src/resolv/async_resolv.c

dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina/*
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   SSSD
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   Async resolver
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   Authors:
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina        Martin Nagy <mnagy@redhat.com>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina        Jakub Hrozek <jhrozek@redhat.com>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   Copyright (C) Red Hat, Inc 2009
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   This program is free software; you can redistribute it and/or modify
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   it under the terms of the GNU General Public License as published by
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   the Free Software Foundation; either version 3 of the License, or
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   (at your option) any later version.
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   This program is distributed in the hope that it will be useful,
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   but WITHOUT ANY WARRANTY; without even the implied warranty of
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   GNU General Public License for more details.
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   You should have received a copy of the GNU General Public License
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina   along with this program.  If not, see <http://www.gnu.org/licenses/>.
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina*/
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <sys/select.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <arpa/inet.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <arpa/nameser.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <ares.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <talloc.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <tevent.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <errno.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <netdb.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <stddef.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <string.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include <unistd.h>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include "config.h"
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include "resolv/async_resolv.h"
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include "util/dlinklist.h"
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#include "util/util.h"
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#define DNS__16BIT(p)                   (((p)[0] << 8) | (p)[1])
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina/*
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina * Macro DNS__32BIT reads a network long (32 bit) given in network
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina * byte order, and returns its value as an unsigned int. Copied
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina * from c-ares source code.
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina */
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina#define DNS__32BIT(p)  ((unsigned int) \
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina                         (((unsigned int)((unsigned char)(p)[0]) << 24U) | \
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina                          ((unsigned int)((unsigned char)(p)[1]) << 16U) | \
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina                          ((unsigned int)((unsigned char)(p)[2]) <<  8U) | \
                          ((unsigned int)((unsigned char)(p)[3]))))

#define DNS_HEADER_ANCOUNT(h)           DNS__16BIT((h) + 6)
#define DNS_RR_LEN(r)                   DNS__16BIT((r) + 8)
#define DNS_RR_TTL(r)                   DNS__32BIT((r) + 4)

#define RESOLV_TIMEOUTMS  2000

enum host_database default_host_dbs[] = { DB_FILES, DB_DNS, DB_SENTINEL };

struct fd_watch {
    struct fd_watch *prev;
    struct fd_watch *next;

    int fd;
    struct resolv_ctx *ctx;
    struct tevent_fd *fde;
};

struct resolv_ctx {
    struct tevent_context *ev_ctx;
    ares_channel channel;

    /* List of file descriptors that are watched by tevent. */
    struct fd_watch *fds;

    /* Time in milliseconds before canceling a DNS request */
    int timeout;

    /* The timeout watcher periodically calls ares_process_fd() to check
     * if our pending requests didn't timeout. */
    int pending_requests;
    struct tevent_timer *timeout_watcher;
};

struct request_watch {
    struct tevent_req *req;
    struct resolv_request *rr;
};

struct resolv_request {
    struct resolv_ctx *ctx;
    struct request_watch *rwatch;
    struct tevent_timer *request_timeout;
};

static int
return_code(int ares_code)
{
    switch (ares_code) {
    case ARES_SUCCESS:
        return EOK;
    case ARES_ENOMEM:
        return ENOMEM;
    case ARES_EFILE:
    default:
        return EIO;
    }
}

const char *
resolv_strerror(int ares_code)
{
    return ares_strerror(ares_code);
}

static int
fd_watch_destructor(struct fd_watch *f)
{
    DLIST_REMOVE(f->ctx->fds, f);
    f->fd = -1;

    return 0;
}

static void
fd_input_available(struct tevent_context *ev, struct tevent_fd *fde,
                   uint16_t flags, void *data)
{
    struct fd_watch *watch = talloc_get_type(data, struct fd_watch);

    if (watch->ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Invalid ares channel - this is likely a bug\n");
        return;
    }

    if (flags & TEVENT_FD_READ) {
        ares_process_fd(watch->ctx->channel, watch->fd, ARES_SOCKET_BAD);
    }
    if (flags & TEVENT_FD_WRITE) {
        ares_process_fd(watch->ctx->channel, ARES_SOCKET_BAD, watch->fd);
    }
}

static void
check_fd_timeouts(struct tevent_context *ev, struct tevent_timer *te,
                  struct timeval current_time, void *private_data);

static void
add_timeout_timer(struct tevent_context *ev, struct resolv_ctx *ctx)
{
    struct timeval tv = { 0, 0 };
    struct timeval *tvp;

    if (ctx->timeout_watcher) {
        return;
    }

    tvp = ares_timeout(ctx->channel, NULL, &tv);

    if (tvp == NULL) {
        tvp = &tv;
    }

    /* Enforce a minimum of 1 second. */
    if (tvp->tv_sec < 1) {
        tv = tevent_timeval_current_ofs(1, 0);
    } else {
        tv = tevent_timeval_current_ofs(tvp->tv_sec, tvp->tv_usec);
    }

    ctx->timeout_watcher = tevent_add_timer(ev, ctx, tv, check_fd_timeouts,
                                            ctx);
    if (ctx->timeout_watcher == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE, "Out of memory\n");
    }
}

static void
check_fd_timeouts(struct tevent_context *ev, struct tevent_timer *te,
                  struct timeval current_time, void *private_data)
{
    struct resolv_ctx *ctx = talloc_get_type(private_data, struct resolv_ctx);

    DEBUG(SSSDBG_TRACE_ALL, "Checking for DNS timeouts\n");

    /* NULLify the timeout_watcher so we don't
     * free it in the _done() function if it
     * gets called. Now that we're already in
     * the handler, tevent will take care of
     * freeing it when it returns.
     */
    ctx->timeout_watcher = NULL;

    ares_process_fd(ctx->channel, ARES_SOCKET_BAD, ARES_SOCKET_BAD);

    if (ctx->pending_requests > 0) {
        add_timeout_timer(ev, ctx);
    }
}

static void
resolv_request_timeout(struct tevent_context *ev,
                       struct tevent_timer *te,
                       struct timeval tv, void *pvt)
{
    struct resolv_request *rreq;

    DEBUG(SSSDBG_MINOR_FAILURE, "The resolve request timed out\n");

    rreq = talloc_get_type(pvt, struct resolv_request);
    if (rreq->rwatch == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE, "The request already completed\n");
        return;
    }

    tevent_req_error(rreq->rwatch->req, ETIMEDOUT);
    rreq->rwatch = NULL;
}

static int
request_watch_destructor(struct request_watch *rwatch)
{
    DEBUG(SSSDBG_TRACE_FUNC, "Deleting request watch\n");
    if (rwatch->rr) rwatch->rr->rwatch = NULL;
    return 0;
}

static struct resolv_request *
schedule_request_timeout(struct tevent_context *ev, struct resolv_ctx *ctx,
                         struct tevent_req *req)
{
    struct resolv_request *rreq;
    struct timeval tv;

    DEBUG(SSSDBG_TRACE_INTERNAL, "Scheduling a timeout of %d seconds\n",
                                  ctx->timeout);
    tv = tevent_timeval_current_ofs(ctx->timeout, 0);

    /* Intentionally allocating on ctx, because the request might go away
     * before c-ares returns */
    rreq = talloc(ctx, struct resolv_request);
    if (!rreq) {
        talloc_zfree(req);
        return NULL;
    }
    rreq->ctx = ctx;
    rreq->request_timeout = tevent_add_timer(ev, rreq, tv,
                                             resolv_request_timeout,
                                             rreq);
    if (rreq->request_timeout == NULL) {
        talloc_free(rreq);
        return NULL;
    }

    /* The watch will go away when the request finishes */
    rreq->rwatch = talloc(req, struct request_watch);
    if (!rreq->rwatch) {
        talloc_zfree(req);
        return NULL;
    }

    rreq->rwatch->req = req;
    rreq->rwatch->rr = rreq;
    talloc_set_destructor(rreq->rwatch, request_watch_destructor);

    return rreq;
}

static struct resolv_request *
schedule_timeout_watcher(struct tevent_context *ev, struct resolv_ctx *ctx,
                         struct tevent_req *req)
{
    struct resolv_request *rreq;

    rreq = schedule_request_timeout(ev, ctx, req);
    if (!rreq) return NULL;

    ctx->pending_requests++;

