LINUX SOCKET PROGRAMMING

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LINUX SOCKET PROGRAMMING

• LAB 3

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Outline

• Introduce to Client/Server
• Introduce to IPV4
• Introduction to Socket
• Socket Attributes
• TCP/IP Components
• TCP Socket Function
• TCP Client/Server Structure
• UDP Socket Function
• UDP Client/Server Structure
• Socket Example

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Outline (cont)

• Blocking and Nonblocking

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Introduction to Client-Server

• Client-server is computing architecture which
  separates a client from a server, and is almost
  always implemented over a computer network. Each
  client or server connected to a network can also
  be referred to as a node. The most basic type of
  client-server architecture employs only two types
  of nodes clients and servers. This type of
  architecture is sometimes referred to as
  two-tier. It allows devices to share files and
  resources.

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Introduction to Client-Server (cont)

• Each instance of the client software can send
  data requests to one or more connected servers.
  In turn, the servers can accept these requests,
  process them, and return the requested
  information to the client. Although this concept
  can be applied for a variety of reasons to many
  different kinds of applications, the architecture
  remains fundamentally the same.
• These days, clients are most often web browsers,
  although that has not always been the case.
  Servers typically include web servers, database
  servers and mail servers.

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Introduction IPV4

• Internet Protocol version 4 is the fourth
  iteration of the Internet Protocol (IP) and it is
  the first version of the protocol to be widely
  deployed. IPv4 is the dominant network layer
  protocol on the Internet and apart from IPv6 it
  is the only protocol used on the Internet.

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Introduction to Socket

• A socket is one of the most fundamental
  technologies of computer networking. Sockets
  allow applications to communicate using standard
  mechanisms built into network hardware and
  operating systems.

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Socket Attributes

• Socket Domains
• Socket Types
• Stream Sockets
• Datagram Sockets
• Socket Protocols

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Socket Attributes Socket Domain (cont)

• Domains specify the network medium that the
  socket communication will use it.
• The most common socket domain is AF_INET, which
  refers to Internet networking
• AF_UNIX UNIX internal
• AF_INET ARPA Internet protocol
• AF_ISO ISO standard protocols
• AF_NS Xerox Network System protocols
• AF_IPX Novell IPX protocol
• AF_APPLETALK Appletalk DDS
• AF_X25 X.25 protocol

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Socket Attributes Socket Type (cont)

• Stream Sockets
• Stream sockets (in some ways similar to standard
  input/output streams) provide a connection that
  is a sequence and a reliable two-way byte stream.
• Datagram Sockets
• Datagram sockets are implemented in the AF_INET
  domain by UDP/IP connections and provide a
  non-sequence, unreliable service.

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Socket Attributes - Socket Protocol (cont)

• Where the underlying transport mechanism allows
  for more than one protocol to provide the
  requested socket type, you can select a specific
  protocol for a socket.
• Well concentrate on UNIX network and file system
  sockets, which dont require you to choose a
  protocol other than the default.

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TCP/IP Components - Overview

• Telnet
• File Transfer Protocol
• Simple Mail Transfer Protocol
• Kerberos
• Domain Name System
• Simple Network Management Protocol
• Network File System
• Remote Procedure Call
• Trivial File Transfer Protocol

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TCP/IP Components Overview (cont)

• Transmission Control Protocol
• User Datagram Protocol
• Internet Protocol
• Internet Control Message Protocol

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TCP Socket Function

• Create and bind function socket and bind
• Listening socket function listen
• Accept connect require accept
• Create connection and close connect and close
• I/O function read and write
• Advance I/O recv, send, readv, writev

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TCP Client-Server Structure

• Client
• Set up socket
• Connect
• I/O
• close
• Server
• Set up socket
• Bind socket
• Listen
• Accept
• I/O

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TCP Client-Server Structure (cont)
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TCP Client-Server Structure - Q A (cont)

• How many clients to one server we can have each
  time?
• Can you explain the priority for a normal
  connection between client and server?
• How is the situation of client when server is
  gone ?

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UDP Socket Function

• UDP
• Connectionless
• Unreliable
• Real-time
• Create and bind function socket and bind
• Connect interface connect
• I/O function recvfrom and sendto

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UDP Client-Server Structure

• UDP client
• Socket
• Sendto (write)
• Recvfrom (read)
• UDP sever
• Socket
• Bind
• Recvfrom
• sendto

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UDP Client-Server Structure (cont)
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Socket Example- TCP Server
void main() sockfd socket(AF_INET,
SOCK_STREAM, 0) server_address.sun_family
AF_INET server_address.sin_addr.s_addrinet_addr
(127.0.0.1) server_address.sin_port
9734 server_len sizeof(addres) bind(server_s
ockfd,(struct sockaddr) server_address,
server_len) listen(server_sockfd,5) while(1)
char ch printf(server waiting\n) client_
len sizeof(client_address) client_sockfd
accept(server_sockfd, (struct sockaddr
)client_address, client_len) read(client_sock
fd, ch, 1) ch write(client_sockfd) clo
se(client_sockfd)
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Socket Example- TCP Client (cont)
void main() char chA sockfd
socket(AF_INET, SOCK_STREAM, 0) address.sun_fami
ly AF_INET address.sin_addr.s_addrinet_addr(1
27.0.0.1) address.sin_port 9734 len
sizeof(addres) result connect(sockfd, (struct
sockaddr )address) if(result
-1) perror(oops client1) exit(1) w
rite( sockfd, ch , 1) read ( sockfd, ch ,
1) close( sockfd)
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Socket Example- Socket Function (cont)
include ltsys/types.hgt include
ltsys/socket.hgt int socket(int domain, int type,
int protocol)

• Domain
• AF_UNIX, AF_INET, AF_ISO
• Type
• SOCK_STREAM
• TCP
• SOCK_DGRAM
• UDP
• Protocol
• 0 default protocol setting

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Socket Example- IPV4 Address Structure (cont)
struct socketaddr_in short int sin_family
/ AF_INET / unsigned short int
sin_port / Port number / struct in_addr
sin_addr / Internet address /
struct in_addr unsigned long int s_addr

• address.sin_family AF_INET
• address.sin_addr.s_addrinet_addr(127.0.0.1)
• inet_addr(), this function translate IP address
  into specified format for socket
• address.sin_port 9734 //1234? or abcd?

