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#
# Makefile for tinysvcmdns
#
CFLAGS += -Wall -pedantic -std=gnu99
#CFLAGS += -g
CFLAGS += -O2 -DNDEBUG
LDLIBS = -lpthread
BIN=testmdnsd
LIBTINYSVCMDNS_OBJS = mdns.o mdnsd.o
.PHONY: all clean
all: $(BIN) libtinysvcmdns.a
clean:
-$(RM) *.o
-$(RM) *.bin
-$(RM) mdns
-$(RM) $(BIN)
-$(RM) libtinysvcmdns.a
mdns: mdns.o
mdnsd: mdns.o mdnsd.o
testmdnsd: testmdnsd.o libtinysvcmdns.a
libtinysvcmdns.a: $(patsubst %, libtinysvcmdns.a(%), $(LIBTINYSVCMDNS_OBJS))

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tinysvcmdns
============
tinysvcmdns is a tiny MDNS responder implementation for publishing services.
This implementation is only concerned with publishing services, without a
system-wide daemon like Bonjour or Avahi. Its other goal is to be extremely
small, embeddable, and have no external dependencies.
It only answers queries related to its own hostname (the A record), the
service PTRs, and the "_services.dns-sd._udp.local" name, which advertises
all services on a particular host.
Services consist of a single SRV and TXT record.
Decoding of MDNS packets is only done to retrieve the questions and answer RRs.
The purpose for decoding answer RRs is to make sure the service PTR is not
sent out if it is already included in the answer RRs.
It also only utilizes multicast packets, so no "QU" queries are accepted.
There is no name collision detection, so this means no queries are generated
before publishing the services. However compliant responders will avoid using
our names, since the implementation will respond to queries that match our
name.
TODO
-----
* better, more stable & complete API
* name collision detection
FILES
------
* mdns.c - provides data structures, parsing & encoding of MDNS packets
* mdnsd.c - implements the server socket, communication and thread
* testmdnsd.c - an example that creates an instance until terminated
LICENSE
--------
Copyright (C) 2011 Darell Tan
This library 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.
This library 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 this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

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/*
* tinysvcmdns - a tiny MDNS implementation for publishing services
* Copyright (C) 2011 Darell Tan
*
* This library 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.
*
* This library 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 this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "mdns.h"
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <netinet/in.h>
#define DEFAULT_TTL 120
struct name_comp {
uint8_t *label; // label
size_t pos; // position in msg
struct name_comp *next;
};
// ----- label functions -----
// compares 2 names
static inline int cmp_nlabel(const uint8_t *L1, const uint8_t *L2) {
return strcmp((char *) L1, (char *) L2);
}
// 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 -----
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_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->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)
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;
}
}
// 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 = ntohs( * (uint16_t *) p );
p += sizeof(uint16_t);
rr->unicast_query = (*p & 0x80) == 0x80;
rr->rr_class = ntohs( * (uint16_t *) 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;
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 = ntohs( * (uint16_t *) p );
p += sizeof(uint16_t);
rr->cache_flush = (*p & 0x80) == 0x80;
rr->rr_class = ntohs( * (uint16_t *) p) & ~0x80;
p += sizeof(uint16_t);
rr->ttl = ntohl( * (uint32_t *) p );
p += sizeof(uint32_t);
// RR data
rr_data_len = ntohs( * (uint16_t *) p );
p += sizeof(uint16_t);
e = p + rr_data_len;
// see if we can parse the RR data
switch (rr->type) {
case RR_A:
rr->data.A.addr = ntohl( * (uint32_t *) p );
p += sizeof(uint32_t);
break;
case RR_PTR:
rr->data.PTR.name = uncompress_nlabel(pkt_buf, pkt_len, p - pkt_buf);
p += rr_data_len;
break;
case RR_TXT:
txt_rec = &rr->data.TXT;
while (1) {
txt_rec->txt = copy_label(pkt_buf, pkt_len, p - pkt_buf);
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;
}
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) {
uint16_t *p = (uint16_t *) 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 = ntohs(*p); p++;
pkt->flags = ntohs(*p); p++;
pkt->num_qn = ntohs(*p); p++;
pkt->num_ans_rr = ntohs(*p); p++;
pkt->num_auth_rr = ntohs(*p); p++;
pkt->num_add_rr = ntohs(*p); p++;
off = (uint8_t *) 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) {
*(uint16_t *) p = htons(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
*(uint16_t *) p = htons(rr->type);
p += sizeof(uint16_t);
// class & cache flush
*(uint16_t *) p = htons((rr->rr_class & ~0x8000) | (rr->cache_flush << 15));
p += sizeof(uint16_t);
// TTL
*(uint32_t *) p = htonl(rr->ttl);
p += sizeof(uint32_t);
// data length (filled in later)
p += sizeof(uint16_t);
// start of data marker
p_data = p;
switch (rr->type) {
case RR_A:
*(uint32_t *) p = (rr->data.A.addr);
p += sizeof(uint32_t);
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:
*(uint16_t *) p = htons(rr->data.SRV.priority);
p += sizeof(uint16_t);
*(uint16_t *) p = htons(rr->data.SRV.weight);
p += sizeof(uint16_t);
*(uint16_t *) p = htons(rr->data.SRV.port);
p += sizeof(uint16_t);
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
*(uint16_t *) (p - l - sizeof(uint16_t)) = htons(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;
uint16_t *p = (uint16_t *) 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++ = htons(answer->id);
*p++ = htons(answer->flags);
*p++ = htons(answer->num_qn);
*p++ = htons(answer->num_ans_rr);
*p++ = htons(answer->num_auth_rr);
*p++ = htons(answer->num_add_rr);
off = (uint8_t *) 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;
}

