Connectionless client

The following socket interface functions are used by the client in these program examples:

• socket(): create socket

• gethostbyname() / getipnodebyname(): get the host name entry

• sendto(): send a message to a socket

• soc_close(): close socket

  
Example: Connectionless client for AF_INET

#include <stdio.h>
#include <sys.types.h>
#include <sys.socket.h>
#include <ioctl.h>
#include <signal.h>
#include <netinet.in.h>
#include <netdb.h>
  
#define DATA " The sea is calm, the tide is full ..."
#define TESTPORT 2222
  
/*
 * This program sends a datagram to a receiver whose name is passed 
 * as an argument in the command line.
 */
main(argc,argv)
    int argc;
    char *argv[];
{
    int sock;
    struct sockaddr_in to;
    struct hostent *hp, *gethostbyname();
   
    /* Create the socket to be sent on. */
    sock = socket(AF_INET, SOCK_DGRAM, 0);
    if (sock < 0 )
       { perror("Socket datagram");
         exit(1);
       }
  
    /* Construct the name of the socket to be sent on, without using
     * wildcards. gethostbyname returns a structure which contains the
     * network address of the specified host.
     * The port number is taken from the TESTPORT constant.
     */
hp =gethostbyname(argv[1]);
    if (hp == 0) {
        fprintf(stderr, "%s:unknown host\n", argv[1]);
        exit(1);
    }
     memcpy((char *)&to.sin_addr, (char *)hp->h_addr,hp->h_length);
    to.sin_family = AF_INET;
    to.sin_port = htons(TESTPORT);
   
    /* Send message. */
    if (sendto(sock, DATA, sizeof DATA, 0, &to, sizeof to) < 0) {
         perror("Sending datagram message");
         exit(1);
    }
    soc_close(sock);
}

   
Example: Connectionless client for AF_INET6

#include <stdio.h>
#include <sys.types.h>
#include <sys.socket.h>
#include <ioctl.h>
#include <signal.h>
#include <netinet.in.h>
#include <netdb.h>
#define DATA " The sea is calm, the tide is full ..."
#define TESTPORT 2222

/*
* This program sends a datagram to a receiver whose name is passed
* as an argument in the command line. */
main(argc,argv)
    int argc;
    char *argv[];
{
    int sock;
    int error_num;
    struct sockaddr_in6 to;
    struct hostent *hp;
 
    /* Create the socket to be sent on. */
    sock = socket(AF_INET6, SOCK_DGRAM, 0);
    if (sock < 0 )
       { 
         perror("Socket datagram");
         exit(1);
       }
 
    /* Construct the name of the socket to be sent on, without using
    * wildcards. gethostbyname returns a structure which contains the
    * network address of the specified host.
    * The port number is taken from the TESTPORT constant.
    */
    hp =getipnodebyname(argv[1], AF_INET6, 0, &error_num);
    if ((hp = = 0) || (error_num != NETDB_SUCCESS))
       {
         fprintf(stderr, "%s:unknown host\n", argv[1]);
         exit(1);
       }
    memcpy((char *)&to.sin6_addr, (char *)hp->h_addr,hp->h_length);
    to.sin6_family = AF_INET6;
    to.sin6_port = htons(TESTPORT);
 
    /* Release the dynamic memory of hostent */
    freehostent(hp);

    /* Send message. */
    if (sendto(sock, DATA, sizeof DATA, 0, &to, sizeof to) < 0) 
       {
         perror("Sending datagram message");
         exit(1);
       }
    soc_close(sock);
}

The client creates a communications endpoint (socket) and corresponding descriptor with socket().The following steps are executed in the program examples for AF_INET and AF_INET6:

1. The client queries the address of the host with gethostbyname() (for AF_INET); the host name is passed as a parameter.
   The client queries the IPv6 address of the host name passed as a parameter with getipnodebyname(). This new function could also be used for the AF_INET example. The address structure is then initialized.

2. The client sends a datagram with sendto(), which returns the number of transferred characters.

3. The client closes the socket with soc_close().