recv_multicast.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>
#if !defined(_WIN32)
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <net/if.h>
#endif
#if defined(_WIN32)
#define WINVER 0x0A00
#define _WIN32_WINNT 0x0A00
#include <winsock2.h>
#include <windows.h>
#include <netioapi.h>
#include <ws2tcpip.h>
#endif

#if defined(_WIN32)
void die(const char *msg) {
    char *wsa_message = NULL;
    FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
            NULL,
            WSAGetLastError(),
            MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
            (LPSTR)&wsa_message,
            0,
            NULL);
    printf("%s : %s\n", msg, wsa_message);
    LocalFree(wsa_message);
    exit(1);
}
#else
void die(const char *msg) {
    perror(msg);
    exit(1);
}
#endif

int main(int argc, char **argv) {
#if defined (_WIN32)
    WSADATA WSAData;
    WSAStartup(MAKEWORD(2,2), &WSAData);
#endif
    /* premier argument: nom de l'interface */
    if(argc == 1) {
        printf("usage: %s intf\n", argv[0]);
        printf("Interfaces:\n");
        for(int i = 0; i < 10; i++) {
            char ifname[IF_NAMESIZE];
            if(if_indextoname(i, ifname))
                printf("- %s\n", ifname);
        }
        return 1;
    }
    const char *intfname = argv[1];
    /* socket IPv6 UDP */
    int s = socket(AF_INET6, SOCK_DGRAM, 0);
    if(s < 0) die("impossible de créer la socket");
    /* seulement IPv6 */
    int value = 1;
    int rc = setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY, &value, sizeof(value));
    if(rc < 0) die("impossible de mettre l'option IPV6_V6ONLY");
    rc = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &value, sizeof(value));
    if(rc < 0) die("impossible de mettre l'option SO_REUSEADDR");
    /* bind sur le port 4242 */
    struct sockaddr_in6 server;
    memset(&server, 0, sizeof(server));
    server.sin6_family = AF_INET6;
    server.sin6_port = htons(4242);
    rc = bind(s, (struct sockaddr*)&server, sizeof(server));
    if(rc < 0) die("bind() a échoué");
    /* abonnement au groupe */
    unsigned char maddr[16];
    rc = inet_pton(AF_INET6, "ff02::4242:4242", maddr);
    if(rc < 1) die("impossible de convertir l'adresse");
    int ifindex = if_nametoindex(intfname);
    if(ifindex <= 0) {
        printf("l'interface %s n'existe pas\n", intfname);
        return 1;
    }
    struct ipv6_mreq mreq;
    memset(&mreq, 0, sizeof(mreq));
    memcpy(&mreq.ipv6mr_multiaddr, maddr, 16);
    mreq.ipv6mr_interface = ifindex;
    rc = setsockopt(s, IPPROTO_IPV6, IPV6_JOIN_GROUP, &mreq, sizeof(mreq));
    if(rc < 0) die("impossible de s'abonner au groupe");

    /* on écoute les messages */
    while(1) {
        char msg[1024];
        char from[256];
        struct sockaddr_in6 sin6;
        socklen_t sin_size = sizeof(sin6);
        ssize_t size = recvfrom(s, msg, sizeof(msg) - 1, 0, (struct sockaddr *)&sin6, &sin_size);
        if(size == 0)
            continue;
        if(size < 0)
            die("impossible de recevoir");
        from[0] = 0;
        inet_ntop(AF_INET6, &sin6, from, sizeof(from));
        msg[size] = 0; // ajoute un zéro, on a soustrait 1 à la taille au dessus pour être sûr d'avoir la place
        printf("message de %s: %s\n", from, msg);
    }
    return 0;
}