src/libsystemd/sd-resolve/sd-resolve.c

/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2005-2008 Lennart Poettering

  systemd 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.

  systemd 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 systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#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>
#include <sys/prctl.h>
#include <sys/poll.h>

#include "util.h"
#include "list.h"
#include "socket-util.h"
#include "sd-resolve.h"

#define WORKERS_MIN 1
#define WORKERS_MAX 16
#define QUERIES_MAX 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
} QueryType;

enum {
        REQUEST_RECV_FD,
        REQUEST_SEND_FD,
        RESPONSE_RECV_FD,
        RESPONSE_SEND_FD,
        _FD_MAX
};

struct sd_resolve {
        bool dead:1;
        pid_t original_pid;

        int fds[_FD_MAX];

        pthread_t workers[WORKERS_MAX];
        unsigned n_valid_workers;

        unsigned current_id, current_index;
        sd_resolve_query* queries[QUERIES_MAX];
        unsigned n_queries;

        LIST_HEAD(sd_resolve_query, done);
        sd_resolve_query *done_tail;
        unsigned n_done;
};

struct sd_resolve_query {
        sd_resolve *resolve;
        bool done:1;
        unsigned id;
        QueryType type;

        int ret;
        int _errno;
        int _h_errno;
        struct addrinfo *addrinfo;
        char *serv, *host;

        void *userdata;

        LIST_FIELDS(sd_resolve_query, done);
};

typedef struct RHeader {
        QueryType type;
        unsigned id;
        size_t length;
} RHeader;

typedef struct AddrInfoRequest {
        struct RHeader header;
        bool hints_valid;
        int ai_flags;
        int ai_family;
        int ai_socktype;
        int ai_protocol;
        size_t node_len, service_len;
} AddrInfoRequest;

typedef struct AddrInfoResponse {
        struct RHeader header;
        int ret;
        int _errno;
        int _h_errno;
        /* followed by addrinfo_serialization[] */
} AddrInfoResponse;

typedef struct AddrInfoSerialization {
        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 */
} AddrInfoSerialization;

typedef struct NameInfoRequest {
        struct RHeader header;
        int flags;
        socklen_t sockaddr_len;
        bool gethost:1, getserv:1;
} NameInfoRequest;

typedef struct NameInfoResponse {
        struct RHeader header;
        size_t hostlen, servlen;
        int ret;
        int _errno;
        int _h_errno;
} NameInfoResponse;

typedef struct ResRequest {
        struct RHeader header;
        int class;
        int type;
        size_t dname_len;
} ResRequest;

typedef struct ResResponse {
        struct RHeader header;
        int ret;
        int _errno;
        int _h_errno;
} ResResponse;

typedef union Packet {
        RHeader rheader;
        AddrInfoRequest addrinfo_request;
        AddrInfoResponse addrinfo_response;
        NameInfoRequest nameinfo_request;
        NameInfoResponse nameinfo_response;
        ResRequest res_request;
        ResResponse res_response;
} Packet;

static int send_died(int out_fd) {
        RHeader rh = {};

        assert(out_fd >= 0);

        rh.type = RESPONSE_DIED;
        rh.length = sizeof(rh);

        if (send(out_fd, &rh, rh.length, MSG_NOSIGNAL) < 0)
                return -errno;

        return 0;
}

static void *serialize_addrinfo(void *p, const struct addrinfo *ai, size_t *length, size_t maxlength) {
        AddrInfoSerialization 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(AddrInfoSerialization) + 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(AddrInfoSerialization));
        memcpy((uint8_t*) p + sizeof(AddrInfoSerialization), ai->ai_addr, ai->ai_addrlen);

        if (ai->ai_canonname)
                memcpy((char*) p + sizeof(AddrInfoSerialization) + ai->ai_addrlen, ai->ai_canonname, cnl);