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mdns.h Normal file
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/*
* tinysvcmdns - a tiny MDNS implementation for publishing services
* Copyright (C) 2011 Darell Tan
*
* This library 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.
*
* This library 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 this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef __MDNS_H__
#define __MDNS_H__
#include <stdint.h>
#include <stdlib.h>
#define MALLOC_ZERO_STRUCT(x, type) \
x = malloc(sizeof(struct type)); \
memset(x, 0, sizeof(struct type));
#define DECL_MALLOC_ZERO_STRUCT(x, type) \
struct type * MALLOC_ZERO_STRUCT(x, type)
#ifndef NDEBUG
#define DEBUG_PRINTF(...) printf(__VA_ARGS__)
#else
#define DEBUG_PRINTF(...) ((void) 0)
#endif
struct rr_data_srv {
uint16_t priority;
uint16_t weight;
uint16_t port;
uint8_t *target; // host
};
struct rr_data_txt {
struct rr_data_txt *next;
uint8_t *txt;
};
struct rr_data_nsec {
//uint8_t *name; // same as record
// NSEC occupies the 47th bit, 5 bytes
//uint8_t bitmap_len; // = 5
uint8_t bitmap[5]; // network order: first byte contains LSB
};
struct rr_data_ptr {
uint8_t *name; // NULL if entry is to be used
struct rr_entry *entry;
};
struct rr_data_a {
uint32_t addr;
};
struct rr_entry {
uint8_t *name;
enum rr_type {
RR_A = 0x01,
RR_PTR = 0x0C,
RR_TXT = 0x10,
RR_AAAA = 0x1C,
RR_SRV = 0x21,
RR_NSEC = 0x2F,
RR_ANY = 0xFF,
} type;
uint32_t ttl;
// for use in Questions only
char unicast_query;
// for use in Answers only
char cache_flush;
uint16_t rr_class;
// RR data
union {
struct rr_data_nsec NSEC;
struct rr_data_srv SRV;
struct rr_data_txt TXT;
struct rr_data_ptr PTR;
struct rr_data_a A;
} data;
};
struct rr_list {
struct rr_entry *e;
struct rr_list *next;
};
struct rr_group {
uint8_t *name;
struct rr_list *rr;
struct rr_group *next;
};
#define MDNS_FLAG_RESP (1 << 15) // Query=0 / Response=1
#define MDNS_FLAG_AA (1 << 10) // Authoritative
#define MDNS_FLAG_TC (1 << 9) // TrunCation
#define MDNS_FLAG_RD (1 << 8) // Recursion Desired
#define MDNS_FLAG_RA (1 << 7) // Recursion Available
#define MDNS_FLAG_Z (1 << 6) // Reserved (zero)
#define MDNS_FLAG_GET_RCODE(x) (x & 0x0F)
#define MDNS_FLAG_GET_OPCODE(x) ((x >> 11) & 0x0F)
struct mdns_pkt {
uint16_t id; // transaction ID
uint16_t flags;
uint16_t num_qn;
uint16_t num_ans_rr;
uint16_t num_auth_rr;
uint16_t num_add_rr;
struct rr_list *rr_qn; // questions
struct rr_list *rr_ans; // answer RRs
struct rr_list *rr_auth; // authority RRs
struct rr_list *rr_add; // additional RRs
};
struct mdns_pkt *mdns_parse_pkt(uint8_t *pkt_buf, size_t pkt_len);
void mdns_init_reply(struct mdns_pkt *pkt, uint16_t id);
size_t mdns_encode_pkt(struct mdns_pkt *answer, uint8_t *pkt_buf, size_t pkt_len);
void mdns_pkt_destroy(struct mdns_pkt *p);
void rr_group_destroy(struct rr_group *group);
struct rr_group *rr_group_find(struct rr_group *g, uint8_t *name);
struct rr_entry *rr_entry_find(struct rr_list *rr_list, uint8_t *name, uint16_t type);
void rr_group_add(struct rr_group **group, struct rr_entry *rr);
int rr_list_count(struct rr_list *rr);
int rr_list_append(struct rr_list **rr_head, struct rr_entry *rr);
struct rr_entry *rr_list_remove(struct rr_list **rr_head, struct rr_entry *rr);
void rr_list_destroy(struct rr_list *rr, char destroy_items);
struct rr_entry *rr_create_ptr(uint8_t *name, struct rr_entry *d_rr);
struct rr_entry *rr_create_srv(uint8_t *name, uint16_t port, uint8_t *target);
struct rr_entry *rr_create_a(uint8_t *name, uint32_t addr);
struct rr_entry *rr_create(uint8_t *name, enum rr_type type);
void rr_set_nsec(struct rr_entry *rr_nsec, enum rr_type type);
void rr_add_txt(struct rr_entry *rr_txt, const char *txt);
uint8_t *create_label(const char *txt);
uint8_t *create_nlabel(const char *name);
char *nlabel_to_str(const uint8_t *name);
uint8_t *dup_label(const uint8_t *label);
uint8_t *dup_nlabel(const uint8_t *n);
uint8_t *join_nlabel(const uint8_t *n1, const uint8_t *n2);
#endif /*!__MDNS_H__*/

