Socket-programming using TCP
Socket: a door between application process and endend-transport protocol (UCP or TCP)
TCP service: reliable transfer of bytes from one
process to another
Socket Programming
controlled by
application
developer
controlled by
operating
system
process
process
socket
TCP with
buffers,
variables
internet
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
2: Application Layer
❒
input
stream
Client
Process
process
4) client reads, prints modified
line from socket
(inFromServer stream)
to network
4
Client
(running on hostid)
create socket,
port=x, for
incoming request:
welcomeSocket =
ServerSocket()
input
stream
client
TCP
clientSocket
socket
to network
TCP
socket
from network
2: Application Layer
Server
monitor
inFromServer
output
stream
input
stream
client
TCP
clientSocket
socket
TCP
2) server reads line from socket
3) server converts line to
uppercase, sends back to
client
output
stream
An output stream is
attached to an output
source, eg, monitor or
socket.
wait for incoming
connection request connection
connectionSocket =
welcomeSocket.accept()
outToServer
1) client reads line from
standard input (inFromUser
stream) , sends to server via
socket (outToServer
stream)
input
stream
Client
Process
process
monitor
Client/server socket interaction: TCP
inFromUser
keyboard
An input stream is
attached to some input
source for the process,
eg, keyboard or socket.
keyboard
3
Socket programming with TCP
Example client-server app:
A stream is a sequence
of characters that flow
into or out of a process.
inFromServer
❒
server process must first be
running
inFromUser
❒
2
Stream jargon
outToServer
Client must contact server
2: Application Layer
1
Socket programming with TCP
controlled by
operating
system
host or
server
host or
server
2: Application Layer
socket
TCP with
buffers,
variables
controlled by
application
developer
read request from
connectionSocket
write reply to
connectionSocket
TCP
socket
close
connectionSocket
from network
2: Application Layer
5
setup
create socket,
connect to hostid, port=x
clientSocket =
Socket()
send request using
clientSocket
read reply from
clientSocket
close
clientSocket
2: Application Layer
6
1
Example: Java client (TCP)
Example: Java client (TCP), cont.
import java.io.*;
import java.net.*;
class TCPClient {
Create
input stream
attached to socket
public static void main(String argv[]) throws Exception
{
String sentence;
String modifiedSentence;
Create
input stream
sentence = inFromUser.readLine();
Send line
to server
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
Create
client socket,
connect to server
Create
output stream
attached to socket
BufferedReader inFromServer =
new BufferedReader(new
InputStreamReader(clientSocket.getInputStream()));
outToServer.writeBytes(sentence + '\n');
Read line
from server
modifiedSentence = inFromServer.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
Socket clientSocket = new Socket("hostname", 6789);
clientSocket.close();
DataOutputStream outToServer =
new DataOutputStream(clientSocket.getOutputStream());
}
}
2: Application Layer
Example: Java server (TCP)
Create output
stream, attached
to socket
class TCPServer {
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;
DataOutputStream outToClient =
new DataOutputStream(connectionSocket.getOutputStream());
Read in line
from socket
clientSentence = inFromClient.readLine();
capitalizedSentence = clientSentence.toUpperCase() + '\n';
ServerSocket welcomeSocket = new ServerSocket(6789);
Write out line
to socket
while(true) {
outToClient.writeBytes(capitalizedSentence);
}
}
Socket connectionSocket = welcomeSocket.accept();
}
BufferedReader inFromClient =
new BufferedReader(new
InputStreamReader(connectionSocket.getInputStream()));
2: Application Layer
IP address and port of
destination to each packet
❒ server must extract IP
2: Application Layer
Server
application viewpoint
UDP provides unreliable transfer
of groups of bytes (“datagrams”)
between client and server
address, port of sender
from received packet
(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
UDP: transmitted data may
be received out of order,
or lost
2: Application Layer
10
Client/server socket interaction: UDP
UDP: no “connection” between
client and server
❒ sender explicitly attaches
End of while loop,
loop back and wait for
another client connection
9
Socket programming with UDP
❒ no handshaking
8
Example: Java server (TCP), cont
import java.io.*;
import java.net.*;
Create
welcoming socket
at port 6789
2: Application Layer
7
11
Client
create socket,
clientSocket =
DatagramSocket()
Create, address (hostid, port=x,
send datagram request
using clientSocket
read reply from
clientSocket
close
clientSocket
2: Application Layer
12
2
Example: Java client (UDP)
input
stream
import java.io.*;
import java.net.*;
Client
Process
process
sendPacket
UDP
packet
receivePacket
Input: receives
Output: sends
packet (TCP sent
“byte stream”)
Example: Java client (UDP)
monitor
inFromUser
keyboard
Create
client socket
UDP
packet
client
UDP
clientSocket
socket
to network
Create
input stream
packet (TCP
received “byte
stream”)
class UDPClient {
public static void main(String args[]) throws Exception
{
Translate
hostname to IP
address using DNS
UDP
socket
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];
from network
String sentence = inFromUser.readLine();
sendData = sentence.getBytes();
2: Application Layer
Example: Java client (UDP), cont.
Create datagram
with data-to-send,
length, IP addr, port
2: Application Layer
13
Example: Java server (UDP)
import java.io.*;
import java.net.*;
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
Send datagram
to server
clientSocket.send(sendPacket);
Create
datagram socket
at port 9876
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
Read datagram
from server
class UDPServer {
public static void main(String args[]) throws Exception
{
clientSocket.receive(receivePacket);
while(true)
{
System.out.println("FROM SERVER:" + modifiedSentence);
clientSocket.close();
}
Create space for
received datagram
Receive
datagram
}
2: Application Layer
❒
int port = receivePacket.getPort();
String capitalizedSentence = sentence.toUpperCase();
sendData = capitalizedSentence.getBytes();
}
serverSocket.send(sendPacket);
accepts the request
❒
parses header
❒
}
handles one HTTP
request
❒
❒
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress,
port);
End of while loop,
loop back and wait for
another datagram
obtains requested file
from server’s file
system
17
❒
❒
❒
after creating server,
you can request file
using a browser (eg IE
explorer)
see text for details
creates HTTP response
message:
❍
2: Application Layer
16
Building a simple Web server
InetAddress IPAddress = receivePacket.getAddress();
}
serverSocket.receive(receivePacket);
2: Application Layer
String sentence = new String(receivePacket.getData());
Write out
datagram
to socket
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
15
Example: Java server (UDP), cont
Create datagram
to send to client
DatagramSocket serverSocket = new DatagramSocket(9876);
byte[] receiveData = new byte[1024];
byte[] sendData = new byte[1024];
String modifiedSentence =
new String(receivePacket.getData());
Get IP addr
port #, of
sender
14
header lines + file
sends response to client
2: Application Layer
18
3