tinysvcmdns.c

// This file is the concatenation of mdnsd.c and mdns.c
// from tinysvcmdns with minor modifications
// The code was taken from https://bitbucket.org/geekman/tinysvcmdns at revision e34b562

/*
 * tinysvcmdns - a tiny MDNS implementation for publishing services
 * Copyright (C) 2011 Darell Tan
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "tinysvcmdns.h"
#include "common.h"

#define DEBUG_PRINTF(...) debug(1, __VA_ARGS__)
#define log_message(level, ...)         \
    do {                                \
        switch(level)                   \
        {                               \
            case LOG_ERR:               \
                warn(__VA_ARGS__);      \
                break;                  \
            default:                    \
                debug(1, __VA_ARGS__);   \
        }                               \
    } while (0)


//******************************************************//
//                      mdns.c                          //
//******************************************************//
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>

#ifdef _WIN32
#include <winsock.h>
#include <in6addr.h>
#else
#include <netinet/in.h>
#endif


#define DEFAULT_TTL             120


struct name_comp {
        uint8_t *label; // label
        size_t pos;             // position in msg

        struct name_comp *next;
};

// ----- label functions -----

// duplicates a name
inline uint8_t *dup_nlabel(const uint8_t *n) {
        assert(n[0] <= 63);     // prevent mis-use
        return (uint8_t *) strdup((char *) n);
}

// duplicates a label
uint8_t *dup_label(const uint8_t *label) {
        int len = *label + 1;
        if (len > 63)
                return NULL;
        uint8_t *newlabel = malloc(len + 1);
        strncpy((char *) newlabel, (char *) label, len);
        newlabel[len] = '\0';
        return newlabel;
}

uint8_t *join_nlabel(const uint8_t *n1, const uint8_t *n2) {
        int len1, len2;
        uint8_t *s;

        assert(n1[0] <= 63 && n2[0] <= 63);     // detect misuse

        len1 = strlen((char *) n1);
        len2 = strlen((char *) n2);

        s = malloc(len1 + len2 + 1);
        strncpy((char *) s, (char *) n1, len1);
        strncpy((char *) s+len1, (char *) n2, len2);
        s[len1 + len2] = '\0';
        return s;
}

// returns a human-readable name label in dotted form
char *nlabel_to_str(const uint8_t *name) {
        char *label, *labelp;
        const uint8_t *p;

        assert(name != NULL);

        label = labelp = malloc(256);

        for (p = name; *p; p++) {
                strncpy(labelp, (char *) p + 1, *p);
                labelp += *p;
                *labelp = '.';
                labelp++;

                p += *p;
        }

        *labelp = '\0';

        return label;
}

// returns the length of a label field
// does NOT uncompress the field, so it could be as small as 2 bytes
// or 1 for the root
static size_t label_len(uint8_t *pkt_buf, size_t pkt_len, size_t off) {
        uint8_t *p;
        uint8_t *e = pkt_buf + pkt_len;
        size_t len = 0;

        for (p = pkt_buf + off; p < e; p++) {
                if (*p == 0) {
                        return len + 1;
                } else if ((*p & 0xC0) == 0xC0) {
                        return len + 2;
                } else {
                        len += *p + 1;
                        p += *p;
                }
        }

        return len;
}

// creates a label
// free() after use
uint8_t *create_label(const char *txt) {
        int len;
        uint8_t *s;

        assert(txt != NULL);
        len = strlen(txt);
        if (len > 63)
                return NULL;

        s = malloc(len + 2);
        s[0] = len;
        strncpy((char *) s + 1, txt, len);
        s[len + 1] = '\0';

        return s;
}

// creates a uncompressed name label given a DNS name like "apple.b.com"
// free() after use
uint8_t *create_nlabel(const char *name) {
        char *label;
        char *p, *e, *lenpos;
        int len = 0;

        assert(name != NULL);

        len = strlen(name);
        label = malloc(len + 1 + 1);
        if (label == NULL)
                return NULL;

        strncpy((char *) label + 1, name, len);
        label[len + 1] = '\0';

        p = label;
        e = p + len;
        lenpos = p;

        while (p < e) {
                *lenpos = 0;
                char *dot = memchr(p + 1, '.', e - p - 1);
                if (dot == NULL)
                        dot = e + 1;
                *lenpos = dot - p - 1;

                p = dot;
                lenpos = dot;
        }

        return (uint8_t *) label;
}

// copies a label from the buffer into a newly-allocated string
// free() after use
static uint8_t *copy_label(uint8_t *pkt_buf, size_t pkt_len, size_t off) {
        int len;

        if (off > pkt_len)
                return NULL;

        len = pkt_buf[off] + 1;
        if (off + len > pkt_len) {
                DEBUG_PRINTF("label length exceeds packet buffer\n");
                return NULL;
        }

        return dup_label(pkt_buf + off);
}

// uncompresses a name
// free() after use
static uint8_t *uncompress_nlabel(uint8_t *pkt_buf, size_t pkt_len, size_t off) {
        uint8_t *p;
        uint8_t *e = pkt_buf + pkt_len;
        size_t len = 0;
        char *str, *sp;
        if (off >= pkt_len)
                return NULL;

        // calculate length of uncompressed label
        for (p = pkt_buf + off; *p && p < e; p++) {
                size_t llen = 0;
                if ((*p & 0xC0) == 0xC0) {
                        uint8_t *p2 = pkt_buf + (((p[0] & ~0xC0) << 8) | p[1]);
                        llen = *p2 + 1;
                        p = p2 + llen - 1;
                } else {
                        llen = *p + 1;
                        p += llen - 1;
                }
                len += llen;
        }

        str = sp = malloc(len + 1);
        if (str == NULL)
                return NULL;

        // FIXME: must merge this with above code
        for (p = pkt_buf + off; *p && p < e; p++) {
                size_t llen = 0;
                if ((*p & 0xC0) == 0xC0) {
                        uint8_t *p2 = pkt_buf + (((p[0] & ~0xC0) << 8) | p[1]);
                        llen = *p2 + 1;
                        strncpy(sp, (char *) p2, llen);
                        p = p2 + llen - 1;
                } else {
                        llen = *p + 1;
                        strncpy(sp, (char *) p, llen);
                        p += llen - 1;
                }
                sp += llen;
        }
        *sp = '\0';

        return (uint8_t *) str;
}

// ----- RR list & group functions -----

const char *rr_get_type_name(enum rr_type type) {
        switch (type) {
                case RR_A:              return "A";
                case RR_PTR:    return "PTR";
                case RR_TXT:    return "TXT";
                case RR_AAAA:   return "AAAA";
                case RR_SRV:    return "SRV";
                case RR_NSEC:   return "NSEC";
                case RR_ANY:    return "ANY";
        }
        return NULL;
}

void rr_entry_destroy(struct rr_entry *rr) {
        struct rr_data_txt *txt_rec;
        assert(rr);

