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bonjour/src/mdns.h

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/* mdns.h - mDNS/DNS-SD library - Public Domain - 2017 Mattias Jansson
*
* This library provides a cross-platform mDNS and DNS-SD library in C.
* The implementation is based on RFC 6762 and RFC 6763.
*
* The latest source code is always available at
*
* https://github.com/mjansson/mdns
*
* This library is put in the public domain; you can redistribute it and/or modify it without any
* restrictions.
*
*/
#pragma once
#include <stdint.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#ifdef _WIN32
#include <Winsock2.h>
#include <Ws2tcpip.h>
#define strncasecmp _strnicmp
#else
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#endif
#ifdef __cplusplus
extern "C" {
#endif
#define MDNS_INVALID_POS ((size_t)-1)
#define MDNS_STRING_CONST(s) (s), (sizeof((s)) - 1)
#define MDNS_STRING_FORMAT(s) (int)((s).length), s.str
#define MDNS_POINTER_OFFSET(p, ofs) ((void*)((char*)(p) + (ptrdiff_t)(ofs)))
#define MDNS_POINTER_OFFSET_CONST(p, ofs) ((const void*)((const char*)(p) + (ptrdiff_t)(ofs)))
#define MDNS_POINTER_DIFF(a, b) ((size_t)((const char*)(a) - (const char*)(b)))
#define MDNS_PORT 5353
#define MDNS_UNICAST_RESPONSE 0x8000U
#define MDNS_CACHE_FLUSH 0x8000U
enum mdns_record_type {
MDNS_RECORDTYPE_IGNORE = 0,
// Address
MDNS_RECORDTYPE_A = 1,
// Domain Name pointer
MDNS_RECORDTYPE_PTR = 12,
// Arbitrary text string
MDNS_RECORDTYPE_TXT = 16,
// IP6 Address [Thomson]
MDNS_RECORDTYPE_AAAA = 28,
// Server Selection [RFC2782]
MDNS_RECORDTYPE_SRV = 33
};
enum mdns_entry_type {
MDNS_ENTRYTYPE_QUESTION = 0,
MDNS_ENTRYTYPE_ANSWER = 1,
MDNS_ENTRYTYPE_AUTHORITY = 2,
MDNS_ENTRYTYPE_ADDITIONAL = 3
};
enum mdns_class { MDNS_CLASS_IN = 1 };
typedef enum mdns_record_type mdns_record_type_t;
typedef enum mdns_entry_type mdns_entry_type_t;
typedef enum mdns_class mdns_class_t;
typedef int (*mdns_record_callback_fn)(int sock, const struct sockaddr* from, size_t addrlen,
mdns_entry_type_t entry, uint16_t query_id, uint16_t rtype,
uint16_t rclass, uint32_t ttl, const void* data, size_t size,
size_t name_offset, size_t name_length, size_t record_offset,
size_t record_length, void* user_data);
typedef struct mdns_string_t mdns_string_t;
typedef struct mdns_string_pair_t mdns_string_pair_t;
typedef struct mdns_record_srv_t mdns_record_srv_t;
typedef struct mdns_record_txt_t mdns_record_txt_t;
#ifdef _WIN32
typedef int mdns_size_t;
#else
typedef size_t mdns_size_t;
#endif
struct mdns_string_t {
const char* str;
size_t length;
};
struct mdns_string_pair_t {
size_t offset;
size_t length;
int ref;
};
struct mdns_record_srv_t {
uint16_t priority;
uint16_t weight;
uint16_t port;
mdns_string_t name;
};
struct mdns_record_txt_t {
mdns_string_t key;
mdns_string_t value;
};
struct mdns_header_t {
uint16_t query_id;
uint16_t flags;
uint16_t questions;
uint16_t answer_rrs;
uint16_t authority_rrs;
uint16_t additional_rrs;
};
// mDNS/DNS-SD public API
//! Open and setup a IPv4 socket for mDNS/DNS-SD. To bind the socket to a specific interface,
// pass in the appropriate socket address in saddr, otherwise pass a null pointer for INADDR_ANY.
// To send one-shot discovery requests and queries pass a null pointer or set 0 as port to assign
// a random user level ephemeral port. To run discovery service listening for incoming
// discoveries and queries, you must set MDNS_PORT as port.
static int
mdns_socket_open_ipv4(struct sockaddr_in* saddr);
//! Setup an already opened IPv4 socket for mDNS/DNS-SD. To bind the socket to a specific interface,
// pass in the appropriate socket address in saddr, otherwise pass a null pointer for INADDR_ANY.
