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Special Topics in Computer Engineering Application Layer 2: Socket programming

Special Topics in Computer Engineering Application Layer 2: Socket programming. Some of these Slides are Based on Slides by Kurose and Ross Prepared for Sections 2.7 , 2.8 and 2.9 of the Book Computer Networking: A Top Down Approach Featuring the Internet &

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Special Topics in Computer Engineering Application Layer 2: Socket programming

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  1. Special Topics in Computer EngineeringApplication Layer 2: Socket programming Some of these Slides are Based on Slides by Kurose and Ross Prepared for Sections 2.7 , 2.8 and 2.9 of the Book Computer Networking: A Top Down Approach Featuring the Internet & TCP/IP Sockets in Java : Practical Guide for Programmers CPE 0907532: Application Layer II

  2. 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P file sharing 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2.9 Building a Web server Chapter 2: Application layer CPE 0907532: Application Layer II

  3. 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 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 CPE 0907532: Application Layer II

  4. process process TCP with buffers, variables TCP with buffers, variables socket socket Socket-programming using TCP Socket: a door between application process and end-end-transport protocol (UCP or TCP) TCP service: reliable transfer of bytesfrom one process to another controlled by application developer controlled by application developer controlled by operating system controlled by operating system internet host or server host or server CPE 0907532: Application Layer II

  5. Client must contact server server process must first be running server must have created socket (door) that welcomes client’s contact (e.g. welcomeSocket ) Client contacts server by: creating client-local TCP socket specifying IP address, port number of server process When client creates socket (e.g.clientSocket): client TCP establishes connection to server TCP When contacted by client, server TCP creates new socket (e.g.connectionSocket) for server process to communicate with client allows server to talk with multiple clients source port numbers used to distinguish clients TCP provides reliable, in-order transfer of bytes (“pipe”) between client and server application viewpoint Socket programming with TCP CPE 0907532: Application Layer II

  6. Why use Java • Applications are more neatly and cleanly written in Java • fewer lines of code • each line can be explained without much difficulty • Client/server programming in Java is becoming increasingly popular CPE 0907532: Application Layer II

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

  8. CPE 0907532: Application Layer II

  9. 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, e.g., keyboard or socket. An output stream is attached to an output destination, e.g., monitor or socket. Stream jargon Client process client TCP socket CPE 0907532: Application Layer II

  10. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Server starts by getting ready to receive client connections…

  11. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction ServerSocket welcomeSocket = new ServerSocket(servPort);

  12. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction for (;;) { Socket connectionSocket = welcomeSocket .accept();

  13. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Server is now blocked waiting for connection from a client

  14. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Later, a client decides to talk to the server…

  15. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Socket clientSocket = new Socket(server, servPort);

  16. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction OutputStream out = clientSocket.getOutputStream(); out.write(byteBuffer);

  17. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Socket connectionSocket = welcomeSocket .accept();

  18. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction InputStream in = connectionSocket.getInputStream(); recvMsgSize = in.read(byteBuffer);

  19. Client Create a TCP socket Establish connection Communicate Close the connection Server Create a TCP socket Bind socket to a port Set socket to listen Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction close( clientSocket ); close(connectionSocket)

  20. Example client-server app: 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) Socket programming with TCP CPE 0907532: Application Layer II

  21. for creation of stream objects For creation of Socket objects 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 CPE 0907532: Application Layer II

  22. Example: Java client (TCP), cont. Create input stream attached to socket 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(); } } Send line to server Read line from server CPE 0907532: Application Layer II

  23. 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 CPE 0907532: Application Layer II

  24. Example: Java server (TCP), cont DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream()); clientSentence = inFromClient.readLine(); capitalizedSentence = clientSentence.toUpperCase() + '\n'; outToClient.writeBytes(capitalizedSentence); } } } Create output stream, attached to socket Read in line from socket Write out line to socket End of while loop, loop back and wait for another client connection CPE 0907532: Application Layer II

  25. 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P file sharing 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2.9 Building a Web server Chapter 2: Application layer CPE 0907532: Application Layer II

  26. 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 UDP: transmitted data may be received out of order, or lost UDP provides unreliable transfer of groups of bytes (“datagrams”) between client and server application viewpoint Socket programming with UDP CPE 0907532: Application Layer II

  27. Client create socket, port=x, for incoming request: serverSocket = DatagramSocket() create socket, clientSocket = DatagramSocket() Create, address (hostid, port=x) send datagram request using clientSocket read request from serverSocket write reply to serverSocket specifying client host address, port number read reply from clientSocket close clientSocket Client/server socket interaction: UDP Server (running on hostid) CPE 0907532: Application Layer II

  28. Example: Java client (UDP) Client process Input: receives packet (recall thatTCP received “byte stream”) Output: sends packet (recall that TCP sent “byte stream”) client UDP socket CPE 0907532: Application Layer II

  29. Example: Java client (UDP) import java.io.*; import java.net.*; 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(); Create input stream Create client socket Translate hostname to IP address using DNS Convert a string to an array of bytes

  30. Convert an array of bytes into string 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); DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); clientSocket.receive(receivePacket); String modifiedSentence = new String(receivePacket.getData()); System.out.println("FROM SERVER:" + modifiedSentence); clientSocket.close(); } } Send datagram to server Read datagram from server CPE 0907532: Application Layer II

  31. Example: Java server (UDP) import java.io.*; import java.net.*; 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) { DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); serverSocket.receive(receivePacket); Create datagram socket at port 9876 Create space for received datagram Receive datagram CPE 0907532: Application Layer II

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

  33. 2.1 Principles of network applications app architectures app requirements 2.2 Web and HTTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P file sharing 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2.9 Building a Web server Chapter 2: Application layer CPE 0907532: Application Layer II

  34. handles one HTTP request accepts the request parses header obtains requested file from server’s file system creates HTTP response message: header lines + file sends response to client after creating server, you can request file using a browser (e.g., IE explorer) see text for details Building a simple Web server CPE 0907532: Application Layer II

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