        // check rr_type and free data elements
        switch (rr->type) {
                case RR_PTR:
                        if (rr->data.PTR.name)
                                free(rr->data.PTR.name);
                        // don't free entry
                        break;

                case RR_TXT:
                        txt_rec = &rr->data.TXT;
                        while (txt_rec) {
                                struct rr_data_txt *next = txt_rec->next;
                                if (txt_rec->txt)
                                        free(txt_rec->txt);

                                // only free() if it wasn't part of the struct
                                if (txt_rec != &rr->data.TXT)
                                        free(txt_rec);

                                txt_rec = next;
                        }
                        break;

                case RR_SRV:
                        if (rr->data.SRV.target)
                                free(rr->data.SRV.target);
                        break;

                default:
                        // nothing to free
                        break;
        }

        free(rr->name);
        free(rr);
}

// destroys an RR list (and optionally, items)
void rr_list_destroy(struct rr_list *rr, char destroy_items) {
        struct rr_list *rr_next;

        for (; rr; rr = rr_next) {
                rr_next = rr->next;
                if (destroy_items)
                        rr_entry_destroy(rr->e);
                free(rr);
        }
}

int rr_list_count(struct rr_list *rr) {
        int i = 0;
        for (; rr; i++, rr = rr->next);
        return i;
}

struct rr_entry *rr_list_remove(struct rr_list **rr_head, struct rr_entry *rr) {
        struct rr_list *le = *rr_head, *pe = NULL;
        for (; le; le = le->next) {
                if (le->e == rr) {
                        if (pe == NULL) {
                                *rr_head = le->next;
                                free(le);
                                return rr;
                        } else {
                                pe->next = le->next;
                                free(le);
                                return rr;
                        }
                }
                pe = le;
        }
        return NULL;
}

// appends an rr_entry to an RR list
// if the RR is already in the list, it will not be added
// RRs are compared by memory location - not its contents
// return value of 0 means item not added
int rr_list_append(struct rr_list **rr_head, struct rr_entry *rr) {
        struct rr_list *node = malloc(sizeof(struct rr_list));
        node->e = rr;
        node->next = NULL;

        if (*rr_head == NULL) {
                *rr_head = node;
        } else {
                struct rr_list *e = *rr_head, *taile;
                for (; e; e = e->next) {
                        // already in list - don't add
                        if (e->e == rr) {
                                free(node);
                                return 0;
                        }
                        if (e->next == NULL)
                                taile = e;
                }
                taile->next = node;
        }
        return 1;
}

#define FILL_RR_ENTRY(rr, _name, _type) \
        rr->name = _name;                       \
        rr->type = _type;                       \
        rr->ttl  = DEFAULT_TTL;         \
        rr->cache_flush = 1;            \
        rr->rr_class  = 1;

struct rr_entry *rr_create_a(uint8_t *name, uint32_t addr) {
        DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
        FILL_RR_ENTRY(rr, name, RR_A);
        rr->data.A.addr = addr;
        return rr;
}

struct rr_entry *rr_create_aaaa(uint8_t *name, struct in6_addr *addr) {
        DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
        FILL_RR_ENTRY(rr, name, RR_AAAA);
        rr->data.AAAA.addr = addr;
        return rr;
}

struct rr_entry *rr_create_srv(uint8_t *name, uint16_t port, uint8_t *target) {
        DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
        FILL_RR_ENTRY(rr, name, RR_SRV);
        rr->data.SRV.port = port;
        rr->data.SRV.target = target;
        return rr;
}

struct rr_entry *rr_create_ptr(uint8_t *name, struct rr_entry *d_rr) {
        DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
        FILL_RR_ENTRY(rr, name, RR_PTR);
        rr->cache_flush = 0;    // PTRs shouldn't have their cache flush bit set
        rr->data.PTR.entry = d_rr;
        return rr;
}

struct rr_entry *rr_create(uint8_t *name, enum rr_type type) {
        DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
        FILL_RR_ENTRY(rr, name, type);
        return rr;
}

void rr_set_nsec(struct rr_entry *rr_nsec, enum rr_type type) {
        assert(rr_nsec->type = RR_NSEC);
        assert((type / 8) < sizeof(rr_nsec->data.NSEC.bitmap));

        rr_nsec->data.NSEC.bitmap[ type / 8 ] = 1 << (7 - (type % 8));
}

void rr_add_txt(struct rr_entry *rr_txt, const char *txt) {
        struct rr_data_txt *txt_rec;
        assert(rr_txt->type == RR_TXT);

        txt_rec = &rr_txt->data.TXT;

        // is current data filled?
        if (txt_rec->txt == NULL) {
                txt_rec->txt = create_label(txt);
                return;
        }

        // find the last node
        for (; txt_rec->next; txt_rec = txt_rec->next);

        // create a new empty node
        txt_rec->next = malloc(sizeof(struct rr_data_txt));

        txt_rec = txt_rec->next;
        txt_rec->txt = create_label(txt);
        txt_rec->next = NULL;
}

// adds a record to an rr_group
void rr_group_add(struct rr_group **group, struct rr_entry *rr) {
        struct rr_group *g;

        assert(rr != NULL);

        if (*group) {
                g = rr_group_find(*group, rr->name);
                if (g) {
                        rr_list_append(&g->rr, rr);
                        return;
                }
        }

        MALLOC_ZERO_STRUCT(g, rr_group);
        g->name = dup_nlabel(rr->name);
        rr_list_append(&g->rr, rr);

        // prepend to list
        g->next = *group;
        *group = g;
}

// finds a rr_group matching the given name
struct rr_group *rr_group_find(struct rr_group* g, uint8_t *name) {
        for (; g; g = g->next) {
                if (cmp_nlabel(g->name, name) == 0)
                        return g;
        }
        return NULL;
}

struct rr_entry *rr_entry_find(struct rr_list *rr_list, uint8_t *name, uint16_t type) {
        struct rr_list *rr = rr_list;
        for (; rr; rr = rr->next) {
                if (rr->e->type == type && cmp_nlabel(rr->e->name, name) == 0)
                        return rr->e;
        }
        return NULL;
}