        *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) {

        AddrInfoResponse resp = {};
        struct msghdr mh = {};
        struct iovec iov[2];
        union {
                AddrInfoSerialization ais;
                uint8_t space[BUFSIZE];
        } buffer;

        assert(out_fd >= 0);

        resp.header.type = RESPONSE_ADDRINFO;
        resp.header.id = id;
        resp.header.length = sizeof(AddrInfoResponse);
        resp.ret = ret;
        resp._errno = _errno;
        resp._h_errno = _h_errno;

        if (ret == 0 && ai) {
                void *p = &buffer;
                struct addrinfo *k;

                for (k = ai; k; k = k->ai_next) {
                        p = serialize_addrinfo(p, k, &resp.header.length, (uint8_t*) &buffer + BUFSIZE - (uint8_t*) p);
                        if (!p) {
                                freeaddrinfo(ai);
                                return -ENOBUFS;
                        }
                }
        }

        if (ai)
                freeaddrinfo(ai);

        iov[0] = (struct iovec) { .iov_base = &resp, .iov_len = sizeof(AddrInfoResponse) };
        iov[1] = (struct iovec) { .iov_base = &buffer, .iov_len = resp.header.length - sizeof(AddrInfoResponse) };

        mh.msg_iov = iov;
        mh.msg_iovlen = ELEMENTSOF(iov);

        if (sendmsg(out_fd, &mh, MSG_NOSIGNAL) < 0)
                return -errno;

        return 0;
}

static int send_nameinfo_reply(
                int out_fd,
                unsigned id,
                int ret,
                const char *host,
                const char *serv,
                int _errno,
                int _h_errno) {

        NameInfoResponse resp = {};
        struct msghdr mh = {};
        struct iovec iov[3];
        size_t hl, sl;

        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(NameInfoResponse) + hl + sl;
        resp.ret = ret;
        resp._errno = _errno;
        resp._h_errno = _h_errno;
        resp.hostlen = hl;
        resp.servlen = sl;

        iov[0] = (struct iovec) { .iov_base = &resp, .iov_len = sizeof(NameInfoResponse) };
        iov[1] = (struct iovec) { .iov_base = (void*) host, .iov_len = hl };
        iov[2] = (struct iovec) { .iov_base = (void*) serv, .iov_len = sl };

        mh.msg_iov = iov;
        mh.msg_iovlen = ELEMENTSOF(iov);

        if (sendmsg(out_fd, &mh, MSG_NOSIGNAL) < 0)
                return -errno;

        return 0;
}

static int send_res_reply(int out_fd, unsigned id, const unsigned char *answer, int ret, int _errno, int _h_errno) {
        struct msghdr mh = {};
        struct iovec iov[2];
        ResResponse resp = {};
        size_t l;

        assert(out_fd >= 0);

        l = ret > 0 ? (size_t) ret : 0;

        resp.header.type = RESPONSE_RES;
        resp.header.id = id;
        resp.header.length = sizeof(ResResponse) + l;
        resp.ret = ret;
        resp._errno = _errno;
        resp._h_errno = _h_errno;

        iov[0] = (struct iovec) { .iov_base = &resp, .iov_len = sizeof(ResResponse) };
        iov[1] = (struct iovec) { .iov_base = (void*) answer, .iov_len = l };

        mh.msg_iov = iov;
        mh.msg_iovlen = ELEMENTSOF(iov);

        if (sendmsg(out_fd, &mh, MSG_NOSIGNAL) < 0)
                return -errno;

        return 0;
}

static int handle_request(int out_fd, const Packet *packet, size_t length) {
        const RHeader *req;

        assert(out_fd >= 0);
        assert(packet);

        req = &packet->rheader;

        assert(length >= sizeof(RHeader));
        assert(length == req->length);

        switch (req->type) {

        case REQUEST_ADDRINFO: {
               const AddrInfoRequest *ai_req = &packet->addrinfo_request;
               struct addrinfo hints = {}, *result = NULL;
               const char *node, *service;
               int ret;

