sd-dns: initial commit

Origin: <http://0pointer.de/lennart/projects/libasyncns/>

[tomegun: renamed some more files asyncns -> sd-dns and moved to libsystemd-bus as
requested by Lennart]

4 files changed, 1486 insertions, 0 deletions

diff --git a/src/libsystemd-bus/dns-util.h b/src/libsystemd-bus/dns-util.h
new file mode 100644
index 0000000000..31d19bd95a
--- /dev/null
+++ b/src/libsystemd-bus/dns-util.h
@@ -0,0 +1,8 @@
+#pragma once
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(asyncns_t*, asyncns_free);
+DEFINE_TRIVIAL_CLEANUP_FUNC(unsigned char *, asyncns_freeanswer);
+DEFINE_TRIVIAL_CLEANUP_FUNC(struct addrinfo*, asyncns_freeaddrinfo);
+#define _cleanup_asyncns_free_ _cleanup_(asyncns_freep)
+#define _cleanup_asyncns_answer_free_ _cleanup_(asyncns_freeanswerp)
+#define _cleanup_asyncns_addrinfo_free_ _cleanup_(asyncns_freeaddrinfop)
diff --git a/src/libsystemd-bus/sd-dns.c b/src/libsystemd-bus/sd-dns.c
new file mode 100644
index 0000000000..508f6b0945
--- /dev/null
+++ b/src/libsystemd-bus/sd-dns.c
@@ -0,0 +1,1158 @@
+/***
+  This file is part of libasyncns.
+
+  Copyright 2005-2008 Lennart Poettering
+
+  libasyncns 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.
+
+  libasyncns 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 libasyncns. If not, see
+  <http://www.gnu.org/licenses/>.
+ ***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <assert.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/select.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/wait.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <netinet/in.h>
+#include <arpa/nameser.h>
+#include <resolv.h>
+#include <dirent.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <stdint.h>
+#include <pthread.h>
+
+#ifdef HAVE_SYS_PRCTL_H
+#include <sys/prctl.h>
+#endif
+
+#include "sd-dns.h"
+#include "util.h"
+
+#define MAX_WORKERS 16
+#define MAX_QUERIES 256
+#define BUFSIZE (10240)
+
+typedef enum {
+        REQUEST_ADDRINFO,
+        RESPONSE_ADDRINFO,
+        REQUEST_NAMEINFO,
+        RESPONSE_NAMEINFO,
+        REQUEST_RES_QUERY,
+        REQUEST_RES_SEARCH,
+        RESPONSE_RES,
+        REQUEST_TERMINATE,
+        RESPONSE_DIED
+} query_type_t;
+
+enum {
+        REQUEST_RECV_FD = 0,
+        REQUEST_SEND_FD = 1,
+        RESPONSE_RECV_FD = 2,
+        RESPONSE_SEND_FD = 3,
+        MESSAGE_FD_MAX = 4
+};
+
+struct asyncns {
+        int fds[MESSAGE_FD_MAX];
+
+        pthread_t workers[MAX_WORKERS];
+        unsigned valid_workers;
+
+        unsigned current_id, current_index;
+        asyncns_query_t* queries[MAX_QUERIES];
+
+        asyncns_query_t *done_head, *done_tail;
+
+        int n_queries;
+        int dead;
+};
+
+struct asyncns_query {
+        asyncns_t *asyncns;
+        int done;
+        unsigned id;
+        query_type_t type;
+        asyncns_query_t *done_next, *done_prev;
+        int ret;
+        int _errno;
+        int _h_errno;
+        struct addrinfo *addrinfo;
+        char *serv, *host;
+        void *userdata;
+};
+
+typedef struct rheader {
+        query_type_t type;
+        unsigned id;
+        size_t length;
+} rheader_t;
+
+typedef struct addrinfo_request {
+        struct rheader header;
+        int hints_is_null;
+        int ai_flags;
+        int ai_family;
+        int ai_socktype;
+        int ai_protocol;
+        size_t node_len, service_len;
+} addrinfo_request_t;
+
+typedef struct addrinfo_response {
+        struct rheader header;
+        int ret;
+        int _errno;
+        int _h_errno;
+        /* followed by addrinfo_serialization[] */
+} addrinfo_response_t;
+
+typedef struct addrinfo_serialization {
+        int ai_flags;
+        int ai_family;
+        int ai_socktype;
+        int ai_protocol;
+        size_t ai_addrlen;
+        size_t canonname_len;
+        /* Followed by ai_addr amd ai_canonname with variable lengths */
+} addrinfo_serialization_t;
+
+typedef struct nameinfo_request {
+        struct rheader header;
+        int flags;
+        socklen_t sockaddr_len;
+        int gethost, getserv;
+} nameinfo_request_t;
+
+typedef struct nameinfo_response {
+        struct rheader header;
+        size_t hostlen, servlen;
+        int ret;
+        int _errno;
+        int _h_errno;
+} nameinfo_response_t;
+
+typedef struct res_request {
+        struct rheader header;
+        int class;
+        int type;
+        size_t dname_len;
+} res_request_t;
+
+typedef struct res_response {
+        struct rheader header;
+        int ret;
+        int _errno;
+        int _h_errno;
+} res_response_t;
+
+typedef union packet {
+        rheader_t rheader;
+        addrinfo_request_t addrinfo_request;
+        addrinfo_response_t addrinfo_response;
+        nameinfo_request_t nameinfo_request;
+        nameinfo_response_t nameinfo_response;
+        res_request_t res_request;
+        res_response_t res_response;
+} packet_t;
+
+static int send_died(int out_fd) {
+        rheader_t rh = {};
+        assert(out_fd > 0);
+
+        rh.type = RESPONSE_DIED;
+        rh.id = 0;
+        rh.length = sizeof(rh);
+
+        return send(out_fd, &rh, rh.length, MSG_NOSIGNAL);
+}
+
+static void *serialize_addrinfo(void *p, const struct addrinfo *ai, size_t *length, size_t maxlength) {
+        addrinfo_serialization_t s;
+        size_t cnl, l;
+        assert(p);
+        assert(ai);
+        assert(length);
+        assert(*length <= maxlength);
+
+        cnl = (ai->ai_canonname ? strlen(ai->ai_canonname)+1 : 0);
+        l = sizeof(addrinfo_serialization_t) + ai->ai_addrlen + cnl;
+
+        if (*length + l > maxlength)
+                return NULL;
+
+        s.ai_flags = ai->ai_flags;
+        s.ai_family = ai->ai_family;
+        s.ai_socktype = ai->ai_socktype;
+        s.ai_protocol = ai->ai_protocol;
+        s.ai_addrlen = ai->ai_addrlen;
+        s.canonname_len = cnl;
+