// looks for a matching entry in rr_list
// if entry is a PTR, we need to check if the PTR target also matches
struct rr_entry *rr_entry_match(struct rr_list *rr_list, struct rr_entry *entry) {
        struct rr_list *rr = rr_list;
        for (; rr; rr = rr->next) {
                if (rr->e->type == entry->type && cmp_nlabel(rr->e->name, entry->name) == 0) {
                        if (entry->type != RR_PTR) {
                                return rr->e;
                        } else if (cmp_nlabel(MDNS_RR_GET_PTR_NAME(entry), MDNS_RR_GET_PTR_NAME(rr->e)) == 0) {
                                // if it's a PTR, we need to make sure PTR target also matches
                                return rr->e;
                        }
                }
        }
        return NULL;
}

void rr_group_destroy(struct rr_group *group) {
        struct rr_group *g = group;

        while (g) {
                struct rr_group *nextg = g->next;
                free(g->name);
                rr_list_destroy(g->rr, 1);
                free(g);
                g = nextg;
        }
}

uint8_t *mdns_write_u16(uint8_t *ptr, const uint16_t v) {
        *ptr++ = (uint8_t) (v >> 8) & 0xFF;
        *ptr++ = (uint8_t) (v >> 0) & 0xFF;
        return ptr;
}

uint8_t *mdns_write_u32(uint8_t *ptr, const uint32_t v) {
        *ptr++ = (uint8_t) (v >> 24) & 0xFF;
        *ptr++ = (uint8_t) (v >> 16) & 0xFF;
        *ptr++ = (uint8_t) (v >>  8) & 0xFF;
        *ptr++ = (uint8_t) (v >>  0) & 0xFF;
        return ptr;
}

uint16_t mdns_read_u16(const uint8_t *ptr) {
        return  ((ptr[0] & 0xFF) << 8) |
                        ((ptr[1] & 0xFF) << 0);
}

uint32_t mdns_read_u32(const uint8_t *ptr) {
        return  ((ptr[0] & 0xFF) << 24) |
                        ((ptr[1] & 0xFF) << 16) |
                        ((ptr[2] & 0xFF) <<  8) |
                        ((ptr[3] & 0xFF) <<  0);
}

// initialize the packet for reply
// clears the packet of list structures but not its list items
void mdns_init_reply(struct mdns_pkt *pkt, uint16_t id) {
        // copy transaction ID
        pkt->id = id;

        // response flags
        pkt->flags = MDNS_FLAG_RESP | MDNS_FLAG_AA;

        rr_list_destroy(pkt->rr_qn,   0);
        rr_list_destroy(pkt->rr_ans,  0);
        rr_list_destroy(pkt->rr_auth, 0);
        rr_list_destroy(pkt->rr_add,  0);

        pkt->rr_qn    = NULL;
        pkt->rr_ans   = NULL;
        pkt->rr_auth  = NULL;
        pkt->rr_add   = NULL;

        pkt->num_qn = 0;
        pkt->num_ans_rr = 0;
        pkt->num_auth_rr = 0;
        pkt->num_add_rr = 0;
}

// destroys an mdns_pkt struct, including its contents
void mdns_pkt_destroy(struct mdns_pkt *p) {
        rr_list_destroy(p->rr_qn, 1);
        rr_list_destroy(p->rr_ans, 1);
        rr_list_destroy(p->rr_auth, 1);
        rr_list_destroy(p->rr_add, 1);

        free(p);
}


// parse the MDNS questions section
// stores the parsed data in the given mdns_pkt struct
static size_t mdns_parse_qn(uint8_t *pkt_buf, size_t pkt_len, size_t off,
                struct mdns_pkt *pkt) {
        const uint8_t *p = pkt_buf + off;
        struct rr_entry *rr;
        uint8_t *name;

        assert(pkt != NULL);

        rr = malloc(sizeof(struct rr_entry));
        memset(rr, 0, sizeof(struct rr_entry));

        name = uncompress_nlabel(pkt_buf, pkt_len, off);
        p += label_len(pkt_buf, pkt_len, off);
        rr->name = name;

        rr->type = mdns_read_u16(p);
        p += sizeof(uint16_t);

        rr->unicast_query = (*p & 0x80) == 0x80;
        rr->rr_class = mdns_read_u16(p) & ~0x80;
        p += sizeof(uint16_t);

        rr_list_append(&pkt->rr_qn, rr);

        return p - (pkt_buf + off);
}

// parse the MDNS RR section
// stores the parsed data in the given mdns_pkt struct
static size_t mdns_parse_rr(uint8_t *pkt_buf, size_t pkt_len, size_t off,
                struct mdns_pkt *pkt) {
        const uint8_t *p = pkt_buf + off;
        const uint8_t *e = pkt_buf + pkt_len;
        struct rr_entry *rr;
        uint8_t *name;
        size_t rr_data_len = 0;
        struct rr_data_txt *txt_rec;
        int parse_error = 0;

        assert(pkt != NULL);

        if (off > pkt_len)
                return 0;

        rr = malloc(sizeof(struct rr_entry));
        memset(rr, 0, sizeof(struct rr_entry));

        name = uncompress_nlabel(pkt_buf, pkt_len, off);
        p += label_len(pkt_buf, pkt_len, off);
        rr->name = name;

        rr->type = mdns_read_u16(p);
        p += sizeof(uint16_t);

        rr->cache_flush = (*p & 0x80) == 0x80;
        rr->rr_class = mdns_read_u16(p) & ~0x80;
        p += sizeof(uint16_t);

        rr->ttl = mdns_read_u32(p);
        p += sizeof(uint32_t);

        // RR data
        rr_data_len = mdns_read_u16(p);
        p += sizeof(uint16_t);

        if (p + rr_data_len > e) {
                DEBUG_PRINTF("rr_data_len goes beyond packet buffer: %lu > %lu\n", rr_data_len, e - p);
                rr_entry_destroy(rr);
                return 0;
        }

        e = p + rr_data_len;