    DEBUG(SSSDBG_TRACE_INTERNAL, "Scheduling DNS timeout watcher\n");
    add_timeout_timer(ev, ctx);
    return rreq;
}

static void
unschedule_timeout_watcher(struct resolv_ctx *ctx, struct resolv_request *rreq)
{
    /* Unlink the watch if the request is still active */
    if (rreq->rwatch) {
        rreq->rwatch->rr = NULL;
    }
    talloc_free(rreq); /* Cancels the tevent timeout as well */

    if (ctx->pending_requests <= 0) {
        DEBUG(SSSDBG_CRIT_FAILURE, "Pending DNS requests mismatch\n");
        return;
    }

    ctx->pending_requests--;
    if (ctx->pending_requests == 0) {
        DEBUG(SSSDBG_TRACE_ALL, "Unscheduling DNS timeout watcher\n");
        talloc_zfree(ctx->timeout_watcher);
    }
}

static void fd_event_add(struct resolv_ctx *ctx, int s, int flags);
static void fd_event_close(struct resolv_ctx *ctx, int s);

/*
 * When ares is ready to read or write to a file descriptor, it will
 * call this callback. If both read and write are 0, it means that ares
 * will soon close the socket. We are mainly using this function to register
 * new file descriptors with tevent.
 */
static void
fd_event(void *data, int s, int fd_read, int fd_write)
{
    struct resolv_ctx *ctx = talloc_get_type(data, struct resolv_ctx);
    struct fd_watch *watch;
    int flags;

    /* The socket is about to get closed. */
    if (fd_read == 0 && fd_write == 0) {
        fd_event_close(ctx, s);
        return;
    }

    flags = fd_read ? TEVENT_FD_READ : 0;
    flags |= fd_write ? TEVENT_FD_WRITE : 0;

    /* Are we already watching this file descriptor? */
    watch = ctx->fds;
    while (watch) {
        if (watch->fd == s) {
            tevent_fd_set_flags(watch->fde, flags);
            return;
        }
        watch = watch->next;
    }

    fd_event_add(ctx, s, flags);
}

static void
fd_event_add(struct resolv_ctx *ctx, int s, int flags)
{
    struct fd_watch *watch;

    /* The file descriptor is new, register it with tevent. */
    watch = talloc(ctx, struct fd_watch);
    if (watch == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Out of memory allocating fd_watch structure\n");
        return;
    }
    talloc_set_destructor(watch, fd_watch_destructor);

    watch->fd = s;
    watch->ctx = ctx;

    watch->fde = tevent_add_fd(ctx->ev_ctx, watch, s, flags,
                               fd_input_available, watch);
    if (watch->fde == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE, "tevent_add_fd() failed\n");
        talloc_free(watch);
        return;
    }
    DLIST_ADD(ctx->fds, watch);
}

static void
fd_event_close(struct resolv_ctx *ctx, int s)
{
    struct fd_watch *watch;

    /* Remove the socket from list */
    watch = ctx->fds;
    while (watch) {
        if (watch->fd == s) {
            talloc_free(watch);
            return;
        }
        watch = watch->next;
    }
}

static int
resolv_ctx_destructor(struct resolv_ctx *ctx)
{
    ares_channel channel;

    if (ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE, "Ares channel already destroyed?\n");
        return -1;
    }

    /* Set ctx->channel to NULL first, so that callbacks that get
     * ARES_EDESTRUCTION won't retry. */
    channel = ctx->channel;
    ctx->channel = NULL;
    ares_destroy(channel);

    return 0;
}

static int
recreate_ares_channel(struct resolv_ctx *ctx)
{
    int ret;
    ares_channel new_channel;
    ares_channel old_channel;
    struct ares_options options;

    DEBUG(SSSDBG_CONF_SETTINGS, "Initializing new c-ares channel\n");
    /* FIXME: the options would contain
     * the nameservers to contact, the domains
     * to search... => get from confdb
     */
    options.sock_state_cb = fd_event;
    options.sock_state_cb_data = ctx;
    options.timeout = RESOLV_TIMEOUTMS;
    /* Only affects ares_gethostbyname */
    options.lookups = discard_const("f");
    options.tries = 1;
    ret = ares_init_options(&new_channel, &options,
                            ARES_OPT_SOCK_STATE_CB |
                            ARES_OPT_TIMEOUTMS |
                            ARES_OPT_LOOKUPS |
                            ARES_OPT_TRIES);
    if (ret != ARES_SUCCESS) {
        DEBUG(SSSDBG_CRIT_FAILURE, "Failed to initialize ares channel: %s\n",
                  resolv_strerror(ret));
        return return_code(ret);
    }

    old_channel = ctx->channel;
    ctx->channel = new_channel;
    if (old_channel != NULL) {
        DEBUG(SSSDBG_CONF_SETTINGS, "Destroying the old c-ares channel\n");
        ares_destroy(old_channel);
    }

    return EOK;
}

int
resolv_init(TALLOC_CTX *mem_ctx, struct tevent_context *ev_ctx,
            int timeout, struct resolv_ctx **ctxp)
{
    int ret;
    struct resolv_ctx *ctx;

    if (timeout < 1) {
        DEBUG(SSSDBG_MINOR_FAILURE,
              "The timeout is too short, DNS operations are going to fail. "
               "This is a bug outside unit tests\n");
    }

    ctx = talloc_zero(mem_ctx, struct resolv_ctx);
    if (ctx == NULL)
        return ENOMEM;

    ctx->ev_ctx = ev_ctx;
    ctx->timeout = timeout;

    ret = recreate_ares_channel(ctx);
    if (ret != EOK) {
        goto done;
    }

    talloc_set_destructor(ctx, resolv_ctx_destructor);

    *ctxp = ctx;
    return EOK;

done:
    talloc_free(ctx);
    return ret;
}

void
resolv_reread_configuration(struct resolv_ctx *ctx)
{
    recreate_ares_channel(ctx);
}

static errno_t
resolv_copy_in_addr(TALLOC_CTX *mem_ctx, struct resolv_addr *ret,
                    struct ares_addrttl *attl)
{
    ret->ipaddr = talloc_array(mem_ctx, uint8_t, sizeof(struct in_addr));
    if (!ret->ipaddr) return ENOMEM;

    memcpy(ret->ipaddr, &attl->ipaddr, sizeof(struct in_addr));
    ret->ttl = attl->ttl;

    return EOK;
}

static errno_t
resolv_copy_in6_addr(TALLOC_CTX *mem_ctx, struct resolv_addr *ret,
                     struct ares_addr6ttl *a6ttl)
{
    ret->ipaddr = talloc_array(mem_ctx, uint8_t, sizeof(struct in6_addr));
    if (!ret->ipaddr) return ENOMEM;

    memcpy(ret->ipaddr, &a6ttl->ip6addr, sizeof(struct in6_addr));
    ret->ttl = a6ttl->ttl;

    return EOK;
}

static struct resolv_hostent *
resolv_copy_hostent_common(TALLOC_CTX *mem_ctx, struct hostent *src)
{
    struct resolv_hostent *ret;
    int len;
    int i;

    ret = talloc_zero(mem_ctx, struct resolv_hostent);
    if (ret == NULL) {
        return NULL;
    }

    if (src->h_name != NULL) {
        ret->name = talloc_strdup(ret, src->h_name);
        if (ret->name == NULL) {
            goto fail;
        }
    }
    if (src->h_aliases != NULL) {
        for (len = 0; src->h_aliases[len] != NULL; len++);

        ret->aliases = talloc_array(ret, char *, len + 1);
        if (ret->aliases == NULL) {
            goto fail;
        }

        for (i = 0; i < len; i++) {
            ret->aliases[i] = talloc_strdup(ret->aliases, src->h_aliases[i]);
            if (ret->aliases[i] == NULL) {
                goto fail;
            }
        }
        ret->aliases[len] = NULL;
    }

    ret->family = src->h_addrtype;
    return ret;

fail:
    talloc_free(ret);
    return NULL;
}

struct resolv_hostent *
resolv_copy_hostent(TALLOC_CTX *mem_ctx, struct hostent *src)
{
    struct resolv_hostent *ret;
    int len;
    int i;