+        memcpy((uint8_t*) p, &s, sizeof(addrinfo_serialization_t));
+        memcpy((uint8_t*) p + sizeof(addrinfo_serialization_t), ai->ai_addr, ai->ai_addrlen);
+
+        if (ai->ai_canonname)
+                strcpy((char*) p + sizeof(addrinfo_serialization_t) + ai->ai_addrlen, ai->ai_canonname);
+
+        *length += l;
+        return (uint8_t*) p + l;
+}
+
+static int send_addrinfo_reply(int out_fd, unsigned id, int ret, struct addrinfo *ai, int _errno, int _h_errno) {
+        addrinfo_response_t data[BUFSIZE/sizeof(addrinfo_response_t) + 1] = {};
+        addrinfo_response_t *resp = data;
+        assert(out_fd >= 0);
+
+        resp->header.type = RESPONSE_ADDRINFO;
+        resp->header.id = id;
+        resp->header.length = sizeof(addrinfo_response_t);
+        resp->ret = ret;
+        resp->_errno = _errno;
+        resp->_h_errno = _h_errno;
+
+        if (ret == 0 && ai) {
+                void *p = data + 1;
+                struct addrinfo *k;
+
+                for (k = ai; k; k = k->ai_next) {
+                        if (!(p = serialize_addrinfo(p, k, &resp->header.length, (char*) data + BUFSIZE - (char*) p))) {
+                                resp->ret = EAI_MEMORY;
+                                break;
+                        }
+                }
+        }
+
+        if (ai)
+                freeaddrinfo(ai);
+
+        return send(out_fd, resp, resp->header.length, MSG_NOSIGNAL);
+}
+
+static int send_nameinfo_reply(int out_fd, unsigned id, int ret, const char *host, const char *serv, int _errno, int _h_errno) {
+        nameinfo_response_t data[BUFSIZE/sizeof(nameinfo_response_t) + 1] = {};
+        size_t hl, sl;
+        nameinfo_response_t *resp = data;
+
+        assert(out_fd >= 0);
+
+        sl = serv ? strlen(serv)+1 : 0;
+        hl = host ? strlen(host)+1 : 0;
+
+        resp->header.type = RESPONSE_NAMEINFO;
+        resp->header.id = id;
+        resp->header.length = sizeof(nameinfo_response_t) + hl + sl;
+        resp->ret = ret;
+        resp->_errno = _errno;
+        resp->_h_errno = _h_errno;
+        resp->hostlen = hl;
+        resp->servlen = sl;
+
+        assert(sizeof(data) >= resp->header.length);
+
+        if (host)
+                memcpy((uint8_t *)data + sizeof(nameinfo_response_t), host, hl);
+
+        if (serv)
+                memcpy((uint8_t *)data + sizeof(nameinfo_response_t) + hl, serv, sl);
+
+        return send(out_fd, resp, resp->header.length, MSG_NOSIGNAL);
+}
+
+static int send_res_reply(int out_fd, unsigned id, const unsigned char *answer, int ret, int _errno, int _h_errno) {
+        res_response_t data[BUFSIZE/sizeof(res_response_t) + 1] = {};
+        res_response_t *resp = data;
+
+        assert(out_fd >= 0);
+
+        resp->header.type = RESPONSE_RES;
+        resp->header.id = id;
+        resp->header.length = sizeof(res_response_t) + (ret < 0 ? 0 : ret);
+        resp->ret = ret;
+        resp->_errno = _errno;
+        resp->_h_errno = _h_errno;
+
+        assert(sizeof(data) >= resp->header.length);
+
+        if (ret > 0)
+                memcpy((uint8_t *)data + sizeof(res_response_t), answer, ret);
+
+        return send(out_fd, resp, resp->header.length, MSG_NOSIGNAL);
+}
+
+static int handle_request(int out_fd, const packet_t *packet, size_t length) {
+        const rheader_t *req;
+        assert(out_fd >= 0);
+
+        req = &packet->rheader;
+        assert(req);
+        assert(length >= sizeof(rheader_t));
+        assert(length == req->length);
+
+        switch (req->type) {
+        case REQUEST_ADDRINFO: {
+               struct addrinfo ai = {}, *result = NULL;
+               const addrinfo_request_t *ai_req = &packet->addrinfo_request;
+               const char *node, *service;
+               int ret;
+
+               assert(length >= sizeof(addrinfo_request_t));
+               assert(length == sizeof(addrinfo_request_t) + ai_req->node_len + ai_req->service_len);
+
+               ai.ai_flags = ai_req->ai_flags;
+               ai.ai_family = ai_req->ai_family;
+               ai.ai_socktype = ai_req->ai_socktype;
+               ai.ai_protocol = ai_req->ai_protocol;
+
+               node = ai_req->node_len ? (const char*) ai_req + sizeof(addrinfo_request_t) : NULL;
+               service = ai_req->service_len ? (const char*) ai_req + sizeof(addrinfo_request_t) + ai_req->node_len : NULL;
+
+               ret = getaddrinfo(node, service,
+                               ai_req->hints_is_null ? NULL : &ai,
+                               &result);
+
+               /* send_addrinfo_reply() frees result */
+               return send_addrinfo_reply(out_fd, req->id, ret, result, errno, h_errno);
+        }
+
+        case REQUEST_NAMEINFO: {
+               int ret;
+               const nameinfo_request_t *ni_req = &packet->nameinfo_request;
+               char hostbuf[NI_MAXHOST], servbuf[NI_MAXSERV];
+               struct sockaddr_storage sa;
+
+               assert(length >= sizeof(nameinfo_request_t));
+               assert(length == sizeof(nameinfo_request_t) + ni_req->sockaddr_len);
+
+               memcpy(&sa, (const uint8_t *) ni_req + sizeof(nameinfo_request_t), ni_req->sockaddr_len);
+
+               ret = getnameinfo((struct sockaddr *)&sa, ni_req->sockaddr_len,
+                               ni_req->gethost ? hostbuf : NULL, ni_req->gethost ? sizeof(hostbuf) : 0,
+                               ni_req->getserv ? servbuf : NULL, ni_req->getserv ? sizeof(servbuf) : 0,
+                               ni_req->flags);
+
+               return send_nameinfo_reply(out_fd, req->id, ret,
+                               ret == 0 && ni_req->gethost ? hostbuf : NULL,
+                               ret == 0 && ni_req->getserv ? servbuf : NULL,
+                               errno, h_errno);
+        }
+
+        case REQUEST_RES_QUERY:
+        case REQUEST_RES_SEARCH: {
+                 int ret;
+                 HEADER answer[BUFSIZE/sizeof(HEADER) + 1];
+                 const res_request_t *res_req = &packet->res_request;
+                 const char *dname;
+
+                 assert(length >= sizeof(res_request_t));
+                 assert(length == sizeof(res_request_t) + res_req->dname_len);
+
+                 dname = (const char *) req + sizeof(res_request_t);
+
+                 if (req->type == REQUEST_RES_QUERY)
+                         ret = res_query(dname, res_req->class, res_req->type, (unsigned char *) answer, BUFSIZE);
+                 else
+                         ret = res_search(dname, res_req->class, res_req->type, (unsigned char *) answer, BUFSIZE);
+
+                 return send_res_reply(out_fd, req->id, (unsigned char *) answer, ret, errno, h_errno);
+        }
+
+        case REQUEST_TERMINATE:
+                 /* Quit */
+                 return -1;
+
+        default:
+                 ;
+        }
+
+        return 0;
+}
+
+static void* thread_worker(void *p) {
+        asyncns_t *asyncns = p;
+        sigset_t fullset;
+
+        /* No signals in this thread please */
+        sigfillset(&fullset);
+        pthread_sigmask(SIG_BLOCK, &fullset, NULL);
+
+        while (!asyncns->dead) {
+                packet_t buf[BUFSIZE/sizeof(packet_t) + 1];
+                ssize_t length;
+
+                length = recv(asyncns->fds[REQUEST_RECV_FD], buf, sizeof(buf), 0);
+
+                if (length <= 0) {
+                        if (length < 0 && (errno == EAGAIN || errno == EINTR))
+                                continue;
+                        break;
+                }
+
+                if (asyncns->dead)
+                        break;
+
+                if (handle_request(asyncns->fds[RESPONSE_SEND_FD], buf, (size_t) length) < 0)
+                        break;
+        }
+
+        send_died(asyncns->fds[RESPONSE_SEND_FD]);
+
+        return NULL;
+}
+
+asyncns_t* asyncns_new(unsigned n_proc) {
+        int i;
+        asyncns_t *asyncns = NULL;
+
+        assert(n_proc >= 1);
+
+        if (n_proc > MAX_WORKERS)
+                n_proc = MAX_WORKERS;
+
+        asyncns = malloc(sizeof(asyncns_t));
+        if (!asyncns) {
+                errno = ENOMEM;
+                goto fail;
+        }
+
+        asyncns->dead = 0;
+        asyncns->valid_workers = 0;
+
+        for (i = 0; i < MESSAGE_FD_MAX; i++)
+                asyncns->fds[i] = -1;
+
+        memset(asyncns->queries, 0, sizeof(asyncns->queries));
+
+#ifdef SOCK_CLOEXEC
+        if (socketpair(PF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, asyncns->fds) < 0 ||
+                        socketpair(PF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, asyncns->fds+2) < 0) {
+
+                /* Try again, without SOCK_CLOEXEC */
+                if (errno == EINVAL) {
+#endif
+                        if (socketpair(PF_UNIX, SOCK_DGRAM, 0, asyncns->fds) < 0 ||
+                                        socketpair(PF_UNIX, SOCK_DGRAM, 0, asyncns->fds+2) < 0)
+                                goto fail;
+#ifdef SOCK_CLOEXEC
+                } else
+                        goto fail;
+        }
+#endif
+
+        for (i = 0; i < MESSAGE_FD_MAX; i++)
+                fd_cloexec(asyncns->fds[i], true);
+
+        for (asyncns->valid_workers = 0; asyncns->valid_workers < n_proc; asyncns->valid_workers++) {
+                int r;
+
+                if ((r = pthread_create(&asyncns->workers[asyncns->valid_workers], NULL, thread_worker, asyncns)) != 0) {
+                        errno = r;
+                        goto fail;
+                }
+        }
+
+        asyncns->current_index = asyncns->current_id = 0;
+        asyncns->done_head = asyncns->done_tail = NULL;
+        asyncns->n_queries = 0;
+
+        fd_nonblock(asyncns->fds[RESPONSE_RECV_FD], true);
+
+        return asyncns;
+
+fail:
+        if (asyncns)
+                asyncns_free(asyncns);
+
+        return NULL;
+}
+
+void asyncns_free(asyncns_t *asyncns) {
+        int i;
+        int saved_errno = errno;
+        unsigned p;
+
+        assert(asyncns);
+
+        asyncns->dead = 1;
+
+        if (asyncns->fds[REQUEST_SEND_FD] >= 0) {
+                rheader_t req = {};
+
+                req.type = REQUEST_TERMINATE;
+                req.length = sizeof(req);
+                req.id = 0;
+
+                /* Send one termination packet for each worker */
+                for (p = 0; p < asyncns->valid_workers; p++)
+                        send(asyncns->fds[REQUEST_SEND_FD], &req, req.length, MSG_NOSIGNAL);
+        }
+
+        /* Now terminate them and wait until they are gone. */
+        for (p = 0; p < asyncns->valid_workers; p++) {
+                for (;;) {
+                        if (pthread_join(asyncns->workers[p], NULL) != EINTR)
+                                break;
+                }
+        }
+
+        /* Close all communication channels */
+        for (i = 0; i < MESSAGE_FD_MAX; i++)
+                if (asyncns->fds[i] >= 0)
+                        close(asyncns->fds[i]);
+
+        for (p = 0; p < MAX_QUERIES; p++)
+                if (asyncns->queries[p])
+                        asyncns_cancel(asyncns, asyncns->queries[p]);
+
+        free(asyncns);
+
+        errno = saved_errno;
+}
+
+int asyncns_fd(asyncns_t *asyncns) {
+        assert(asyncns);
+
+        return asyncns->fds[RESPONSE_RECV_FD];
+}
+
+static asyncns_query_t *lookup_query(asyncns_t *asyncns, unsigned id) {
+        asyncns_query_t *q;
+        assert(asyncns);
+
+        if ((q = asyncns->queries[id % MAX_QUERIES]))
+                if (q->id == id)
+                        return q;
+
+        return NULL;
+}
+
+static void complete_query(asyncns_t *asyncns, asyncns_query_t *q) {
+        assert(asyncns);
+        assert(q);