               assert(length >= sizeof(AddrInfoRequest));
               assert(length == sizeof(AddrInfoRequest) + ai_req->node_len + ai_req->service_len);

               hints.ai_flags = ai_req->ai_flags;
               hints.ai_family = ai_req->ai_family;
               hints.ai_socktype = ai_req->ai_socktype;
               hints.ai_protocol = ai_req->ai_protocol;

               node = ai_req->node_len ? (const char*) ai_req + sizeof(AddrInfoRequest) : NULL;
               service = ai_req->service_len ? (const char*) ai_req + sizeof(AddrInfoRequest) + ai_req->node_len : NULL;

               ret = getaddrinfo(
                               node, service,
                               ai_req->hints_valid ? &hints : NULL,
                               &result);

               /* send_addrinfo_reply() frees result */
               return send_addrinfo_reply(out_fd, req->id, ret, result, errno, h_errno);
        }

        case REQUEST_NAMEINFO: {
               const NameInfoRequest *ni_req = &packet->nameinfo_request;
               char hostbuf[NI_MAXHOST], servbuf[NI_MAXSERV];
               union sockaddr_union sa;
               int ret;

               assert(length >= sizeof(NameInfoRequest));
               assert(length == sizeof(NameInfoRequest) + ni_req->sockaddr_len);
               assert(sizeof(sa) >= ni_req->sockaddr_len);

               memcpy(&sa, (const uint8_t *) ni_req + sizeof(NameInfoRequest), ni_req->sockaddr_len);

               ret = getnameinfo(&sa.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: {
                 const ResRequest *res_req = &packet->res_request;
                 union {
                         HEADER header;
                         uint8_t space[BUFSIZE];
                 } answer;
                 const char *dname;
                 int ret;

                 assert(length >= sizeof(ResRequest));
                 assert(length == sizeof(ResRequest) + res_req->dname_len);

                 dname = (const char *) req + sizeof(ResRequest);

                 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 -ECONNRESET;

        default:
                assert_not_reached("Unknown request");
        }

        return 0;
}

static void* thread_worker(void *p) {
        sd_resolve *resolve = p;
        sigset_t fullset;

        /* No signals in this thread please */
        assert_se(sigfillset(&fullset) == 0);
        assert_se(pthread_sigmask(SIG_BLOCK, &fullset, NULL) == 0);

        /* Assign a pretty name to this thread */
        prctl(PR_SET_NAME, (unsigned long) "sd-resolve");

        while (!resolve->dead) {
                union {
                        Packet packet;
                        uint8_t space[BUFSIZE];
                } buf;
                ssize_t length;

                length = recv(resolve->fds[REQUEST_RECV_FD], &buf, sizeof(buf), 0);
                if (length < 0) {
                        if (errno == EINTR)
                                continue;

                        break;
                }
                if (length == 0)
                        break;

                if (resolve->dead)
                        break;

                if (handle_request(resolve->fds[RESPONSE_SEND_FD], &buf.packet, (size_t) length) < 0)
                        break;
        }

        send_died(resolve->fds[RESPONSE_SEND_FD]);

        return NULL;
}

static int start_threads(sd_resolve *resolve, unsigned extra) {
        unsigned n;
        int r;

        n = resolve->n_queries - resolve->n_done + extra;

        if (n < WORKERS_MIN)
                n = WORKERS_MIN;
        if (n > WORKERS_MAX)
                n = WORKERS_MAX;

        while (resolve->n_valid_workers < n) {

                r = pthread_create(&resolve->workers[resolve->n_valid_workers], NULL, thread_worker, resolve);
                if (r != 0)
                        return -r;

                resolve->n_valid_workers ++;
        }

        return 0;
}

static bool resolve_pid_changed(sd_resolve *r) {
        assert(r);

