Part 3.1(supp)

1. Part 3.1(supp) Java Socket Details (supplemental materials) (Client-Server Concept, Use of Protocol Ports, Socket API) CSI 4118 – UNIVERSITY OF OTTAWA

2. Creating a Socket • Application calls socket function • OS returns descriptor for socket • Descriptor valid until application closes socket or exits • Common: protofamily = PF_INET, type = SOCK_STREAM or SOCK_DGRAM • In Java, to create a client socket: Socket socket = new Socket(string host, int port) • To create a server socket: ServerSocket sSocket = new ServerSocket(int port) desc = socket(protofamily,type,proto); CSI 4118 – UNIVERSITY OF OTTAWA

3. Socket Functionality • Socket completely general • Can be used • By client • By server • With a CO transport protocol • With a CL transport protocol • To send data, receive data, or both • Large set of operations CSI 4118 – UNIVERSITY OF OTTAWA

4. Socket Operations • Close • Terminate use of socket • Permanent In Java, use socket.close(); or sSocket.close(); close(socket); CSI 4118 – UNIVERSITY OF OTTAWA

5. Socket Operations • Bind • Specify protocol port for a socket • Specify local IP address for a socket • Can use INADDR_ANY for any IP address • In Java, use socket.bind(SocketAddress endpoint) to bind the socket to a IP address and port. bind(socket,localaddr,addrlen); CSI 4118 – UNIVERSITY OF OTTAWA

6. Generic Address Format struct sockaddr { u_char sa_len; /*length of address*/ u_char sa_family; /*family of address*/ char sa_data[14]; /*address itself*/ } CSI 4118 – UNIVERSITY OF OTTAWA

7. TCP/IP Address Format struct sockaddr_in { u_char sin_len; /*length of address*/ u_char sin_family; /*family of address*/ u_short sin_port; /*protocol port number*/ struct in_addr sin_addr; /*IP address*/ char sin_zero[8]; /*not used(set to zero)*/ } CSI 4118 – UNIVERSITY OF OTTAWA

8. Socket Operations (continued) • Listen • Used by server • Prepares socket to accept incoming connections • Accept • Used by server • Waits for next connection and returns new socket • In Java, method accept() in java.net.ServerSocket class listens for a connection and accepts it. listen(socket,queuesize); newsock = accept(socket,caddr,caddrlen); CSI 4118 – UNIVERSITY OF OTTAWA

9. Socket Operations (continued) • Connect • Used by client • Either • Performs a TCP connection • Fully specifies addresses for UDP • In Java, connect(SocketAddress server) to connect the socket to aspecific server. connect(socket,saddr,saddrlen); CSI 4118 – UNIVERSITY OF OTTAWA

10. Two Purposes of the Connect Function The connect function, which is called by clients, has two uses. With connection-oriented transport, connect establishes a transport connection to a specified server. With connectionless transport, connect records the server’s address in the socket, allowing the client to send many messages to the same server without specifying the destination address with each message. CSI 4118 – UNIVERSITY OF OTTAWA

11. Socket Operations (continued) • Send, sendto, and sndmsg • Transfer outgoing data from application • In java, java.io.PrintStream is used to send data. e.g. method println() send(socket,data,length,flags); sendto(socket,data,length,flags, destaddr,addrlen); sendmsg(socket,msgstruct,flags); CSI 4118 – UNIVERSITY OF OTTAWA

12. Format of msgstruct struct msgstruct { struct sockaddr *m_saddr; /*dest address*/ struct datavec *m_dvec; /*message (vector)*/ int mdvlength; /*size of vector*/ struct access *m_rights; /*access rights*/ int m_alength; /*size of access rights*/ } CSI 4118 – UNIVERSITY OF OTTAWA

13. Socket Operations (continued) • Recv, recvfrom, and recvmsg • Transfer incoming data to application • In Java, java.io.BufferReader used to receive data. E.g. method readline() recv(socket,buffer,length,flags); recvfrom(socket,buffer,length,flags, senderaddr,saddrlen); recvmsg(socket,msgstruct,flags); CSI 4118 – UNIVERSITY OF OTTAWA

14. Java Code Equivalent to Example in Chapter 30 CSI 4118 – UNIVERSITY OF OTTAWA

15. Example Server Java Code import java.io.*; import java.net.*; public class server{ public static void main(String[] args) { // variable declaration int visits = 0; ServerSocket srv = null; PrintStream os; Socket clientSocket = null; String msg = ""; //check command-line argument ... //(omited) CSI 4118 – UNIVERSITY OF OTTAWA

16. /* create socket */ try { srv = new ServerSocket(Integer.parseInt(args[0])); } catch (IOException e) { System.out.println(e); } /* Main server loop - accept and handle requests */ while(true){ try {// listen for a connection from client and accept it. clientSocket = srv.accept(); } catch(IOException e) { System.out.println("accept failed"); System.exit(1); } CSI 4118 – UNIVERSITY OF OTTAWA

17. try{ os = new PrintStream(clientSocket.getOutputStream()); visits++; msg = "This server has been contacted " + visits + " times"; os.println(msg); //sends msg os.close(); clientSocket.close(); } catch(IOException e) { System.out.println(e); } } } } CSI 4118 – UNIVERSITY OF OTTAWA

18. Example Client Java Code import java.io.*; import java.net.*; public class client { public static void main(String[] args) { //variable declaration Socket socket = null; BufferedReader in = null; //check command-line argument... //(omited) CSI 4118 – UNIVERSITY OF OTTAWA

19. try { /* create a socket and connect to the specified server. */ socket = new Socket(args[0], Integer.parseInt(args[1])); } catch (UnknownHostException e) { System.exit(1); } catch (IOException e) { System.out.println("connect failed"); System.exit(1); } /* read data from socket and write to user's screen. */ try{ in = new BufferedReader(new InputStreamReader(socket.getInputStream())); System.out.println(in.readLine()); in.close(); socket.close(); } catch(IOException e) { System.out.println(e); }}} CSI 4118 – UNIVERSITY OF OTTAWA