Project 2 Socket Programming Overview Sockets Working with

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 *) &serv. Addr, sizeof(serv. Addr) – Communicate with server • send(sock, msg, string. Len, 0) • recv(sock, buffer, RCVBUFSIZE - 1, 0) – Close the connection • close(sock)

A Client-Server Example (cont. ) • TCP Server – Create a TCP socket • serv. Sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) – Assign a port number to the socket • bind(serv. Sock, (struct sockaddr *) &serv. Addr, sizeof(serv. Addr) – Tell the system to allow connections for that port • listen(serv. Sock, MAXPENDING) – Accept new client connection • clnt. Sock = accept(serv. Sock, (struct sockaddr *) &clnt. Addr, &clnt. Len) – Communicate (send, recv) using clnt. Sock – Close client connection (close clnt. Sock )

Project 2 • Requirements – Implement a chat program that incorporates both client and server functionalities Server 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