        /* We don't support people creating a resolver and keeping it
         * around after fork(). Let's complain. */

        return r->original_pid != getpid();
}

_public_ int sd_resolve_new(sd_resolve **ret) {
        sd_resolve *resolve = NULL;
        int i, r;

        assert_return(ret, -EINVAL);

        resolve = new0(sd_resolve, 1);
        if (!resolve)
                return -ENOMEM;

        for (i = 0; i < _FD_MAX; i++)
                resolve->fds[i] = -1;

        resolve->original_pid = getpid();

        r = socketpair(PF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, resolve->fds + REQUEST_RECV_FD);
        if (r < 0) {
                r = -errno;
                goto fail;
        }

        r = socketpair(PF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, resolve->fds + RESPONSE_RECV_FD);
        if (r < 0) {
                r = -errno;
                goto fail;
        }

        fd_inc_sndbuf(resolve->fds[REQUEST_SEND_FD], QUERIES_MAX * BUFSIZE);
        fd_inc_rcvbuf(resolve->fds[REQUEST_RECV_FD], QUERIES_MAX * BUFSIZE);
        fd_inc_sndbuf(resolve->fds[RESPONSE_SEND_FD], QUERIES_MAX * BUFSIZE);
        fd_inc_rcvbuf(resolve->fds[RESPONSE_RECV_FD], QUERIES_MAX * BUFSIZE);

        fd_nonblock(resolve->fds[RESPONSE_RECV_FD], true);

        *ret = resolve;
        return 0;

fail:
        if (resolve)
                sd_resolve_unref(resolve);

        return r;
}

_public_ sd_resolve* sd_resolve_unref(sd_resolve *resolve) {
        PROTECT_ERRNO;

        unsigned i;

        assert_return(resolve, NULL);
        assert_return(!resolve_pid_changed(resolve), NULL);

        resolve->dead = true;

        if (resolve->fds[REQUEST_SEND_FD] >= 0) {

                RHeader req = {
                        .type = REQUEST_TERMINATE,
                        .length = sizeof(req)
                };

                /* Send one termination packet for each worker */
                for (i = 0; i < resolve->n_valid_workers; i++)
                        send(resolve->fds[REQUEST_SEND_FD], &req, req.length, MSG_NOSIGNAL);
        }

        /* Now terminate them and wait until they are gone. */
        for (i = 0; i < resolve->n_valid_workers; i++) {
                for (;;) {
                        if (pthread_join(resolve->workers[i], NULL) != EINTR)
                                break;
                }
        }

        /* Close all communication channels */
        for (i = 0; i < _FD_MAX; i++)
                if (resolve->fds[i] >= 0)
                        close_nointr_nofail(resolve->fds[i]);

        for (i = 0; i < QUERIES_MAX && resolve->n_queries > 0; i++)
                if (resolve->queries[i])
                        sd_resolve_cancel(resolve->queries[i]);

        free(resolve);
        return NULL;
}

_public_ int sd_resolve_get_fd(sd_resolve *resolve) {
        assert_return(resolve, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        return resolve->fds[RESPONSE_RECV_FD];
}

_public_ int sd_resolve_get_events(sd_resolve *resolve) {
        assert_return(resolve, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        return resolve->n_queries > resolve->n_done ? POLLIN : 0;
}

_public_ int sd_resolve_get_timeout(sd_resolve *resolve, uint64_t *usec) {
        assert_return(resolve, -EINVAL);
        assert_return(usec, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        *usec = (uint64_t) -1;
        return 0;
}

static sd_resolve_query *lookup_query(sd_resolve *resolve, unsigned id) {
        sd_resolve_query *q;

        assert(resolve);

        q = resolve->queries[id % QUERIES_MAX];
        if (q)
                if (q->id == id)
                        return q;

        return NULL;
}

static void complete_query(sd_resolve_query *q) {
        assert(q);
        assert(!q->done);

        q->done = true;
        LIST_PREPEND(done, q->resolve->done, q);
        q->resolve->n_done ++;
}