// To send one-shot discovery requests and queries pass a null pointer or set 0 as port to assign
// a random user level ephemeral port. To run discovery service listening for incoming
// discoveries and queries, you must set MDNS_PORT as port.
static int
mdns_socket_setup_ipv4(int sock, struct sockaddr_in* saddr);
//! Open and setup a IPv6 socket for mDNS/DNS-SD. To bind the socket to a specific interface,
// pass in the appropriate socket address in saddr, otherwise pass a null pointer for in6addr_any.
// To send one-shot discovery requests and queries pass a null pointer or set 0 as port to assign
// a random user level ephemeral port. To run discovery service listening for incoming
// discoveries and queries, you must set MDNS_PORT as port.
static int
mdns_socket_open_ipv6(struct sockaddr_in6* saddr);
//! Setup an already opened IPv6 socket for mDNS/DNS-SD. To bind the socket to a specific interface,
// pass in the appropriate socket address in saddr, otherwise pass a null pointer for in6addr_any.
// To send one-shot discovery requests and queries pass a null pointer or set 0 as port to assign
// a random user level ephemeral port. To run discovery service listening for incoming
// discoveries and queries, you must set MDNS_PORT as port.
static int
mdns_socket_setup_ipv6(int sock, struct sockaddr_in6* saddr);
//! Close a socket opened with mdns_socket_open_ipv4 and mdns_socket_open_ipv6.
static void
mdns_socket_close(int sock);
//! Listen for incoming multicast DNS-SD and mDNS query requests. The socket should have been
// opened on port MDNS_PORT using one of the mdns open or setup socket functions. Returns the
// number of queries parsed.
static size_t
mdns_socket_listen(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
void* user_data);
//! Send a multicast DNS-SD reqeuest on the given socket to discover available services. Returns
// 0 on success, or <0 if error.
static int
mdns_discovery_send(int sock);
//! Recieve unicast responses to a DNS-SD sent with mdns_discovery_send. Any data will be piped to
// the given callback for parsing. Returns the number of responses parsed.
static size_t
mdns_discovery_recv(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
void* user_data);
//! Send a unicast DNS-SD answer with a single record to the given address. Returns 0 if success,
// or <0 if error.
static int
mdns_discovery_answer(int sock, const void* address, size_t address_size, void* buffer,
size_t capacity, const char* record, size_t length);
//! Send a multicast mDNS query on the given socket for the given service name. The supplied buffer
// will be used to build the query packet. The query ID can be set to non-zero to filter responses,
// however the RFC states that the query ID SHOULD be set to 0 for multicast queries. The query
// will request a unicast response if the socket is bound to an ephemeral port, or a multicast
// response if the socket is bound to mDNS port 5353.
// Returns the used query ID, or <0 if error.
static int
mdns_query_send(int sock, mdns_record_type_t type, const char* name, size_t length, void* buffer,
size_t capacity, uint16_t query_id);
//! Receive unicast responses to a mDNS query sent with mdns_discovery_recv, optionally filtering
// out any responses not matching the given query ID. Set the query ID to 0 to parse
// all responses, even if it is not matching the query ID set in a specific query. Any data will
// be piped to the given callback for parsing. Returns the number of responses parsed.
static size_t
mdns_query_recv(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
void* user_data, int query_id);
//! Send a unicast or multicast mDNS query answer with a single record to the given address. The
// answer will be sent multicast if address size is 0, otherwise it will be sent unicast to the
// given address. Use the top bit of the query class field (MDNS_UNICAST_RESPONSE) to determine
// if the answer should be sent unicast (bit set) or multicast (bit not set).
// Returns 0 if success, or <0 if error.
