Example: IPv4 or IPv6 client

/**************************************************************************/
/* This is an IPv4 or IPv6 client.                                        */
/**************************************************************************/

/**************************************************************************/
/* Header files needed for this sample program                            */
/**************************************************************************/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

/**************************************************************************/
/* Constants used by this program                                         */
/**************************************************************************/
#define BUFFER_LENGTH    250
#define FALSE              0
#define SERVER_NAME     "ServerHostName"

/* Pass in 1 parameter which is either the */
/* address or host name of the server, or  */
/* set the server name in the #define      */
/* SERVER_NAME.                            */
void main(int argc, char *argv[])
{
   /***********************************************************************/
   /* Variable and structure definitions.                                 */
   /***********************************************************************/
   int    sd=-1, rc, bytesReceived=0;
   char   buffer[BUFFER_LENGTH];
   char   server[NETDB_MAX_HOST_NAME_LENGTH];
   char   servport[] = "3005";
   struct in6_addr serveraddr;
   struct addrinfo hints, *res=NULL;

   /***********************************************************************/
   /* A do/while(FALSE) loop is used to make error cleanup easier.  The   */
   /* close() of the socket descriptor is only done once at the very end  */
   /* of the program along with the free of the list of addresses.        */
 /***********************************************************************/
   do
   {
      /********************************************************************/
      /* If an argument was passed in, use this as the server, otherwise  */
      /* use the #define that is located at the top of this program.      */
      /********************************************************************/
      if (argc > 1)
         strcpy(server, argv[1]);
      else
         strcpy(server, SERVER_NAME);

      memset(&hints, 0x00, sizeof(hints));
      hints.ai_flags    = AI_NUMERICSERV;
      hints.ai_family   = AF_UNSPEC;
      hints.ai_socktype = SOCK_STREAM;
      /********************************************************************/
      /* Check if we were provided the address of the server using        */
      /* inet_pton() to convert the text form of the address to binary    */
      /* form. If it is numeric then we want to prevent getaddrinfo()     */
      /* from doing any name resolution.                                  */
      /********************************************************************/
      rc = inet_pton(AF_INET, server, &serveraddr);
      if (rc == 1)    /* valid IPv4 text address? */
      {
         hints.ai_family = AF_INET;
         hints.ai_flags |= AI_NUMERICHOST;
      }
      else
      {
         rc = inet_pton(AF_INET6, server, &serveraddr);
         if (rc == 1) /* valid IPv6 text address? */
         {

            hints.ai_family = AF_INET6;
            hints.ai_flags |= AI_NUMERICHOST;
         }
      }
      /********************************************************************/
      /* Get the address information for the server using getaddrinfo().  */
      /********************************************************************/
      rc = getaddrinfo(server, servport, &hints, &res);
      if (rc != 0)
      {
         printf("Host not found --> %s\n", gai_strerror(rc));
         if (rc == EAI_SYSTEM)
            perror("getaddrinfo() failed");
         break;
      }

      /********************************************************************/
      /* The socket() function returns a socket descriptor, which represents   */
      /* an endpoint.  The statement also identifies the address family,  */
      /* socket type, and protocol using the information returned from    */
      /* getaddrinfo().                                                   */
      /********************************************************************/
      sd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
      if (sd < 0)
      {
         perror("socket() failed");
         break;
      }
      /********************************************************************/
      /* Use the connect() function to establish a connection to the      */
      /* server.                                                          */
      /********************************************************************/
      rc = connect(sd, res->ai_addr, res->ai_addrlen);
      if (rc < 0)
      {
         /*****************************************************************/
         /* Note: the res is a linked list of addresses found for server. */
         /* If the connect() fails to the first one, subsequent addresses */
         /* (if any) in the list can be tried if required.               */
         /*****************************************************************/
         perror("connect() failed");
         break;
      }

      /********************************************************************/
      /* Send 250 bytes of a's to the server                              */
      /********************************************************************/
      memset(buffer, 'a', sizeof(buffer));
      rc = send(sd, buffer, sizeof(buffer), 0);
      if (rc < 0)
      {
         perror("send() failed");
         break;
      }

      /********************************************************************/
      /* In this example we know that the server is going to respond with */
      /* the same 250 bytes that we just sent.  Since we know that 250    */
      /* bytes are going to be sent back to us, we can use the          */
      /* SO_RCVLOWAT socket option and then issue a single recv() and     */
      /* retrieve all of the data.                                        */
      /*                                                                  */
      /* The use of SO_RCVLOWAT is already illustrated in the server      */
      /* side of this example, so we will do something different here.    */
      /* The 250 bytes of the data may arrive in separate packets,        */
      /* therefore we will issue recv() over and over again until all     */
      /* 250 bytes have arrived.                                          */
      /********************************************************************/
      while (bytesReceived < BUFFER_LENGTH)
      {
         rc = recv(sd, & buffer[bytesReceived],
                   BUFFER_LENGTH - bytesReceived, 0);
         if (rc < 0)
         {
            perror("recv() failed");
            break;
         }
         else if (rc == 0)
         {
            printf("The server closed the connection\n");
            break;
         }

         /*****************************************************************/
         /* Increment the number of bytes that have been received so far  */
         /*****************************************************************/
         bytesReceived += rc;
      }

   } while (FALSE);

   /***********************************************************************/
   /* Close down any open socket descriptors                              */
   /***********************************************************************/
   if (sd != -1)
      close(sd);
   /***********************************************************************/
   /* Free any results returned from getaddrinfo                          */
   /***********************************************************************/
   if (res != NULL)
      freeaddrinfo(res);
}