Transcript PPT

Part 3.1(supp)
Java Socket Details
(supplemental materials)
(Client-Server Concept,
Use of Protocol Ports, Socket API)
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Creating a Socket
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Application calls socket function
desc = socket(protofamily,type,proto);
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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)
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Socket Functionality
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Socket completely general
Can be used
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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
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Socket Operations
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Close
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Terminate use of socket
Permanent
close(socket);
In Java, use socket.close();
or sSocket.close();
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Socket Operations
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Bind
Specify protocol port for a socket
Specify local IP address for a socket
Can use INADDR_ANY for any IP address
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bind(socket,localaddr,addrlen);
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In Java, use socket.bind(SocketAddress
endpoint) to bind the socket to a IP address and
port.
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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*/
}
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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)*/
}
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Socket Operations (continued)
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Listen
 Used by server
 Prepares socket to accept incoming connections
listen(socket,queuesize);
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Accept
 Used by server
 Waits for next connection and returns new socket
newsock = accept(socket,caddr,caddrlen);
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In Java, method accept() in java.net.ServerSocket class
listens for a connection and accepts it.
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Socket Operations (continued)
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Connect
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Used by client
Either
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Performs a TCP connection
Fully specifies addresses for UDP
connect(socket,saddr,saddrlen);
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In Java, connect(SocketAddress server) to
connect the socket to a specific server.
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Two Purposes of the
Connect Function
The connect function, which is called by
clients, has two uses. With connectionoriented 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.
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Socket Operations (continued)
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Send, sendto, and sndmsg
Transfer outgoing data from application
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send(socket,data,length,flags);
sendto(socket,data,length,flags,
destaddr,addrlen);
sendmsg(socket,msgstruct,flags);
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FALL 2005
In java, java.io.PrintStream is used to send data.
e.g. method println()
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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*/
}
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Socket Operations (continued)
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Recv, recvfrom, and recvmsg
Transfer incoming data to application
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recv(socket,buffer,length,flags);
recvfrom(socket,buffer,length,flags,
senderaddr,saddrlen);
recvmsg(socket,msgstruct,flags);
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In Java, java.io.BufferReader used to receive
data. E.g. method readline()
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Java Code Equivalent to Example
in Chapter 30
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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)
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/* 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);
}
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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);
}
}
}
}
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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)
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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);
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}}}
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