Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes...

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Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison Wesley 2002)

Transcript of Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes...

Page 1: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

Network Programming and Sockets

CPSC 363 Computer Networks

Ellen Walker

Hiram College

(Includes figures from Computer Networking by Kurose & Ross, © Addison Wesley 2002)

Page 2: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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!

Page 3: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

TCP Sockets

process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperating

system

host orserver

process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperatingsystem

host orserver

internet

Page 4: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

Socket Programming in Java

• Uses java.net.* library• Same interface on all platforms• Nicely object-oriented; fairly self-documenting• Covered in our textbook

Page 5: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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

Page 6: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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 (incl

udes sample code)• Winsock FAQ

Page 7: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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

Page 8: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

Client/server socket interaction: TCP

wait for incomingconnection requestconnectionSocket =welcomeSocket.accept()

create socket,port=x, forincoming request:welcomeSocket =

ServerSocket()

create socket,connect to hostid, port=xclientSocket =

Socket()

closeconnectionSocket

read reply fromclientSocket

closeclientSocket

Server (running on hostid) Client

send request usingclientSocketread request from

connectionSocket

write reply toconnectionSocket

TCP connection setup

Page 9: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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());

Createinput stream

Create client socket,

connect to server

Createoutput stream

attached to socket

Page 10: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

Example: Java client (TCP), cont.

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(); } }

Createinput stream

attached to socket

Send lineto server

Read linefrom server

Page 11: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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()));

Createwelcoming socket

at port 6789

Wait, on welcomingsocket for contact

by client

Create inputstream, attached

to socket

Page 12: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

Example: Java server (TCP), cont

DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());

clientSentence = inFromClient.readLine();

capitalizedSentence = clientSentence.toUpperCase() + '\n';

outToClient.writeBytes(capitalizedSentence); } } }

Read in linefrom socket

Create outputstream,

attached to socket

Write out lineto socket

End of while loop,loop back and wait foranother client connection

Page 13: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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

Page 14: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

Client/server socket interaction: UDP

closeclientSocket

Server (running on hostid)

read reply fromclientSocket

create socket,clientSocket = DatagramSocket()

Client

Create, address (hostid, port=x,send datagram request using clientSocket

create socket,port=x, forincoming request:serverSocket = DatagramSocket()

read request fromserverSocket

write reply toserverSocketspecifying clienthost address,port number

Page 15: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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();

Createinput stream

Create client socket

Translate hostname to IP

address using DNS

Page 16: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

Example: Java client (UDP), cont.

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(); }

}

Create datagram with data-to-send,

length, IP addr, port

Send datagramto server

Read datagramfrom server

Page 17: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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);

Createdatagram socket

at port 9876

Create space forreceived datagram

Receivedatagra

m

Page 18: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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 addrport #, of

sender

Write out datagramto socket

End of while loop,loop back and wait foranother datagram

Create datagramto send to client

Page 19: Network Programming and Sockets CPSC 363 Computer Networks Ellen Walker Hiram College (Includes figures from Computer Networking by Kurose & Ross, © Addison.

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)