        // see if we can parse the RR data
        switch (rr->type) {
                case RR_A:
                        if (rr_data_len < sizeof(uint32_t)) {
                                DEBUG_PRINTF("invalid rr_data_len=%lu for A record\n", rr_data_len);
                                parse_error = 1;
                                break;
                        }
                        rr->data.A.addr = ntohl(mdns_read_u32(p)); /* addr already in net order */
                        p += sizeof(uint32_t);
                        break;

                case RR_AAAA:
                        if (rr_data_len < sizeof(struct in6_addr)) {
                                DEBUG_PRINTF("invalid rr_data_len=%lu for AAAA record\n", rr_data_len);
                                parse_error = 1;
                                break;
                        }
                        rr->data.AAAA.addr = malloc(sizeof(struct in6_addr));
                        int i;
                        for (i = 0; i < sizeof(struct in6_addr); i++)
                                rr->data.AAAA.addr->s6_addr[i] = p[i];
                        p += sizeof(struct in6_addr);
                        break;

                case RR_PTR:
                        rr->data.PTR.name = uncompress_nlabel(pkt_buf, pkt_len, p - pkt_buf);
                        if (rr->data.PTR.name == NULL) {
                                DEBUG_PRINTF("unable to parse/uncompress label for PTR name\n");
                                parse_error = 1;
                                break;
                        }
                        p += rr_data_len;
                        break;

                case RR_TXT:
                        txt_rec = &rr->data.TXT;

                        // not supposed to happen, but we should handle it
                        if (rr_data_len == 0) {
                                DEBUG_PRINTF("WARN: rr_data_len for TXT is 0\n");
                                txt_rec->txt = create_label("");
                                break;
                        }

                        while (1) {
                                txt_rec->txt = copy_label(pkt_buf, pkt_len, p - pkt_buf);
                                if (txt_rec->txt == NULL) {
                                        DEBUG_PRINTF("unable to copy label for TXT record\n");
                                        parse_error = 1;
                                        break;
                                }
                                p += txt_rec->txt[0] + 1;

                                if (p >= e)
                                        break;

                                // allocate another record
                                txt_rec->next = malloc(sizeof(struct rr_data_txt));
                                txt_rec = txt_rec->next;
                                txt_rec->next = NULL;
                        }
                        break;

                default:
                        // skip to end of RR data
                        p = e;
        }

        // if there was a parse error, destroy partial rr_entry
        if (parse_error) {
                rr_entry_destroy(rr);
                return 0;
        }

        rr_list_append(&pkt->rr_ans, rr);

        return p - (pkt_buf + off);
}

// parse a MDNS packet into an mdns_pkt struct
struct mdns_pkt *mdns_parse_pkt(uint8_t *pkt_buf, size_t pkt_len) {
        uint8_t *p = pkt_buf;
        size_t off;
        struct mdns_pkt *pkt;
        int i;

        if (pkt_len < 12)
                return NULL;

        MALLOC_ZERO_STRUCT(pkt, mdns_pkt);

        // parse header
        pkt->id                         = mdns_read_u16(p); p += sizeof(uint16_t);
        pkt->flags                      = mdns_read_u16(p); p += sizeof(uint16_t);
        pkt->num_qn             = mdns_read_u16(p); p += sizeof(uint16_t);
        pkt->num_ans_rr         = mdns_read_u16(p); p += sizeof(uint16_t);
        pkt->num_auth_rr        = mdns_read_u16(p); p += sizeof(uint16_t);
        pkt->num_add_rr         = mdns_read_u16(p); p += sizeof(uint16_t);

        off = p - pkt_buf;

        // parse questions
        for (i = 0; i < pkt->num_qn; i++) {
                size_t l = mdns_parse_qn(pkt_buf, pkt_len, off, pkt);
                if (! l) {
                        DEBUG_PRINTF("error parsing question #%d\n", i);
                        mdns_pkt_destroy(pkt);
                        return NULL;
                }

                off += l;
        }

        // parse answer RRs
        for (i = 0; i < pkt->num_ans_rr; i++) {
                size_t l = mdns_parse_rr(pkt_buf, pkt_len, off, pkt);
                if (! l) {
                        DEBUG_PRINTF("error parsing answer #%d\n", i);
                        mdns_pkt_destroy(pkt);
                        return NULL;
                }

                off += l;
        }

        // TODO: parse the authority and additional RR sections

        return pkt;
}

// encodes a name (label) into a packet using the name compression scheme
// encoded names will be added to the compression list for subsequent use
static size_t mdns_encode_name(uint8_t *pkt_buf, size_t pkt_len, size_t off,
                const uint8_t *name, struct name_comp *comp) {
        struct name_comp *c, *c_tail = NULL;
        uint8_t *p = pkt_buf + off;
        size_t len = 0;

        if (name) {
                while (*name) {
                        // find match for compression
                        for (c = comp; c; c = c->next) {
                                if (cmp_nlabel(name, c->label) == 0) {
                                        mdns_write_u16(p, 0xC000 | (c->pos & ~0xC000));
                                        return len + sizeof(uint16_t);
                                }

                                if (c->next == NULL)
                                        c_tail = c;
                        }

                        // copy this segment
                        int segment_len = *name + 1;
                        strncpy((char *) p, (char *) name, segment_len);

                        // cache the name for subsequent compression
                        DECL_MALLOC_ZERO_STRUCT(new_c, name_comp);

                        new_c->label = (uint8_t *) name;
                        new_c->pos = p - pkt_buf;
                        c_tail->next = new_c;

                        // advance to next name segment
                        p += segment_len;
                        len += segment_len;
                        name += segment_len;
                }
        }

        *p = '\0';      // root "label"
        len += 1;

        return len;
}

// encodes an RR entry at the given offset
// returns the size of the entire RR entry
static size_t mdns_encode_rr(uint8_t *pkt_buf, size_t pkt_len, size_t off,
                struct rr_entry *rr, struct name_comp *comp) {
        uint8_t *p = pkt_buf + off, *p_data;
        size_t l;
        struct rr_data_txt *txt_rec;
        uint8_t *label;
        int i;

        assert(off < pkt_len);

        // name
        l = mdns_encode_name(pkt_buf, pkt_len, off, rr->name, comp);
        assert(l != 0);
        p += l;

        // type
        p = mdns_write_u16(p, rr->type);

        // class & cache flush
        p = mdns_write_u16(p, (rr->rr_class & ~0x8000) | (rr->cache_flush << 15));

        // TTL
        p = mdns_write_u32(p, rr->ttl);

        // data length (filled in later)
        p += sizeof(uint16_t);