static int unserialize_addrinfo(const void **p, size_t *length, struct addrinfo **ret_ai) {
        AddrInfoSerialization s;
        size_t l;
        struct addrinfo *ai;

        assert(p);
        assert(*p);
        assert(ret_ai);
        assert(length);

        if (*length < sizeof(AddrInfoSerialization))
                return -EBADMSG;

        memcpy(&s, *p, sizeof(s));

        l = sizeof(AddrInfoSerialization) + s.ai_addrlen + s.canonname_len;
        if (*length < l)
                return -EBADMSG;

        ai = new0(struct addrinfo, 1);
        if (!ai)
                return -ENOMEM;

        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 (s.ai_addrlen > 0) {
                ai->ai_addr = memdup((const uint8_t*) *p + sizeof(AddrInfoSerialization), s.ai_addrlen);
                if (!ai->ai_addr) {
                        free(ai);
                        return -ENOMEM;
                }
        }

        if (s.canonname_len > 0) {
                ai->ai_canonname = memdup((const uint8_t*) *p + sizeof(AddrInfoSerialization) + s.ai_addrlen, s.canonname_len);
                if (!ai->ai_canonname) {
                        free(ai->ai_addr);
                        free(ai);
                        return -ENOMEM;
                }
        }

        *length -= l;
        *ret_ai = ai;
        *p = ((const uint8_t*) *p) + l;

        return 0;
}

static int handle_response(sd_resolve *resolve, const Packet *packet, size_t length) {
        const RHeader *resp;
        sd_resolve_query *q;
        int r;

        assert(resolve);

        resp = &packet->rheader;
        assert(resp);
        assert(length >= sizeof(RHeader));
        assert(length == resp->length);

        if (resp->type == RESPONSE_DIED) {
                resolve->dead = true;
                return 0;
        }

        q = lookup_query(resolve, resp->id);
        if (!q)
                return 0;

        switch (resp->type) {

        case RESPONSE_ADDRINFO: {
                const AddrInfoResponse *ai_resp = &packet->addrinfo_response;
                const void *p;
                size_t l;
                struct addrinfo *prev = NULL;

                assert(length >= sizeof(AddrInfoResponse));
                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(AddrInfoResponse);
                p = (const uint8_t*) resp + sizeof(AddrInfoResponse);

                while (l > 0 && p) {
                        struct addrinfo *ai = NULL;

                        r = unserialize_addrinfo(&p, &l, &ai);
                        if (r < 0) {
                                q->ret = EAI_SYSTEM;
                                q->_errno = -r;
                                q->_h_errno = 0;
                                freeaddrinfo(q->addrinfo);
                                q->addrinfo = NULL;
                                break;
                        }

                        if (prev)
                                prev->ai_next = ai;
                        else
                                q->addrinfo = ai;

                        prev = ai;
                }

                complete_query(q);
                break;
        }

        case RESPONSE_NAMEINFO: {
                const NameInfoResponse *ni_resp = &packet->nameinfo_response;

                assert(length >= sizeof(NameInfoResponse));
                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 > 0) {
                        q->host = strndup((const char*) ni_resp + sizeof(NameInfoResponse), ni_resp->hostlen-1);
                        if (!q->host) {
                                q->ret = EAI_MEMORY;
                                q->_errno = ENOMEM;
                                q->_h_errno = 0;
                        }
                }

                if (ni_resp->servlen > 0) {
                        q->serv = strndup((const char*) ni_resp + sizeof(NameInfoResponse) + ni_resp->hostlen, ni_resp->servlen-1);
                        if (!q->serv) {
                                q->ret = EAI_MEMORY;
                                q->_errno = ENOMEM;
                                q->_h_errno = 0;
                        }
                }

                complete_query(q);
                break;
        }

        case RESPONSE_RES: {
                const ResResponse *res_resp = &packet->res_response;

