client-publish-service.c

Example how to register a DNS-SD service using the client interface to avahi-daemon. It behaves like a network printer registering both an IPP and a BSD LPR service.

/***
  This file is part of avahi.

  avahi is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as
  published by the Free Software Foundation; either version 2.1 of the
  License, or (at your option) any later version.

  avahi is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
  Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with avahi; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  USA.
***/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

#include <avahi-client/client.h>
#include <avahi-client/publish.h>

#include <avahi-common/alternative.h>
#include <avahi-common/simple-watch.h>
#include <avahi-common/malloc.h>
#include <avahi-common/error.h>
#include <avahi-common/timeval.h>

static AvahiEntryGroup *group = NULL;
static AvahiSimplePoll *simple_poll = NULL;
static char *name = NULL;

static void create_services(AvahiClient *c);

static void entry_group_callback(AvahiEntryGroup *g, AvahiEntryGroupState state, AVAHI_GCC_UNUSED void *userdata) {
    assert(g == group || group == NULL);
    group = g;

    /* Called whenever the entry group state changes */

    switch (state) {
        case AVAHI_ENTRY_GROUP_ESTABLISHED :
            /* The entry group has been established successfully */
            fprintf(stderr, "Service '%s' successfully established.\n", name);
            break;

        case AVAHI_ENTRY_GROUP_COLLISION : {
            char *n;

            /* A service name collision with a remote service
             * happened. Let's pick a new name */
            n = avahi_alternative_service_name(name);
            avahi_free(name);
            name = n;

            fprintf(stderr, "Service name collision, renaming service to '%s'\n", name);

            /* And recreate the services */
            create_services(avahi_entry_group_get_client(g));
            break;
        }

        case AVAHI_ENTRY_GROUP_FAILURE :

            fprintf(stderr, "Entry group failure: %s\n", avahi_strerror(avahi_client_errno(avahi_entry_group_get_client(g))));

            /* Some kind of failure happened while we were registering our services */
            avahi_simple_poll_quit(simple_poll);
            break;

        case AVAHI_ENTRY_GROUP_UNCOMMITED:
        case AVAHI_ENTRY_GROUP_REGISTERING:
            ;
    }
}

static void create_services(AvahiClient *c) {
    char *n, r[128];
    int ret;
    assert(c);

    /* If this is the first time we're called, let's create a new
     * entry group if necessary */

    if (!group)
        if (!(group = avahi_entry_group_new(c, entry_group_callback, NULL))) {
            fprintf(stderr, "avahi_entry_group_new() failed: %s\n", avahi_strerror(avahi_client_errno(c)));
            goto fail;
        }

    /* If the group is empty (either because it was just created, or
     * because it was reset previously, add our entries.  */

    if (avahi_entry_group_is_empty(group)) {
        fprintf(stderr, "Adding service '%s'\n", name);

        /* Create some random TXT data */
        snprintf(r, sizeof(r), "random=%i", rand());

        /* We will now add two services and one subtype to the entry
         * group. The two services have the same name, but differ in
         * the service type (IPP vs. BSD LPR). Only services with the
         * same name should be put in the same entry group. */

        /* Add the service for IPP */
        if ((ret = avahi_entry_group_add_service(group, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC, 0, name, "_ipp._tcp", NULL, NULL, 651, "test=blah", r, NULL)) < 0) {

            if (ret == AVAHI_ERR_COLLISION)
                goto collision;

            fprintf(stderr, "Failed to add _ipp._tcp service: %s\n", avahi_strerror(ret));
            goto fail;
        }

        /* Add the same service for BSD LPR */
        if ((ret = avahi_entry_group_add_service(group, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC, 0, name, "_printer._tcp", NULL, NULL, 515, NULL)) < 0) {

            if (ret == AVAHI_ERR_COLLISION)
                goto collision;

            fprintf(stderr, "Failed to add _printer._tcp service: %s\n", avahi_strerror(ret));
            goto fail;
        }

