Greg Jernegan Brandon Simmons

The Beginning…  The problem Huge demand for internet enabled applications and programs that communicate over a network.  Basic Level Server-client-media for communication ○ Client makes request ○ Server offers services for request

What is Socket Programming  Sockets provide an interface for programming networks at the transport layer. Similar to file I/O Communication is independent of programming language ○ This allows communication to exist among any languages even if they’re different Example java talks to C++

How it works…  Server has one socket is bound to a specific port  Listens for connection request Upon request if all goes well connection is made  After connection made the server gets a new socket bound to a different port New port # needed so original socket can listen for connection request as well as serve the connected client

What that means…  Socket programming introduces a multitasking environment More clients can be served at once with out a bottle neck or delay in service.

Types of Socket Programming  SP can connected using both Connection Oriented server an client program and Connectionless TCP beginning or UDP beginning  Programming may happen among many languages in Python ○ Example: tcpserver.py and tcpclient.py in Perl ○ Example: tcpserver.pl and tcpclient.pl In C ○ Example: tcpserver.c and tcpclient.ctcpserver.c in Java ○ TCPServer.java and TCPClient.java

Simple Server in JAVA // SimpleServer.java: A simple server program. import java.net.*; import java.io.*; public class SimpleServer { public static void main(String args[]) throws IOException { // Register service on port 1254 ServerSocket s = new ServerSocket(1254); Socket s1=s.accept(); // Wait and accept a connection // Get a communication stream associated with the socket OutputStream s1out = s1.getOutputStream(); DataOutputStream dos = new DataOutputStream (s1out); // Send a string! dos.writeUTF(“Hi there”); // Close the connection, but not the server socket dos.close(); s1out.close(); s1.close(); }

Simple Client in JAVA // SimpleClient.java: A simple client program. import java.net.*; import java.io.*; public class SimpleClient { public static void main(String args[]) throws IOException { // Open your connection to a server, at port 1254 Socket s1 = new Socket(“localhost”,1254); // Get an input file handle from the socket and read the input InputStream s1In = s1.getInputStream(); DataInputStream dis = new DataInputStream(s1In); String st = new String (dis.readUTF()); System.out.println(st); // When done, just close the connection and exit dis.close(); s1In.close(); s1.close(); }

Commands  socket() creates a new socket of a certain socket type, identified by an integer number, and allocates system resources to it.  bind() is typically used on the server side, and associates a socket with a socket address structure, i.e. a specified local port number and IP address.  listen() is used on the server side, and causes a bound TCP socket to enter listening state.  connect() is used on the client side, and assigns a free local port number to a socket. In case of a TCP socket, it causes an attempt to establish a new TCP connection.  accept() is used on the server side. It accepts a received incoming attempt to create a new TCP connection from the remote client, and creates a new socket associated with the socket address pair of this connection.  send(), recv(), write(), read(), sendto() and recvfrom(), are used for sending and receiving data to/from a remote socket.  close() causes the system to release resources allocated to a socket. In case of TCP, the connection is terminated.  gethostbyname(), gethostbyaddr() are used to resolve host names and addresses. IPv4 only.  select() is used to prune a provided list of sockets for those that are ready to read, ready to write, or that have errors.  poll() is used to check on the state of a socket in a set of sockets. The set can be tested to see if any socket can be written to, read from or if an error occurred.  getsockopt() is used to retrieve the current value of a particular socket option for the specified socket.  setsockopt() is used to set a particular socket option for the specified socket.