Project 2: Socket Programming

Overview

• Sockets

• Working with sockets

• Client-Server example

• Project 1

• Hints

Socket

• What is socket?– An abstraction through which an application

may send and receive data– Different types

• Stream sockets we will use for our project

• Datagram sockets

Berkeley Sockets

The socket primitives for TCP.

Working with Sockets• Sender creates a new socket

• Attach a local address to the socket: binding operation

• Receiver listens, announces willingness to accept socket connection with a queue size announcement

• Block the caller/receiver until a connection establishment attempt arrives

• Sender and Receiver are connected

• Send data (by sender) and receive data (by receiver)

• When done sending and receiving data explicitly close the connection

A Client-Server Example

• TCP Client– Create a TCP socket

• sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);

– Establish a connection to the server• connect(sock, (struct sockaddr *) &servAddr,

sizeof(servAddr)

– Communicate with server• send(sock, msg, stringLen, 0)

• recv(sock, buffer, RCVBUFSIZE - 1, 0)

– Close the connection• close(sock)

A Client-Server Example (cont.)

• TCP Server– Create a TCP socket

• servSock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)

– Assign a port number to the socket• bind(servSock, (struct sockaddr *) &servAddr, sizeof(servAddr)

– Tell the system to allow connections for that port• listen(servSock, MAXPENDING)

– Accept new client connection• clntSock = accept(servSock, (struct sockaddr *) &clntAddr,

&clntLen)

– Communicate (send, recv) using clntSock – Close client connection (close clntSock )

Project 2

• Requirements– Implement a chat program that incorporates

both client and server functionalities

Server

client client client

Illustration

• ssh-server% chat– connect 192.168.1.3 10000 // connect to the server in

192.168.1.3 in port 10000– accept connection from 192.168.1.4 // accept a connection from

the client in 192.168.1.4– receive HELLO from 192.168.1.4 // get data message from the

client in 192.168.1.4– receive HELLO from 192.168.1.3 // get data message from the

server in 192.168.1.3– send 192.168.1.3 HELLO // send message to the server

in 192.168.1.3– send 192.168.1.4 HELLO // send message to the client

in 192.168.1.4

Notes for Our Project

• Need for “multiple” requests– Server needs to receive

• New client connection attempts

• Connected clients’ data

• User’s input (standard input)

– Client needs to receive• Server’s data

• User’s input (standard input)

Notes for Our Project (cont.)

• Solution for “multiple” requests– Using “select” -- a single process handles multiple

requests – select() works by blocking until something happens on a

file descriptor (e.g., a socket)– Usage (http://www.lowtek.com/sockets/select.html)

• Fill up a fd_set structure with the file descriptors you want to know when data comes in on.

• Call select() and block until something happens• Once select() returns, check to see if any of your file descriptors

was the reason you woke up, then do the following operation • Repeat this process

Submission Details

• Submit the electronic copy

• Set up appointment with the instructor/TA to demonstrate the functionality