+        assert(!q->done);
+
+        q->done = 1;
+
+        if ((q->done_prev = asyncns->done_tail))
+                asyncns->done_tail->done_next = q;
+        else
+                asyncns->done_head = q;
+
+        asyncns->done_tail = q;
+        q->done_next = NULL;
+}
+
+static const void *unserialize_addrinfo(const void *p, struct addrinfo **ret_ai, size_t *length) {
+        addrinfo_serialization_t s;
+        size_t l;
+        struct addrinfo *ai;
+        assert(p);
+        assert(ret_ai);
+        assert(length);
+
+        if (*length < sizeof(addrinfo_serialization_t))
+                return NULL;
+
+        memcpy(&s, p, sizeof(s));
+
+        l = sizeof(addrinfo_serialization_t) + s.ai_addrlen + s.canonname_len;
+        if (*length < l)
+                return NULL;
+
+        if (!(ai = malloc(sizeof(struct addrinfo))))
+                goto fail;
+
+        ai->ai_addr = NULL;
+        ai->ai_canonname = NULL;
+        ai->ai_next = NULL;
+
+        if (s.ai_addrlen && !(ai->ai_addr = malloc(s.ai_addrlen)))
+                goto fail;
+
+        if (s.canonname_len && !(ai->ai_canonname = malloc(s.canonname_len)))
+                goto fail;
+
+        ai->ai_flags = s.ai_flags;
+        ai->ai_family = s.ai_family;
+        ai->ai_socktype = s.ai_socktype;
+        ai->ai_protocol = s.ai_protocol;
+        ai->ai_addrlen = s.ai_addrlen;
+
+        if (ai->ai_addr)
+                memcpy(ai->ai_addr, (const uint8_t*) p + sizeof(addrinfo_serialization_t), s.ai_addrlen);
+
+        if (ai->ai_canonname)
+                memcpy(ai->ai_canonname, (const uint8_t*) p + sizeof(addrinfo_serialization_t) + s.ai_addrlen, s.canonname_len);
+
+        *length -= l;
+        *ret_ai = ai;
+
+        return (const uint8_t*) p + l;
+
+
+fail:
+        if (ai)
+                asyncns_freeaddrinfo(ai);
+
+        return NULL;
+}
+
+static int handle_response(asyncns_t *asyncns, const packet_t *packet, size_t length) {
+        const rheader_t *resp;
+        asyncns_query_t *q;
+
+        assert(asyncns);
+
+        resp = &packet->rheader;
+        assert(resp);
+        assert(length >= sizeof(rheader_t));
+        assert(length == resp->length);
+
+        if (resp->type == RESPONSE_DIED) {
+                asyncns->dead = 1;
+                return 0;
+        }
+
+        if (!(q = lookup_query(asyncns, resp->id)))
+                return 0;
+
+        switch (resp->type) {
+        case RESPONSE_ADDRINFO: {
+                const addrinfo_response_t *ai_resp = &packet->addrinfo_response;
+                const void *p;
+                size_t l;
+                struct addrinfo *prev = NULL;
+
+                assert(length >= sizeof(addrinfo_response_t));
+                assert(q->type == REQUEST_ADDRINFO);
+
+                q->ret = ai_resp->ret;
+                q->_errno = ai_resp->_errno;
+                q->_h_errno = ai_resp->_h_errno;
+                l = length - sizeof(addrinfo_response_t);
+                p = (const uint8_t*) resp + sizeof(addrinfo_response_t);
+
+                while (l > 0 && p) {
+                        struct addrinfo *ai = NULL;
+                        p = unserialize_addrinfo(p, &ai, &l);
+
+                        if (!p || !ai) {
+                                q->ret = EAI_MEMORY;
+                                break;
+                        }
+
+                        if (prev)
+                                prev->ai_next = ai;
+                        else
+                                q->addrinfo = ai;
+
+                        prev = ai;
+                }
+
+                complete_query(asyncns, q);
+                break;
+        }
+
+        case RESPONSE_NAMEINFO: {
+                const nameinfo_response_t *ni_resp = &packet->nameinfo_response;
+
+                assert(length >= sizeof(nameinfo_response_t));
+                assert(q->type == REQUEST_NAMEINFO);
+
+                q->ret = ni_resp->ret;
+                q->_errno = ni_resp->_errno;
+                q->_h_errno = ni_resp->_h_errno;
+
+                if (ni_resp->hostlen)
+                        if (!(q->host = strndup((const char*) ni_resp + sizeof(nameinfo_response_t), ni_resp->hostlen-1)))
+                                q->ret = EAI_MEMORY;
+
+                if (ni_resp->servlen)
+                        if (!(q->serv = strndup((const char*) ni_resp + sizeof(nameinfo_response_t) + ni_resp->hostlen, ni_resp->servlen-1)))
+                                q->ret = EAI_MEMORY;
+
+                complete_query(asyncns, q);
+                break;
+        }
+
+        case RESPONSE_RES: {
+                const res_response_t *res_resp = &packet->res_response;
+
+                assert(length >= sizeof(res_response_t));
+                assert(q->type == REQUEST_RES_QUERY || q->type == REQUEST_RES_SEARCH);
+
+                q->ret = res_resp->ret;
+                q->_errno = res_resp->_errno;
+                q->_h_errno = res_resp->_h_errno;
+
+                if (res_resp->ret >= 0)  {
+                        if (!(q->serv = malloc(res_resp->ret))) {
+                                q->ret = -1;
+                                q->_errno = ENOMEM;
+                        } else
+                                memcpy(q->serv, (const char *)resp + sizeof(res_response_t), res_resp->ret);
+                }
+
+                complete_query(asyncns, q);
+                break;
+        }
+
+        default:
+                ;
+        }
+
+        return 0;
+}
+
+int asyncns_wait(asyncns_t *asyncns, int block) {
+        int handled = 0;
+        assert(asyncns);
+
+        for (;;) {
+                packet_t buf[BUFSIZE/sizeof(packet_t) + 1];
+                ssize_t l;
+
+                if (asyncns->dead) {
+                        errno = ECHILD;
+                        return -1;
+                }
