Download ppt file

Chapter 2 outline
 2.1 Principles of app
layer protocols


clients and servers
app requirements
 2.2 Web and HTTP
 2.3 FTP
 2.4 Electronic Mail
 SMTP, POP3, IMAP
 2.5 DNS
 2.6 Socket programming
with TCP
 2.7 Socket programming
with UDP
 2.8 Building a Web
server
 2.9 Content distribution



Network Web caching
Content distribution
networks
P2P file sharing
Lecture7
1
Socket programming
Goal: learn how to build client/server application that
communicate using sockets
Socket API
 introduced in BSD4.1 UNIX,
1981
 explicitly created, used,
released by apps
 client/server paradigm
 two types of transport
service via socket API:
 unreliable datagram
 reliable, byte streamoriented
socket
a host-local,
application-created,
OS-controlled interface
(a “door”) into which
application process can
both send and
receive messages to/from
another application
process
Lecture7
2
Socket-programming using TCP
Socket: a door between application process and endend-transport protocol (UDP or TCP)
TCP service: reliable transfer of bytes from one
process to another
controlled by
application
developer
controlled by
operating
system
process
process
socket
TCP with
buffers,
variables
host or
server
internet
socket
TCP with
buffers,
variables
controlled by
application
developer
controlled by
operating
system
host or
server
Lecture7
3
Socket programming with TCP
Client must contact server
 server process must first
be running
 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
Lecture7
4
Stream jargon
 A stream is a sequence of characters that flow
into or out of a process.
 An input stream is attached to some input source
for the process, eg, keyboard or socket.
 An output stream is attached to an output source,
eg, monitor or socket.
Lecture7
5
Socket programming with TCP
Client
Process
process
input
stream
output
stream
inFromServer
1) client reads line from
standard input (inFromUser
stream) , sends to server via
socket (outToServer
stream)
2) server reads line from socket
3) server converts line to
uppercase, sends back to
client
4) client reads, prints modified
line from socket
(inFromServer stream)
outToServer
Example client-server app:
monitor
inFromUser
keyboard
input
stream
client
TCP
clientSocket
socket
to network
TCP
socket
from network
Lecture7
6
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
Lecture7
7
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());
Lecture7
8
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();
}
}
Lecture7
9
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()));
Lecture7
10
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
Lecture7
11
Chapter 2 outline
 2.1 Principles of app
layer protocols


clients and servers
app requirements
 2.2 Web and HTTP
 2.3 FTP
 2.4 Electronic Mail
 SMTP, POP3, IMAP
 2.5 DNS
 2.6 Socket programming
with TCP
 2.7 Socket programming
with UDP
 2.8 Building a Web
server
 2.9 Content distribution



Network Web caching
Content distribution
networks
P2P file sharing
Lecture7
12
Socket programming with UDP
UDP: no “connection” between
client and server
 no handshaking
 sender explicitly attaches
IP address and port of
destination to each packet
 server must extract IP
address, port of sender
from received packet
application viewpoint
UDP provides unreliable transfer
of groups of bytes (“datagrams”)
between client and server
UDP: transmitted data may be
received out of order, or
lost
Lecture7
13
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
Lecture7
14
Example: Java client (UDP)
input
stream
Client
process
monitor
inFromUser
keyboard
Process
Input: receives
packet (TCP
received “byte
stream”)
UDP
packet
receivePacket
packet (TCP sent
“byte stream”)
sendPacket
Output: sends
client
UDP
clientSocket
socket
to network
UDP
packet
UDP
socket
from network
Lecture7
15
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();
Lecture7
16
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();
}
}
Lecture7
17
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);
Lecture7
18
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
Lecture7
19
Building a simple Web server
 handles one HTTP




request
accepts the request
parses header
obtains requested file
from server’s file
system
creates HTTP response
message:

 after creating server,
you can request file
using a browser (eg IE
explorer)
 see text for details
 If you are familiar
with Java, practice
this by yourself
header lines + file
 sends response to client
Lecture7
20
Socket programming: references
Java-tutorials:
 “All About Sockets” (Sun tutorial),
http://java.sun.com/docs/books/tutorial/networking/so
ckets/
 “Socket Programming in Java: a tutorial,”
http://www.javaworld.com/javaworld/jw-12-1996/jw12-sockets.html
Lecture7
21
Socket programming API
 Unix systems
 System calls
 Proj1: simple HTTP client/server
 Using UNIX BSD sockets
C-language tutorial:
 “Unix Network Programming” (J. Kurose),
http://manic.cs.umass.edu/~amldemo/courseware/intro
 Beej's Guide to Network Programming
http://www.ecst.csuchico.edu/~beej/guide/net/
 See useful links fore more infor on class web page
Lecture7
22
Unix Programming: Mechanism
 UNIX system calls and library routines
(functions called from C/C++ programs)
 man <function name>
 A word on style: check all return codes
if ((code = syscall()) < 0) {
perror("syscall");
}
Lecture7
23
Creating Sockets
#include <sys/types.h>
#include <sys/socket.h>
int socket(int domain, int type, int protocol);
- creates an endpoint for communication
- return value: -1 if an error occurs;
otherwise the return value is a descriptor
referencing the socket
Lecture7
24
Creating Sockets: Parameters
 domain : address family (protocol family)
determine address structure
 e.g. AF_UNIX, AF_INET, AF_INET6
 we will use AF_INET only

 type : service of a socket
 e.g. SOCK_DGRAM provides unreliable,
connectionless service
 e.g. SOCK_STREAM provides connectionoriented reliable byte-stream service
Lecture7
25
Creating Sockets: Parameters (cont.)
 protocol : specifies particular protocol
Usually already defined by domain and type (e.g.
TCP for AF_INET and SOCK_STREAM; UDP for
AF_INET and SOCK_DGRAM)
 we will use 0 (default protocol)