static int
mdns_query_answer(int sock, const void* address, size_t address_size, void* buffer, size_t capacity,
uint16_t query_id, const char* service, size_t service_length,
const char* hostname, size_t hostname_length, uint32_t ipv4, const uint8_t* ipv6,
uint16_t port, const char* txt, size_t txt_length);
// Internal functions
static mdns_string_t
mdns_string_extract(const void* buffer, size_t size, size_t* offset, char* str, size_t capacity);
static int
mdns_string_skip(const void* buffer, size_t size, size_t* offset);
static int
mdns_string_equal(const void* buffer_lhs, size_t size_lhs, size_t* ofs_lhs, const void* buffer_rhs,
size_t size_rhs, size_t* ofs_rhs);
static void*
mdns_string_make(void* data, size_t capacity, const char* name, size_t length);
static void*
mdns_string_make_ref(void* data, size_t capacity, size_t ref_offset);
static void*
mdns_string_make_with_ref(void* data, size_t capacity, const char* name, size_t length,
size_t ref_offset);
static mdns_string_t
mdns_record_parse_ptr(const void* buffer, size_t size, size_t offset, size_t length,
char* strbuffer, size_t capacity);
static mdns_record_srv_t
mdns_record_parse_srv(const void* buffer, size_t size, size_t offset, size_t length,
char* strbuffer, size_t capacity);
static struct sockaddr_in*
mdns_record_parse_a(const void* buffer, size_t size, size_t offset, size_t length,
struct sockaddr_in* addr);
static struct sockaddr_in6*
mdns_record_parse_aaaa(const void* buffer, size_t size, size_t offset, size_t length,
struct sockaddr_in6* addr);
static size_t
mdns_record_parse_txt(const void* buffer, size_t size, size_t offset, size_t length,
mdns_record_txt_t* records, size_t capacity);
// Implementations
static int
mdns_socket_open_ipv4(struct sockaddr_in* saddr) {
int sock = (int)socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (sock < 0)
return -1;
if (mdns_socket_setup_ipv4(sock, saddr)) {
mdns_socket_close(sock);
return -1;
}
return sock;
}
static int
mdns_socket_setup_ipv4(int sock, struct sockaddr_in* saddr) {
unsigned char ttl = 1;
unsigned char loopback = 1;
unsigned int reuseaddr = 1;
struct ip_mreq req;
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (const char*)&reuseaddr, sizeof(reuseaddr));
#ifdef SO_REUSEPORT
setsockopt(sock, SOL_SOCKET, SO_REUSEPORT, (const char*)&reuseaddr, sizeof(reuseaddr));
#endif
setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, (const char*)&ttl, sizeof(ttl));
setsockopt(sock, IPPROTO_IP, IP_MULTICAST_LOOP, (const char*)&loopback, sizeof(loopback));
memset(&req, 0, sizeof(req));
req.imr_multiaddr.s_addr = htonl((((uint32_t)224U) << 24U) | ((uint32_t)251U));
if (saddr)
req.imr_interface = saddr->sin_addr;
if (setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*)&req, sizeof(req)))
return -1;
struct sockaddr_in sock_addr;
if (!saddr) {
saddr = &sock_addr;
memset(saddr, 0, sizeof(struct sockaddr_in));
saddr->sin_family = AF_INET;
saddr->sin_addr.s_addr = INADDR_ANY;
#ifdef __APPLE__
saddr->sin_len = sizeof(struct sockaddr_in);
#endif
} else {
setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF, (const char*)&saddr->sin_addr,
sizeof(saddr->sin_addr));
#ifndef _WIN32
saddr->sin_addr.s_addr = INADDR_ANY;
#endif
}
if (bind(sock, (struct sockaddr*)saddr, sizeof(struct sockaddr_in)))
return -1;
#ifdef _WIN32
unsigned long param = 1;
ioctlsocket(sock, FIONBIO, &param);
#else
const int flags = fcntl(sock, F_GETFL, 0);
fcntl(sock, F_SETFL, flags | O_NONBLOCK);
#endif
return 0;
}
static int
mdns_socket_open_ipv6(struct sockaddr_in6* saddr) {
int sock = (int)socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
if (sock < 0)
return -1;
if (mdns_socket_setup_ipv6(sock, saddr)) {
mdns_socket_close(sock);
return -1;
}
return sock;
}
static int
mdns_socket_setup_ipv6(int sock, struct sockaddr_in6* saddr) {
int hops = 1;
unsigned int loopback = 1;
unsigned int reuseaddr = 1;
struct ipv6_mreq req;
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (const char*)&reuseaddr, sizeof(reuseaddr));
