1. TCP Socket Programming CPSC 441 Department of Computer Science University of Calgary

2. CPSC 441 - Application Layer 2 Socket programming Socket API r introduced in BSD4.1 UNIX, 1981 r explicitly created, used, released by apps r client/server paradigm r two types of transport service via socket API:  unreliable datagram  reliable, byte stream- oriented a host-local, application-created, OS-controlled interface (a “door”) into which application process can both send and receive messages to/from another application process socket Goal: learn how to build client/server application that communicate using sockets

3. r SOCK_STREAM  TCP  connection oriented, bidirectional  reliable, in-order delivery Two types of sockets SOCK_DGRAM  UDP  no connection  unreliable delivery, no guarantee on the order  can se nd/receive

4. CPSC 441 - Application Layer 4 Socket-programming using TCP Socket: a door between application process and end- end-transport protocol (UCP or TCP) TCP service: reliable transfer of bytes from one process to another process TCP with buffers, variables socket controlled by application developer controlled by operating system host or server process TCP with buffers, variables socket controlled by application developer controlled by operating system host or server internet

5. CPSC 441 - Application Layer 5 Client process client TCP socket Stream jargon r A stream is a sequence of characters that flow into or out of a process. r An input stream is attached to some input source for the process, e.g., keyboard or socket. r An output stream is attached to an output source, e.g., monitor or socket.

6. CPSC 441 - Application Layer 6 Example: Java client (TCP) import java.io.*; import java.net.*; class TCPClient { public static void main(String argv[]) throws Exception { String sentence; String modifiedSentence; BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); Socket clientSocket = new Socket("hostname“,6789); DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream()); Create input stream Create client socket, connect to server Create output stream attached to socket

7. CPSC 441 - Application Layer 7 Example: Java client (TCP), cont. BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); sentence = inFromUser.readLine(); outToServer.writeBytes(sentence + '\n'); modifiedSentence = inFromServer.readLine(); System.out.println ("FROM SERVER: " + modifiedSentence ); clientSocket.close(); } Create input stream attached to socket Send line to server Read line from server

8. CPSC 441 - Application Layer 8 Example: Java server (TCP) import java.io.*; import java.net.*; class TCPServer { public static void main(String argv[]) throws Exception { String clientSentence; String capitalizedSentence; ServerSocket welcomeSocket = new ServerSocket(6789); while(true) { Socket connectionSocket = welcomeSocket.accept(); BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream())); Create welcoming socket at port 6789 Wait, on welcoming socket for contact by client Create input stream, attached to socket

9. CPSC 441 - Application Layer 9 Example: Java server (TCP), cont DataOutputStream outToClient = new DataOutputStream (connectionSocket.getOutputStream()); clientSentence = inFromClient.readLine(); capitalizedSentence = clientSentence.toUpperCase() + '\n'; outToClient.writeBytes(capitalizedSentence); } Read in line from socket Create output stream, attached to socket Write out line to socket End of while loop, loop back and wait for another client connection

10. 10 Threading Mechanisms  Create a class that extends the Thread class  Create a class that implements the Runnable interface Thread MyThread Runnable MyClass Thread (objects are threads) (objects with run() body) [a][b] CPSC 441 - Tutorials

11. 11 1st method: Extending Thread class r Create a class by extending Thread class and override run() method: class MyThread extends Thread { public void run() { // thread body of execution }  Create a thread: MyThread thr1 = new MyThread();  Start Execution of threads: thr1.start(); r Create and Execute: new MyThread().start(); CPSC 441 - Tutorials

12. 12 Template class MyThread extends Thread { public void run() { System.out.println(" this thread is running... "); } class ThreadEx1 { public static void main(String [] args ) { MyThread t = new MyThread(); t.start(); } CPSC 441 - Tutorials

13. 13 2nd method: Threads by implementing Runnable interface r Create a class that implements the interface Runnable and override run() method: class MyThread implements Runnable {..... public void run() { // thread body of execution } r Creating Object: MyThread myObject = new MyThread(); r Creating Thread Object: Thread thr1 = new Thread( myObject ); r Start Execution: thr1.start(); CPSC 441 - Tutorials

14. 14 Template class MyThread implements Runnable { public void run() { System.out.println(" this thread is running... "); } class ThreadEx2 { public static void main(String [] args ) { Thread t = new Thread(new MyThread()); t.start(); } CPSC 441 - Tutorials

15. Example of Java Threads public class ThreadExample implements Runnable { private String greeting; public ThreadExample(String greeting) { this.greeting = greeting; } public void run( ) { while(true) { System.out.println(Thread.currentThread( ).getName( ) + ": "+greeting); try { TimeUnit.MILLISECONDS.sleep(((long) Math.random( ) * 100)); } catch(InterruptedException e) { } public static void main(String [ ] args) { new Thread(new ThreadExample(“Greeting 1")).start( ); new Thread(new ThreadExample(“Greeting 2")).start( ); new Thread(new ThreadExample(“Greeting 3")).start( ); } Returns reference to current thread Returns name of thread as string Suspend the thread; Thread sleeps for random amount of time. 1. Create new instance of ThreadExample with different greeting 2. Passes new instance to the constructor of Thread. 3. Calls new Thread instance's start() Each thread independently executes run() of ThreadExample, while the main thread terminates. Upon execution an interleaving of three greeting messages is printed 3-15 CPSC 441 - Tutorials

16. r Socket Programming, Dan Rubinstein, http://www1.cs.columbia.edu/~danr/courses/6761/Fall00/intro/6761-1b- sockets.ppt http://www1.cs.columbia.edu/~danr/courses/6761/Fall00/intro/6761-1b- sockets.ppt r 15-441 Socket Programming, www.cs.cmu.edu/afs/cs/academic/class/15441- f01/www/lectures/lecture03.pptwww.cs.cmu.edu/afs/cs/academic/class/15441- f01/www/lectures/lecture03.ppt r Network Programming, Geoff Kuenning, www.cs.hmc.edu/~geoff/classes/hmc.cs105.200701/slides/class21_net2.ppt www.cs.hmc.edu/~geoff/classes/hmc.cs105.200701/slides/class21_net2.ppt References