Project 2: Socket Programming

1. Project 2: Socket Programming

2. Overview • Sockets • Working with sockets • Client-Server example • Project 1 • Hints

3. 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

4. Berkeley Sockets The socket primitives for TCP.

5. 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

6. 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)

7. 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 )

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

9. 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

10. 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)

11. 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

12. Submission Details • Submit the electronic copy • Set up appointment with the instructor/TA to demonstrate the functionality