Networking: Protocol, Sockets, Knowing IP Address, URL, Reading the Source Code of a Web Page, Downloading a Web Page from Internet, Downloading an Image from Internet, A TCP/IP Server, A TCP/IP Client, A UDP Server, A UDP Client, File Server, File Client, Two-Way Communication between Server and Client, Sending a Simple Mail,

1. Chapter - 5
Network – 5.2
Maulik Borsaniya
Gardividyapith

2. What is network ?
• A computer network, or data network, is a digital
telecommunications network which allows
nodes to share resources. In computer networks,
computing devices exchange data with each
other using connections between nodes

3. What is protocol ?
• A network protocol defines rules and conventions for
communication between network devices.
• Network protocols include mechanisms for devices to
identify and make connections with each other, as well
as formatting rules that specify how data is packaged
into messages sent and received
• FTP: File Transfer Protocol. ...
• SSL: Secure Sockets Layer. ...
• TELNET (telnet) ...
• SMTP: Simple Mail Transfer Protocol. ...
• POP3: Post Office Protocol.

4. Starting With the Socket Programming
• 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

5. • 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.

6. Here is an example of a script for connecting to Google
An example script to connect to Google using socket
# programming in Python
import socket # for socket
import sys
try:
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print ("Socket successfully created")
except socket.error as err:
print ("socket creation failed with error")
# default port for socket
port = 80
try:
host_ip = socket.gethostbyname('www.google.com')
except socket.gaierror:
# this means could not resolve the host
print ("there was an error resolving the host")
sys.exit()
# connecting to the server
s.connect((host_ip, port))
print ("the socket has successfully connected to google on port == %s" %(host_ip))

7. Http Request Reponses
• HTTP is based on the client-server architecture model and a
stateless request/response protocol that operates by
exchanging messages across a reliable TCP/IP connection.
• An HTTP "client" is a program (Web browser or any other
client) that establishes a connection to a server for the
purpose of sending one or more HTTP request messages. An
HTTP "server" is a program ( generally a web server like
Apache Web Server or Internet Information Services IIS, etc. )
• that accepts connections in order to serve HTTP requests by
sending HTTP response messages.

8. Installation of http requests
Navigate  Python34/script
Pip install requests

9. Download images from web – with
request response
import requests
image_url = "https://www.python.org/static/community_logos/python-logo-master-v3-
TM.png"
# URL of the image to be downloaded is defined as image_url
r = requests.get(image_url) # create HTTP response object
# send a HTTP request to the server and save
# the HTTP response in a response object called r
with open("python_logo.png",'wb') as f:
# Saving received content as a png file in
# binary format
# write the contents of the response (r.content)
# to a new file in binary mode.
f.write(r.content)

10. Client Server Connection
Establishment
#Server
# first of all import the socket library
import socket
# next create a socket object
s = socket.socket()
print ("Socket successfully created")
# reserve a port on your computer in our
# case it is 12345 but it can be anything
port = 12345
# Next bind to the port
# we have not typed any ip in the ip field
# instead we have inputted an empty string
# this makes the server listen to requests
# coming from other computers on the network
s.bind(('', port))
print ("socket binded to %s" %(port))
# put the socket into listening mode
s.listen(5)
print ("socket is listening")
# a forever loop until we interrupt it or
# an error occurs
while True:
# Establish connection with client.
c, addr = s.accept()
print ('Got connection from', addr)
# send a thank you message to the client.
c.send('Thank you for connecting')
# Close the connection with the client
Python server.py
telnet localhost 12345

11. 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.

12. • 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 try's 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.

13. #Client
# Import socket module
import socket
# Create a socket object
s = socket.socket()
# Define the port on which you want to connect
port = 12345
# connect to the server on local computer
s.connect(('127.0.0.1', port))
# receive data from the server
s.recv(1024)
# close the connection
s.close()

14. TCP & UDP
• The user datagram protocol (UDP) works differently
from TCP/IP.
• Where TCP is a stream oriented protocol, ensuring that
all of the data is transmitted in the right order,
• UDP is a message oriented protocol.
• UDP does not require a long-lived connection, so setting
up a UDP socket is a little simpler.
• On the other hand, UDP messages must fit within a
single packet (for IPv4, that means they can only hold
65,507 bytes because the 65,535 byte packet also
includes header information) and delivery is not
guaranteed as it is with TCP.

15. Sending mail
# Python code to illustrate Sending mail from
#error
# your Gmail account
import smtplib
# creates SMTP session
s = smtplib.SMTP('smtp.gmail.com', 587)
# start TLS for security
s.starttls()
# Authentication
s.login("patelmaulik752@gmail.com", “password")
# message to be sent
message = "Test Message"
# sending the mail
s.sendmail("borsaniyamaulik@gmail.com", "inspirationalstory1@gmail.com", message)
# terminating the session
s.quit()

16. success
import smtplib
gmailaddress = input("what is your gmail address? n ")
gmailpassword = input("what is the password for that
email address? n ")
mailto = input("what email address do you want to send
your message to? n ")
msg = input("What is your message? n ")
mailServer = smtplib.SMTP('smtp.gmail.com' , 587)
mailServer.starttls()
mailServer.login(gmailaddress , gmailpassword)
mailServer.sendmail(gmailaddress, mailto , msg)
print(" n Sent!")
mailServer.quit()