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/*
* tinysvcmdns - a tiny MDNS implementation for publishing services
* Copyright (C) 2011 Darell Tan
*
* This library 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.
*
* This library 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 this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.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>
#include <syslog.h>
#include "mdns.h"
#include "mdnsd.h"
#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 void log_message(int loglevel, char *fmt_str, ...) {
va_list ap;
char buf[2048];
va_start(ap, fmt_str);
vsnprintf(buf, 2047, fmt_str, ap);
va_end(ap);
buf[2047] = 0;
fprintf(stderr, "%s\n", buf);
}
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;
struct rr_entry *rr;
// 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;
}
// include all records?
if (type == RR_ANY) {
struct rr_list *n = ans_grp->rr;
for (; n; n = n->next) {
// exclude NSEC
if (n->e->type == RR_NSEC)
continue;
num_ans += rr_list_append(rr_head, n->e);
}
} else {
// match record type
rr = rr_entry_find(ans_grp->rr, name, type);
if (rr)
num_ans += rr_list_append(rr_head, rr);
}
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,
(ans->data.PTR.name ?
ans->data.PTR.name :
ans->data.PTR.entry->name),
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;
char *namestr = nlabel_to_str(qn->name);
DEBUG_PRINTF("qn #%d: type 0x%02x %s - ", i, 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;
}
// see if it is in the answers
if (rr_entry_find(pkt->rr_ans, qn->name, qn->type)) {
DEBUG_PRINTF("our record is already in their answers\n");
continue;
}
reply->num_ans_rr += populate_answers(svr, &reply->rr_ans, qn->name, qn->type);
DEBUG_PRINTF("adding %d answers\n", reply->num_ans_rr);
}
// 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;
}
// 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;
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) {
struct timeval tv = {
.tv_sec = 0,
.tv_usec = 0,
};
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, &tv);
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);
}
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(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);
}
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_nlabel(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(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 (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 timeval tv = {
.tv_sec = 0,
.tv_usec = 500 * 1000,
};
s->stop_flag = 1;
write(s->notify_pipe[1], ".", 1);
while (s->stop_flag != 2)
select(0, NULL, NULL, NULL, &tv);
close(s->notify_pipe[0]);
close(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);
}

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/*
* tinysvcmdns - a tiny MDNS implementation for publishing services
* Copyright (C) 2011 Darell Tan
*
* This library 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.
*
* This library 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 this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef __MDNSD_H__
#define __MDNSD_H__
#include <stdint.h>
struct mdnsd;
struct mdns_service;
// starts a MDNS responder instance
// returns NULL if unsuccessful
struct mdnsd *mdnsd_start();
// stops the given MDNS responder instance
void mdnsd_stop(struct mdnsd *s);
// sets the hostname for the given MDNS responder instance
void mdnsd_set_hostname(struct mdnsd *svr, const char *hostname, uint32_t ip);
// registers a service with the MDNS responder instance
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[]);
// destroys the mdns_service struct returned by mdnsd_register_svc()
void mdns_service_destroy(struct mdns_service *srv);
#endif/*!__MDNSD_H__*/

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/*
* tinysvcmdns - a tiny MDNS implementation for publishing services
* Copyright (C) 2011 Darell Tan
*
* This library 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.
*
* This library 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 this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include "mdns.h"
#include "mdnsd.h"
int main(int argc, char *argv[]) {
// create host entries
char *hostname = "some-random-host.local";
struct mdnsd *svr = mdnsd_start();
if (svr == NULL) {
printf("mdnsd_start() error\n");
return 1;
}
printf("mdnsd_start OK. press ENTER to add hostname & service\n");
getchar();
mdnsd_set_hostname(svr, hostname, inet_addr("192.168.0.29"));
const char *txt[] = {
"path=/mywebsite",
NULL
};
struct mdns_service *svc = mdnsd_register_svc(svr, "My Website",
"_http._tcp.local", 8080, NULL, txt);
mdns_service_destroy(svc);
printf("added service and hostname. press ENTER to exit\n");
getchar();
mdnsd_stop(svr);
return 0;
}