                assert(length >= sizeof(ResResponse));
                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)  {
                        q->serv = memdup((const char *)resp + sizeof(ResResponse), res_resp->ret);
                        if (!q->serv) {
                                q->ret = -1;
                                q->_errno = ENOMEM;
                                q->_h_errno = 0;
                        }
                }

                complete_query(q);
                break;
        }

        default:
                ;
        }

        return 0;
}

_public_ int sd_resolve_process(sd_resolve *resolve) {
        int n_processed = 0, r;

        assert_return(resolve, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        for (;;) {
                ssize_t l;
                union {
                        Packet packet;
                        uint8_t space[BUFSIZE];
                } buf;

                l = recv(resolve->fds[RESPONSE_RECV_FD], &buf, sizeof(buf), 0);
                if (l < 0) {
                        if (errno == EAGAIN)
                                return n_processed;

                        return -errno;
                }
                if (l == 0)
                        return -ECONNREFUSED;

                r = handle_response(resolve, &buf.packet, (size_t) l);
                if (r < 0)
                        return r;

                n_processed++;
        }
}

_public_ int sd_resolve_wait(sd_resolve *resolve, uint64_t timeout_usec) {
        int r;

        assert_return(resolve, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        if (resolve->n_queries <= 0)
                return 0;

        do {
                r = fd_wait_for_event(resolve->fds[RESPONSE_RECV_FD], POLLIN, timeout_usec);
        } while (r == -EINTR);

        if (r < 0)
                return r;

        return sd_resolve_process(resolve);
}

static int alloc_query(sd_resolve *resolve, sd_resolve_query **_q) {
        sd_resolve_query *q;
        int r;

        assert(resolve);
        assert(_q);

        if (resolve->n_queries >= QUERIES_MAX)
                return -ENOBUFS;

        r = start_threads(resolve, 1);
        if (r < 0)
                return r;

        while (resolve->queries[resolve->current_index]) {
                resolve->current_index++;
                resolve->current_id++;

                resolve->current_index %= QUERIES_MAX;
        }

        q = resolve->queries[resolve->current_index] = new0(sd_resolve_query, 1);
        if (!q)
                return -ENOMEM;

        resolve->n_queries++;

        q->resolve = resolve;
        q->id = resolve->current_id;

        *_q = q;
        return 0;
}

_public_ int sd_resolve_getaddrinfo(
                sd_resolve *resolve,
                sd_resolve_query **_q,
                const char *node,
                const char *service,
                const struct addrinfo *hints) {

        AddrInfoRequest req = {};
        struct msghdr mh = {};
        struct iovec iov[3];
        sd_resolve_query *q;
        int r;

        assert_return(resolve, -EINVAL);
        assert_return(node || service, -EINVAL);
        assert_return(_q, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        r = alloc_query(resolve, &q);
        if (r < 0)
                return r;

        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(AddrInfoRequest) + req.node_len + req.service_len;

        if (hints) {
                req.hints_valid = true;
                req.ai_flags = hints->ai_flags;
                req.ai_family = hints->ai_family;
                req.ai_socktype = hints->ai_socktype;
                req.ai_protocol = hints->ai_protocol;
        }

        iov[mh.msg_iovlen++] = (struct iovec) { .iov_base = &req, .iov_len = sizeof(AddrInfoRequest) };

        if (node)
                iov[mh.msg_iovlen++] = (struct iovec) { .iov_base = (void*) node, .iov_len = req.node_len };

        if (service)
                iov[mh.msg_iovlen++] = (struct iovec) { .iov_base = (void*) service, .iov_len = req.service_len };

        mh.msg_iov = iov;

        if (sendmsg(resolve->fds[REQUEST_SEND_FD], &mh, MSG_NOSIGNAL) < 0) {
                sd_resolve_cancel(q);
                return -errno;
        }