    ret = resolv_copy_hostent_common(mem_ctx, src);
    if (ret == NULL) {
        return NULL;
    }

    if (src->h_addr_list != NULL) {
        for (len = 0; src->h_addr_list[len] != NULL; len++);

        ret->addr_list = talloc_array(ret, struct resolv_addr *, len + 1);
        if (ret->addr_list == NULL) {
            goto fail;
        }

        for (i = 0; i < len; i++) {
            ret->addr_list[i] = talloc_zero(ret->addr_list,
                                            struct resolv_addr);
            if (ret->addr_list[i] == NULL) {
                goto fail;
            }

            ret->addr_list[i]->ipaddr = talloc_memdup(ret->addr_list[i],
                                                      src->h_addr_list[i],
                                                      src->h_length);
            if (ret->addr_list[i]->ipaddr == NULL) {
                goto fail;
            }
            ret->addr_list[i]->ttl = RESOLV_DEFAULT_TTL;
        }
        ret->addr_list[len] = NULL;
    }
    return ret;

fail:
    talloc_free(ret);
    return NULL;
}

struct resolv_hostent *
resolv_copy_hostent_ares(TALLOC_CTX *mem_ctx, struct hostent *src,
                         int family, void *ares_ttl_data,
                         int num_ares_ttl_data)
{
    struct resolv_hostent *ret;
    errno_t cret;
    int i;

    ret = resolv_copy_hostent_common(mem_ctx, src);
    if (ret == NULL) {
        return NULL;
    }

    if (num_ares_ttl_data > 0) {
        ret->addr_list = talloc_array(ret, struct resolv_addr *,
                                      num_ares_ttl_data + 1);
        if (ret->addr_list == NULL) {
            goto fail;
        }

        for (i = 0; i < num_ares_ttl_data; i++) {
            ret->addr_list[i] = talloc_zero(ret->addr_list,
                                            struct resolv_addr);
            if (ret->addr_list[i] == NULL) {
                goto fail;
            }

            switch (family) {
            case AF_INET:
                cret = resolv_copy_in_addr(ret->addr_list, ret->addr_list[i],
                                &((struct ares_addrttl *) ares_ttl_data)[i]);
                break;
            case AF_INET6:
                cret = resolv_copy_in6_addr(ret->addr_list, ret->addr_list[i],
                                &((struct ares_addr6ttl *) ares_ttl_data)[i]);
                break;
            default:
                DEBUG(SSSDBG_CRIT_FAILURE,
                      "Unknown address family %d\n", family);
                goto fail;
            }

            if (cret != EOK) {
                DEBUG(SSSDBG_CRIT_FAILURE, "Could not copy address\n");
                goto fail;
            }
        }
        ret->addr_list[num_ares_ttl_data] = NULL;
    }

    ret->family = family;
    return ret;

fail:
    talloc_free(ret);
    return NULL;
}

/* =================== Resolve host name in files =========================*/
struct gethostbyname_files_state {
    struct resolv_ctx *resolv_ctx;

    /* Part of the query. */
    const char *name;
    int family;

    /* query result */
    struct resolv_hostent *rhostent;

    /* returned by ares. */
    int status;
};

/* Fake up an async interface even though files would
 * always be blocking */
static struct tevent_req *
resolv_gethostbyname_files_send(TALLOC_CTX *mem_ctx,
                                struct tevent_context *ev,
                                struct resolv_ctx *ctx,
                                const char *name,
                                int family)
{
    struct tevent_req *req;
    struct gethostbyname_files_state *state;
    struct hostent *hostent = NULL;

    req = tevent_req_create(mem_ctx, &state,
                            struct gethostbyname_files_state);
    if (req == NULL) {
        return NULL;
    }

    state->resolv_ctx = ctx;
    state->name = name;
    state->rhostent = NULL;
    state->family = family;

    DEBUG(SSSDBG_CONF_SETTINGS,
          "Trying to resolve %s record of '%s' in files\n",
              state->family == AF_INET ? "A" : "AAAA", state->name);

    state->status = ares_gethostbyname_file(state->resolv_ctx->channel,
                                            state->name, state->family,
                                            &hostent);

    if (state->status == ARES_SUCCESS) {
        state->rhostent = resolv_copy_hostent(state, hostent);
        if (state->rhostent == NULL) {
            tevent_req_error(req, ENOMEM);
            goto done;
        }
    } else if (state->status == ARES_ENOTFOUND ||
               state->status == ARES_ENODATA) {
        /* Just say we didn't find anything and let the caller decide
         * about retrying */
        tevent_req_error(req, ENOENT);
        goto done;
    } else {
        tevent_req_error(req, return_code(state->status));
        goto done;
    }

    tevent_req_done(req);
done:
    if (hostent) ares_free_hostent(hostent);
    tevent_req_post(req, ev);
    return req;
}

static errno_t
resolv_gethostbyname_files_recv(struct tevent_req *req, TALLOC_CTX *mem_ctx,
                                int *status, struct resolv_hostent **rhostent)
{
    struct gethostbyname_files_state *state = tevent_req_data(req,
                                        struct gethostbyname_files_state);

    /* Fill in even in case of error as status contains the
     * c-ares return code */
    if (status) {
        *status = state->status;
    }
    if (rhostent) {
        *rhostent = talloc_steal(mem_ctx, state->rhostent);
    }

    TEVENT_REQ_RETURN_ON_ERROR(req);

    return EOK;
}

/* ==================== Resolve host name in DNS =========================*/
struct gethostbyname_dns_state {
    struct resolv_ctx *resolv_ctx;
    struct tevent_context *ev;

    /* Part of the query. */
    const char *name;
    int family;

    /* query result */
    struct resolv_hostent *rhostent;

    /* These are returned by ares. */
    int status;
    int timeouts;
    int retrying;
};

static void
resolv_gethostbyname_dns_wakeup(struct tevent_req *subreq);
static void
resolv_gethostbyname_dns_query(struct tevent_req *req,
                               struct gethostbyname_dns_state *state);
static void
resolv_gethostbyname_dns_query_done(void *arg, int status, int timeouts,
                                    unsigned char *abuf, int alen);
static int
resolv_gethostbyname_dns_parse(struct gethostbyname_dns_state *state,
                               int status, unsigned char *abuf, int alen);

static struct tevent_req *
resolv_gethostbyname_dns_send(TALLOC_CTX *mem_ctx, struct tevent_context *ev,
                              struct resolv_ctx *ctx, const char *name,
                              int family)
{
    struct tevent_req *req, *subreq;
    struct gethostbyname_dns_state *state;
    struct timeval tv = { 0, 0 };

    if (ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Invalid ares channel - this is likely a bug\n");
        return NULL;
    }

    req = tevent_req_create(mem_ctx, &state, struct gethostbyname_dns_state);
    if (req == NULL) {
        return NULL;
    }

    state->resolv_ctx = ctx;
    state->ev = ev;
    state->name = name;
    state->rhostent = NULL;
    state->status = 0;
    state->timeouts = 0;
    state->retrying = 0;
    state->family = family;

    /* We need to have a wrapper around ares async calls, because
     * they can in some cases call it's callback immediately.
     * This would not let our caller to set a callback for req. */
    subreq = tevent_wakeup_send(req, ev, tv);
    if (subreq == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Failed to add critical timer to run next operation!\n");
        talloc_zfree(req);
        return NULL;
    }
    tevent_req_set_callback(subreq, resolv_gethostbyname_dns_wakeup, req);

    return req;
}

static void
resolv_gethostbyname_dns_wakeup(struct tevent_req *subreq)
{
    struct tevent_req *req = tevent_req_callback_data(subreq,
                                                struct tevent_req);
    struct gethostbyname_dns_state *state = tevent_req_data(req,
                                        struct gethostbyname_dns_state);

    if (!tevent_wakeup_recv(subreq)) {
        tevent_req_error(req, EIO);
        return;
    }
    talloc_zfree(subreq);

    if (state->resolv_ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Invalid ares channel - this is likely a bug\n");
        tevent_req_error(req, EIO);
        return;
    }

    resolv_gethostbyname_dns_query(req, state);
}

static void
resolv_gethostbyname_dns_query(struct tevent_req *req,
                               struct gethostbyname_dns_state *state)
{
    struct resolv_request *rreq;

