Network Programming Overview PDF

02 Python Networking Overview Network Programming University of Tripoli Faculty of Information Technology Department of Networking Assistant Lecturer / Marwa Ebrahim Elwakedy  What is Network Programming? ◼ Network programs: Programs that use...

02 Python Networking Overview Network Programming University of Tripoli Faculty of Information Technology Department of Networking Assistant Lecturer / Marwa Ebrahim Elwakedy  What is Network Programming? ◼ Network programs: Programs that use network in some way to do their work. Send/receive data across a network Provide/invoke services over a network Mobile computing through wireless networks Cloud/edge computing ◼Network programming is the discipline of designing and implementing network programs. 02 Python Networking Overview  Python Networking 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++. 02 Python Networking Overview  Python Networking Levels ◼ Python provides two levels of access to network services. ◼ Low level: can access the basic socket support in the underlying OS connection-oriented connectionless ◼ High level (protocol level): libraries for various application level network protocols FTP, HTTP, POP3, SMTP, … 02 Python Networking Overview  The Problem ◼Communication between computers NETWORK ◼It’s just sending/receiving bits 02 Python Networking Overview  Three Main Issues: ◼ Addressing Specifying a remote computer and service ◼ Data transport Moving data(bits) back and forth ◼ Meaningful conversation Conversation in proper order Understand each other 02 Python Networking Overview  Networking Address: ◼ Addressing Specifying a remote computer and service Foo.Bar.com 205.172.13.4 WWW.EXAMPLE.COM port: 1234 NETWORK 42.92.237.218 port: 80 02 Python Networking Overview  Standard Ports: ◼ Ports for common services are preassigned 21 FTP 22 SSH 23 Telnet 25 SMTP (Mail) 80 HTTP (Web) 1 10 POP3 (Mail) 119 NNTP (News) 443 HTTPS (web) ◼ Other port numbers may just be randomly assigned to programs by the OS 02 Python Networking Overview  Using netstat ◼ Use 'netstat' to view active network connections shell % netstat -a Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 *:imaps *:* LISTEN tcp 0 0 *:pop3s *:* LISTEN tcp 0 0 localhost:mysql *:* LISTEN tcp 0 0 *:pop3 *:* LISTEN tcp 0 0 *:imap2 *:* LISTEN tcp 0 0 *:8880 *:* LISTEN tcp 0 0 *:www *:* LISTEN ◼ Note: Must execute from the command shell on both Unix and Windows 02 Python Networking Overview  Connections: ◼ Each endpoint of a network connection is always represented by a host and port # ◼ In Python you write it out as a tuple (host, port) ("www.python.org", 80) "205.172.13.4", 443) ◼ In almost all of the network programs you’ll write, you use this convention to specify a network address 02 Python Networking Overview  Client/Server Concept: ◼ Each endpoint is a running program ◼Servers wait for incoming connections and provide a service (e.g., web, mail, etc.) ◼ Clients make connections to servers Clients macbooks-air.64568 205.172.13.4 Server WWW.EXAMPLE.COM port: 1234 NETWORK 42.92.237.218 browser Web port: 80 02 Python Networking Overview  Request/Response Cycle import requests def request_response(url): response = requests.get(url) status_code = response.status_code print("Status code:", status_code) if status_code == 200: content = response.content print("Content:", content) else: print("Error:", response.reason) if __name__ == "__main__": url = "https://www.google.com" request_response(url) 02 Python Networking Overview  Request/Response Cycle ◼ The first line imports the requests library. This library provides a simple and easy-to-use interface for making HTTP requests. import requests ◼ The request_response() function takes a URL as input and makes a GET request to that URL. The function returns a Response object, which contains information about the response, such as the status code, the content, and the headers def request_response(url): ◼ The requests.get() method makes a GET request to the specified URL and returns a Response object. response = requests.get(url) 02 Python Networking Overview  Request/Response Cycle ◼ The status_code attribute of the Response object contains the status code of the response. The status code is an integer that indicates the success or failure of the request. status_code = response.status_code ◼ The print() statement prints the status code of the response. print("Status code:", status_code) ◼ The if statement checks if the status code is 200. The status code 200 indicates that the request was successful. if status_code == 200: 02 Python Networking Overview  Request/Response Cycle ◼ The content attribute of the Response object contains the content of the response. The content is the data that was returned by the server in response to the request. content = response.content ◼ The print() statement prints the content of the response. print("Content:", content) ◼ The else block is executed if the status code is not 200. else: print("Error:", response.reason) 02 Python Networking Overview  Request/Response Cycle ◼ The print() statement prints the reason for the error. The reason is a string that describes the error that occurred. print("Error:", response.reason) ◼ The if __name__ == "__main__": block is executed if the script is run as the main program. The url variable is set to the URL of the Google website. The request_response() function is called with the url variable as input. if __name__ == "__main__": url = "https://www.google.com" request_response(url) 02 Python Networking Overview  Request/Response Cycle ◼ Most network programs use a request/response model based on messages. ◼ Client sends a request message (e.g., HTTP) GET /index.html HTTP/1.0 ◼ Server sends back a response message HTTP/1.0 200 OK Content- type: text/html Content- length: 48823... ◼ The exact format depends on the application 02 Python Networking Overview  Using Telnet: ◼ As a debugging aid, telnet can be used to directly communicate with many services telnet hostname portnum ◼ Example: shell % telnet www.python.org 80 Trying 82.94.237.218... Connected to www.python.org. Escape character is '^]'. Type this and press GET /index.html HTTP/1.0 return a few times HTTP/1.1 200 OK Date: Mon, 31 Mar 2008 13:34:03 GMT Server: Apache/2.2.3 (Debian) DAV/2 SVN/1.4.2 mod_ssl/2.2.3 OpenSSL/0.9.8c 02 Python Networking Overview  Data Transport ◼ 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. 02 Python Networking Overview  Sockets: ◼ Programming abstraction for network code ◼ Socket: A communication endpoint socket Socket NETWORK ◼ Supported by socket library module. ◼ Allows connections to be made and data to be transmitted in either direction 02 Python Networking Overview  Python Socket Support ◼ Python supports socket networking through the socket module. ◼ The module provides the BSD socket interface. ◼ The socket() function create socket objects. ◼ Various functions(gethostbyname(), gethostbyaddr() …) to get commn related info. ◼ The send()/recv() function send/receive data through the socket. 02 Python Networking Overview  Python Socket Support import socket def print_machine_info(): host_name = socket.gethostname() ip_address = socket.gethostbyname('localhost') print ("Host name: %s" %host_name) print ("IP address: %s" %ip_address) if __name__ == '__main__': print_machine_info() 02 Python Networking Overview  Protocols ◼ Send/receive data back and forth is meaningless if we can’t understand each other. ◼ To conduct meaningful conversation: Follow agreed upon rules of message exchange Provide data in proper format ◼ This is done through protocols. ◼ Python offers protocol modules for many networking tasks/applications. 02 Python Networking Overview  Finding service name import socket def find_service_name(): protocolname = 'tcp' for port in [80, 25]: print ("Port: %s => service name: %s" %(port, socket.getservbyport(port, protocolname))) print ("Port: %s => service name: %s" %(53, socket.getservbyport(53, 'udp'))) if __name__ == '__main__': find_service_name() 02 Python Networking Overview  Conclusion ◼ Python networking support is rich and friendly. ◼ Use socket programming for low-level or short/simple message exchange. ◼ Use TCP/UDP for normal client-server programming. ◼ Use application protocol modules for corresponding services. 02 Python Networking Overview