Transcript Data Modeling

Network Programming and Sockets
CPSC 363 Computer Networks
Ellen Walker
Hiram College
(Includes figures from Computer Networking by Kurose & Ross, © Addison Wesley
2002)
Sockets
• Data structures representing a connection
• Provide communication between process,
O/S (and network card, etc)
– Buffers for sent / received information
– Variables with addresses, port information, etc.
– Methods (functions) for send / receive
• A socket looks much like a stream to the
application programmer
– Open, read and write, close!
TCP Sockets
controlled by
application
developer
controlled by
operating
system
process
process
socket
TCP with
buffers,
variables
host or
server
internet
socket
TCP with
buffers,
variables
host or
server
controlled by
application
developer
controlled by
operating
system
Socket Programming in Java
•
•
•
•
Uses java.net.* library
Same interface on all platforms
Nicely object-oriented; fairly self-documenting
Covered in our textbook
Socket Programming for Linux / Unix
• Basic C libraries go back to BSD Unix
– Libraries include sys/socket.h, netinet/in.h, netdb.h,
arpa/inet.h
– Socket is an int, also struct for address
– Requires explicit conversion for byte order, etc.
• C++ encapsulation of BSD socket interface by Rob
Tougher
– Makes sockets look like I/O streams
– May not be standard, but easy to use
– http://www.linuxgazette.com/issue74/tougher.html
Socket Programming for MS
Windows
• Windows sockets (winsock) - Not originally
standardized, but now Microsoft distributes a
library (WSOCK32.LIB)
• Calls are very similar to BSD socket code
• Microsoft MSDN Winsock documentation
(includes sample code)
• Winsock FAQ
Client/Server Application Programs
(TCP)
• Client
–
–
–
–
Requests a connection with the server
Receives connection info
Communicates (sends/receives)
Closes the connection
• Server
– Infinite loop…
• Wait for connection request
• Generate & send connection info
• Communicate until connection is closed
Client/server socket interaction: TCP
Server (running on hostid)
Client
create socket,
port=x, for
incoming request:
welcomeSocket =
ServerSocket()
TCP
wait for incoming
connection request connection
connectionSocket =
welcomeSocket.accept()
read request from
connectionSocket
write reply to
connectionSocket
close
connectionSocket
setup
create socket,
connect to hostid, port=x
clientSocket =
Socket()
send request using
clientSocket
read reply from
clientSocket
close
clientSocket
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());
Example: Java client (TCP), cont.
Create
input stream
attached to socket
BufferedReader inFromServer =
new BufferedReader(new
InputStreamReader(clientSocket.getInputStream()));
sentence = inFromUser.readLine();
Send line
to server
outToServer.writeBytes(sentence + '\n');
Read line
from server
modifiedSentence = inFromServer.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
clientSocket.close();
}
}
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()));
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
UDP Connection
• No explicit connection
– No setup
– Each packet contains address, port of destination
– Server extracts return address, port from packet
• No guarantee packets received in the order
sent
• No guarantee all packets received
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
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();
Example: Java client (UDP), cont.
Create datagram
with data-to-send,
length, IP addr, port
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
Send datagram
to server
clientSocket.send(sendPacket);
Read datagram
from server
clientSocket.receive(receivePacket);
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
String modifiedSentence =
new String(receivePacket.getData());
System.out.println("FROM SERVER:" + modifiedSentence);
clientSocket.close();
}
}
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);
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
Building a Web Server
• Create a listening socket
• Wait for connection (establish socket)
• Create a buffered reader and a data output stream
• Read and parse the request line (GET filename)
• Read the file into a temporary buffer
• Output header lines (including MIME type)
• Output the file
• Close the connection socket
(see code pp 151-152)