    DEBUG(SSSDBG_CONF_SETTINGS, "Trying to resolve %s record of '%s' in DNS\n",
              state->family == AF_INET ? "A" : "AAAA", state->name);

    rreq = schedule_timeout_watcher(state->ev, state->resolv_ctx, req);
    if (!rreq) {
        tevent_req_error(req, ENOMEM);
        return;
    }

    ares_search(state->resolv_ctx->channel,
                state->name, ns_c_in,
                (state->family == AF_INET) ? ns_t_a : ns_t_aaaa,
                resolv_gethostbyname_dns_query_done, rreq);
}

static void
resolv_gethostbyname_dns_query_done(void *arg, int status, int timeouts,
                                    unsigned char *abuf, int alen)
{
    errno_t ret;
    struct gethostbyname_dns_state *state;
    struct resolv_request *rreq = talloc_get_type(arg, struct resolv_request);
    struct tevent_req *req;


    if (rreq->rwatch == NULL) {
        /* The tevent request was cancelled while the ares call was still in
         * progress so nobody cares about the result now. Quit. */
        unschedule_timeout_watcher(rreq->ctx, rreq);
        return;
    }

    req = rreq->rwatch->req;
    unschedule_timeout_watcher(rreq->ctx, rreq);

    state = tevent_req_data(req, struct gethostbyname_dns_state);

    state->status = status;
    state->timeouts = timeouts;

    /* If resolv.conf changed during processing of a request we might
     * destroy the old channel before the request has a chance to finish.
     * We must resend the request in this case */
    if (state->retrying == 0 && status == ARES_EDESTRUCTION
        && state->resolv_ctx->channel != NULL) {
        state->retrying = 1;
        resolv_gethostbyname_dns_query(req, state);
        return;
    }

    if (status == ARES_ENOTFOUND || status == ARES_ENODATA) {
        /* Just say we didn't find anything and let the caller decide
         * about retrying */
        tevent_req_error(req, ENOENT);
        return;
    }

    if (status != ARES_SUCCESS) {
        /* Any other error indicates a server error,
         * so don't bother trying again
         */
        tevent_req_error(req, return_code(status));
        return;
    }

    ret = resolv_gethostbyname_dns_parse(state, status, abuf, alen);
    if (ret != EOK) {
        tevent_req_error(req, ret);
        return;
    }

    tevent_req_done(req);
}

static int
resolv_gethostbyname_dns_parse(struct gethostbyname_dns_state *state,
                               int status, unsigned char *abuf, int alen)
{
    struct hostent *hostent;
    int naddrttls;
    errno_t ret;
    void *addr = NULL;

    naddrttls = DNS_HEADER_ANCOUNT(abuf);

    switch (state->family) {
        case AF_INET:
            DEBUG(SSSDBG_TRACE_LIBS, "Parsing an A reply\n");

            addr = talloc_array(state, struct ares_addrttl, naddrttls);
            if (!addr) {
                ret = ENOMEM;
                goto fail;
            }

            status = ares_parse_a_reply(abuf, alen, &hostent,
                                        (struct ares_addrttl *) addr,
                                        &naddrttls);
            break;
        case AF_INET6:
            DEBUG(SSSDBG_TRACE_LIBS, "Parsing an AAAA reply\n");

            addr = talloc_array(state, struct ares_addr6ttl, naddrttls);
            if (!addr) {
                ret = ENOMEM;
                goto fail;
            }

            status = ares_parse_aaaa_reply(abuf, alen, &hostent,
                                           (struct ares_addr6ttl *) addr,
                                           &naddrttls);
            break;
        default:
            DEBUG(SSSDBG_CRIT_FAILURE, "Unknown family %d\n", state->family);
            ret = EAFNOSUPPORT;
            goto fail;
    }

    if (hostent != NULL) {
        state->rhostent = resolv_copy_hostent_ares(state, hostent,
                                                   state->family,
                                                   addr, naddrttls);
        ares_free_hostent(hostent);
        if (state->rhostent == NULL) {
            ret = ENOMEM;
            goto fail;
        }

        /* The address list is NULL. This is probably a bug in
         * c-ares, but we need to handle it gracefully.
         */
        if (state->rhostent->addr_list == NULL) {
            talloc_zfree(state->rhostent);
            return ENOENT;
        }
    }

    talloc_free(addr);
    return return_code(status);

fail:
    talloc_free(addr);
    return ret;
}

static int
resolv_gethostbyname_dns_recv(struct tevent_req *req, TALLOC_CTX *mem_ctx,
                              int *status, int *timeouts,
                              struct resolv_hostent **rhostent)
{
    struct gethostbyname_dns_state *state = tevent_req_data(req,
                                        struct gethostbyname_dns_state);

    /* Fill in even in case of error as status contains the
     * c-ares return code */
    if (status) {
        *status = state->status;
    }
    if (timeouts) {
        *timeouts = state->timeouts;
    }

    TEVENT_REQ_RETURN_ON_ERROR(req);

    if (rhostent) {
        *rhostent = talloc_steal(mem_ctx, state->rhostent);
    }

    return EOK;
}

/*******************************************************************
 * Get host by name.                                               *
 *******************************************************************/

struct gethostbyname_state {
    struct resolv_ctx *resolv_ctx;
    struct tevent_context *ev;

    /* Part of the query. */
    const char *name;
    int family;

    /* In which order to use IPv4, or v6 */
    enum restrict_family family_order;

    /* Known hosts databases and index to the current one */
    enum host_database *db;
    int dbi;

    /* These are returned by ares. The hostent struct will be freed
     * when the user callback returns. */
    struct resolv_hostent *rhostent;
    int status;
    int timeouts;
    int retrying;
};

static errno_t
resolv_gethostbyname_address(TALLOC_CTX *mem_ctx, const char *address,
                             struct resolv_hostent **_rhostent);
static inline int
resolv_gethostbyname_family_init(enum restrict_family family_order);
static errno_t
resolv_gethostbyname_step(struct tevent_req *req);

struct tevent_req *
resolv_gethostbyname_send(TALLOC_CTX *mem_ctx, struct tevent_context *ev,
                          struct resolv_ctx *ctx, const char *name,
                          enum restrict_family family_order,
                          enum host_database *db)
{
    struct tevent_req *req;
    struct gethostbyname_state *state;
    errno_t ret;

    if (ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Invalid ares channel - this is likely a bug\n");
        return NULL;
    }

    req = tevent_req_create(mem_ctx, &state, struct gethostbyname_state);
    if (req == NULL) {
        return NULL;
    }

    state->resolv_ctx = ctx;
    state->ev = ev;
    state->name = talloc_strdup(state, name);
    if (state->name == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE, "talloc_strdup() failed\n");
        goto fail;
    }

    state->rhostent = NULL;
    state->status = 0;
    state->timeouts = 0;
    state->retrying = 0;
    state->family_order = family_order;
    state->family = resolv_gethostbyname_family_init(state->family_order);
    state->db = db;
    state->dbi = 0;