        // start of data marker
        p_data = p;

        switch (rr->type) {
                case RR_A:
                        /* htonl() needed coz addr already in net order */
                        p = mdns_write_u32(p, htonl(rr->data.A.addr));
                        break;

                case RR_AAAA:
                        for (i = 0; i < sizeof(struct in6_addr); i++)
                                *p++ = rr->data.AAAA.addr->s6_addr[i];
                        break;

                case RR_PTR:
                        label = rr->data.PTR.name ?
                                        rr->data.PTR.name :
                                        rr->data.PTR.entry->name;
                        p += mdns_encode_name(pkt_buf, pkt_len, p - pkt_buf, label, comp);
                        break;

                case RR_TXT:
                        txt_rec = &rr->data.TXT;
                        for (; txt_rec; txt_rec = txt_rec->next) {
                                int len = txt_rec->txt[0] + 1;
                                strncpy((char *) p, (char *) txt_rec->txt, len);
                                p += len;
                        }
                        break;

                case RR_SRV:
                        p = mdns_write_u16(p, rr->data.SRV.priority);

                        p = mdns_write_u16(p, rr->data.SRV.weight);

                        p = mdns_write_u16(p, rr->data.SRV.port);

                        p += mdns_encode_name(pkt_buf, pkt_len, p - pkt_buf,
                                        rr->data.SRV.target, comp);
                        break;

                case RR_NSEC:
                        p += mdns_encode_name(pkt_buf, pkt_len, p - pkt_buf,
                                        rr->name, comp);

                        *p++ = 0;       // bitmap window/block number

                        *p++ = sizeof(rr->data.NSEC.bitmap);    // bitmap length

                        for (i = 0; i < sizeof(rr->data.NSEC.bitmap); i++)
                                *p++ = rr->data.NSEC.bitmap[i];

                        break;

                default:
                        DEBUG_PRINTF("unhandled rr type 0x%02x\n", rr->type);
        }

        // calculate data length based on p
        l = p - p_data;

        // fill in the length
        mdns_write_u16(p - l - sizeof(uint16_t), l);

        return p - pkt_buf - off;
}

// encodes a MDNS packet from the given mdns_pkt struct into a buffer
// returns the size of the entire MDNS packet
size_t mdns_encode_pkt(struct mdns_pkt *answer, uint8_t *pkt_buf, size_t pkt_len) {
        struct name_comp *comp;
        uint8_t *p = pkt_buf;
        //uint8_t *e = pkt_buf + pkt_len;
        size_t off;
        int i;

        assert(answer != NULL);
        assert(pkt_len >= 12);

        if (p == NULL)
                return -1;

        // this is an Answer - number of qns should be zero
        assert(answer->num_qn == 0);

        p = mdns_write_u16(p, answer->id);
        p = mdns_write_u16(p, answer->flags);
        p = mdns_write_u16(p, answer->num_qn);
        p = mdns_write_u16(p, answer->num_ans_rr);
        p = mdns_write_u16(p, answer->num_auth_rr);
        p = mdns_write_u16(p, answer->num_add_rr);

        off = p - pkt_buf;

        // allocate list for name compression
        comp = malloc(sizeof(struct name_comp));
        if (comp == NULL)
                return -1;
        memset(comp, 0, sizeof(struct name_comp));

        // dummy entry
        comp->label = (uint8_t *) "";
        comp->pos = 0;

        // skip encoding of qn

        struct rr_list *rr_set[] = {
                answer->rr_ans,
                answer->rr_auth,
                answer->rr_add
        };

        // encode answer, authority and additional RRs
        for (i = 0; i < sizeof(rr_set) / sizeof(rr_set[0]); i++) {
                struct rr_list *rr = rr_set[i];
                for (; rr; rr = rr->next) {
                        size_t l = mdns_encode_rr(pkt_buf, pkt_len, off, rr->e, comp);
                        off += l;

                        if (off >= pkt_len) {
                                DEBUG_PRINTF("packet buffer too small\n");
                                return -1;
                        }
                }

        }

        // free name compression list
        while (comp) {
                struct name_comp *c = comp->next;
                free(comp);
                comp = c;
        }

        return off;
}

//******************************************************//
//                      mdnsd.c                         //
//******************************************************//

#ifdef _WIN32
#include <winsock2.h>
#include <ws2tcpip.h>
#define LOG_ERR 3
#else
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <syslog.h>
#endif

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <unistd.h>
#include <assert.h>
#include <pthread.h>

/*
 * Define a proper IP socket level if not already done.
 * Required to compile on OS X
 */
#ifndef SOL_IP
#define SOL_IP IPPROTO_IP
#endif

#define MDNS_ADDR "224.0.0.251"
#define MDNS_PORT 5353

#define PACKET_SIZE 65536

#define SERVICES_DNS_SD_NLABEL \
                ((uint8_t *) "\x09_services\x07_dns-sd\x04_udp\x05local")

struct mdnsd {
        pthread_mutex_t data_lock;
        int sockfd;
        int notify_pipe[2];
        int stop_flag;

        struct rr_group *group;
        struct rr_list *announce;
        struct rr_list *services;
        uint8_t *hostname;
};

struct mdns_service {
        struct rr_list *entries;
};

/////////////////////////////////



static int create_recv_sock() {
        int sd = socket(AF_INET, SOCK_DGRAM, 0);
        if (sd < 0) {
                log_message(LOG_ERR, "recv socket(): %m");
                return sd;
        }

        int r = -1;

        int on = 1;
        if ((r = setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *) &on, sizeof(on))) < 0) {
                log_message(LOG_ERR, "recv setsockopt(SO_REUSEADDR): %m");
                return r;
        }

        /* bind to an address */
        struct sockaddr_in serveraddr;
        memset(&serveraddr, 0, sizeof(serveraddr));
        serveraddr.sin_family = AF_INET;
        serveraddr.sin_port = htons(MDNS_PORT);
        serveraddr.sin_addr.s_addr = htonl(INADDR_ANY); /* receive multicast */
        if ((r = bind(sd, (struct sockaddr *)&serveraddr, sizeof(serveraddr))) < 0) {
                log_message(LOG_ERR, "recv bind(): %m");
        }

        // add membership to receiving socket
        struct ip_mreq mreq;
        memset(&mreq, 0, sizeof(struct ip_mreq));
        mreq.imr_interface.s_addr = htonl(INADDR_ANY);
        mreq.imr_multiaddr.s_addr = inet_addr(MDNS_ADDR);
        if ((r = setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *) &mreq, sizeof(mreq))) < 0) {
                log_message(LOG_ERR, "recv setsockopt(IP_ADD_MEMBERSHIP): %m");
                return r;
        }