        *_q = q;
        return 0;
}

_public_ int sd_resolve_getaddrinfo_done(sd_resolve_query* q, struct addrinfo **ret_res) {
        int ret;

        if (!q) {
                errno = EINVAL;
                return EAI_SYSTEM;
        }

        if (q->type != REQUEST_ADDRINFO) {
                errno = ENOTTY;
                return EAI_SYSTEM;
        }

        if (resolve_pid_changed(q->resolve)) {
                errno = ECHILD;
                return EAI_SYSTEM;
        }
        if (!q->done)
                return EAI_AGAIN;

        if (ret_res) {
                *ret_res = q->addrinfo;
                q->addrinfo = NULL;
        }

        ret = q->ret;

        if (ret != 0) {
                errno = q->_errno;
                h_errno = q->_h_errno;
        }

        sd_resolve_cancel(q);

        return ret;
}

_public_ int sd_resolve_getnameinfo(
                sd_resolve *resolve,
                sd_resolve_query**_q,
                const struct sockaddr *sa, socklen_t salen,
                int flags,
                int gethost, int getserv) {

        NameInfoRequest req = {};
        struct msghdr mh = {};
        struct iovec iov[2];
        sd_resolve_query *q;
        int r;

        assert_return(resolve, -EINVAL);
        assert_return(sa, -EINVAL);
        assert_return(salen >= sizeof(struct sockaddr), -EINVAL);
        assert_return(salen <= sizeof(union sockaddr_union), -EINVAL);
        assert_return(_q, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        r = alloc_query(resolve, &q);
        if (r < 0)
                return r;

        req.header.id = q->id;
        req.header.type = q->type = REQUEST_NAMEINFO;
        req.header.length = sizeof(NameInfoRequest) + salen;

        req.flags = flags;
        req.sockaddr_len = salen;
        req.gethost = !!gethost;
        req.getserv = !!getserv;

        iov[0] = (struct iovec) { .iov_base = &req, .iov_len = sizeof(NameInfoRequest) };
        iov[1] = (struct iovec) { .iov_base = (void*) sa, .iov_len = salen };

        mh.msg_iov = iov;
        mh.msg_iovlen = 2;

        if (sendmsg(resolve->fds[REQUEST_SEND_FD], &mh, MSG_NOSIGNAL) < 0) {
                sd_resolve_cancel(q);
                return -errno;
        }

        *_q = q;
        return 0;
}

_public_ int sd_resolve_getnameinfo_done(sd_resolve_query* q, char **ret_host, char **ret_serv) {
        int ret;

        if (!q) {
                errno = EINVAL;
                return EAI_SYSTEM;
        }

        if (q->type != REQUEST_NAMEINFO) {
                errno = ENOTTY;
                return EAI_SYSTEM;
        }

        if (resolve_pid_changed(q->resolve)) {
                errno = ECHILD;
                return EAI_SYSTEM;
        }

        if (!q->done)
                return EAI_AGAIN;

        if (ret_host) {
                *ret_host = q->host;
                q->host = NULL;
        }

        if (ret_serv) {
                *ret_serv = q->serv;
                q->serv = NULL;
        }

        ret = q->ret;

        if (ret != 0) {
                errno = q->_errno;
                h_errno = q->_h_errno;
        }

        sd_resolve_cancel(q);

        return ret;
}

static int resolve_res(
                sd_resolve *resolve,
                sd_resolve_query **_q,
                QueryType qtype,
                const char *dname,
                int class, int type) {

        struct msghdr mh = {};
        struct iovec iov[2];
        ResRequest req = {};
        sd_resolve_query *q;
        int r;

        assert_return(resolve, -EINVAL);
        assert_return(dname, -EINVAL);
        assert_return(_q, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        r = alloc_query(resolve, &q);
        if (r < 0)
                return r;

        req.dname_len = strlen(dname) + 1;
        req.class = class;
        req.type = type;

        req.header.id = q->id;
        req.header.type = q->type = qtype;
        req.header.length = sizeof(ResRequest) + req.dname_len;

        iov[0] = (struct iovec) { .iov_base = &req, .iov_len = sizeof(ResRequest) };
        iov[1] = (struct iovec) { .iov_base = (void*) dname, .iov_len = req.dname_len };

        mh.msg_iov = iov;
        mh.msg_iovlen = 2;

        if (sendmsg(resolve->fds[REQUEST_SEND_FD], &mh, MSG_NOSIGNAL) < 0) {
                sd_resolve_cancel(q);
                return -errno;
        }

