Client

/* A simple client using TCP. Server name and port number are passed as an argument */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <netinet/in.h>
#include <netdb.h>
#include <errno.h>

void error(const char *msg)
{
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[])
{
    int sockfd, portno, n;
    struct sockaddr_in serv_addr; /*server adress*/
    struct hostent *server; /*server name*/
	struct iovec iov[1]; /*points to the segments of the (noncontiguous)outgoing message.*/
	struct msghdr mh; /*contains parameter information for sendmsg.*/

	char *string = "random string";
	char primo[256];
	strcpy(primo, string);

	/* Specify the components of the message in an "iovec".*/
	iov[0].iov_base = (caddr_t)primo;
	iov[0].iov_len = sizeof(primo);

    char buffer[256];
    if (argc < 3) {
       fprintf(stderr,"usage %s hostname port\n", argv[0]);
       exit(0);
    }
    portno = atoi(argv[2]); /*port number*/
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("ERROR opening socket");
    server = gethostbyname(argv[1]);
    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host\n");
        exit(0);
    }
    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    bcopy((char *)server->h_addr,
         (char *)&serv_addr.sin_addr.s_addr,
         server->h_length);
    serv_addr.sin_port = htons(portno);

    /* The message header contains parameters for sendmsg.    */
	mh.msg_name = (caddr_t) &server->h_addr;
	mh.msg_namelen = sizeof(server->h_addr);
	mh.msg_iov = iov;
	mh.msg_iovlen = sizeof(iov);

	printf("mh structure initialized \n");

	if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0) {
		error("ERROR connecting");
	}
	else printf("Connect() successful \n");

	n = sendmsg(sockfd, &mh, 0);            /* no flags used*/
	if (n == -1) {
		perror("sendmsg failed ");
		strerror(errno);
		return -1;
		/* The  output queue for a network interface was full.  This gener‐
		 * ally indicates that the interface has stopped sending,  but  may
		 * be  caused  by  transient  congestion.  (Normally, this does not
		 * occur in Linux.  Packets are just silently dropped when a device
		 * queue overflows.) */
	}
	else printf("Sendmsg successfully executed \n");

    bzero(buffer,256); /*azzera il buffer*/
    n = read(sockfd,buffer,255);
    if (n < 0)
         error("ERROR reading from socket");
    printf("%s\n",buffer);
    close(sockfd);
    return 0;
}