Socket Programming TCP and UDP 2: Application Layer 1

Socket Programming TCP and UDP 2: Application Layer 1

Socket programming Goal: learn how to build client/server application that communicate using sockets Socket API introduced in BSD4.1 UNIX, 1981 explicitly created, used, released by apps client/server paradigm two types of transport service via socket API: unreliable datagram reliable, byte stream-oriented socket 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 2: Application Layer 2

TCP 2: Application Layer 3

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 controlled by application developer controlled by operating system process process socket TCP with buffers, variables socket TCP with buffers, variables host or server internet controlled by application developer controlled by operating system host or server 2: Application Layer 4

Socket programming with TCP Client must contact server server process must first be running server must have created socket (door) that welcomes client’s contact Client contacts server by: creating client-local TCP socket specifying IP address, port number of server process When client creates socket: client TCP establishes connection to server TCP When contacted by client, server TCP creates new socket for server process to communicate with client allows server to talk with multiple clients source port numbers used to distinguish clients (more in Chap 3) application viewpoint TCP provides reliable, in-order transfer of bytes (“pipe”) between client and server 2: Application Layer 5

Stream jargon A stream is a sequence of characters that flow into or out of a process. An input stream is attached to some input source for the process, eg, keyboard or socket. An output stream is attached to an output source, eg, monitor or socket. 2: Application Layer 6

Socket programming with TCP keyboard monitor Client Process process output stream inFromServer input stream outToServer 1) client reads line from standard input (inFromUser stream) , sends to server via socket (outToServer stream) 2) server reads line from socket 3) server converts line to uppercase, sends back to client 4) client reads, prints modified line from socket (inFromServer stream) inFromUser Example client-server app: client TCP clientSocket socket to network input stream TCP socket from network 2: Application Layer 7

Client/server socket interaction: TCP Server (running on hostid) Client create socket, port x, for incoming request: welcomeSocket ServerSocket() TCP wait for incoming connection setup connection request connectionSocket welcomeSocket.accept() read request from connectionSocket write reply to connectionSocket close connectionSocket create socket, connect to hostid, port x clientSocket Socket() send request using clientSocket read reply from clientSocket close clientSocket 2: Application Layer 8

Example: Java client (TCP) import java.io.*; import java.net.*; class TCPClient { public static void main(String argv[]) throws Exception { String sentence; String modifiedSentence; Create input stream Create client socket, connect to server Create output stream attached to socket BufferedReader inFromUser new BufferedReader(new InputStreamReader(System.in)); Socket clientSocket new Socket("hostname", 6789); DataOutputStream outToServer new DataOutputStream(clientSocket.getOutputStream()); 2: Application Layer 9

Example: Java client (TCP), cont. BufferedReader inFromServer new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); Create input stream attached to socket sentence inFromUser.readLine(); Send line to server outToServer.writeBytes(sentence '\n'); modifiedSentence inFromServer.readLine(); Read line from server System.out.println("FROM SERVER: " modifiedSentence); clientSocket.close(); } } 2: Application Layer 10

Example: Java server (TCP) import java.io.*; import java.net.*; class TCPServer { Create welcoming socket at port 6789 Wait, on welcoming socket for contact by client Create input stream, attached to socket 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())); 2: Application Layer 11

Example: Java server (TCP), cont Create output stream, attached to socket DataOutputStream outToClient new DataOutputStream(connectionSocket.getOutputStream()); Read in line from socket clientSentence inFromClient.readLine(); capitalizedSentence clientSentence.toUpperCase() '\n'; Write out line to socket outToClient.writeBytes(capitalizedSentence); } } } End of while loop, loop back and wait for another client connection 2: Application Layer 12

UDP 2: Application Layer 13

Socket programming with UDP UDP: no “connection” between client and server no handshaking sender explicitly attaches IP address and port of destination to each packet server must extract IP address, port of sender from received packet application viewpoint UDP provides unreliable transfer of groups of bytes (“datagrams”) between client and server UDP: transmitted data may be received out of order, or lost 2: Application Layer 14

Client/server socket interaction: UDP Server (running on hostid) create socket, port x, for incoming request: serverSocket DatagramSocket() read request from serverSocket write reply to serverSocket specifying client host address, port number Client create socket, clientSocket DatagramSocket() Create, address (hostid, port x, send datagram request using clientSocket read reply from clientSocket close clientSocket 2: Application Layer 15

Example: Java client (UDP) input stream Client Process monitor inFromUser keyboard Input: receives packet process (TCP received “byte stream”) UDP packet receivePacket (TCP sent “byte stream”) sendPacket Output: sends packet client clientSocket UDP socket to network UDP packet UDP socket from network 2: Application Layer 16

Example: Java client (UDP) import java.io.*; import java.net.*; Create input stream Create client socket Translate hostname to IP address using DNS class UDPClient { public static void main(String args[]) throws Exception { BufferedReader inFromUser new BufferedReader(new InputStreamReader(System.in)); DatagramSocket clientSocket new DatagramSocket(); InetAddress IPAddress InetAddress.getByName("hostname"); byte[] sendData new byte[1024]; byte[] receiveData new byte[1024]; String sentence inFromUser.readLine(); sendData sentence.getBytes(); 2: Application Layer 17

Example: Java client (UDP), cont. Create datagram with data-to-send, length, IP addr, port DatagramPacket sendPacket new DatagramPacket(sendData, sendData.length, IPAddress, 9876); clientSocket.send(sendPacket); Send datagram to server DatagramPacket receivePacket new DatagramPacket(receiveData, receiveData.length); Read datagram from server clientSocket.receive(receivePacket); String modifiedSentence new String(receivePacket.getData(),0,receivePacket.getLength()); System.out.println("FROM SERVER:" modifiedSentence); clientSocket.close(); } } 2: Application Layer 18

Example: Java server (UDP) import java.io.*; import java.net.*; Create datagram socket at port 9876 class UDPServer { public static void main(String args[]) throws Exception { DatagramSocket serverSocket new DatagramSocket(9876); byte[] receiveData new byte[1024]; byte[] sendData new byte[1024]; while(true) { Create space for received datagram Receive datagram DatagramPacket receivePacket new DatagramPacket(receiveData, receiveData.length); serverSocket.receive(receivePacket); 2: Application Layer 19

Example: Java server (UDP), cont String sentence new String(receivePacket.getData()); Get IP addr port #, of sender InetAddress IPAddress receivePacket.getAddress(); int port receivePacket.getPort(); String capitalizedSentence sentence.toUpperCase(); sendData capitalizedSentence.getBytes(); Create datagram to send to client DatagramPacket sendPacket new DatagramPacket(sendData, sendData.length, IPAddress, port); Write out datagram to socket serverSocket.send(sendPacket); } } } End of while loop, loop back and wait for another datagram 2: Application Layer 20

Implementation 2: Application Layer 21

In Eclipse Open a Java Project (not Android) File - New - Java Project - UDP Client Extend Object Copy the code in the website inside Run the program Modify the program to read two sentences and print two answers. Repeat both for TCP and UDP (separate projects) 2: Application Layer 22

Socket programming: references C-language tutorial (audio/slides): “Unix Network Programming” (J. Kurose), http://manic.cs.umass.edu/ amldemo/courseware/intro. Java-tutorials: “All About Sockets” (Sun tutorial), http://www.javaworld.com/javaworld/jw-12-1996/jw-12-sockets.html “Socket Programming in Java: a tutorial,” http://www.javaworld.com/javaworld/jw-12-1996/jw-12-sockets.html 2: Application Layer 23