        // enable loopback in case someone else needs the data
        if ((r = setsockopt(sd, IPPROTO_IP, IP_MULTICAST_LOOP, (char *) &on, sizeof(on))) < 0) {
                log_message(LOG_ERR, "recv setsockopt(IP_MULTICAST_LOOP): %m");
                return r;
        }


#ifdef IP_PKTINFO
        if ((r = setsockopt(sd, SOL_IP, IP_PKTINFO, (char *) &on, sizeof(on))) < 0) {
                log_message(LOG_ERR, "recv setsockopt(IP_PKTINFO): %m");
                return r;
        }
#endif

        return sd;
}

static ssize_t send_packet(int fd, const void *data, size_t len) {
        static struct sockaddr_in toaddr;
        if (toaddr.sin_family != AF_INET) {
                memset(&toaddr, 0, sizeof(struct sockaddr_in));
                toaddr.sin_family = AF_INET;
                toaddr.sin_port = htons(MDNS_PORT);
                toaddr.sin_addr.s_addr = inet_addr(MDNS_ADDR);
        }

        return sendto(fd, data, len, 0, (struct sockaddr *) &toaddr, sizeof(struct sockaddr_in));
}


// populate the specified list which matches the RR name and type
// type can be RR_ANY, which populates all entries EXCEPT RR_NSEC
static int populate_answers(struct mdnsd *svr, struct rr_list **rr_head, uint8_t *name, enum rr_type type) {
        int num_ans = 0;

        // check if we have the records
        pthread_mutex_lock(&svr->data_lock);
        struct rr_group *ans_grp = rr_group_find(svr->group, name);
        if (ans_grp == NULL) {
                pthread_mutex_unlock(&svr->data_lock);
                return num_ans;
        }

        // decide which records should go into answers
        struct rr_list *n = ans_grp->rr;
        for (; n; n = n->next) {
                // exclude NSEC for RR_ANY
                if (type == RR_ANY && n->e->type == RR_NSEC)
                        continue;

                if ((type == n->e->type || type == RR_ANY) && cmp_nlabel(name, n->e->name) == 0) {
                        num_ans += rr_list_append(rr_head, n->e);
                }
        }

        pthread_mutex_unlock(&svr->data_lock);

        return num_ans;
}

// given a list of RRs, look up related records and add them
static void add_related_rr(struct mdnsd *svr, struct rr_list *list, struct mdns_pkt *reply) {
        for (; list; list = list->next) {
                struct rr_entry *ans = list->e;

                switch (ans->type) {
                        case RR_PTR:
                                // target host A, AAAA records
                                reply->num_add_rr += populate_answers(svr, &reply->rr_add,
                                                                                MDNS_RR_GET_PTR_NAME(ans), RR_ANY);
                                break;

                        case RR_SRV:
                                // target host A, AAAA records
                                reply->num_add_rr += populate_answers(svr, &reply->rr_add,
                                                                                ans->data.SRV.target, RR_ANY);

                                // perhaps TXT records of the same name?
                                // if we use RR_ANY, we risk pulling in the same RR_SRV
                                reply->num_add_rr += populate_answers(svr, &reply->rr_add,
                                                                                ans->name, RR_TXT);
                                break;

                        case RR_A:
                        case RR_AAAA:
                                reply->num_add_rr += populate_answers(svr, &reply->rr_add,
                                                                                ans->name, RR_NSEC);
                                break;

                        default:
                                // nothing to add
                                break;
                }
        }
}

// creates an announce packet given the type name PTR
static void announce_srv(struct mdnsd *svr, struct mdns_pkt *reply, uint8_t *name) {
        mdns_init_reply(reply, 0);

        reply->num_ans_rr += populate_answers(svr, &reply->rr_ans, name, RR_PTR);

        // remember to add the services dns-sd PTR too
        reply->num_ans_rr += populate_answers(svr, &reply->rr_ans,
                                                                SERVICES_DNS_SD_NLABEL, RR_PTR);

        // see if we can match additional records for answers
        add_related_rr(svr, reply->rr_ans, reply);

        // additional records for additional records
        add_related_rr(svr, reply->rr_add, reply);
}

// processes the incoming MDNS packet
// returns >0 if processed, 0 otherwise
static int process_mdns_pkt(struct mdnsd *svr, struct mdns_pkt *pkt, struct mdns_pkt *reply) {
        int i;

        assert(pkt != NULL);

        // is it standard query?
        if ((pkt->flags & MDNS_FLAG_RESP) == 0 &&
                        MDNS_FLAG_GET_OPCODE(pkt->flags) == 0) {
                mdns_init_reply(reply, pkt->id);

                DEBUG_PRINTF("flags = %04x, qn = %d, ans = %d, add = %d\n",
                                                pkt->flags,
                                                pkt->num_qn,
                                                pkt->num_ans_rr,
                                                pkt->num_add_rr);

                // loop through questions
                struct rr_list *qnl = pkt->rr_qn;
                for (i = 0; i < pkt->num_qn; i++, qnl = qnl->next) {
                        struct rr_entry *qn = qnl->e;
                        int num_ans_added = 0;

                        char *namestr = nlabel_to_str(qn->name);
                        DEBUG_PRINTF("qn #%d: type %s (%02x) %s - ", i, rr_get_type_name(qn->type), qn->type, namestr);
                        free(namestr);

                        // check if it's a unicast query - we ignore those
                        if (qn->unicast_query) {
                                DEBUG_PRINTF("skipping unicast query\n");
                                continue;
                        }

                        num_ans_added = populate_answers(svr, &reply->rr_ans, qn->name, qn->type);
                        reply->num_ans_rr += num_ans_added;

                        DEBUG_PRINTF("added %d answers\n", num_ans_added);
                }

                // remove our replies if they were already in their answers
                struct rr_list *ans = NULL, *prev_ans = NULL;
                for (ans = reply->rr_ans; ans; ) {
                        struct rr_list *next_ans = ans->next;
                        struct rr_entry *known_ans = rr_entry_match(pkt->rr_ans, ans->e);

                        // discard answers that have at least half of the actual TTL
                        if (known_ans != NULL && known_ans->ttl >= ans->e->ttl / 2) {
                                char *namestr = nlabel_to_str(ans->e->name);
                                DEBUG_PRINTF("removing answer for %s\n", namestr);
                                free(namestr);