    /* Do not attempt to resolve IP addresses */
    if (resolv_is_address(state->name)) {
        ret = resolv_gethostbyname_address(state, state->name,
                                           &state->rhostent);
        if (ret != EOK) {
            DEBUG(SSSDBG_CRIT_FAILURE,
                  "Canot create a fake hostent structure\n");
            goto fail;
        }

        tevent_req_done(req);
        tevent_req_post(req, ev);
        return req;
    }

    ret = resolv_gethostbyname_step(req);
    if (ret != EOK) {
        DEBUG(SSSDBG_CRIT_FAILURE, "Cannot start the resolving\n");
        goto fail;
    }

    return req;

fail:
    talloc_zfree(req);
    return NULL;
}

bool
resolv_is_address(const char *name)
{
    struct addrinfo hints;
    struct addrinfo *res = NULL;
    int ret;

    memset((void *) &hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;
    hints.ai_flags = AI_NUMERICHOST; /* No network lookups */

    ret = getaddrinfo(name, NULL, &hints, &res);
    if (ret != 0) {
        if (ret == -2) {
            DEBUG(SSSDBG_TRACE_ALL,
                  "[%s] does not look like an IP address\n", name);
        } else {
            DEBUG(SSSDBG_OP_FAILURE, "getaddrinfo failed [%d]: %s\n",
                      ret, gai_strerror(ret));
        }
    } else { /* ret == 0 */
        freeaddrinfo(res);
    }

    return ret == 0;
}

static errno_t
resolv_gethostbyname_address(TALLOC_CTX *mem_ctx, const char *address,
                             struct resolv_hostent **_rhostent)
{
    struct resolv_hostent *rhostent;
    TALLOC_CTX *tmp_ctx;
    errno_t ret;
    int family;

    tmp_ctx = talloc_new(NULL);
    if (!tmp_ctx) return ENOMEM;

    rhostent = talloc_zero(tmp_ctx, struct resolv_hostent);
    if (!rhostent) {
        ret = ENOMEM;
        goto done;
    }

    rhostent->name = talloc_strdup(rhostent, address);
    rhostent->addr_list = talloc_array(rhostent, struct resolv_addr *, 2);

    if (!rhostent->name ||
        !rhostent->addr_list) {
        ret = ENOMEM;
        goto done;
    }

    rhostent->addr_list[0] = talloc_zero(rhostent->addr_list,
                                         struct resolv_addr);
    if (!rhostent->addr_list[0]) {
        ret = ENOMEM;
        goto done;
    }
    rhostent->addr_list[0]->ipaddr = talloc_array(rhostent->addr_list[0],
                                                  uint8_t,
                                                  sizeof(struct in6_addr));
    if (!rhostent->addr_list[0]->ipaddr) {
        ret = ENOMEM;
        goto done;
    }

    family = AF_INET;
    ret = inet_pton(family, address,
                    rhostent->addr_list[0]->ipaddr);
    if (ret != 1) {
        family = AF_INET6;
        ret = inet_pton(family, address,
                        rhostent->addr_list[0]->ipaddr);
        if (ret != 1) {
            DEBUG(SSSDBG_CRIT_FAILURE,
                  "Could not parse address as neither v4 nor v6\n");
            ret = EINVAL;
            goto done;
        }
    }

    rhostent->addr_list[0]->ttl = RESOLV_DEFAULT_TTL;
    rhostent->addr_list[1] = NULL;
    rhostent->family = family;
    rhostent->aliases = NULL;

    *_rhostent = talloc_move(mem_ctx, &rhostent);
    ret = EOK;
done:
    talloc_free(tmp_ctx);
    return ret;
}

static inline int
resolv_gethostbyname_family_init(enum restrict_family family_order)
{
    switch(family_order) {
        case IPV4_ONLY:
        case IPV4_FIRST:
            return AF_INET;
        case IPV6_ONLY:
        case IPV6_FIRST:
            return AF_INET6;
    }

    DEBUG(SSSDBG_CRIT_FAILURE,
          "Unknown address family order %d\n", family_order);
    return -1;
}

static int
resolv_gethostbyname_next(struct gethostbyname_state *state)
{
    if (state->family_order == IPV4_FIRST &&
        state->family == AF_INET) {
        state->family = AF_INET6;
        return EOK;
    } else if (state->family_order == IPV6_FIRST &&
               state->family == AF_INET6) {
        state->family = AF_INET;
        return EOK;
    } else {
        /* No more address families for this DB, check if
         * there is another DB to try */
        DEBUG(SSSDBG_FUNC_DATA, "No more address families to retry\n");
        state->dbi++;
        if (state->db[state->dbi] != DB_SENTINEL) {
            state->family = resolv_gethostbyname_family_init(
                                                state->family_order);
            return EOK;
        }
    }

    DEBUG(SSSDBG_CONF_SETTINGS, "No more hosts databases to retry\n");
    return ENOENT;
}

static void
resolv_gethostbyname_done(struct tevent_req *subreq);

static errno_t
resolv_gethostbyname_step(struct tevent_req *req)
{
    struct gethostbyname_state *state = tevent_req_data(req,
                                                struct gethostbyname_state);
    struct tevent_req *subreq;

    switch(state->db[state->dbi]) {
        case DB_FILES:
            DEBUG(SSSDBG_TRACE_INTERNAL, "Querying files\n");
            subreq = resolv_gethostbyname_files_send(state, state->ev,
                                                     state->resolv_ctx,
                                                     state->name,
                                                     state->family);
            break;
        case DB_DNS:
            DEBUG(SSSDBG_TRACE_INTERNAL, "Querying DNS\n");
            subreq = resolv_gethostbyname_dns_send(state, state->ev,
                                                   state->resolv_ctx,
                                                   state->name,
                                                   state->family);
            break;
        default:
            DEBUG(SSSDBG_CRIT_FAILURE, "Invalid hosts database\n");
            return EINVAL;
    }

    if (subreq == NULL) {
        return ENOMEM;
    }

    tevent_req_set_callback(subreq, resolv_gethostbyname_done, req);
    return EOK;
}

static void
resolv_gethostbyname_done(struct tevent_req *subreq)
{
    struct tevent_req *req = tevent_req_callback_data(subreq,
                                                      struct tevent_req);
    struct gethostbyname_state *state = tevent_req_data(req,
                                                struct gethostbyname_state);
    errno_t ret;

    switch(state->db[state->dbi]) {
        case DB_FILES:
            ret = resolv_gethostbyname_files_recv(subreq, state,
                                                  &state->status,
                                                  &state->rhostent);
            /* files is synchronous, there can be no timeouts */
            state->timeouts = 0;
            break;
        case DB_DNS:
            ret = resolv_gethostbyname_dns_recv(subreq, state,
                                                &state->status, &state->timeouts,
                                                &state->rhostent);
            break;
        default:
            DEBUG(SSSDBG_CRIT_FAILURE, "Invalid hosts database\n");
            tevent_req_error(req, EINVAL);
            return;
    }

    talloc_zfree(subreq);

    if (ret == ENOENT) {
        ret = resolv_gethostbyname_next(state);
        if (ret == EOK) {
            ret = resolv_gethostbyname_step(req);
            if (ret != EOK) {
                tevent_req_error(req, ret);
            }
            return;
        }

        /* No more databases and/or address families */
        tevent_req_error(req, ENOENT);
        return;
    } else if (ret == ETIMEDOUT) {
        /* In case we killed the request before c-ares answered */
        state->status = ARES_ETIMEOUT;
    }

    if (ret != EOK) {
        DEBUG(SSSDBG_OP_FAILURE, "querying hosts database failed [%d]: %s\n",
                  ret, strerror(ret));
        tevent_req_error(req, ret);
        return;
    }

    tevent_req_done(req);
}

int
resolv_gethostbyname_recv(struct tevent_req *req, TALLOC_CTX *mem_ctx,
                          int *status, int *timeouts,
                          struct resolv_hostent **rhostent)
{
    struct gethostbyname_state *state = tevent_req_data(req, struct gethostbyname_state);

    /* Fill in even in case of error as status contains the
     * c-ares return code */
    if (status) {
        *status = state->status;
    }
    if (timeouts) {
        *timeouts = state->timeouts;
    }
    if (rhostent) {
        *rhostent = talloc_steal(mem_ctx, state->rhostent);
    }