        /* Add an additional (hypothetic) subtype */
        if ((ret = avahi_entry_group_add_service_subtype(group, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC, 0, name, "_printer._tcp", NULL, "_magic._sub._printer._tcp") < 0)) {
            fprintf(stderr, "Failed to add subtype _magic._sub._printer._tcp: %s\n", avahi_strerror(ret));
            goto fail;
        }

        /* Tell the server to register the service */
        if ((ret = avahi_entry_group_commit(group)) < 0) {
            fprintf(stderr, "Failed to commit entry group: %s\n", avahi_strerror(ret));
            goto fail;
        }
    }

    return;

collision:

    /* A service name collision with a local service happened. Let's
     * pick a new name */
    n = avahi_alternative_service_name(name);
    avahi_free(name);
    name = n;

    fprintf(stderr, "Service name collision, renaming service to '%s'\n", name);

    avahi_entry_group_reset(group);

    create_services(c);
    return;

fail:
    avahi_simple_poll_quit(simple_poll);
}

static void client_callback(AvahiClient *c, AvahiClientState state, AVAHI_GCC_UNUSED void * userdata) {
    assert(c);

    /* Called whenever the client or server state changes */

    switch (state) {
        case AVAHI_CLIENT_S_RUNNING:

            /* The server has startup successfully and registered its host
             * name on the network, so it's time to create our services */
            create_services(c);
            break;

        case AVAHI_CLIENT_FAILURE:

            fprintf(stderr, "Client failure: %s\n", avahi_strerror(avahi_client_errno(c)));
            avahi_simple_poll_quit(simple_poll);

            break;

        case AVAHI_CLIENT_S_COLLISION:

            /* Let's drop our registered services. When the server is back
             * in AVAHI_SERVER_RUNNING state we will register them
             * again with the new host name. */

        case AVAHI_CLIENT_S_REGISTERING:

            /* The server records are now being established. This
             * might be caused by a host name change. We need to wait
             * for our own records to register until the host name is
             * properly esatblished. */

            if (group)
                avahi_entry_group_reset(group);

            break;

        case AVAHI_CLIENT_CONNECTING:
            ;
    }
}

static void modify_callback(AVAHI_GCC_UNUSED AvahiTimeout *e, void *userdata) {
    AvahiClient *client = userdata;

    fprintf(stderr, "Doing some weird modification\n");

    avahi_free(name);
    name = avahi_strdup("Modified MegaPrinter");

    /* If the server is currently running, we need to remove our
     * service and create it anew */
    if (avahi_client_get_state(client) == AVAHI_CLIENT_S_RUNNING) {

        /* Remove the old services */
        if (group)
            avahi_entry_group_reset(group);

        /* And create them again with the new name */
        create_services(client);
    }
}

int main(AVAHI_GCC_UNUSED int argc, AVAHI_GCC_UNUSED char*argv[]) {
    AvahiClient *client = NULL;
    int error;
    int ret = 1;
    struct timeval tv;

    /* Allocate main loop object */
    if (!(simple_poll = avahi_simple_poll_new())) {
        fprintf(stderr, "Failed to create simple poll object.\n");
        goto fail;
    }

    name = avahi_strdup("MegaPrinter");

    /* Allocate a new client */
    client = avahi_client_new(avahi_simple_poll_get(simple_poll), 0, client_callback, NULL, &error);

    /* Check wether creating the client object succeeded */
    if (!client) {
        fprintf(stderr, "Failed to create client: %s\n", avahi_strerror(error));
        goto fail;
    }

    /* After 10s do some weird modification to the service */
    avahi_simple_poll_get(simple_poll)->timeout_new(
        avahi_simple_poll_get(simple_poll),
        avahi_elapse_time(&tv, 1000*10, 0),
        modify_callback,
        client);

    /* Run the main loop */
    avahi_simple_poll_loop(simple_poll);

    ret = 0;

fail:

    /* Cleanup things */

    if (client)
        avahi_client_free(client);

    if (simple_poll)
        avahi_simple_poll_free(simple_poll);

    avahi_free(name);

    return ret;
}