Hands On Networking Socket Programming Ram P Rustagi, ISE Dept Abhishek Gupta, ISE Dept Laxmi Kuber, MCA Dept June 28-30, 2012

Socket programming Sockets –Protocol independent method of creating a connection a connection –Can be either Connection based or connection less –Connection established before communication –Destination information provided with each packet –Packet based or stream based Message boundaries vs one stream –Reliable vs unreliable Message recovered in case –Loss, duplication, corruption, out of order delivery 2

Socket programming Ports –Three categories –Well known ports Assigned and managed by IANA Ranges from –Registered ports Can be registered by IANA Ranges from 1024 to –Dynamic ports Free to be used by application at will 3

Socket characteristics Sockets are charaterized by –Domain, type and transport protocol Common domains are –AF-UNIX –AF_INET –AF_INET6 Types are –Datagram vs streams Transport protocols –TCP –UDP 4

5 Socket Programming Server side –Concurrent connections handling Multi processing Single threaded using select(), poll() Non-blocking communication WE-1 –Simple client server programming (using C) WE-2 –Multi-processing server side programming WE-3 –Server side single threaded concurrent connections Using select() Using poll() WE-4 –Using non-blocking I/O 5

6 Socket Programming Socket programming concepts –Client side and server side differences –Well known ports, reserved ports and ephemeral ports –UDP vs TCP programming Client side programming –Socket() –Connect() // only for TCP –Read(), write() –Close() Server side programming –Socket() –Bind() –Listen() –Accept() –Read(), write() –Close() 6

Socket API’s socket: creates a socket of a given domain, type, protocol (buy a phone) bind: assigns a name to the socket (get a telephone number) listen: specifies the number of pending connections that can be queued for a server socket. (call waiting allowance) accept: server accepts a connection request from a client (answer phone) connect: client requests a connection request to a server (call) send, sendto: write to connection (speak) recv, recvfrom: read from connection (listen) shutdown: end the call

socket Bind Listen accept Send/recv Close shutdown close socket connect Send/recv shutdown close serverclient

Non-Blocking I/O Programs that use non-blocking I/O –every function has to return immediately –Can not wait or get blocked To make a non-blocking program –make the socket non-blocking –ioctl(sockfd, FIONBIO, (char *)&on);

programs WE-1 –Simple client/server programs –Sample given for both in C and Java WE-2 –multi-processing server side –C –based, server creates a child for each connection –Java based, server creates a thread for each connection WE-3 –Available only for C based –Use of select 10