CIS 345 Socket Quiz

gethostname ( )

returns IP name of the host computer running the Python interpreter; Raises exception if computer does not have an IP address returns computer name to get hostName

gethostbyname(hostName)

returns the IP number of the computer whoese IP name is ipName. raises exception if ipName cannot be found returns IP address

listen ()

s.listen ( ) enables the server to accept connections; makes a listening socket. - also specifies the number of unaccepted connections that the system will allow before refusing new connections

PORT

should be an integer from 1- 65,535 if less than 1024, might require superuser priveleges

SOCK_STREAM

socket type for TCP, protocol used to transport messages in the network

What happens when you create a socket object and specify socket type

socket.socket() socket.SOCK_STREAM default protocol(TCP) is called

sockets

used to send messages across a network; provide a form of inter-process communication(IPC)

blocking method

when you call method, code is blocked; doesn't return until it receives a connect request from a client; infinite loop and won't return until something happens. receive and accept are blocking codes

Server ; to set up a listening socket

1. Socket 2. Bind 3. Listen 4. Accept

Server full

1. Socket 2.Bind 3.Listen 4. Accept 5. Receive 6.Send 7.Receive 8. Close extra receive bc client sends closing message

Client

1. socket 2.connect (to establish connection to server) 3. send 4. Receive 5. Close

computers referenced by

IP address and host name

IP address

IPv4 is 4 numbers from 0-255 separated by periods

AF_INET

Internet address family for IPv4

Diagram

NIC has two connection ports: ETH0 & ETH1 ETH0 connects to outside of computer Connect to router Router receives messages in packets and connect to modem modem connects to ISP socket is a pipeline and clients and servers connect to it

TCP

Transmission Control Protocol

after getting client socket object from accept:

an infinite while loop is used to loop over blocking calls to conn.recv(). This reads whatever data the client sends and echoes it back using conn.sendall(). while True: data = conn.recv(1024) if not data: break conn.sendall(data)

Client server applications

applications or processes that can run locally on a single computer or remotely across a network of computers. need: IP Addresses Sockets Threads

Bind

bind is used to associate the socket with a specific network interface (HOST) and port number (PORT); bind depends on address family of socket (AF_INET) s.bind(HOST,PORT) or s.bind(ADDR)

accept ( )

conn, addr = s.accept( ) with conn: print('Connected by', addr) blocks and waits for an incoming connection and when a client connects, it returns a new socket object representing the connection and a tuple holding the address of the client.

socket

connection to the server to communicate between client and server; multiple clients can connect to a server

Client side summary

creates a socket object, connects to server, calls sendall to send its message and recv( ) to read server reply and print

Client

from socket import * HOST='10.153.76.226' #HOST ='localhost' PORT=65000 ADDR=(HOST, PORT) sock= socket(AF_INET,SOCK_STREAM) sock.connect(ADDR) sock.sendall(b' Hello world') data = s.recv(1024) print( 'Received', repr(data) )

server code

from socket import * HOST = 'localhost' PORT = 65000 ADDR = (HOST, PORT) s = socket(AF_INET, SOCK_STREAM) s.bind(ADDR) s.listen (5) conn,addr = s. accept( ) with conn: print ('Connected by', addr) while True: data = conn.recv(1024) if not data: break conn.sendall(data)

Creating a socket object

import socket socket.socket( socket.AF_INET, socket.SOCK_STREAM) as s or from socket import * s = socket(AF_INET, SOCK_STREAM)

Listening socket

listens to connections from clients; when client connects, the server calls accept() to accept the connection

127.0.0.1

loopback address; message you send does not get broadcasted, does not leave your machine. goes to NIC card and loops back to be sent to destination

NIC

network interface card

Port

pipeline into computer; door into house. which room to go in? IP address gets u to a computer port number is where the computer is supposed to communicate through need the port that the server is listening to

Why TCP

reliable- packets dropped in network are detected and retransmitted by sender in order data delivery- data is read by application in order it was written by sender don't have to worry about packet loss, out of order data