                                // check if list item is head
                                if (prev_ans == NULL)
                                        reply->rr_ans = ans->next;
                                else
                                        prev_ans->next = ans->next;
                                free(ans);

                                ans = prev_ans;

                                // adjust answer count
                                reply->num_ans_rr--;
                        }

                        prev_ans = ans;
                        ans = next_ans;
                }


                // see if we can match additional records for answers
                add_related_rr(svr, reply->rr_ans, reply);

                // additional records for additional records
                add_related_rr(svr, reply->rr_add, reply);

                DEBUG_PRINTF("\n");

                return reply->num_ans_rr;
        }

        return 0;
}

int create_pipe(int handles[2]) {
#ifdef _WIN32
        SOCKET sock = socket(AF_INET, SOCK_STREAM, 0);
        if (sock == INVALID_SOCKET) {
                return -1;
        }
        struct sockaddr_in serv_addr;
        memset(&serv_addr, 0, sizeof(serv_addr));
        serv_addr.sin_family = AF_INET;
        serv_addr.sin_port = htons(0);
        serv_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
        if (bind(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == SOCKET_ERROR) {
                closesocket(sock);
                return -1;
        }
        if (listen(sock, 1) == SOCKET_ERROR) {
                closesocket(sock);
                return -1;
        }
        int len = sizeof(serv_addr);
        if (getsockname(sock, (SOCKADDR*)&serv_addr, &len) == SOCKET_ERROR) {
                closesocket(sock);
                return -1;
        }
        if ((handles[1] = socket(PF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET) {
                closesocket(sock);
                return -1;
        }
        if (connect(handles[1], (struct sockaddr*)&serv_addr, len) == SOCKET_ERROR) {
                closesocket(sock);
                return -1;
        }
        if ((handles[0] = accept(sock, (struct sockaddr*)&serv_addr, &len)) == INVALID_SOCKET) {
                closesocket((SOCKET)handles[1]);
                handles[1] = INVALID_SOCKET;
                closesocket(sock);
                return -1;
        }
        closesocket(sock);
        return 0;
#else
        return pipe(handles);
#endif
}

int read_pipe(int s, char* buf, int len) {
#ifdef _WIN32
        int ret = recv(s, buf, len, 0);
        if (ret < 0 && WSAGetLastError() == WSAECONNRESET) {
                ret = 0;
        }
        return ret;
#else
        return read(s, buf, len);
#endif
}

int write_pipe(int s, char* buf, int len) {
#ifdef _WIN32
        return send(s, buf, len, 0);
#else
        return write(s, buf, len);
#endif
}

int close_pipe(int s) {
#ifdef _WIN32
        return closesocket(s);
#else
        return close(s);
#endif
}

// main loop to receive, process and send out MDNS replies
// also handles MDNS service announces
static void main_loop(struct mdnsd *svr) {
        fd_set sockfd_set;
        int max_fd = svr->sockfd;
        char notify_buf[2];     // buffer for reading of notify_pipe

        void *pkt_buffer = malloc(PACKET_SIZE);

        if (svr->notify_pipe[0] > max_fd)
                max_fd = svr->notify_pipe[0];

        struct mdns_pkt *mdns_reply = malloc(sizeof(struct mdns_pkt));
        memset(mdns_reply, 0, sizeof(struct mdns_pkt));

        while (! svr->stop_flag) {
                FD_ZERO(&sockfd_set);
                FD_SET(svr->sockfd, &sockfd_set);
                FD_SET(svr->notify_pipe[0], &sockfd_set);
                select(max_fd + 1, &sockfd_set, NULL, NULL, NULL);

                if (FD_ISSET(svr->notify_pipe[0], &sockfd_set)) {
                        // flush the notify_pipe
                        read_pipe(svr->notify_pipe[0], (char*)&notify_buf, 1);
                } else if (FD_ISSET(svr->sockfd, &sockfd_set)) {
                        struct sockaddr_in fromaddr;
                        socklen_t sockaddr_size = sizeof(struct sockaddr_in);

                        ssize_t recvsize = recvfrom(svr->sockfd, pkt_buffer, PACKET_SIZE, 0,
                                (struct sockaddr *) &fromaddr, &sockaddr_size);
                        if (recvsize < 0) {
                                log_message(LOG_ERR, "recv(): %m");
                        }

                        DEBUG_PRINTF("data from=%s size=%ld\n", inet_ntoa(fromaddr.sin_addr), (long) recvsize);
                        struct mdns_pkt *mdns = mdns_parse_pkt(pkt_buffer, recvsize);
                        if (mdns != NULL) {
                                if (process_mdns_pkt(svr, mdns, mdns_reply)) {
                                        size_t replylen = mdns_encode_pkt(mdns_reply, pkt_buffer, PACKET_SIZE);
                                        send_packet(svr->sockfd, pkt_buffer, replylen);
                                } else if (mdns->num_qn == 0) {
                                        DEBUG_PRINTF("(no questions in packet)\n\n");
                                }

                                mdns_pkt_destroy(mdns);
                        }
                }

                // send out announces
                while (1) {
                        struct rr_entry *ann_e = NULL;

                        // extract from head of list
                        pthread_mutex_lock(&svr->data_lock);
                        if (svr->announce)
                                ann_e = rr_list_remove(&svr->announce, svr->announce->e);
                        pthread_mutex_unlock(&svr->data_lock);

                        if (! ann_e)
                                break;

                        char *namestr = nlabel_to_str(ann_e->name);
                        DEBUG_PRINTF("sending announce for %s\n", namestr);
                        free(namestr);

                        announce_srv(svr, mdns_reply, ann_e->name);

                        if (mdns_reply->num_ans_rr > 0) {
                                size_t replylen = mdns_encode_pkt(mdns_reply, pkt_buffer, PACKET_SIZE);
                                send_packet(svr->sockfd, pkt_buffer, replylen);
                        }
                }
        }

        // main thread terminating. send out "goodbye packets" for services
        mdns_init_reply(mdns_reply, 0);

        pthread_mutex_lock(&svr->data_lock);
        struct rr_list *svc_le = svr->services;
        for (; svc_le; svc_le = svc_le->next) {
                // set TTL to zero
                svc_le->e->ttl = 0;
                mdns_reply->num_ans_rr += rr_list_append(&mdns_reply->rr_ans, svc_le->e);
        }
        pthread_mutex_unlock(&svr->data_lock);