#ifdef SO_REUSEPORT
setsockopt(sock, SOL_SOCKET, SO_REUSEPORT, (const char*)&reuseaddr, sizeof(reuseaddr));
#endif
setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, (const char*)&hops, sizeof(hops));
setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, (const char*)&loopback, sizeof(loopback));
memset(&req, 0, sizeof(req));
req.ipv6mr_multiaddr.s6_addr[0] = 0xFF;
req.ipv6mr_multiaddr.s6_addr[1] = 0x02;
req.ipv6mr_multiaddr.s6_addr[15] = 0xFB;
if (setsockopt(sock, IPPROTO_IPV6, IPV6_JOIN_GROUP, (char*)&req, sizeof(req)))
return -1;
struct sockaddr_in6 sock_addr;
if (!saddr) {
saddr = &sock_addr;
memset(saddr, 0, sizeof(struct sockaddr_in6));
saddr->sin6_family = AF_INET6;
saddr->sin6_addr = in6addr_any;
#ifdef __APPLE__
saddr->sin6_len = sizeof(struct sockaddr_in6);
#endif
} else {
unsigned int ifindex = 0;
setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_IF, (const char*)&ifindex, sizeof(ifindex));
#ifndef _WIN32
saddr->sin6_addr = in6addr_any;
#endif
}
if (bind(sock, (struct sockaddr*)saddr, sizeof(struct sockaddr_in6)))
return -1;
#ifdef _WIN32
unsigned long param = 1;
ioctlsocket(sock, FIONBIO, &param);
#else
const int flags = fcntl(sock, F_GETFL, 0);
fcntl(sock, F_SETFL, flags | O_NONBLOCK);
#endif
return 0;
}
static void
mdns_socket_close(int sock) {
#ifdef _WIN32
closesocket(sock);
#else
close(sock);
#endif
}
static int
mdns_is_string_ref(uint8_t val) {
return (0xC0 == (val & 0xC0));
}
static mdns_string_pair_t
mdns_get_next_substring(const void* rawdata, size_t size, size_t offset) {
const uint8_t* buffer = (const uint8_t*)rawdata;
mdns_string_pair_t pair = {MDNS_INVALID_POS, 0, 0};
if (!buffer[offset]) {
pair.offset = offset;
return pair;
}
if (mdns_is_string_ref(buffer[offset])) {
if (size < offset + 2)
return pair;
offset = 0x3fff & ntohs(*(uint16_t*)MDNS_POINTER_OFFSET(buffer, offset));
if (offset >= size)
return pair;
pair.ref = 1;
}
size_t length = (size_t)buffer[offset++];
if (size < offset + length)
return pair;
pair.offset = offset;
pair.length = length;
return pair;
}
static int
mdns_string_skip(const void* buffer, size_t size, size_t* offset) {
size_t cur = *offset;
mdns_string_pair_t substr;
do {
substr = mdns_get_next_substring(buffer, size, cur);
if (substr.offset == MDNS_INVALID_POS)
return 0;
if (substr.ref) {
*offset = cur + 2;
return 1;
}
cur = substr.offset + substr.length;
} while (substr.length);
*offset = cur + 1;
return 1;
}
static int
mdns_string_equal(const void* buffer_lhs, size_t size_lhs, size_t* ofs_lhs, const void* buffer_rhs,
size_t size_rhs, size_t* ofs_rhs) {
size_t lhs_cur = *ofs_lhs;
size_t rhs_cur = *ofs_rhs;
size_t lhs_end = MDNS_INVALID_POS;
size_t rhs_end = MDNS_INVALID_POS;
mdns_string_pair_t lhs_substr;
mdns_string_pair_t rhs_substr;
do {
lhs_substr = mdns_get_next_substring(buffer_lhs, size_lhs, lhs_cur);
rhs_substr = mdns_get_next_substring(buffer_rhs, size_rhs, rhs_cur);
if ((lhs_substr.offset == MDNS_INVALID_POS) || (rhs_substr.offset == MDNS_INVALID_POS))
return 0;
if (lhs_substr.length != rhs_substr.length)
return 0;
if (strncasecmp((const char*)buffer_rhs + rhs_substr.offset,
(const char*)buffer_lhs + lhs_substr.offset, rhs_substr.length))
return 0;
if (lhs_substr.ref && (lhs_end == MDNS_INVALID_POS))
lhs_end = lhs_cur + 2;
if (rhs_substr.ref && (rhs_end == MDNS_INVALID_POS))
rhs_end = rhs_cur + 2;
lhs_cur = lhs_substr.offset + lhs_substr.length;
rhs_cur = rhs_substr.offset + rhs_substr.length;
} while (lhs_substr.length);
if (lhs_end == MDNS_INVALID_POS)
lhs_end = lhs_cur + 1;
*ofs_lhs = lhs_end;
if (rhs_end == MDNS_INVALID_POS)
rhs_end = rhs_cur + 1;
*ofs_rhs = rhs_end;
return 1;
}
static mdns_string_t
mdns_string_extract(const void* buffer, size_t size, size_t* offset, char* str, size_t capacity) {
size_t cur = *offset;
size_t end = MDNS_INVALID_POS;
mdns_string_pair_t substr;
mdns_string_t result;
result.str = str;
result.length = 0;
char* dst = str;
size_t remain = capacity;
do {
substr = mdns_get_next_substring(buffer, size, cur);
