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Introduction

Network Programming using Python Sudhir Valsange svalsan@g.clemson.edu. Introduction. •Network programming is a major use of Python •Python standard library has wide support for network

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Introduction

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  1. Network Programming usingPythonSudhirValsange svalsan@g.clemson.edu

  2. Introduction •Network programming is a major use of Python •Python standard library has wide support for network protocols, data encoding/decoding, and other things you need to make it work •Writing network programs in Python tends to be substantially easier than in C/C++

  3. Prerequisites • Python Basics • Don’t need to be an expert on all of its advanced features • Some prior knowledge of networking concepts

  4. Socket • Bidirectional communication endpoint for sending and receiving data • It is defined by IP address and port number • Socket behaves much like a low level file descriptor

  5. Using Socket • To create a socket import socket s = socket(addr_family, type) • Address families socket.AF_INET Internet protocol (IPv4) socket.AF_INET6 Internet protocol (IPv6) • Socket types SOCK_STREAM Connection based stream (TCP) SOCK_DGRAM Datagrams (UDP) • Example from socket import * s = socket(AF_INET,SOCK_STREAM)

  6. TCP Client • How to make an outgoing connection • from socket import * • s = socket(AF_INET,SOCK_STREAM) • # Connect makes connection • s.connect(("www.python.org",80)) • # Send() and recv() to transmit and receive data • s .send(“Hello") • data = s.recv(10000) • # Close() shuts down the connection • s.close()

  7. TCP Server • Simple Server • from socket import * • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • print "Received connection from", a • c.send("Hello”) • c.close()

  8. TCP Server • Address binding • from socket import * • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • print "Received connection from", a • c.send("Hello”) • c.close() Binds the socket to a specific address

  9. TCP Server • Start listening for connections • from socket import * • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • print "Received connection from", a • c.send("Hello”) • c.close() Tells operating system to start listening for connections on the socket

  10. TCP Server • Accepting a new connection • from socket import * • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • print "Received connection from", a • c.send("Hello”) • c.close() Accept a new client connection

  11. TCP Server • Client socket and address • from socket import * • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • print "Received connection from", a • c.send("Hello”) • c.close() Accept returns a pair (client_socket,addr)

  12. TCP Server • Sending data • from socket import * • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • print "Received connection from", a • c.send("Hello”) • c.close() Send data to client

  13. TCP Server • Closing connection • from socket import * • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • print "Received connection from", a • c.send("Hello”) • c.close() Close client connection

  14. Sockets as Files • Sometimes it is easier to work with sockets as a "file" object • f = s.makefile() • This will wrap a socket with a file-like API • f.read() • f.readline() • f.write() • f.writelines() • for line in f: • ... • f.close()

  15. Sockets and Concurrency • Servers usually handle multiple clients • Each client gets its own socket on server • • To manage multiple clients, • • Server must always be ready to accept new connections • • Must allow each client to operate independently

  16. Threaded Server • • Each client is handled by a separate thread • import thread • from socket import * • defhandle_client(c,a): • ... whatever ... • c.close() • return • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • print ‘Connected from ’,a • thread.start_new_thread( handle_client, (c,a) )

  17. Forking Server • • Each client is handled by a subprocess • import os • from socket import * • s = socket(AF_INET,SOCK_STREAM) • s.bind(("",9000)) • s.listen(5) • while True: • c,a= s.accept() • if os.fork() == 0: • # Child process. Manage client • ... • c.close() • os._exit(0) • else: • # Parent process. Clean up and go • # back to wait for more connections • c.close()

  18. Asynchronous Server • • Server handles all clients in an event loop • import select • from socket import * • s = socket(AF_INET,SOCK_STREAM) • ... • clients = [] # List of all active client sockets • while True: • # Look for activity on any of my sockets • input,output,err= select.select(s+clients, clients, clients) • # Process all sockets with input • for i in input: • ... • # Process all sockets ready for output • for o in output: • …

  19. Utility Functions • Get the hostname of the local machine • >>> socket.gethostname() • 'foo.bar.com' • >>> • Get the IP address of a remote machine • >>> socket.gethostbyname("www.python.org") • '82.94.237.218' • >>> • Get name information on a remote IP • >>> socket.gethostbyaddr("82.94.237.218") • ('dinsdale.python.org', [ ], ['82.94.237.218']) • >>>

  20. Exercise –Building Simple Chat Server

  21. THANK YOU

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