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Socket Example- Bind Function (cont)
include ltsys/types.hgt include
ltsys/socket.hgt int bind(int socket, const struct
sockaddr address, size_t address_len)

• The bind() system call assigns an address to an
  unbound socket
• Socket
• File descriptor
• Address
• Assign an address to its
• Address_len
• The length of sockaddr_in

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Socket Example- Listen and Connect (cont)

• Listening socket
• Usually only one in server
• It will exit before server close
• Connected socket
• Every client connect to server will built one I/O
  with client
• When client close, the socket will close

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Socket Example- Listen Function (cont)
include ltsys/socket.hgt int listen(int socket,
int backlog)

• socket
• File descriptor
• backlog
• The length of queue of unhandled request

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Socket Example- Connect Function (cont)
include ltsys/socket.hgt int connect (int socket,
const struct sockaddr address, size_t
address_len)

• socket
• File descriptor
• address
• Address of wanted to connection
• address_len
• The length of sockaddr_in

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Socket Example- I/O Function (cont)
includeltsys/socket.hgt int read (int sockfd,
char buf, intlen)
includeltsys/socket.hgt int write (int sockfd,
char buf, intlen)

• sockfd
• File descriptor
• buf
• The location of preparing for reading data into
  or writing data out
• intlen
• The length of above buf

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Socket Example- Sendto and Recvfrom (cont)

• Sendto
• Recvfrom

includeltsys/socket.hgt int sendto(intsocketfd,
void buff, size_tnbytes, intflag,
Structsockaddr to, socklen_t addrlen)
includeltsys/socket.hgt int recvfrom(int
socketfd, void buff, size_t nbytes, int
flag, Structsockaddr from, socklen_t addrlen)
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Blocking and Nonblocking

• Blocking (synchronous) socket
• In this mode, the program will not resume
  execution until the socket operation has
  completed. Blocking sockets in 16-bit application
  will allow it to be re-entered at a different
  point, and 32-bit applications will stop
  responding to user actions. This can lead to
  complex interactions if there are multiple active
  controls in use by the application.
• Non-blocking (asynchronous) socket
• Allow your application to respond to events. For
  example, when the remote system writes data to
  the socket, a Read event is generated for the
  control. Your application can respond by reading
  the data from the socket, and perhaps send some
  data back, depending on the context of the data
  received.

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Blocking and Nonblocking (cont)

• A combination of blocking and non-blocking socket
  operations
• The ability to switch between blocking and
  non-blocking modes "on the fly" provides a
  powerful and convenient way to perform socket
  operations.

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LAB1- TCP

• Exercise client.c and server.c
• Gcc o client.o client.c
• Gcc o server.o server.c
• Execute server and client
• ./server.o
• ./client.o
• Modify the client file to sum the number 1 up to
  10 and then send the answer including a string in
  advance to server by TCP socket, for example,
  The sum from 1 to 10 is 55
• Please show me what your result is

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LAB2 - UDP

• Exercise udpserv.c
• Gcc o udpserv.o server.c
• Execute ./udpserv
• Enable service program - netstat ln
• Part of output as below

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LAB2 - UDP (cont)

• Active Internet connections (only servers)Proto
  Recv-Q Send-Q Local Address Foreign Address
  Statetcp 0 0 0.0.0.032768 0.0.0.0 LISTEN
• Note1 If udp side has 0.0.0.08888, that means
  you are on the way. Then it is ready to receive
  any IP address and port number 8888?
• Note2 If execute ./udpserv again,you will see
  the information as below
• bind error Address already in use
• Exercise udpclient.c
• Gcc o udpclient.o udpclient.c
• ./client.o 127.0.0.1

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LAB2 - UDP (cont)

• Active client program
• Hello, World!
• Hello, World!
• this is a test
• this is a test
• d
• Please show me what your result is
• Note1
• If execute ./udpclient 127.0.0.1 again,you will
  see the information as below
• testread error Connection refused

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LAB2 - UDP (cont)

• Modify the server file to count the number of
  receiving, for example, receive 1 times-gt
  receive 2 times -gt .

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Homework

• A. List all files in etc directory of your client
  and then save it to list_client_etc.txt. Finally
  send this file, which name is list_server_etc_1.tx
  t, to server by TCP socket
• B. Do the same thing by UDP socket. (Result
  list_server_etc_2.txt)
• C. Where is the difference between
  list_server_etc_1.txt and list_server_etc_2.txt?
• Note If you can done this in Lab, please show me
  and have a bonus.

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Reference

• (ebook) Programming - Teach Yourself TCP-IP in 14
  Days 2nd Edition
• (ebook) Complete UDP-TCP Port Number List
• http//en.wikipedia.org/wiki/Client-server
• http//en.wikipedia.org/wiki/IPv4
• http//www.developerfusion.co.uk/show/28/8/
• http//www.alhem.net/project/example9/index.html
• http//www.cnds.jhu.edu/courses/cs111/lect8_600.11
  1/img5.htm
• http//www.cnpaf.net/class/UDP/0532918532729212.ht
  ml