    TEVENT_REQ_RETURN_ON_ERROR(req);

    return EOK;
}

char *
resolv_get_string_address_index(TALLOC_CTX *mem_ctx,
                                struct resolv_hostent *hostent,
                                unsigned int addrindex)
{
    char *address;

    if (!hostent) return NULL;

    address = talloc_zero_size(mem_ctx, 128);
    if (address == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE, "talloc_zero failed.\n");
        return NULL;
    }

    errno = 0;
    if (inet_ntop(hostent->family, hostent->addr_list[addrindex]->ipaddr,
                  address, 128) == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "inet_ntop failed [%d][%s].\n", errno, strerror(errno));
        talloc_free(address);
        return NULL;
    }

    return address;
}

char *
resolv_get_string_ptr_address(TALLOC_CTX *mem_ctx,
                              int family, uint8_t *address)
{
    char *straddr;

    if (family == AF_INET6) {
        int i;
        char hexbyte[3];

        straddr = talloc_strdup(mem_ctx, "\0");
        if (!straddr) {
            return NULL;
        }

        for (i = 15; i >= 0; i--) {
            snprintf(hexbyte, 3, "%02x", address[i]);
            straddr = talloc_asprintf_append(straddr, "%c.%c.",
                                             hexbyte[1], hexbyte[0]);
        }
        straddr = talloc_asprintf_append(straddr, "ip6.arpa.");
    } else if (family == AF_INET) {
        straddr = talloc_asprintf(mem_ctx,
                                  "%u.%u.%u.%u.in-addr.arpa.",
                                  (address[3]),
                                  (address[2]),
                                  (address[1]),
                                  (address[0]));
    } else {
        DEBUG(SSSDBG_CRIT_FAILURE, "Unknown address family\n");
        return NULL;
    }

    return straddr;
}

struct sockaddr_storage *
resolv_get_sockaddr_address_index(TALLOC_CTX *mem_ctx,
                                  struct resolv_hostent *hostent,
                                  int port, int addrindex)
{
    struct sockaddr_storage *sockaddr;

    if (!hostent) return NULL;

    sockaddr = talloc_zero(mem_ctx, struct sockaddr_storage);
    if (sockaddr == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE, "talloc_zero failed.\n");
        return NULL;
    }

    switch(hostent->family) {
        case AF_INET:
            sockaddr->ss_family = AF_INET;
            memcpy(&((struct sockaddr_in *) sockaddr)->sin_addr,
                   hostent->addr_list[addrindex]->ipaddr,
                   sizeof(struct in_addr));
            ((struct sockaddr_in *) sockaddr)->sin_port = (in_port_t) htons(port);

            break;
        case AF_INET6:
            sockaddr->ss_family = AF_INET6;
            memcpy(&((struct sockaddr_in6 *) sockaddr)->sin6_addr,
                   hostent->addr_list[addrindex]->ipaddr,
                   sizeof(struct in6_addr));
            ((struct sockaddr_in6 *) sockaddr)->sin6_port = (in_port_t) htons(port);
            break;
        default:
            DEBUG(SSSDBG_CRIT_FAILURE,
                  "Unknown address family %d\n", hostent->family);
            return NULL;
    }

    return sockaddr;
}

/*
 * A simple helper function that will take an array of struct ares_srv_reply that
 * was allocated by malloc() in c-ares and copies it using talloc. The old one
 * is freed and the talloc one is put into 'reply_list' instead.
 */
static int
rewrite_talloc_srv_reply(TALLOC_CTX *mem_ctx, struct ares_srv_reply **reply_list)
{
    struct ares_srv_reply *ptr = NULL;
    struct ares_srv_reply *new_list = NULL;
    struct ares_srv_reply *old_list = *reply_list;

    /* Nothing to do, but not an error */
    if (!old_list) {
        return EOK;
    }

    /* Copy the linked list */
    while (old_list) {
        /* Special case for the first node */
        if (!new_list) {
            new_list = talloc_zero(mem_ctx, struct ares_srv_reply);
            if (new_list == NULL) {
                ares_free_data(*reply_list);
                return ENOMEM;
            }
            ptr = new_list;
        } else {
            ptr->next = talloc_zero(new_list, struct ares_srv_reply);
            if (ptr->next == NULL) {
                ares_free_data(*reply_list);
                talloc_free(new_list);
                return ENOMEM;
            }
            ptr = ptr->next;
        }

        ptr->weight = old_list->weight;
        ptr->priority = old_list->priority;
        ptr->port = old_list->port;
        ptr->host = talloc_strdup(ptr, old_list->host);
        if (ptr->host == NULL) {
            ares_free_data(*reply_list);
            talloc_free(new_list);
            return ENOMEM;
        }

        old_list = old_list->next;
    }

    /* Free the old one (uses malloc). */
    ares_free_data(*reply_list);

    /* And now put our own new_list in place. */
    *reply_list = new_list;

    return EOK;
}

/*******************************************************************
 * Get SRV record                                                  *
 *******************************************************************/

struct getsrv_state {
    struct tevent_context *ev;
    struct resolv_ctx *resolv_ctx;
    /* the SRV query - for example _ldap._tcp.example.com */
    const char *query;

    /* parsed data returned by ares */
    struct ares_srv_reply *reply_list;
    uint32_t ttl;
    int status;
    int timeouts;
    int retrying;
};

static void
ares_getsrv_wakeup(struct tevent_req *subreq);
static void
resolv_getsrv_query(struct tevent_req *req,
                    struct getsrv_state *state);

struct tevent_req *
resolv_getsrv_send(TALLOC_CTX *mem_ctx, struct tevent_context *ev,
                   struct resolv_ctx *ctx, const char *query)
{
    struct tevent_req *req, *subreq;
    struct getsrv_state *state;
    struct timeval tv = { 0, 0 };

    DEBUG(SSSDBG_CONF_SETTINGS,
          "Trying to resolve SRV record of '%s'\n", query);

    if (ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Invalid ares channel - this is likely a bug\n");
        return NULL;
    }

    req = tevent_req_create(mem_ctx, &state, struct getsrv_state);
    if (req == NULL)
        return NULL;

    state->resolv_ctx = ctx;
    state->query = query;
    state->reply_list = NULL;
    state->ttl = 0;
    state->status = 0;
    state->timeouts = 0;
    state->retrying = 0;
    state->ev = ev;

    subreq = tevent_wakeup_send(req, ev, tv);
    if (subreq == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Failed to add critical timer to run next operation!\n");
        talloc_zfree(req);
        return NULL;
    }
    tevent_req_set_callback(subreq, ares_getsrv_wakeup, req);

    return req;
}

/*
 * Implemented based on http://tools.ietf.org/html/rfc2181#section-5
 *
 * Especially:
 * 5.2. TTLs of RRs in an RRSet
 *  Consequently the use of differing TTLs in an RRSet is hereby
 *  deprecated, the TTLs of all RRs in an RRSet must be the same.
 *  ...
 *  Should an authoritative source send such a malformed RRSet, the
 *  client should treat the RRs for all purposes as if all TTLs in the
 *  RRSet had been set to the value of the lowest TTL in the RRSet.
 *
 *  On success, returns true and sets the TTL in the _ttl parameter. On
 *  failure, returns false and _ttl is undefined.
 */
static bool
resolv_get_ttl(const unsigned char *abuf, const int alen, uint32_t *_ttl)
{
    const unsigned char *aptr;
    int ret;
    char *name = NULL;
    long len;
    uint32_t ttl = 0;
    uint32_t rr_ttl;
    unsigned int rr_len;
    unsigned int ancount;
    unsigned int i;

    /* Read the number of RRs and then skip past the header */
    if (alen < NS_HFIXEDSZ) {
        return false;
    }

    ancount = DNS_HEADER_ANCOUNT(abuf);
    if (ancount == 0) {
        return false;
    }

    aptr = abuf + NS_HFIXEDSZ;

    /* We only care about len from the question data,
     * so that we can move past hostname */
    ret = ares_expand_name(aptr, abuf, alen, &name, &len);
    ares_free_string(name);
    if (ret != ARES_SUCCESS) {
        return false;
    }

    /* Skip past the question */
    aptr += len + NS_QFIXEDSZ;
    if (aptr > abuf + alen) {
        return false;
    }

    /* Examine each RR in turn and read the lowest TTL */
    for (i = 0; i < ancount; i++) {
        /* Decode the RR up to the data field. */
        ret = ares_expand_name(aptr, abuf, alen, &name, &len);
        ares_free_string(name);
        if (ret != ARES_SUCCESS) {
            return false;
        }

        aptr += len;
        if (aptr + NS_RRFIXEDSZ > abuf + alen) {
            return false;
        }

        rr_len = DNS_RR_LEN(aptr);
        rr_ttl = DNS_RR_TTL(aptr);
        if (aptr + rr_len > abuf + alen) {
            return false;
        }
        aptr += NS_RRFIXEDSZ + rr_len;

        if (ttl > 0) {
            ttl = MIN(ttl, rr_ttl);
        } else {
            ttl = rr_ttl; /* special-case for first TTL */
        }
    }

