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Network programming using python
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- 2. OUTLINE • Data CommunicationsFundamentals • Sockets • Python support for sockets • TCP and UDP communication examples • Higher level programming in Python 2
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- 5. SSH SMTP FTP TRANSPORT LAYER • Providesservice to application layer. • Multiplexes applications. • TCP does much more. • Most applications use TCP. • UDP for real-time or tolerant applications. TCP 5 Source: Data and Computer Communications (Stallings)
- 6. TCP OPERATION 6 Source: Dataand Computer Communications (Stallings)
- 7. TCP VS. UDP 7 Source:Data and Computer Communications (Stallings)
- 8. IP PACKET 8 Source: Dataand Computer Communications (Stallings)
- 9. SOCKETS • Endpoints ofa bidirectional communication channel • Used to address an application on a machine. • Allow multiplexing of applications. • Identified by combination: IP_address + protocol + port_no. • Servers use the well-known port numbers (0 - 1023). • Clients use the ephemeral port numbers (1024 - 65535). • Can be treated as files. 9
- 10. SOCKET MODULE INPYTHON • Used in low-level network programming • Usually used by higher level APIs. • Functions correspond to UNIX system calls. • Except makefile() • Examples: socket(), bind(), listen(), accept(), connect(), send(), recv(), close() • Attributes • family, type, proto • Used to create socket objects. • s = socket.socket( family, type, proto) 10 A subtype, usually 0.
- 11. SOCKET ATTRIBUTES ADDRESS FAMILY •Identifies the domain and a family of protocols • Options for the address family of the socket: • AF_UNIX: a single string for UNIX • Represented by socket.AF_UNIX constant • Addres is just a filename. • AF_INET: a pair of (host, port) for IPv4 • Represented by socket.AF_INET constant • (‘www.yahoo.com’, 80) • (‘209.191.88.254’, 80) • AF_INET6: quadtuple of (host, port, flowid, scopeid) for IPv6 • Represented by socket.AF_INET6 constant 11
- 12. SOCKET ATTRIBUTES TYPE • Commonlyused types: • socket.SOCK_STREAM (for TCP sockets, connection-oriented) • socket.SOCK_DGRAM (for UDP sockets, connectionless) 12
- 13. SERVER TCP 13 import socket HOST =‘ ' # Symbolic name meaning all available interfaces PORT = 50007 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind((HOST, PORT)) s.listen(1) conn, addr = s.accept() print 'Connected by', addr while 1: data = conn.recv(1024) if not data: break conn.sendall(data) conn.close() Source: docs.python.org Would be 80 for a web server.
- 14. SERVER (CONTINUED) TCP 14 import socket HOST= ‘ ' # Symbolic name meaning all available interfaces PORT = 50007 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind((HOST, PORT)) s.listen(1) conn, addr = s.accept() print 'Connected by', addr while 1: data = conn.recv(1024) if not data: break conn.sendall(data) conn.close() Source: docs.python.org
- 15. SERVER (CONTINUED) TCP 15 import socket HOST= ‘ ' # Symbolic name meaning all available interfaces PORT = 50007 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind((HOST, PORT)) s.listen(1) conn, addr = s.accept() print 'Connected by', addr while 1: data = conn.recv(1024) if not data: break conn.sendall(data) conn.close() Source: docs.python.org
- 16. SERVER (CONTINUED) TCP 16 import socket HOST= ‘ ' # Symbolic name meaning all available interfaces PORT = 50007 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind((HOST, PORT)) s.listen(1) conn, addr = s.accept() print 'Connected by', addr while 1: data = conn.recv(1024) if not data: break conn.sendall(data) conn.close() Source: docs.python.org
- 17. SERVER (CONTINUED) TCP 17 import socket HOST= ‘ ' # Symbolic name meaning all available interfaces PORT = 50007 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind((HOST, PORT)) s.listen(1) conn, addr = s.accept() print 'Connected by', addr while 1: data = conn.recv(1024) if not data: break conn.sendall(data) conn.close() Source: docs.python.org
- 18. SERVER (CONTINUED) TCP 18 import socket HOST= ‘ ' # Symbolic name meaning all available interfaces PORT = 50007 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind((HOST, PORT)) s.listen(1) conn, addr = s.accept() print 'Connected by', addr while 1: data = conn.recv(1024) if not data: break conn.sendall(data) conn.close() Source: docs.python.org
- 19. CLIENT TCP import socket HOST ='daring.cwi.nl' # The remote host PORT = 50007 # The same port as used by the server s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((HOST, PORT)) s.sendall('Hello, world') data = s.recv(1024) s.close() print 'Received', repr(data) 19 Source: docs.python.org No need to specify local socket.
- 20. CLIENT (CONTINUED) TCP import socket HOST= 'daring.cwi.nl' # The remote host PORT = 50007 # The same port as used by the server s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((HOST, PORT)) s.sendall('Hello, world') data = s.recv(1024) s.close() print 'Received', repr(data) 20 Source: docs.python.org Could be an HTTP request like (‘GET /index.html HTTP/1.0 nn ’). Transport layer gives service to application layer.
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- 23. HIGH LEVEL NETWORKPROGRAMMING • Support for specific applications e.g. HTTP, FTP, … • Instead of socket module, servers use other modules and libraries, e.g.: • HTTP: httplib, urllib2, xmllib • FTP: ftplib, urllib • SMTP: smtplib • Servers usually use the SocketServer module. • Different file formats and encodings must be handled at the client using various libraries such as csv, htmlparser and json. 23
- 24. SOCKETSERVER EXAMPLE TIME SERVER 24 importSocketServer import time Class TimeHandler(SocketServer.BaseRequestHandler): def handle(self): self.request.sendall(time.ctime()+"n") serv = SocketServer.TCPServer(("",8000),TimeHandler) serv.serve_forever() Source: www.dabeas.com
- 25. APPLICATION LAYER HTTP EXAMPLE •Opening a web page: 25 import urllib2 u = urllib2.urlopen("http://www.python/org/index.html") data = u.read() print data
- 26. SUMMARY • Client/server communicationmodel • TCP and UDP give service to applications. • Use TCP sockets if you need reliability. • A socket identifies a single PID on a single machine. • Use the socket module to create and use socket objects. • Python includes many other higher-level networking modules. 26
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