PL-I Group A: Ass-6 Socket programming in Python · Socket Functions socket() creates a new socket...

By B.A.Khivsara

PL-I Group A: Ass-6

Socket programming in Python

Outline

Socket Basics

Simple TCP Client Server Program

Chat TCP Client Server Program

File Transfer/Sharing Client Server Program

DataTransport

There are two basic types of communication

Streams (TCP): Computers establish a

connection with each other and read/write data in

a continuous stream of bytes---like a file. This is

the most common.

Datagrams (UDP): Computers send discrete

packets (or messages) to each other. Each

packet contains a collection of bytes, but each

packet is separate and self-contained.

UDP Characteristics

Also datagram-based

Connectionless, unreliable, can broadcast

Applications usually message-based

No transport-layer retries

Applications handle (or ignore) errors

Processes identified by port number

Services live at specific ports

Usually below 1024, requiring privilege

TCP Characteristics

Connection-oriented

Two endpoints of a virtual circuit

Reliable

Application needs no error checking

Stream-based

No predefined blocksize

Processes identified by port numbers

Services live at specific ports

Client/Server Concepts

Server opens a specific port

The one associated with its service

Then just waits for requests

Server is the passive opener

Clients get ephemeral ports

Guaranteed unique, 1024 or greater

Uses them to communicate with server

Client is the active opener

Sockets

•Programming abstraction for network code

•Socket: A communication endpoint

•Supported by socket library module

•Allows connections to be made and data to be

transmitted in either direction

socket socketnetwork

Socket API

Socket API

Network programming interface

Socket

APITCP UDP

IP

Application

Transport

Network

Socket Basics

•To create a socketimport socket

s = socket.socket(addr_family,Socket_type)

•Address families

socket.AF_INET Internet protocol (IPv4)

socket.AF_INET6 Internet protocol (IPv6)

•Socket typessocket.SOCK_STREAM Connection based stream (TCP)

socket.SOCK_DGRAM Datagrams (UDP)

Example:

from socket import *

s = socket(AF_INET,SOCK_STREAM)

Socket Basics

End point determined by two things:

Host address: IP address is Network Layer

Port number: is Transport Layer

Two end-points determine a connection: socket

pair

ex: 198.69.10.2, 5500

IP Address Port No

Ports Numbers (typical, since vary by OS):

0-1023 : reserved

1024-5000 : ephemeral

Above 5000 : for general use

(Total 65535 ports)

Well-known, reserved services

ftp 21/tcp

telnet 23/tcp

finger 79/tcp

snmp 161/udp

SocketTypes

•Almost all code will use one of following



s = socket(AF_INET,SOCK_DGRAM)

•TCP connection

s = socket(AF_INET, SOCK_STREAM)

•UDP connection

s = socket(AF_INET, SOCK_DGRAM)

Types of Sockets

Stream socket (TCP)

Connection-oriented Requires connection

establishment & termination

Reliable delivery In-order delivery Retransmission No duplicates

High variance in latency Cost of the reliable service

File-like interface (streaming)

E.g., HTTP, SSH, FTP, …

Datagram socket (UDP)

Connection-less

“Best-effort” delivery Possible out-of-order

delivery No retransmission Possible duplicates

Low variance in latency

Packet-like interface Requires packetizing

E.g., DNS, VoIP, VOD, AOD, …

Socket Functions socket() creates a new socket of a certain socket type, identified by an

integer number, and allocates system resources to it.

bind() is typically used on the server side, and associates a socket with a

socket address structure, i.e. a specified local port number and IP address.

listen() is used on the server side, and causes a bound TCP socket to

enter listening state.

connect() is used on the client side, and assigns a free local port number to

a socket. In case of a TCP socket, it causes an attempt to establish a new

TCP connection.

accept() is used on the server side. It accepts a received incoming attempt

to create a new TCP connection from the remote client, and creates a new

socket associated with the socket address pair of this connection.

send() and recv() are used for sending and receiving data to/from a remote

socket.

close() causes the system to release resources allocated to a socket.

gethostbyname() and gethostbyaddr() are used to resolve host names

and addresses. IPv4 only.

Outline

Socket Basics




A simple TCP server



s.bind(("",5000))

s.listen(5)

while True:

c,a = s.accept()

print "Received connection from", a

c.send("Hello %s\n" % a[0])

c.close()

A Simple TCP Client



s.connect((“localhost",5000)) # Connect

s.send(“Hello”) # Send request

data = s.recv(10000) # Get response

s.close()

Outline

Socket Basics




TCP Client for chatimport socket

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

server_socket.bind(("", 5000))

server_socket.listen(5)

while 1:

client_socket, address = server_socket.accept()

print "I got a connection from ", address

while 1:

data = raw_input ( "SEND( TYPE q or Q to Quit):" )

if (data == 'Q' or data == 'q'):

client_socket.send (data)

client_socket.close()

break;

else:

client_socket.send(data)

data = client_socket.recv(512)

if ( data == 'q' or data == 'Q'):


break;

else:

print "RECIEVED:" , data

TCP Client for chat

import socket

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

client_socket.connect(("localhost", 5000))

while 1:

data = client_socket.recv(512)

if ( data == 'q' or data == 'Q'):


break;

else:

print "RECIEVED:" , data

data = raw_input ( "SEND( TYPE q or Q to Quit):" )

if (data <> 'Q' and data <> 'q'):


else:



break;

Outline

Socket Basics




TCP Server for File Sharingimport socket,os

s = socket.socket()

s.bind(("",12001))

s.listen(2)

while 1:

c,addr=s.accept()

path="/home/snjbcoe/PL-I Program"

dirlist=os.listdir(path)

flist=“ “

for fname in dirlist:

flist=flist+" "+fname

c.send(flist)

data=c.recv(1024)

f = open("/home/snjbcoe/PL-I Program/"+data, "rb")

a=f.read(5100)

c.send(a)

f.close()

c.close()

TCP Client for File Sharing

import socket

c=socket.socket()c.connect((“localhost",12001))

while 1:

print "File listing from server is\n",(c.recv(5000))

data=raw_input("enter file name to download\n :")

c.send(data)f=open(data,"wb")b=c.recv(5000)f.write(b)f.close()

print "File is downloaded successfuly“c.close()

References

http://www.dabeaz.com/python/PythonNetBinder.pdf

PL-I Group A: Ass-6 Socket programming in Python · Socket Functions socket() creates a new socket...

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Transcript of PL-I Group A: Ass-6 Socket programming in Python · Socket Functions socket() creates a new socket...