+
+                if (((l = recv(asyncns->fds[RESPONSE_RECV_FD], buf, sizeof(buf), 0)) < 0)) {
+                        fd_set fds;
+
+                        if (errno != EAGAIN)
+                                return -1;
+
+                        if (!block || handled)
+                                return 0;
+
+                        FD_ZERO(&fds);
+                        FD_SET(asyncns->fds[RESPONSE_RECV_FD], &fds);
+
+                        if (select(asyncns->fds[RESPONSE_RECV_FD]+1, &fds, NULL, NULL, NULL) < 0)
+                                return -1;
+
+                        continue;
+                }
+
+                if (handle_response(asyncns, buf, (size_t) l) < 0)
+                        return -1;
+
+                handled = 1;
+        }
+}
+
+static asyncns_query_t *alloc_query(asyncns_t *asyncns) {
+        asyncns_query_t *q;
+        assert(asyncns);
+
+        if (asyncns->n_queries >= MAX_QUERIES) {
+                errno = ENOMEM;
+                return NULL;
+        }
+
+        while (asyncns->queries[asyncns->current_index]) {
+
+                asyncns->current_index++;
+                asyncns->current_id++;
+
+                while (asyncns->current_index >= MAX_QUERIES)
+                        asyncns->current_index -= MAX_QUERIES;
+        }
+
+        if (!(q = asyncns->queries[asyncns->current_index] = malloc(sizeof(asyncns_query_t)))) {
+                errno = ENOMEM;
+                return NULL;
+        }
+
+        asyncns->n_queries++;
+
+        q->asyncns = asyncns;
+        q->done = 0;
+        q->id = asyncns->current_id;
+        q->done_next = q->done_prev = NULL;
+        q->ret = 0;
+        q->_errno = 0;
+        q->_h_errno = 0;
+        q->addrinfo = NULL;
+        q->userdata = NULL;
+        q->host = q->serv = NULL;
+
+        return q;
+}
+
+asyncns_query_t* asyncns_getaddrinfo(asyncns_t *asyncns, const char *node, const char *service, const struct addrinfo *hints) {
+        addrinfo_request_t data[BUFSIZE/sizeof(addrinfo_request_t) + 1] = {};
+        addrinfo_request_t *req = data;
+        asyncns_query_t *q;
+        assert(asyncns);
+        assert(node || service);
+
+        if (asyncns->dead) {
+                errno = ECHILD;
+                return NULL;
+        }
+
+        if (!(q = alloc_query(asyncns)))
+                return NULL;
+
+
+        req->node_len = node ? strlen(node)+1 : 0;
+        req->service_len = service ? strlen(service)+1 : 0;
+
+        req->header.id = q->id;
+        req->header.type = q->type = REQUEST_ADDRINFO;
+        req->header.length = sizeof(addrinfo_request_t) + req->node_len + req->service_len;
+
+        if (req->header.length > BUFSIZE) {
+                errno = ENOMEM;
+                goto fail;
+        }
+
+        if (!(req->hints_is_null = !hints)) {
+                req->ai_flags = hints->ai_flags;
+                req->ai_family = hints->ai_family;
+                req->ai_socktype = hints->ai_socktype;
+                req->ai_protocol = hints->ai_protocol;
+        }
+
+        if (node)
+                strcpy((char*) req + sizeof(addrinfo_request_t), node);
+
+        if (service)
+                strcpy((char*) req + sizeof(addrinfo_request_t) + req->node_len, service);
+
+        if (send(asyncns->fds[REQUEST_SEND_FD], req, req->header.length, MSG_NOSIGNAL) < 0)
+                goto fail;
+
+        return q;
+
+fail:
+        if (q)
+                asyncns_cancel(asyncns, q);
+
+        return NULL;
+}
+
+int asyncns_getaddrinfo_done(asyncns_t *asyncns, asyncns_query_t* q, struct addrinfo **ret_res) {
+        int ret;
+        assert(asyncns);
+        assert(q);
+        assert(q->asyncns == asyncns);
+        assert(q->type == REQUEST_ADDRINFO);
+
+        if (asyncns->dead) {
+                errno = ECHILD;
+                return EAI_SYSTEM;
+        }
+
+        if (!q->done)
+                return EAI_AGAIN;
+
+        *ret_res = q->addrinfo;
+        q->addrinfo = NULL;
+
+        ret = q->ret;
+
+        if (ret == EAI_SYSTEM)
+                errno = q->_errno;
+
+        if (ret != 0)
+                h_errno = q->_h_errno;
+
+        asyncns_cancel(asyncns, q);
+
+        return ret;
+}
+
+asyncns_query_t* asyncns_getnameinfo(asyncns_t *asyncns, const struct sockaddr *sa, socklen_t salen, int flags, int gethost, int getserv) {
+        nameinfo_request_t data[BUFSIZE/sizeof(nameinfo_request_t) + 1] = {};
+        nameinfo_request_t *req = data;
+        asyncns_query_t *q;
+
+        assert(asyncns);
+        assert(sa);
+        assert(salen > 0);
+
+        if (asyncns->dead) {
+                errno = ECHILD;
+                return NULL;
+        }
+
+        if (!(q = alloc_query(asyncns)))
+                return NULL;
+
+
+        req->header.id = q->id;
+        req->header.type = q->type = REQUEST_NAMEINFO;
+        req->header.length = sizeof(nameinfo_request_t) + salen;
+
+        if (req->header.length > BUFSIZE) {
+                errno = ENOMEM;
+                goto fail;
+        }
+
+        req->flags = flags;
+        req->sockaddr_len = salen;
+        req->gethost = gethost;
+        req->getserv = getserv;
+
+        memcpy((uint8_t*) req + sizeof(nameinfo_request_t), sa, salen);
+
+        if (send(asyncns->fds[REQUEST_SEND_FD], req, req->header.length, MSG_NOSIGNAL) < 0)
+                goto fail;
+
+        return q;
+
+fail:
+        if (q)
+                asyncns_cancel(asyncns, q);
+
+        return NULL;
+}
+
+int asyncns_getnameinfo_done(asyncns_t *asyncns, asyncns_query_t* q, char *ret_host, size_t hostlen, char *ret_serv, size_t servlen) {
+        int ret;
+        assert(asyncns);
+        assert(q);
+        assert(q->asyncns == asyncns);
+        assert(q->type == REQUEST_NAMEINFO);
+        assert(!ret_host || hostlen);
+        assert(!ret_serv || servlen);