    *_ttl = ttl;
    return true;
}

static void
resolv_getsrv_done(void *arg, int status, int timeouts, unsigned char *abuf, int alen)
{
    struct resolv_request *rreq = talloc_get_type(arg, struct resolv_request);
    struct tevent_req *req;
    struct getsrv_state *state;
    int ret;
    bool ok;
    struct ares_srv_reply *reply_list;

    if (rreq->rwatch == NULL) {
        /* The tevent request was cancelled while the ares call was still in
         * progress so nobody cares about the result now. Quit. */
        unschedule_timeout_watcher(rreq->ctx, rreq);
        return;
    }

    req = rreq->rwatch->req;
    unschedule_timeout_watcher(rreq->ctx, rreq);
    state = tevent_req_data(req, struct getsrv_state);

    if (state->retrying == 0 && status == ARES_EDESTRUCTION
        && state->resolv_ctx->channel != NULL) {
        state->retrying = 1;
        resolv_getsrv_query(req, state);
        return;
    }

    state->status = status;
    state->timeouts = timeouts;

    if (status != ARES_SUCCESS) {
        ret = return_code(status);
        goto fail;
    }

    ret = ares_parse_srv_reply(abuf, alen, &reply_list);
    if (ret != ARES_SUCCESS) {
        DEBUG(SSSDBG_OP_FAILURE,
              "SRV record parsing failed: %d: %s\n", ret, ares_strerror(ret));
        ret = return_code(ret);
        goto fail;
    }
    ret = rewrite_talloc_srv_reply(req, &reply_list);
    if (ret != EOK) {
        goto fail;
    }
    state->reply_list = reply_list;
    ok = resolv_get_ttl(abuf, alen, &state->ttl);
    if (ok == false) {
        DEBUG(SSSDBG_MINOR_FAILURE, "Could not read TTL, using the default..\n");
        state->ttl = RESOLV_DEFAULT_SRV_TTL;
    }
    DEBUG(SSSDBG_TRACE_LIBS, "Using TTL [%"PRIu32"]\n", state->ttl);

    tevent_req_done(req);
    return;

fail:
    state->reply_list = NULL;
    tevent_req_error(req, ret);
}

int
resolv_getsrv_recv(TALLOC_CTX *mem_ctx, struct tevent_req *req, int *status,
                   int *timeouts, struct ares_srv_reply **reply_list,
                   uint32_t *ttl)
{
    struct getsrv_state *state = tevent_req_data(req, struct getsrv_state);

    if (status)
        *status = state->status;
    if (timeouts)
        *timeouts = state->timeouts;
    if (reply_list)
        *reply_list = talloc_steal(mem_ctx, state->reply_list);
    if (ttl) {
        *ttl = state->ttl;
    }

    TEVENT_REQ_RETURN_ON_ERROR(req);

    return EOK;
}

static void
ares_getsrv_wakeup(struct tevent_req *subreq)
{
    struct tevent_req *req = tevent_req_callback_data(subreq,
                                                struct tevent_req);
    struct getsrv_state *state = tevent_req_data(req,
                                                struct getsrv_state);

    if (!tevent_wakeup_recv(subreq)) {
        return;
    }
    talloc_zfree(subreq);

    if (state->resolv_ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Invalid ares channel - this is likely a bug\n");
        tevent_req_error(req, EIO);
        return;
    }

    return resolv_getsrv_query(req, state);
}

static void
resolv_getsrv_query(struct tevent_req *req,
                    struct getsrv_state *state)
{
    struct resolv_request *rreq;

    rreq = schedule_timeout_watcher(state->ev, state->resolv_ctx, req);
    if (!rreq) {
        tevent_req_error(req, ENOMEM);
        return;
    }

    ares_query(state->resolv_ctx->channel, state->query,
               ns_c_in, ns_t_srv, resolv_getsrv_done, rreq);
}

/* TXT parsing is not used anywhere in the code yet, so we disable it
 * for now
 */
#ifdef BUILD_TXT

/*
 * A simple helper function that will take an array of struct txt_reply that
 * was allocated by malloc() in c-ares and copies it using talloc. The old one
 * is freed and the talloc one is put into 'reply_list' instead.
 */
static int
rewrite_talloc_txt_reply(TALLOC_CTX *mem_ctx, struct ares_txt_reply **reply_list)
{
    struct ares_txt_reply *ptr = NULL;
    struct ares_txt_reply *new_list = NULL;
    struct ares_txt_reply *old_list = *reply_list;

    /* Nothing to do, but not an error */
    if (!old_list) {
        return EOK;
    }

    /* Copy the linked list */
    while (old_list) {

        /* Special case for the first node */
        if (!new_list) {
            new_list = talloc_zero(mem_ctx, struct ares_txt_reply);
            if (new_list == NULL) {
                ares_free_data(*reply_list);
                talloc_free(new_list);
                return ENOMEM;
            }
            ptr = new_list;
        } else {
            ptr->next = talloc_zero(new_list, struct ares_txt_reply);
            if (ptr->next == NULL) {
                ares_free_data(*reply_list);
                talloc_free(new_list);
                return ENOMEM;
            }
            ptr = ptr->next;
        }

        ptr->length = old_list->length;
        ptr->txt = talloc_memdup(ptr, old_list->txt,
                                 old_list->length);
        if (ptr->txt == NULL) {
            ares_free_data(*reply_list);
            talloc_free(new_list);
            return ENOMEM;
        }

        old_list = old_list->next;
    }

    ares_free_data(*reply_list);

    /* And now put our own new_list in place. */
    *reply_list = new_list;

    return EOK;
}

/*******************************************************************
 * Get TXT record                                                  *
 *******************************************************************/

struct gettxt_state {
    struct tevent_context *ev;
    struct resolv_ctx *resolv_ctx;
    /* the TXT query */
    const char *query;

    /* parsed data returned by ares */
    struct ares_txt_reply *reply_list;
    int status;
    int timeouts;
    int retrying;
};

static void
ares_gettxt_wakeup(struct tevent_req *subreq);
static void
resolv_gettxt_query(struct tevent_req *req,
                    struct gettxt_state *state);

struct tevent_req *
resolv_gettxt_send(TALLOC_CTX *mem_ctx, struct tevent_context *ev,
                          struct resolv_ctx *ctx, const char *query)
{
    struct tevent_req *req, *subreq;
    struct gettxt_state *state;
    struct timeval tv = { 0, 0 };

    DEBUG(SSSDBG_CONF_SETTINGS,
          "Trying to resolve TXT record of '%s'\n", query);

    if (ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Invalid ares channel - this is likely a bug\n");
        return NULL;
    }

    req = tevent_req_create(mem_ctx, &state, struct gettxt_state);
    if (req == NULL)
        return NULL;

    state->resolv_ctx = ctx;
    state->query = query;
    state->reply_list = NULL;
    state->status = 0;
    state->timeouts = 0;
    state->retrying = 0;
    state->ev = ev;

    subreq = tevent_wakeup_send(req, ev, tv);
    if (subreq == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Failed to add critical timer to run next operation!\n");
        talloc_zfree(req);
        return NULL;
    }
    tevent_req_set_callback(subreq, ares_gettxt_wakeup, req);

    return req;
}

static void
resolv_gettxt_done(void *arg, int status, int timeouts, unsigned char *abuf, int alen)
{
    struct resolv_request *rreq = talloc_get_type(arg, struct resolv_request);
    struct tevent_req *req;
    struct gettxt_state *state;
    int ret;
    struct ares_txt_reply *reply_list;

    if (rreq->rwatch == NULL) {
        /* The tevent request was cancelled while the ares call was still in
         * progress so nobody cares about the result now. Quit. */
        unschedule_timeout_watcher(rreq->ctx, rreq);
        return;
    }

    req = rreq->rwatch->req;
    unschedule_timeout_watcher(rreq->ctx, rreq);
    state = tevent_req_data(req, struct gettxt_state);

    if (state->retrying == 0 && status == ARES_EDESTRUCTION
            && state->resolv_ctx->channel != NULL) {
        state->retrying = 1;
        ares_query(state->resolv_ctx->channel, state->query,
                   ns_c_in, ns_t_txt, resolv_gettxt_done, req);
        return;
    }

    state->status = status;
    state->timeouts = timeouts;

    if (status != ARES_SUCCESS) {
        ret = return_code(status);
        goto fail;
    }

    ret = ares_parse_txt_reply(abuf, alen, &reply_list);
    if (status != ARES_SUCCESS) {
        DEBUG(SSSDBG_OP_FAILURE,
              "TXT record parsing failed: %d: %s\n", ret, ares_strerror(ret));
        ret = return_code(ret);
        goto fail;
    }
    ret = rewrite_talloc_txt_reply(req, &reply_list);
    if (ret != EOK) {
        goto fail;
    }
    state->reply_list = reply_list;

    tevent_req_done(req);
    return;

fail:
    state->reply_list = NULL;
    tevent_req_error(req, ret);
}

int
resolv_gettxt_recv(TALLOC_CTX *mem_ctx, struct tevent_req *req, int *status,
                   int *timeouts, struct ares_txt_reply **reply_list)
{
    struct gettxt_state *state = tevent_req_data(req, struct gettxt_state);

    if (status)
        *status = state->status;
    if (timeouts)
        *timeouts = state->timeouts;
    if (reply_list)
        *reply_list = talloc_steal(mem_ctx, state->reply_list);

