows:
  • family: refers to the address family
  • type: refers to the type of the socket
  • proto: this number is usually zero; but can be different in other use-cases

Using Sockets in Python (2)

The socket Module i

• Provides all functionality for writing TCP and UDP clients and servers
• Most applications use the concept of client/server:
  • server: represents an application that is waiting for connection by a client
  • client: represents an application that connects to the server
• These functions are commonly used for both clients and servers:
  • socket.recv(buflen)
    • receives data from the socket; argument indicates the maximum amount of data to be received
  • sockwt.recfrom(buflen)
    • receives data and the address of the sender
  • socket.rec_into(buffer)
    • receives data and is placed into a buffer
  • socket.recfrom_into(buffer)
    • receives data and is placed into a buffer, also returns the address of the sender
  • socket.send(bytes)
    • sends bytes of data to a specified target

Using Sockets in Python (3)

The socket Module ii

• These functions are commonly used for both clients and servers: (continued)
  • socket.sendto(data, address)
    • sends data to a given address
  • socket.sendall(data)
    • sends all the data in the buffer to the socket
  • socket.close()
    • releases the memory and closes the connection
• Want more information about the socket module?

Python Socket Documentation

Using Sockets in Python (4)

The socket Module iii

Example 1: Retrieving Data from a Local Website

import socket
ip = '127.0.0.1'
port = 80
message = "GET /5062CEM.php\r\n"
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.connect((ip, port)) 
    s.sendall(message.encode()) 
    data = s.recv(1024) 

data2 = s.recv(10)

Using Sockets in Python (5)

The socket Module iv

Example 2: Sending Data to a Local Website

import socket
ip = '127.0.0.1'
port = 80
message = "GET /5062CEM.php?lecturer=Ian%20Cornelius \r\n"
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.connect((ip, port))
    s.sendall(message.encode())
    data = s.recv(136)

message = "GET /5062CEM.php?lecturer=Terry%20Richards \r\n"

Using Sockets in Python (6)

Server socket Functions

• With client-server architecture, there is a central server
• The central server provides services to a set of machines that are connected to it
• These functions are commonly used as point of view from the server:
  • socket.bind(address)
    • connects to the address with the socket
    • the requirement is that the socket must be open before establishing a connection with the address
  • socket.listen(count)
    • the argument denotes the maximum number of connections from clients
    • it starts the TCP listener for incoming connections
  • socket.accept()
    • accepts client connections and returns a tuple representing the client socket and client address
    • bind() and listen() should be called before using this function

Using Sockets in Python (7)

Client socket Functions

• These are functions that are used on a client machine to connect with the central server:
  • socket.connect(address)
    • connects to the server IP address
  • socket.connect_ex(address)
    • same functionality as connect()
    • offers the possibility of returning an error if not able to connect

Goodbye (1)

Questions and Support

• Questions? Post them on the Community Page on Aula
• Additional Support? Visit the Module Support Page
• Contact Details:
  • Dr Ian Cornelius, ab6459@coventry.ac.uk