        // send out packet
        if (mdns_reply->num_ans_rr > 0) {
                size_t replylen = mdns_encode_pkt(mdns_reply, pkt_buffer, PACKET_SIZE);
                send_packet(svr->sockfd, pkt_buffer, replylen);
        }

        // destroy packet
        mdns_init_reply(mdns_reply, 0);
        free(mdns_reply);

        free(pkt_buffer);

        close_pipe(svr->sockfd);

        svr->stop_flag = 2;
}

/////////////////////////////////////////////////////


void mdnsd_set_hostname(struct mdnsd *svr, const char *hostname, uint32_t ip) {
        struct rr_entry *a_e = NULL,
                                        *nsec_e = NULL;

        // currently can't be called twice
        // dont ask me what happens if the IP changes
        assert(svr->hostname == NULL);

        a_e = rr_create_a(create_nlabel(hostname), ip);

        nsec_e = rr_create(create_nlabel(hostname), RR_NSEC);
        rr_set_nsec(nsec_e, RR_A);

        pthread_mutex_lock(&svr->data_lock);
        svr->hostname = create_nlabel(hostname);
        rr_group_add(&svr->group, a_e);
        rr_group_add(&svr->group, nsec_e);
        pthread_mutex_unlock(&svr->data_lock);
}

void mdnsd_set_hostname_v6(struct mdnsd *svr, const char *hostname, struct in6_addr *addr)
{
        struct rr_entry *aaaa_e = NULL,
                                        *nsec_e = NULL;

        // currently can't be called twice
        // dont ask me what happens if the IP changes
        assert(svr->hostname == NULL);

        aaaa_e = rr_create_aaaa(create_nlabel(hostname), addr);

        nsec_e = rr_create(create_nlabel(hostname), RR_NSEC);
        rr_set_nsec(nsec_e, RR_AAAA);

        pthread_mutex_lock(&svr->data_lock);
        svr->hostname = create_nlabel(hostname);
        rr_group_add(&svr->group, aaaa_e);
        rr_group_add(&svr->group, nsec_e);
        pthread_mutex_unlock(&svr->data_lock);
}

void mdnsd_add_rr(struct mdnsd *svr, struct rr_entry *rr) {
        pthread_mutex_lock(&svr->data_lock);
        rr_group_add(&svr->group, rr);
        pthread_mutex_unlock(&svr->data_lock);
}

struct mdns_service *mdnsd_register_svc(struct mdnsd *svr, const char *instance_name,
                const char *type, uint16_t port, const char *hostname, const char *txt[]) {
        struct rr_entry *txt_e = NULL,
                                        *srv_e = NULL,
                                        *ptr_e = NULL,
                                        *bptr_e = NULL;
        uint8_t *target;
        uint8_t *inst_nlabel, *type_nlabel, *nlabel;
        struct mdns_service *service = malloc(sizeof(struct mdns_service));
        memset(service, 0, sizeof(struct mdns_service));

        // combine service name
        type_nlabel = create_nlabel(type);
        inst_nlabel = create_label(instance_name);
        nlabel = join_nlabel(inst_nlabel, type_nlabel);

        // create TXT record
        if (txt && *txt) {
                txt_e = rr_create(dup_nlabel(nlabel), RR_TXT);
                rr_list_append(&service->entries, txt_e);

                // add TXTs
                for (; *txt; txt++)
                        rr_add_txt(txt_e, *txt);
        }

        // create SRV record
        assert(hostname || svr->hostname);      // either one as target
        target = hostname ?
                                create_nlabel(hostname) :
                                dup_nlabel(svr->hostname);

        srv_e = rr_create_srv(dup_nlabel(nlabel), port, target);
        rr_list_append(&service->entries, srv_e);

        // create PTR record for type
        ptr_e = rr_create_ptr(type_nlabel, srv_e);

        // create services PTR record for type
        // this enables the type to show up as a "service"
        bptr_e = rr_create_ptr(dup_nlabel(SERVICES_DNS_SD_NLABEL), ptr_e);

        // modify lists here
        pthread_mutex_lock(&svr->data_lock);

        if (txt_e)
                rr_group_add(&svr->group, txt_e);
        rr_group_add(&svr->group, srv_e);
        rr_group_add(&svr->group, ptr_e);
        rr_group_add(&svr->group, bptr_e);

        // append PTR entry to announce list
        rr_list_append(&svr->announce, ptr_e);
        rr_list_append(&svr->services, ptr_e);

        pthread_mutex_unlock(&svr->data_lock);

        // don't free type_nlabel - it's with the PTR record
        free(nlabel);
        free(inst_nlabel);

        // notify server
        write_pipe(svr->notify_pipe[1], ".", 1);

        return service;
}

void mdns_service_destroy(struct mdns_service *srv) {
        assert(srv != NULL);
        rr_list_destroy(srv->entries, 0);
        free(srv);
}

struct mdnsd *mdnsd_start() {
        pthread_t tid;
        pthread_attr_t attr;

        struct mdnsd *server = malloc(sizeof(struct mdnsd));
        memset(server, 0, sizeof(struct mdnsd));

        if (create_pipe(server->notify_pipe) != 0) {
                log_message(LOG_ERR, "pipe(): %m\n");
                free(server);
                return NULL;
        }

        server->sockfd = create_recv_sock();
        if (server->sockfd < 0) {
                log_message(LOG_ERR, "unable to create recv socket");
                free(server);
                return NULL;
        }

        pthread_mutex_init(&server->data_lock, NULL);

        // init thread
        pthread_attr_init(&attr);
        pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

        if (pthread_create(&tid, &attr, (void *(*)(void *)) main_loop, (void *) server) != 0) {
                pthread_mutex_destroy(&server->data_lock);
                free(server);
                return NULL;
        }

        return server;
}

void mdnsd_stop(struct mdnsd *s) {
        assert(s != NULL);

        struct timespec ts = {
                .tv_sec = 0,
                .tv_nsec = 500 * 1000000,
        };

        s->stop_flag = 1;
        write_pipe(s->notify_pipe[1], ".", 1);

        while (s->stop_flag != 2)
                nanosleep(&ts, NULL);

        close_pipe(s->notify_pipe[0]);
        close_pipe(s->notify_pipe[1]);

        pthread_mutex_destroy(&s->data_lock);
        rr_group_destroy(s->group);
        rr_list_destroy(s->announce, 0);
        rr_list_destroy(s->services, 0);

        if (s->hostname)
                free(s->hostname);

        free(s);
}