 Example
if ((sockfd = socket(AF_INET,SOCK_STREAM,0)) {
perror(“socket”);
exit(1);
}
Lecture7
26
Binding the Address for a Socket
#include <sys/types.h>
#include <sys/socket.h>
int bind(int sd, struct sockaddr *my_addr,
socklen_t addrlen);
- assigns the local address of a socket
- return value: -1 if an error occurs;
otherwise 0
Lecture7
27
Socket Address
 Several types of addresses
 We will use sockaddr_in (<netinet/in.h>)
struct sockaddr_in {
sa_family_t
sin_family; /*AF_INET*/
uint16_t
sin_port; /* network order*/
struct in_addr sin_addr;
};
struct in_addr {
uint32_t
s_addr; /* network order*/
};
Two types of byte ordering: little endian, and big endian
(network order)
Lecture7
28
Internet Addresses and Ports
 sin_port
16 bits
 0-1024 reserved for system
 well-known ports are important
 If you specify 0, the OS picks a port

 s_addr
 32 bits
 INADDR_ANY for any local interface address
Lecture7
29
Internet Addresses and Ports: Example
struct sockaddr_in myaddr;
bzero( (char*)myaddr, sizeof(myaddr) );/*initialize*/
myaddr.sin_family = AF_INET;
myaddr.sin_port = htons(80); /* bind to HTTP port*/
myaddr.sin_addr.s_addr = htos(INADDR_ANY); /* any address*/
if ( (bind(sockfd, (struct sockaddr*)&myaddr, sizeof(myaddr)) < 0 ) {
perror(“bind”);
exit(1);
}
Lecture7
30
Set a Socket in the Listening State (Server)
#include <sys/types.h>
#include <sys/socket.h>
int listen(int sd, int backlog);
- Specify the willingness to accept new connection
- backlog : specify the number of pending
connections
- return value: -1 if an error occurs; otherwise 0
Lecture7
31
Initialize Connection Setup (Client)
#include <sys/types.h>
#include <sys/socket.h>
int connect(int sd, const struct sockaddr *serv_addr,
socklen_t addrlen);
- For SOCK_STREAM, initialize connection to the
server; for SOCK_DGRAM, just set the destination
address and set the socket in connected state
- return value: -1 if an error occurs; otherwise 0
Lecture7
32
Accept a Connection (Server)
#include <sys/types.h>
#include <sys/socket.h>
int accept(int sd, struct sockaddr *peer_addr,
socklen_t addrlen);
- remove the first connection from the pending
connection queue, create a new socket in connected
state, the original sd is not changed and still in
listening state
- return value: -1 if an error occurs; otherwise the
descriptor of the newly connected socket
Lecture7
33
Read/Write to a Socket
 read()/write() of the file interface for
connected-oriented
 Socket specific system call
send()/sendto()/sendmsg()
 recv()/recvfrom()/recvmsg()

Lecture7
34
Read from a socket by using read()
#include <unistd.h>
ssize_t read(int sockfd, void *buf, size_t
count);
- read up to count from the socket
- return value: -1 if an error occurs; 0 if end
of file; otherwise number of bytes read
Lecture7
35
Write to a socket by using write()
#include <unistd.h>
ssize_t write(int sockfd, const void *buf,
size_t count);
- write up to count to the socket
- return value: -1 if an error occurs;
otherwise number of bytes write
Lecture7
36
Send to a Socket
#include <sys/types.h>
#include <sys/socket.h>
int send(int sd, const void *msg, size_t len, int flags);
int sendto(int sd, const void *msg, size_t len, int flags,
const struct sockaddr *to, socklen_t tolen);
int sendmsg(int sd, const struct msghdr *msg, int flags)
- return value: -1 if an error occurs; otherwise
the number of bytes sent
Lecture7
37
Receive from a Socket
#include <sys/types.h>
#include <sys/socket.h>
int recv(int sd, void *buf, size_t len, int flags);
int recvfrom(int sd, void *buf, size_t len, int flags,
struct sockaddr *from, socklen_t fromlen);
int recvmsg(int sd, struct msghdr *msg, int flags);
- return value: -1 if an error occurs; otherwise
the number of bytes received
Lecture7
38
Close a Socket
#include <unistd.h>
int close(int sd);
- return value: -1 if an error occurs; otherwise 0
#include <sys/socket.h>
int shutdown(int sd, int how);
- how : if 0, no further receives; if 1, no further sends;
if 2, no further sends or receives
- return value: -1 if an error occurs; otherwise 0
Lecture7
39
Support Routines: Network/Host Order
#include <netinet/in.h>
unsigned long int htonl(unsigned long int hostlong);
unsigned short int htons(unsigned short int hostshort);
unsigned long int ntohl(unsigned long int networklong);
unsigned short int ntohs(unsigned short int
networkshort);
Lecture7
40
DNS Service
#include <netdb.h>
extern int h_errno;
struct hostent *gethostbyname(const char *name);
Struct hostent {
char *h_name;
// official name
char **h_aliases;
// a list of aliases
int
h_addrtype;
int
h_length;
char **h_addr_list;
}
#define h_addr h_addr_list[0]
- return value: NULL if fails
Lecture7
41