CS 355. Computer Networking. Wei Lu, Ph.D., P.Eng.

Transcription

1 CS 355 Computer Networking Wei Lu, Ph.D., P.Eng.

2 Chapter 2: Application Layer Overview: Principles of network applications? Introduction to Wireshark Web and HTTP FTP Electronic Mail: SMTP, POP3, IMAP DNS: Domain Name System (or Service) P2P applications Socket programming with TCP and UDP

3 TCP Socket Programming: Overview of socket programming with TCP Server and Client Sockets TCP socket programming: an example

4 TCP Socket Programming Overview

5 TCP Client/Server Paradigm TCP is Connection-oriented, reliable transfer of bytes from one process to another 1.The server process running before the client process. 2.The server process creates a server socket. 3.TCP connection initiation by the client program create a socket. note: TCP connection establishment based on a three-way handshake (this handshake is done in Transport layer and it is transparent to client and server programs) 4.When the server hears a request, a new socket creation by server dedicated to that particular client (during the handshake). 5.Now Client and Server can exchange messages via socket!

6 Client/Server Socket Interaction: TCP Server (running on hostid) create socket, port=x, for incoming request: welcomesocket = ServerSocket() wait for incoming connection request connectionsocket = welcomesocket.accept() read request from connectionsocket write reply to connectionsocket close connectionsocket TCP connection setup Client create socket, connect to hostid, port=x clientsocket = Socket() send request using clientsocket read reply from clientsocket close clientsocket

7 Terminology on Stream keyboard monitor 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 source, e.g., monitor or socket. Process Client process input stream output stream infromuser outtoserver infromserver input stream clientsocket TCP TCP socket socket to network from network

8 Basics on TCP socket programming 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

9 TCP Server/Client Sockets

10 TCP Server and Client Socket Server sockets Wait for requests to come in over the network Implemented by java.net.serversocket class Client sockets Used to send and receive data Can be thought of as a pair of input and output streams Implemented by java.net.socket class

11 TCP Server and Client Socket TCP Server Socket Welcoming socket Welcomes some initial contact from a client. Connection socket Is created at initial contact of client. New socket that is dedicated to the particular client. TCP Client Socket Client socket Initiate a TCP connection to the server by creating a socket object. (Three-way handshake) Specify the address of the server process, namely, the IP address of the server and the port number of the process.

12 TCP Server and Client Socket Server socket: waiting for connection requests Client socket: transmission of data server socket connection request client socket

13 Server Socket Creating and using server sockets Constructors ServerSocket(int port) Methods accept() close() Description Waits for a connection request and returns a Socket Stops waiting for requests from clients

14 How to Create a Server Socket ServerSocket MyService; try { MyService = new ServerSocket(PortNumber); catch (IOException e) { System.out.println(e);

15 How to Create a Server Socket When implementing a server you also need to create a socket object from the ServerSocket in order to listen for and accept connections from clients. try { servicesocket = MyService.accept(); catch (IOException e) { System.out.println(e);

16 Client Socket Creating client sockets On the client side, Socket(String host, int port) On the server side, accept() of ServerSocket Using client sockets Methods Description getinputstream() Returns an InputStream for receiving data getoutputstream() Returns an OutputStream to send data close() Closes the socket connection

17 How to Create a Client Socket Socket MyClient; MyClient = new Socket("Machine name", PortNumber);

18 How to Create a Client Socket Machine name is the machine you are trying to open a connection to(ex: ip address or workstation name), and PortNumber is the port (a number) on which the server you are trying to connect to is running. When selecting a port number, you should note that port numbers between 0 and 1,023 are reserved for privileged users (that is, super user or root).

19 How to Create a Client Socket These port numbers are reserved for standard services, such as , FTP, and HTTP. When selecting a port number for your server, select one that is greater than 1,023!