        *_q = q;
        return 0;
}

_public_ int sd_resolve_res_query(sd_resolve *resolve, sd_resolve_query** q, const char *dname, int class, int type) {
        return resolve_res(resolve, q, REQUEST_RES_QUERY, dname, class, type);
}

_public_ int sd_resolve_res_search(sd_resolve *resolve, sd_resolve_query** q, const char *dname, int class, int type) {
        return resolve_res(resolve, q, REQUEST_RES_SEARCH, dname, class, type);
}

_public_ int sd_resolve_res_done(sd_resolve_query* q, unsigned char **answer) {
        int ret;

        assert_return(q, -EINVAL);
        assert_return(answer, -EINVAL);
        assert_return(q->type == REQUEST_RES_QUERY || q->type == REQUEST_RES_SEARCH, -ENOTTY);
        assert_return(!resolve_pid_changed(q->resolve), -ECHILD);

        if (!q->done)
                return -EAGAIN;

        *answer = (unsigned char *) q->serv;
        q->serv = NULL;

        ret = q->ret;

        if (ret != 0) {
                errno = q->_errno;
                h_errno = q->_h_errno;
        }

        sd_resolve_cancel(q);

        return ret < 0 ? -errno : ret;
}

_public_ int sd_resolve_get_next(sd_resolve *resolve, sd_resolve_query **q) {
        assert_return(resolve, -EINVAL);
        assert_return(q, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        *q = resolve->done;
        return !!resolve->done;
}

_public_ int sd_resolve_get_n_queries(sd_resolve *resolve) {
        assert_return(resolve, -EINVAL);
        assert_return(!resolve_pid_changed(resolve), -ECHILD);

        return resolve->n_queries;
}

_public_ int sd_resolve_cancel(sd_resolve_query* q) {
        PROTECT_ERRNO;
        int i;

        if (!q)
                return 0;

        assert_return(!resolve_pid_changed(q->resolve), -ECHILD);

        assert(q->resolve);
        assert(q->resolve->n_queries > 0);

        if (q->done) {
                LIST_REMOVE(done, q->resolve->done, q);
                q->resolve->n_done--;
        }

        i = q->id % QUERIES_MAX;
        assert(q->resolve->queries[i] == q);
        q->resolve->queries[i] = NULL;
        q->resolve->n_queries--;

        sd_resolve_freeaddrinfo(q->addrinfo);
        free(q->host);
        free(q->serv);
        free(q);

        return 0;
}

_public_ void sd_resolve_freeaddrinfo(struct addrinfo *ai) {

        while (ai) {
                struct addrinfo *next = ai->ai_next;

                free(ai->ai_addr);
                free(ai->ai_canonname);
                free(ai);

                ai = next;
        }
}

_public_ int sd_resolve_is_done(sd_resolve_query *q) {
        assert_return(q, -EINVAL);
        assert_return(!resolve_pid_changed(q->resolve), -ECHILD);

        return q->done;
}

_public_ void* sd_resolve_set_userdata(sd_resolve_query *q, void *userdata) {
        void *ret;

        assert_return(q, NULL);
        assert_return(!resolve_pid_changed(q->resolve), NULL);

        ret = q->userdata;
        q->userdata = userdata;

        return ret;
}

_public_ void* sd_resolve_get_userdata(sd_resolve_query *q) {
        assert_return(q, NULL);
        assert_return(!resolve_pid_changed(q->resolve), NULL);

        return q->userdata;
}