+
+        if (asyncns->dead) {
+                errno = ECHILD;
+                return EAI_SYSTEM;
+        }
+
+        if (!q->done)
+                return EAI_AGAIN;
+
+        if (ret_host && q->host) {
+                strncpy(ret_host, q->host, hostlen);
+                ret_host[hostlen-1] = 0;
+        }
+
+        if (ret_serv && q->serv) {
+                strncpy(ret_serv, q->serv, servlen);
+                ret_serv[servlen-1] = 0;
+        }
+
+        ret = q->ret;
+
+        if (ret == EAI_SYSTEM)
+                errno = q->_errno;
+
+        if (ret != 0)
+                h_errno = q->_h_errno;
+
+        asyncns_cancel(asyncns, q);
+
+        return ret;
+}
+
+static asyncns_query_t * asyncns_res(asyncns_t *asyncns, query_type_t qtype, const char *dname, int class, int type) {
+        res_request_t data[BUFSIZE/sizeof(res_request_t) + 1];
+        res_request_t *req = data;
+        asyncns_query_t *q;
+
+        assert(asyncns);
+        assert(dname);
+
+        if (asyncns->dead) {
+                errno = ECHILD;
+                return NULL;
+        }
+
+        if (!(q = alloc_query(asyncns)))
+                return NULL;
+
+        req->dname_len = strlen(dname) + 1;
+
+        req->header.id = q->id;
+        req->header.type = q->type = qtype;
+        req->header.length = sizeof(res_request_t) + req->dname_len;
+
+        if (req->header.length > BUFSIZE) {
+                errno = ENOMEM;
+                goto fail;
+        }
+
+        req->class = class;
+        req->type = type;
+
+        strcpy((char*) req + sizeof(res_request_t), dname);
+
+        if (send(asyncns->fds[REQUEST_SEND_FD], req, req->header.length, MSG_NOSIGNAL) < 0)
+                goto fail;
+
+        return q;
+
+fail:
+        if (q)
+                asyncns_cancel(asyncns, q);
+
+        return NULL;
+}
+
+asyncns_query_t* asyncns_res_query(asyncns_t *asyncns, const char *dname, int class, int type) {
+        return asyncns_res(asyncns, REQUEST_RES_QUERY, dname, class, type);
+}
+
+asyncns_query_t* asyncns_res_search(asyncns_t *asyncns, const char *dname, int class, int type) {
+        return asyncns_res(asyncns, REQUEST_RES_SEARCH, dname, class, type);
+}
+
+int asyncns_res_done(asyncns_t *asyncns, asyncns_query_t* q, unsigned char **answer) {
+        int ret;
+        assert(asyncns);
+        assert(q);
+        assert(q->asyncns == asyncns);
+        assert(q->type == REQUEST_RES_QUERY || q->type == REQUEST_RES_SEARCH);
+        assert(answer);
+
+        if (asyncns->dead) {
+                errno = ECHILD;
+                return -ECHILD;
+        }
+
+        if (!q->done) {
+                errno = EAGAIN;
+                return -EAGAIN;
+        }
+
+        *answer = (unsigned char *)q->serv;
+        q->serv = NULL;
+
+        ret = q->ret;
+
+        if (ret < 0) {
+                errno = q->_errno;
+                h_errno = q->_h_errno;
+        }
+
+        asyncns_cancel(asyncns, q);
+
+        return ret < 0 ? -errno : ret;
+}
+
+asyncns_query_t* asyncns_getnext(asyncns_t *asyncns) {
+        assert(asyncns);
+        return asyncns->done_head;
+}
+
+int asyncns_getnqueries(asyncns_t *asyncns) {
+        assert(asyncns);
+        return asyncns->n_queries;
+}
+
+void asyncns_cancel(asyncns_t *asyncns, asyncns_query_t* q) {
+        int i;
+        int saved_errno = errno;
+
+        assert(asyncns);
+        assert(q);
+        assert(q->asyncns == asyncns);
+        assert(asyncns->n_queries > 0);
+
+        if (q->done) {
+
+                if (q->done_prev)
+                        q->done_prev->done_next = q->done_next;
+                else
+                        asyncns->done_head = q->done_next;
+
+                if (q->done_next)
+                        q->done_next->done_prev = q->done_prev;
+                else
+                        asyncns->done_tail = q->done_prev;
+        }
+
+        i = q->id % MAX_QUERIES;
+        assert(asyncns->queries[i] == q);
+        asyncns->queries[i] = NULL;
+
+        asyncns_freeaddrinfo(q->addrinfo);
+        free(q->host);
+        free(q->serv);
+
+        asyncns->n_queries--;
+        free(q);
+
+        errno = saved_errno;
+}
+
+void asyncns_freeaddrinfo(struct addrinfo *ai) {
+        int saved_errno = errno;
+
+        while (ai) {
+                struct addrinfo *next = ai->ai_next;
+
+                free(ai->ai_addr);
+                free(ai->ai_canonname);
+                free(ai);
+
+                ai = next;
+        }
+
+        errno = saved_errno;
+}
+
+void asyncns_freeanswer(unsigned char *answer) {
+        int saved_errno = errno;
+
+        if (!answer)
+                return;
+
+        /* Please note that this function is new in libasyncns 0.4. In
+         * older versions you were supposed to free the answer directly
+         * with free(). Hence, if this function is changed to do more than
+         * just a simple free() this must be considered ABI/API breakage! */
+
+        free(answer);
+
+        errno = saved_errno;
+}
+
+int asyncns_isdone(asyncns_t *asyncns, asyncns_query_t*q) {
+        assert(asyncns);
+        assert(q);
+        assert(q->asyncns == asyncns);
+
+        return q->done;
+}
+
+void asyncns_setuserdata(asyncns_t *asyncns, asyncns_query_t *q, void *userdata) {
+        assert(q);
+        assert(asyncns);
+        assert(q->asyncns = asyncns);
+
+        q->userdata = userdata;
+}
+
+void* asyncns_getuserdata(asyncns_t *asyncns, asyncns_query_t *q) {
+        assert(q);
+        assert(asyncns);
+        assert(q->asyncns = asyncns);
+
+        return q->userdata;
+}
diff --git a/src/libsystemd-bus/test-dns.c b/src/libsystemd-bus/test-dns.c
new file mode 100644
index 0000000000..56654ec047
--- /dev/null
+++ b/src/libsystemd-bus/test-dns.c
@@ -0,0 +1,164 @@
+/***
+  This file is part of libasyncns.
