getaddrinfo

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
 I int getaddrinfo(const char * node , const char * service ,
I                 const struct addrinfo * hints ,
I                 struct addrinfo ** res );
 I void freeaddrinfo(struct addrinfo * res );
 I const char *gai_strerror(int  errcode );

struct addrinfo {
    int              ai_flags;
    int              ai_family;
    int              ai_socktype;
    int              ai_protocol;
    size_t           ai_addrlen;
    struct sockaddr *ai_addr;
    char            *ai_canonname;
    struct addrinfo *ai_next;
};

Extensions to getaddrinfo() for Internationalized Domain Names

#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>

#define BUF_SIZE 500

int
main(int argc, char *argv[])
{
    struct addrinfo hints;
    struct addrinfo *result, *rp;
    int sfd, s;
    struct sockaddr_storage peer_addr;
    socklen_t peer_addr_len;
    ssize_t nread;
    char buf[BUF_SIZE];

    if (argc != 2) {
        fprintf(stderr, "Usage: %s port\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
    hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
    hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address */
    hints.ai_protocol = 0;          /* Any protocol */

    s = getaddrinfo(NULL, argv[1], &hints, &result);
    if (s != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
        exit(EXIT_FAILURE);
    }

    /* getaddrinfo() returns a list of address structures.
       Try each address until we successfully bind().
       If socket(2) (or bind(2)) fails, we (close the socket
       and) try the next address. */

    for (rp = result; rp != NULL; rp = rp->ai_next) {
        sfd = socket(rp->ai_family, rp->ai_socktype,
                rp->ai_protocol);
        if (sfd == -1)
            continue;

        if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0)
            break;                  /* Success */

        close(sfd);
    }

    if (rp == NULL) {               /* No address succeeded */
        fprintf(stderr, "Could not bind\n");
        exit(EXIT_FAILURE);
    }

    freeaddrinfo(result);           /* No longer needed */

    /* Read datagrams and echo them back to sender */

    for (;;) {
        peer_addr_len = sizeof(struct sockaddr_storage);
        nread = recvfrom(sfd, buf, BUF_SIZE, 0,
                (struct sockaddr *) &peer_addr, &peer_addr_len);
        if (nread == -1)
            continue;               /* Ignore failed request */

        char host[NI_MAXHOST], service[NI_MAXSERV];

        s = getnameinfo((struct sockaddr *) &peer_addr,
                        peer_addr_len, host, NI_MAXHOST,
                        service, NI_MAXSERV, NI_NUMERICSERV);
       if (s == 0)
            printf("Received %ld bytes from %s:%s\n",
                    (long) nread, host, service);
        else
            fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));


        if (sendto(sfd, buf, nread, 0,
                    (struct sockaddr *) &peer_addr,
                    peer_addr_len) != nread)
            fprintf(stderr, "Error sending response\n");
    }
}

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define BUF_SIZE 500

int
main(int argc, char *argv[])
{
    struct addrinfo hints;
    struct addrinfo *result, *rp;
    int sfd, s, j;
    size_t len;
    ssize_t nread;
    char buf[BUF_SIZE];

    if (argc < 3) {
        fprintf(stderr, "Usage: %s host port msg...\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    /* Obtain address(es) matching host/port */

    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
    hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
    hints.ai_flags = 0;
    hints.ai_protocol = 0;          /* Any protocol */

    s = getaddrinfo(argv[1], argv[2], &hints, &result);
    if (s != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
        exit(EXIT_FAILURE);
    }

    /* getaddrinfo() returns a list of address structures.
       Try each address until we successfully connect().
       If socket() (or connect()) fails, we (close the socket
       and) try the next address. */

    for (rp = result; rp != NULL; rp = rp->ai_next) {
        sfd = socket(rp->ai_family, rp->ai_socktype,
                     rp->ai_protocol);
        if (sfd == -1)
            continue;

        if (connect(sfd, rp->ai_addr, rp->ai_addrlen) != -1)
            break;                  /* Success */

        close(sfd);
    }

    if (rp == NULL) {               /* No address succeeded */
        fprintf(stderr, "Could not connect\n");
        exit(EXIT_FAILURE);
    }

    freeaddrinfo(result);           /* No longer needed */

    /* Send remaining command-line arguments as separate
       datagrams, and read responses from server */

    for (j = 3; j < argc; j++) {
        len = strlen(argv[j]) + 1;
                /* +1 for terminating null byte */

        if (len + 1 > BUF_SIZE) {
            fprintf(stderr,
                    "Ignoring long message in argument %d\n", j);
            continue;
        }

        if (write(sfd, argv[j], len) != len) {
            fprintf(stderr, "partial/failed write\n");
            exit(EXIT_FAILURE);
        }

        nread = read(sfd, buf, BUF_SIZE);
        if (nread == -1) {
            perror("read");
            exit(EXIT_FAILURE);
        }

        printf("Received %ld bytes: %s\n", (long) nread, buf);
    }

    exit(EXIT_SUCCESS);
}