    TEVENT_REQ_RETURN_ON_ERROR(req);

    return EOK;
}

static void
ares_gettxt_wakeup(struct tevent_req *subreq)
{
    struct tevent_req *req = tevent_req_callback_data(subreq,
                                            struct tevent_req);
    struct gettxt_state *state = tevent_req_data(req,
                                            struct gettxt_state);

    if (!tevent_wakeup_recv(subreq)) {
        return;
    }
    talloc_zfree(subreq);

    if (state->resolv_ctx->channel == NULL) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "Invalid ares channel - this is likely a bug\n");
        tevent_req_error(req, EIO);
        return;
    }

    return resolv_gettxt_query(req, state);
}

static void
resolv_gettxt_query(struct tevent_req *req,
                    struct gettxt_state *state)
{
    struct resolv_request *rreq;

    rreq = schedule_timeout_watcher(state->ev, state->resolv_ctx, req);
    if (!rreq) {
        tevent_req_error(req, ENOMEM);
        return;
    }

    ares_query(state->resolv_ctx->channel, state->query,
               ns_c_in, ns_t_txt, resolv_gettxt_done, rreq);
}

#endif

static struct ares_srv_reply *split_reply_list(struct ares_srv_reply *list)
{
    struct ares_srv_reply *single_step, *double_step, *prev;

    if (!list) {
        return NULL;
    }

    prev        = list;
    single_step = list->next;
    double_step = single_step->next;

    while (double_step && double_step->next) {
        prev = single_step;
        single_step = single_step->next;
        double_step = double_step->next->next;
    }

    prev->next = NULL;
    return single_step;
}

static struct ares_srv_reply *merge_reply_list(struct ares_srv_reply *left,
                                               struct ares_srv_reply *right)
{
    struct ares_srv_reply *l, *r;
    struct ares_srv_reply *res, *res_start;

    if (!left)
        return right;
    if (!right)
        return left;

    if (left->priority < right->priority) {
        res_start = left;
        l = left->next;
        r = right;
    } else {
        res_start = right;
        l = left;
        r = right->next;
    }

    res = res_start;

    while(l && r) {
        if (l->priority < r->priority) {
            res->next = l;
            res = l;
            l = l->next;
        } else {
            res->next = r;
            res = r;
            r = r->next;
        }
    }

    res->next = l ? l : r;

    return res_start;
}

/**
 * sort linked list of struct ares_srv_reply by priority using merge sort.
 *
 * Merge sort is ideal for sorting linked lists as there is no problem
 * with absence of random access into the list. The complexity is O(n log n)
 *
 * For reference, see Robert Sedgewick's "Algorithms in C", Addison-Wesley,
 * ISBN 0-201-51425
 */
static struct ares_srv_reply *reply_priority_sort(struct ares_srv_reply *list)
{
    struct ares_srv_reply *half;

    if (!list || !list->next)
        return list;

    half = split_reply_list(list);
    list = merge_reply_list(reply_priority_sort(list),
                            reply_priority_sort(half));

    return list;
}

static int reply_weight_rearrange(int len,
                                  struct ares_srv_reply **start,
                                  struct ares_srv_reply **end)
{
    int i;
    int total, selected;
    int *totals;
    struct ares_srv_reply *r, *prev, *tmp;
    struct ares_srv_reply *new_start = NULL;
    struct ares_srv_reply *new_end = NULL;
    int ret;

    if (len <= 1) {
        return EOK;
    }

    totals = talloc_array(NULL, int, len);
    if (!totals) {
        return ENOMEM;
    }

    srand(time(NULL) * getpid());

    /* promote all servers with weight==0 to the top */
    r = *(start);
    prev = NULL;
    while (r != NULL) {
        if (r->weight == 0 && r != *start) {
            /* remove from the old list */
            prev->next = r->next;

            /* add to the head of the new list */
            tmp = r;
            r = r->next;

            tmp->next = *start;
            *start = tmp;
        } else {
            prev = r;
            r = r->next;
        }
    }
    *end = prev ? prev : *start;

    while (*start != NULL) {
        /* Commpute the sum of the weights of those RRs, and with each RR
         * associate the running sum in the selected order.
         */
        total = 0;
        memset(totals, -1, sizeof(int) * len);
        for (i = 0, r = *start; r != NULL; r=r->next, ++i) {
            totals[i] = r->weight + total;
            total = totals[i];
        }

        /* choose a  uniform random number between 0 and the sum computed
         * (inclusive), and select the RR whose running sum value is the
         * first in the selected order which is greater than or equal to
         * the random number selected.
         */
        selected = (int)((total + 1) * (rand()/(RAND_MAX + 1.0)));
        for (i = 0, r = *start, prev = NULL; r != NULL; r=r->next, ++i) {
            if (totals[i] >= selected)
                break;

            prev = r;
        }

        if (r == NULL || totals[i] == -1) {
            DEBUG(SSSDBG_CRIT_FAILURE, "Bug: did not select any server!\n");
            ret = EIO;
            goto done;
        }

        /* remove r from the old list */
        if (prev) {
            prev->next = r->next;
        } else {
            *start = r->next;
        }

        /* add r to the end of the new list */
        if (!new_start) {
            new_start = r;
            new_end = r;
        } else {
            new_end->next = r;
            new_end = r;
        }
    }
    new_end->next = NULL;

    /* return the rearranged list */
    *start = new_start;
    *end = new_end;
    ret = EOK;

done:
    talloc_free(totals);
    return ret;
}

int
resolv_sort_srv_reply(struct ares_srv_reply **reply)
{
    int ret;
    struct ares_srv_reply *pri_start, *pri_end, *next, *prev_end;
    int len;

    /* RFC 2782 says: If there is precisely one SRV RR, and its Target is "."
     * (the root domain), abort.
     */
    if (*reply && !(*reply)->next && strcmp((*reply)->host, ".") == 0) {
        DEBUG(SSSDBG_CRIT_FAILURE,
              "DNS returned only the root domain, aborting\n");
        return EIO;
    }

    /* sort the list by priority */
    *reply = reply_priority_sort(*reply);

    pri_start = *reply;
    prev_end  = NULL;

    while (pri_start) {
        pri_end = pri_start;

        /* Find nodes with the same priority */
        len = 1;
        while (pri_end->next && pri_end->priority == pri_end->next->priority) {
            pri_end = pri_end->next;
            len++;
        }

        /* rearrange each priority level according to the weight field */
        next = pri_end->next;
        pri_end->next = NULL;
        ret = reply_weight_rearrange(len, &pri_start, &pri_end);
        if (ret) {
            DEBUG(SSSDBG_CRIT_FAILURE,
                  "Error rearranging priority level [%d]: %s\n",
                      ret, strerror(ret));
            return ret;
        }

        /* Hook the level back into the list */
        if (prev_end) {
            prev_end->next = pri_start;
        } else {
            *reply = pri_start;
        }
        pri_end->next = next;

        /* Move on to the next level */
        prev_end  = pri_end;
        pri_start = next;
    }

    return EOK;
}