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Socket Programming

Greg Jernegan Brandon Simmons. Socket Programming. 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.

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Socket Programming

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  1. Greg Jernegan Brandon Simmons Socket Programming

  2. 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

  3. 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++

  4. 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

  5. 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.

  6. 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.c • in Java • TCPServer.java and TCPClient.java

  7. 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(); }

  8. 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(); DataInputStreamdis = 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(); } }

  9. 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.

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