+
+  Copyright 2005-2008 Lennart Poettering
+
+  libasyncns 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.
+
+  libasyncns 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 libasyncns. If not, see
+  <http://www.gnu.org/licenses/>.
+ ***/
+
+#if HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include <stdio.h>
+#include <netinet/in.h>
+#include <arpa/nameser.h>
+#include <resolv.h>
+#include <assert.h>
+#include <signal.h>
+#include <errno.h>
+
+#include "sd-dns.h"
+#include "dns-util.h"
+#include "macro.h"
+
+int main(int argc, char *argv[]) {
+        int r = 1, ret;
+        _cleanup_asyncns_free_ asyncns_t *asyncns = NULL;
+        _cleanup_asyncns_addrinfo_free_ struct addrinfo *ai = NULL;
+        _cleanup_asyncns_answer_free_ unsigned char *srv = NULL;
+        asyncns_query_t *q1, *q2, *q3;
+        struct addrinfo hints = {};
+        struct sockaddr_in sa = {};
+        char host[NI_MAXHOST] = "", serv[NI_MAXSERV] = "";
+
+        signal(SIGCHLD, SIG_IGN);
+
+        asyncns = asyncns_new(2);
+        if (!asyncns)
+                log_oom();
+
+        /* Make a name -> address query */
+        hints.ai_family = PF_UNSPEC;
+        hints.ai_socktype = SOCK_STREAM;
+
+        q1 = asyncns_getaddrinfo(asyncns, argc >= 2 ? argv[1] : "www.heise.de", NULL, &hints);
+
+        if (!q1)
+                fprintf(stderr, "asyncns_getaddrinfo(): %s\n", strerror(errno));
+
+        /* Make an address -> name query */
+        sa.sin_family = AF_INET;
+        sa.sin_addr.s_addr = inet_addr(argc >= 3 ? argv[2] : "193.99.144.71");
+        sa.sin_port = htons(80);
+
+        q2 = asyncns_getnameinfo(asyncns, (struct sockaddr*) &sa, sizeof(sa), 0, 1, 1);
+
+        if (!q2)
+                fprintf(stderr, "asyncns_getnameinfo(): %s\n", strerror(errno));
+
+        /* Make a res_query() call */
+        q3 = asyncns_res_query(asyncns, "_xmpp-client._tcp.gmail.com", C_IN, T_SRV);
+
+        if (!q3)
+                fprintf(stderr, "asyncns_res_query(): %s\n", strerror(errno));
+
+        /* Wait until the three queries are completed */
+        while (!asyncns_isdone(asyncns, q1)
+                        || !asyncns_isdone(asyncns, q2)
+                        || !asyncns_isdone(asyncns, q3)) {
+                if (asyncns_wait(asyncns, 1) < 0) {
+                        fprintf(stderr, "asyncns_wait(): %s\n", strerror(errno));
+                }
+        }
+
+        /* Interpret the result of the name -> addr query */
+        if ((ret = asyncns_getaddrinfo_done(asyncns, q1, &ai)))
+                fprintf(stderr, "error: %s %i\n", gai_strerror(ret), ret);
+        else {
+                struct addrinfo *i;
+
+                for (i = ai; i; i = i->ai_next) {
+                        char t[256];
+                        const char *p = NULL;
+
+                        if (i->ai_family == PF_INET)
+                                p = inet_ntop(AF_INET, &((struct sockaddr_in*) i->ai_addr)->sin_addr, t, sizeof(t));
+                        else if (i->ai_family == PF_INET6)
+                                p = inet_ntop(AF_INET6, &((struct sockaddr_in6*) i->ai_addr)->sin6_addr, t, sizeof(t));
+
+                        printf("%s\n", p);
+                }
+        }
+
+        /* Interpret the result of the addr -> name query */
+        if ((ret = asyncns_getnameinfo_done(asyncns, q2, host, sizeof(host), serv, sizeof(serv))))
+                fprintf(stderr, "error: %s %i\n", gai_strerror(ret), ret);
+        else
+                printf("%s -- %s\n", host, serv);
+
+        /* Interpret the result of the SRV lookup */
+        if ((ret = asyncns_res_done(asyncns, q3, &srv)) < 0) {
+                fprintf(stderr, "error: %s %i\n", strerror(errno), ret);
+        } else if (ret == 0) {
+                fprintf(stderr, "No reply for SRV lookup\n");
+        } else {
+                int qdcount;
+                int ancount;
+                int len;
+                const unsigned char *pos = srv + sizeof(HEADER);
+                unsigned char *end = srv + ret;
+                HEADER *head = (HEADER *)srv;
+                char name[256];
+
+                qdcount = ntohs(head->qdcount);
+                ancount = ntohs(head->ancount);
+
+                printf("%d answers for srv lookup:\n", ancount);
+
+                /* Ignore the questions */
+                while (qdcount-- > 0 && (len = dn_expand(srv, end, pos, name, 255)) >= 0) {
+                        assert(len >= 0);
+                        pos += len + QFIXEDSZ;
+                }
+
+                /* Parse the answers */
+                while (ancount-- > 0 && (len = dn_expand(srv, end, pos, name, 255)) >= 0) {
+                        /* Ignore the initial string */
+                        uint16_t pref, weight, port;
+                        assert(len >= 0);
+                        pos += len;
+                        /* Ignore type, ttl, class and dlen */
+                        pos += 10;
+
+                        GETSHORT(pref, pos);
+                        GETSHORT(weight, pos);
+                        GETSHORT(port, pos);
+                        len = dn_expand(srv, end, pos, name, 255);
+                        printf("\tpreference: %2d weight: %2d port: %d host: %s\n",
+                                        pref, weight, port, name);
+
+                        pos += len;
+                }
+        }
+
+        r = 0;
+
+        return r;
+}
diff --git a/src/systemd/sd-dns.h b/src/systemd/sd-dns.h
new file mode 100644
index 0000000000..72bc1213ed
--- /dev/null
+++ b/src/systemd/sd-dns.h
@@ -0,0 +1,156 @@
+#ifndef fooasyncnshfoo
+#define fooasyncnshfoo
+
+/***
+  This file is part of libasyncns.
+
+  Copyright 2005-2008 Lennart Poettering
+
+  libasyncns 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.
+
+  libasyncns 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 libasyncns. If not, see
+  <http://www.gnu.org/licenses/>.
