Socket bind() failed with Invalid argument error for program running on MacOS

The addrlen value you pass to bind() must exactly match the address family you specify in socket(). That means addrlen must be set to sizeof(sockaddr_in) for AF_INET, and sizeof(sockaddr_in6) for AF_INET6. Using sizeof(sockaddr_storage) is the wrong value, as sockaddr_storage is designed to be large enough to hold all possible sockaddr_... types, so its size may be larger than sockaddr_in6.

On the other hand, when calling accept(), you need to set addrlen to the full size of addr beforehand, so it knows how much memory it has to work with when writing the client's address to addr. addrlen will be adjusted to the actual size written. However, you can't simply type-cast an int* into a socklen_t*, so addrlen needs to be an actual socklen_t type. Besides, bind() is expecting a socklen_t anyway, not an int.

Try something more like this instead:

int main(int argc, char *argv[])
{
    int socket_fd = -1, af;
    socklen_t addrlen; // <-- add this!
    struct sockaddr_storage addr = {0};
    unsigned connections = 0;
    pthread_t workers[WORKER_NUM] = { 0 };
    int client_sock_fds[WORKER_NUM] = { 0 };
    char ip_string[64];

    if (argc > 1 && strcmp(argv[1], "inet6") == 0) {
        af = AF_INET6;
        addrlen = sizeof(struct sockaddr_in6); // <-- add this!
        init_sockaddr_inet6((struct sockaddr_in6 *)&addr);
    }
    else {
        af = AF_INET;
        addrlen = sizeof(struct sockaddr_in); // <-- add this!
        init_sockaddr_inet((struct sockaddr_in *)&addr);
    }

    printf("[Server] Create socket\n");
    socket_fd = socket(af, SOCK_STREAM, 0);
    if (socket_fd < 0) {
        perror("Create socket failed");
        goto fail;
    }

    printf("[Server] Bind socket\n");
    if (bind(socket_fd, (struct sockaddr *)&addr, addrlen) < 0) {
        perror("Bind failed");
        goto fail;
    }

    printf("[Server] Listening on socket\n");
    if (listen(socket_fd, 3) < 0) {
        perror("Listen failed");
        goto fail;
    }

    printf("[Server] Wait for clients to connect ..\n");
    while (connections < WORKER_NUM) {
        addrlen = sizeof(addr); // <-- add this!
        client_sock_fds[connections] =
            accept(socket_fd, (struct sockaddr *)&addr, &addrlen);
        if (client_sock_fds[connections] < 0) {
            perror("Accept failed");
            break;
        }

        if (sockaddr_to_string((struct sockaddr *)&addr, ip_string,
                               sizeof(ip_string) / sizeof(ip_string[0])) != 0) {
            printf("[Server] failed to parse client address\n");
            goto fail;
        }

        printf("[Server] Client connected (%s)\n", ip_string);
        if (pthread_create(&workers[connections], NULL, run,
                           &client_sock_fds[connections]) != 0) {
            perror("Create a worker thread failed");
            shutdown(client_sock_fds[connections], SHUT_RDWR);
            break;
        }

        connections++;
    }

    if (connections == WORKER_NUM) {
        printf("[Server] Achieve maximum amount of connections\n");
    }

    for (int i = 0; i < connections; i++) { // <-- needs to be the actual thread count, not WORKER_NUM!
        pthread_join(workers[i], NULL);
    }

    printf("[Server] Shuting down ..\n");
    shutdown(socket_fd, SHUT_RDWR);
    sleep(3);
    printf("[Server] BYE \n");
    return EXIT_SUCCESS;

fail:
    printf("[Server] Shuting down ..\n");
    if (socket_fd >= 0)
        close(socket_fd);
    sleep(3);
    return EXIT_FAILURE;
}

That being said, you should use getaddrinfo() instead to initialize the sockaddr_... that you pass to bind(). You should not be initializing it manually at all.

...
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

int main(int argc, char *argv[])
{
    int socket_fd = -1, res;
    ...
    struct addrinfo hints = { 0 };
    struct addrinfo *addrs = NULL;

    if (argc > 1 && strcmp(argv[1], "inet6") == 0)
        hints.ai_family = AF_INET6;
    else
        hints.ai_family = AF_INET;

    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_PASSIVE;

    printf("[Server] Initializing socket address\n");
    res = getaddrinfo(NULL, "1234", &hints, &addrs);
    if (res != 0) {
        fprintf(stderr, "getaddrinfo failed: %s\n", gai_strerror(res));
        goto fail;
    }

    printf("[Server] Create socket\n");
    socket_fd = socket(addrs->ai_family, addrs->ai_socktype, addrs->ai_protocol);
    if (socket_fd < 0) {
        perror("Create socket failed");
        freeaddrinfo(addrs);
        goto fail;
    }

    printf("[Server] Bind socket\n");
    if (bind(socket_fd, addrs->ai_addr, addrs->ai_addrlen) < 0) {
        perror("Bind failed");
        freeaddrinfo(addrs);
        goto fail;
    }

    freeaddrinfo(addrs);

    ...
}