20 How to Create a Client Socket With exception handling, the code look like following: Socket MyClient; try { MyClient = new Socket("Machine name", PortNumber); catch (IOException e) { System.out.println(e);

21 How to Create an Input Stream for Client On the client side, you can use the DataInputStream class to create an input stream to receive response from the server: DataInputStream input; try { input = new DataInputStream(MyClient.getInputStream()); catch (IOException e) { System.out.println(e);

22 How to Create an Input Stream for Client The class DataInputStream allows you to read lines of text and Java primitive data types in a portable way. It has methods such as read, readchar, readint, readdouble, and readline,. Use whichever function you think suits your needs depending on the type of data that you receive from the server.

23 How to Create an Input Stream for Server On the server side, you can use DataInputStream to receive input from the client DataInputStream input; try { input = new DataInputStream(serviceSocket.getInputStream()); catch (IOException e) { System.out.println(e);

24 How to Create an Output Stream for Client On the client side, you can create an output stream to send information to the server socket using the DataOutputStream of java.io:

25 How to Create an Output Stream for Client The class DataOutputStream allows you to write Java primitive data types; many of its methods write a single Java primitive type to the output stream. The method writebytes is a useful one.

26 How to Create an Output Stream for Client DataOutputStream output; try { output = new DataOutputStream(MyClient.getOutputStream()); catch (IOException e) { System.out.println(e);

27 How to Create an Output Stream for Server On the server side, you can use the class DataOutputStream to send information to the client. DataOutputStream output; try { output = new DataOutputStream(serviceSocket.getOutputStream()); catch (IOException e) { System.out.println(e);

28 How to Close Sockets for Client You should always close the output and input stream before you close the socket. try { output.close(); input.close(); MyClient.close(); catch (IOException e) { System.out.println(e);

29 How to Close Sockets for Server try { output.close(); input.close(); servicesocket.close(); MyService.close(); catch (IOException e) { System.out.println(e);

30 TCP socket programming: an example

31 TCP Socket programming: an example We will try to build a simple client/server application as following: 1. A client reads a line from its standard input (keyboard) or (infromuser stream) and sends the line out its socket (outtoserver stream) to the server. 2. The server reads a line from its connection socket. 3. The server converts the line to uppercase. 4. The server sends the modified line out its connection socket to the client. 5. The client reads the modified line from its socket (infromserver stream) and prints the line on its standard output (monitor).

32 Summary on JAVA TCP Sockets java.net.serversocket Implements server sockets. Waits for requests to come in over the network., Performs some operation based on the request. Constructor and Methods ServerSocket(int port) Socket Accept(): Listens for a connection to be made to this socket and accepts it. This method blocks until a connection is made.

33 Summary on JAVA TCP Sockets In Package java.net java.net.socket Implements client sockets (also called just sockets ). An endpoint for communication between two machines. Constructor and Methods Socket(String host, int port): Creates a stream socket and connects it to the specified port number on the named host. InputStream getinputstream(), Returns an input stream for this socket. OutputStream getoutputstream(), Returns an output stream for this socket. close()

34 TCP Socket programming: an example When programming a client, you must follow these four steps: 1.Open a socket. 2.Open an input and output stream to the Socket. 3.Read from and write to the socket according to the server's protocol. 4.Clean up. These steps are pretty much the same for all clients. The only step that varies is step three, since it depends on the server you are talking to.

35 TCP Socket programming: an example On the server side, server receives text from the client and then sends that capitalized text back to the client.

36 Example: JAVA TCP client import java.io.*; import java.net.*; class TCPClient { Create input stream Create client socket, connect to server Create output stream attached to socket 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());

37 Example: JAVA TCP client Create input stream attached to socket Send line to server Read line from server 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();

38 Example: JAVA TCP server 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()));

39 Example: JAVA TCP server Create output stream, attached to socket Read in line from socket DataOutputStream outtoclient = new DataOutputStream(connectionSocket.getOutputStream()); 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

40 Conclusion Programming client/server applications in Java is fun and challenging. Programming socket programming in Java is much easier than doing it in other languages such as C. Keywords: Clients, servers, TCP/IP, port number, sockets, Java sockets

41 Thank you for your attendance Any questions?