+***/
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include "macro.h"
+#include "util.h"
+/** \mainpage
+ *
+ * \section moo Method of operation
+ *
+ * To use libasyncns allocate an asyncns_t object with
+ * asyncns_new(). This will spawn a number of worker threads (or processes, depending on what is available) which
+ * are subsequently used to process the queries the controlling
+ * program issues via asyncns_getaddrinfo() and
+ * asyncns_getnameinfo(). Use asyncns_free() to shut down the worker
+ * threads/processes.
+ *
+ * Since libasyncns may fork off new processes you have to make sure that
+ * your program is not irritated by spurious SIGCHLD signals.
+ */
+
+/** \example asyncns-test.c
+ * An example program */
+
+/** An opaque libasyncns session structure */
+typedef struct asyncns asyncns_t;
+
+/** An opaque libasyncns query structure */
+typedef struct asyncns_query asyncns_query_t;
+
+/** Allocate a new libasyncns session with n_proc worker processes/threads */
+asyncns_t* asyncns_new(unsigned n_proc);
+
+/** Free a libasyncns session. This destroys all attached
+ * asyncns_query_t objects automatically */
+void asyncns_free(asyncns_t *asyncns);
+
+/** Return the UNIX file descriptor to select() for readability
+ * on. Use this function to integrate libasyncns with your custom main
+ * loop. */
+int asyncns_fd(asyncns_t *asyncns);
+
+/** Process pending responses. After this function is called you can
+ * get the next completed query object(s) using asyncns_getnext(). If
+ * block is non-zero wait until at least one response has been
+ * processed. If block is zero, process all pending responses and
+ * return. */
+int asyncns_wait(asyncns_t *asyncns, int block);
+
+/** Issue a name to address query on the specified session. The
+ * arguments are compatible with the ones of libc's
+ * getaddrinfo(3). The function returns a new query object. When the
+ * query is completed you may retrieve the results using
+ * asyncns_getaddrinfo_done().*/
+asyncns_query_t* asyncns_getaddrinfo(asyncns_t *asyncns, const char *node, const char *service, const struct addrinfo *hints);
+
+/** Retrieve the results of a preceding asyncns_getaddrinfo()
+ * call. Returns a addrinfo structure and a return value compatible
+ * with libc's getaddrinfo(3). The query object q is destroyed by this
+ * call and may not be used any further. Make sure to free the
+ * returned addrinfo structure with asyncns_freeaddrinfo() and not
+ * libc's freeaddrinfo(3)! If the query is not completed yet EAI_AGAIN
+ * is returned.*/
+int asyncns_getaddrinfo_done(asyncns_t *asyncns, asyncns_query_t* q, struct addrinfo **ret_res);
+
+/** Issue an address to name query on the specified session. The
+ * arguments are compatible with the ones of libc's
+ * getnameinfo(3). The function returns a new query object. When the
+ * query is completed you may retrieve the results using
+ * asyncns_getnameinfo_done(). Set gethost (resp. getserv) to non-zero
+ * if you want to query the hostname (resp. the service name). */
+asyncns_query_t* asyncns_getnameinfo(asyncns_t *asyncns, const struct sockaddr *sa, socklen_t salen, int flags, int gethost, int getserv);
+
+/** Retrieve the results of a preceding asyncns_getnameinfo()
+ * call. Returns the hostname and the service name in ret_host and
+ * ret_serv. The query object q is destroyed by this call and may not
+ * be used any further. If the query is not completed yet EAI_AGAIN is
+ * returned. */
+int asyncns_getnameinfo_done(asyncns_t *asyncns, asyncns_query_t* q, char *ret_host, size_t hostlen, char *ret_serv, size_t servlen);
+
+/** Issue a resolver query on the specified session. The arguments are
+ * compatible with the ones of libc's res_query(3). The function returns a new
+ * query object. When the query is completed you may retrieve the results using
+ * asyncns_res_done().  */
+asyncns_query_t* asyncns_res_query(asyncns_t *asyncns, const char *dname, int class, int type);
+
+/** Issue an resolver query on the specified session. The arguments are
+ * compatible with the ones of libc's res_search(3). The function returns a new
+ * query object. When the query is completed you may retrieve the results using
+ * asyncns_res_done().  */
+asyncns_query_t* asyncns_res_search(asyncns_t *asyncns, const char *dname, int class, int type);
+
+/** Retrieve the results of a preceding asyncns_res_query() or
+ * asyncns_res_search call.  The query object q is destroyed by this
+ * call and may not be used any further. Returns a pointer to the
+ * answer of the res_query call. If the query is not completed yet
+ * -EAGAIN is returned, on failure -errno is returned, otherwise the
+ * length of answer is returned. Make sure to free the answer is a
+ * call to asyncns_freeanswer(). */
+int asyncns_res_done(asyncns_t *asyncns, asyncns_query_t* q, unsigned char **answer);
+
+/** Return the next completed query object. If no query has been
+ * completed yet, return NULL. Please note that you need to run
+ * asyncns_wait() before this function will return sensible data.  */
+asyncns_query_t* asyncns_getnext(asyncns_t *asyncns);
+
+/** Return the number of query objects (completed or not) attached to
+ * this session */
+int asyncns_getnqueries(asyncns_t *asyncns);
+
+/** Cancel a currently running query. q is is destroyed by this call
+ * and may not be used any futher. */
+void asyncns_cancel(asyncns_t *asyncns, asyncns_query_t* q);
+
+/** Free the addrinfo structure as returned by
+ * asyncns_getaddrinfo_done(). Make sure to use this functions instead
+ * of the libc's freeaddrinfo()! */
+void asyncns_freeaddrinfo(struct addrinfo *ai);
+
+/** Free the answer data as returned by asyncns_res_done().*/
+void asyncns_freeanswer(unsigned char *answer);
+
+/** Returns non-zero when the query operation specified by q has been completed */
+int asyncns_isdone(asyncns_t *asyncns, asyncns_query_t*q);
+
+/** Assign some opaque userdata with a query object */
+void asyncns_setuserdata(asyncns_t *asyncns, asyncns_query_t *q, void *userdata);
+
+/** Return userdata assigned to a query object. Use
+ * asyncns_setuserdata() to set this data. If no data has been set
+ * prior to this call it returns NULL. */
+void* asyncns_getuserdata(asyncns_t *asyncns, asyncns_query_t *q);
+
+#endif