UDP Server-Client interaction
UDP SERVER
//Programme for UDP server
#include<stdio.h>
#include<string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<unistd.h>
#include<netdb.h>
#include<fcntl.h>
#define PORT_NUM 1500 //port number on which message will recieve and send
int main()
{
int sock; //variable for socket descriptor(server)
int len; //variable for initialize structure length
char out_buf[100],in_buf[100]; //variable for input and output message initialize
struct sockaddr_in server,client;
sock=socket(AF_INET,SOCK_DGRAM,0); //socket descripter for server(using ipv4)
server.sin_family=AF_INET;
server.sin_port=htons(PORT_NUM); //host to network short byte word
server.sin_addr.s_addr=htonl(INADDR_ANY);//host to network long byte order
len=sizeof(struct sockaddr_in); //storing length of structure (define below)
bind(sock,(struct sockaddr*)&server,len);//binding the socket with port num and ip
printf("server is waiting.....\n"); //server goes to listen mode(explicitely define in tcp server)
recvfrom(sock,in_buf,sizeof(in_buf),0,(struct sockaddr *)&client,&len);//recieve byte by byte stream from client
//at 'in_buf' through server socket
printf("request accepted.................\n");
printf("recieve from client...message:=%s\n",in_buf); //display message recieve from client
strcpy(out_buf,"HI mr.client I have got your message"); //storing string at 'out_buf'
sendto(sock,out_buf,(strlen(out_buf)+1),0,(struct sockaddr *)&client,len);//stream send to client through socket
//(here length is increase by 1 because to assign null //explicitely at the end of the stream 'out_buf')
close(sock);
}
UDP CLIENT
//programmme for udp client
#include<stdio.h>
#include<string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<unistd.h>
#include<netdb.h>
#include<fcntl.h>
#define PORT_NUM 1500 //port number on which message will recieve and send
#define SERVER_IP "127.127.127.127"//loop back address as i am using same system for botth server and client
int main()
{
int sock; //variable for socket descriptor(client)
int len; //variable for initialize structure length
char out_buf[100],in_buf[100]; //variable for input and output message initialize
struct sockaddr_in server; //server address is required by client but viceversa is not needed
sock=socket(AF_INET,SOCK_DGRAM,0);//socket descripter for server(using ipv4)
server.sin_family=AF_INET;
server.sin_port=htons(PORT_NUM); //host to network short byte word
server.sin_addr.s_addr=inet_addr(SERVER_IP);//function 'inet_addr()' converts the Internet host address cp from
// IPv4 numbers-and-dots notation into binary data in network byte order.
len=sizeof(struct sockaddr_in); //storing length of structure (define below)
strcpy(out_buf,"hey server i am connecting with you..");//storing stream at out_buf for sending to server
sendto(sock,out_buf,(strlen(out_buf)+1),0,(struct sockaddr *)&server,len);//stream send to client through socket
//(here length is increase by 1 because to assign null
//explicitely at the end of the stream 'out_buf')
recvfrom(sock,in_buf,sizeof(in_buf),0,(struct sockaddr *)&server,&len); //recieve byte by byte stream from client
//at 'in_buf' through server socket
printf("recieve from server message:=%s\n",in_buf);
close(sock);
}
Explanation of different functions and structure
Data structure used to hold address information
unsigned short sa_family;
char sa_data[14];
}
sa_family is the domain type ex-
AF_UNIX, AF_LOCAL Local communication
AF_INET IPv4 Internet protocols
AF_INET6 IPv6 Internet protocols
AF_IPX IPX - Novell protocols
AF_NETLINK Kernel user interface device
short sin_family;
unsigned short sin_port;
struct in_addr sin_addr;
char sin_zero[8];
}
sin_family is same as above sa_family i,e domain type ex-
AF_UNIX, AF_LOCAL Local communication
AF_INET IPv4 Internet protocols
AF_INET6 IPv6 Internet protocols
AF_IPX IPX - Novell protocols
AF_NETLINK Kernel user interface device
sin_port---It is for assignning port number
in_addr sin_addr----here in_addr is a structure whose variable is sin_addr,it is used for assigning ip address.
sin_zero----It is used for padding
unsigned long s_addr; //4 byte
}
s_addr---- it is used for storing 4 byte IP address(32 bit IP
socket() - A Connection End point
- This creates an end point for network connection.
int socket(int domain,int type,int protocol)
domin=AF_INET(ipv4 protocol)
type= SOCK_STREAM(TCP), SOCK_DGRAM(UDP)
protocol=0
- Eample :=socket(AF_INET,SOCK_STREAM,0)
this will create a TCP socket
- This al returns 1 ,when socket descriptor on success and -1 on an error
bind() - Attaching to an IP and Port
- Aserver call bind to attach itself to a specific port and IP address
int bind(int sockfd, const struct sockaddr *my_address, socklen_t address_length);
my_addr=pointer to a valid sockaddr_in structure cast as a sockaddr *pointer
addrlen=lngth of the sockaddr_in structur
listen() - wait for a connection
- The serverprocess calls listen to tell the kernal to initialize a wait queueof connection for this socket
listen(int sock, int backlog);
sock=socket returned by socket()
backlog=maximum length of the pending connections queue
This will allow a maximum of 10 connections to be in pending state
Accept() - A new connection!
> Accept is called by a Server process to accept new connections from new clients trying to connect to the server
accept(int soccket, (struct sockaddr *)&client, socklen_t *client_len)
socket= the socket in listen state
client=will hold new clients information when accept returns
client_len=pointer to size of the client structure
>Example:
struct sockaddr_in client;
int len=sizeof(client);
accept(sock, (struct sockaddr *)&client, &len);
connect() - connect to a service
>Connect is automatically called by a client to connect to a serverport
conect(int sock, (struct sockaddr *)&server_addr, socklen_t len)
sock : a socket returned by socket()
server_addr : a sockaddr_in struct pointer filled with all the remote server detailes and cast as a sockaddr struct pointer
len : size of the server_addr struct
>Example:
connect(sock, (struct sockaddr *)&server_addr, len);
Send/Recv - Finally Data !!
> send(),recv(),read(),write() etc calls are used to send or recieve data
int send(int sock, void *mesg, size_t len,int flag)
int recv(int sock, void *mesg, size_t len, int flag)
sock=Aconnected socket
mesg=pointer to a buffered to send /recieve data from/in
len=size of the message buffer
flags=0
The return value is the number of bytes actually sent/recieved
>EXAMPLE:
char send_buffer[1024];
char recv_buffer[1024];
int sent_bytes;
int recv_bytes;
sent_bytes=send(sock,send_buffer,1024,0);
recv_bytes=recv(sock, recv buffer,1024,0);
close) - T termiate the connection
>close() =This signal indicates the end of the communication between server &c lient, this also closes the socket
close(int sock)
sock=the socketto close
>EXAMPLE:close(sock);