if (substr.offset == MDNS_INVALID_POS)
return result;
if (substr.ref && (end == MDNS_INVALID_POS))
end = cur + 2;
if (substr.length) {
size_t to_copy = (substr.length < remain) ? substr.length : remain;
memcpy(dst, (const char*)buffer + substr.offset, to_copy);
dst += to_copy;
remain -= to_copy;
if (remain) {
*dst++ = '.';
--remain;
}
}
cur = substr.offset + substr.length;
} while (substr.length);
if (end == MDNS_INVALID_POS)
end = cur + 1;
*offset = end;
result.length = capacity - remain;
return result;
}
static size_t
mdns_string_find(const char* str, size_t length, char c, size_t offset) {
const void* found;
if (offset >= length)
return MDNS_INVALID_POS;
found = memchr(str + offset, c, length - offset);
if (found)
return (size_t)((const char*)found - str);
return MDNS_INVALID_POS;
}
static void*
mdns_string_make(void* data, size_t capacity, const char* name, size_t length) {
size_t pos = 0;
size_t last_pos = 0;
size_t remain = capacity;
unsigned char* dest = (unsigned char*)data;
while ((last_pos < length) &&
((pos = mdns_string_find(name, length, '.', last_pos)) != MDNS_INVALID_POS)) {
size_t sublength = pos - last_pos;
if (sublength < remain) {
*dest = (unsigned char)sublength;
memcpy(dest + 1, name + last_pos, sublength);
dest += sublength + 1;
remain -= sublength + 1;
} else {
return 0;
}
last_pos = pos + 1;
}
if (last_pos < length) {
size_t sublength = length - last_pos;
if (sublength < remain) {
*dest = (unsigned char)sublength;
memcpy(dest + 1, name + last_pos, sublength);
dest += sublength + 1;
remain -= sublength + 1;
} else {
return 0;
}
}
if (!remain)
return 0;
*dest++ = 0;
return dest;
}
static void*
mdns_string_make_ref(void* data, size_t capacity, size_t ref_offset) {
if (capacity < 2)
return 0;
uint16_t* udata = (uint16_t*)data;
*udata++ = htons(0xC000 | (uint16_t)ref_offset);
return udata;
}
static void*
mdns_string_make_with_ref(void* data, size_t capacity, const char* name, size_t length,
size_t ref_offset) {
void* remaindata = mdns_string_make(data, capacity, name, length);
capacity -= MDNS_POINTER_DIFF(remaindata, data);
if (!data || !capacity)
return 0;
return mdns_string_make_ref(MDNS_POINTER_OFFSET(remaindata, -1), capacity + 1, ref_offset);
}
static size_t
mdns_records_parse(int sock, const struct sockaddr* from, size_t addrlen, const void* buffer,
size_t size, size_t* offset, mdns_entry_type_t type, uint16_t query_id,
size_t records, mdns_record_callback_fn callback, void* user_data) {
size_t parsed = 0;
int do_callback = (callback ? 1 : 0);
for (size_t i = 0; i < records; ++i) {
size_t name_offset = *offset;
mdns_string_skip(buffer, size, offset);
size_t name_length = (*offset) - name_offset;
const uint16_t* data = (const uint16_t*)((const char*)buffer + (*offset));
uint16_t rtype = ntohs(*data++);
uint16_t rclass = ntohs(*data++);
uint32_t ttl = ntohl(*(const uint32_t*)(const void*)data);
data += 2;
uint16_t length = ntohs(*data++);
*offset += 10;
if (do_callback) {
++parsed;
if (callback(sock, from, addrlen, type, query_id, rtype, rclass, ttl, buffer, size,
name_offset, name_length, *offset, length, user_data))
do_callback = 0;
}
*offset += length;
}
return parsed;
}
static int
mdns_unicast_send(int sock, const void* address, size_t address_size, const void* buffer,
size_t size) {
if (sendto(sock, (const char*)buffer, (mdns_size_t)size, 0, (const struct sockaddr*)address,
(socklen_t)address_size) < 0)
return -1;
return 0;
}
static int
mdns_multicast_send(int sock, const void* buffer, size_t size) {
struct sockaddr_storage addr_storage;
struct sockaddr_in addr;
struct sockaddr_in6 addr6;
struct sockaddr* saddr = (struct sockaddr*)&addr_storage;
socklen_t saddrlen = sizeof(struct sockaddr_storage);
if (getsockname(sock, saddr, &saddrlen))
return -1;
if (saddr->sa_family == AF_INET6) {
memset(&addr6, 0, sizeof(addr6));
addr6.sin6_family = AF_INET6;
#ifdef __APPLE__
addr6.sin6_len = sizeof(addr6);
#endif
addr6.sin6_addr.s6_addr[0] = 0xFF;
addr6.sin6_addr.s6_addr[1] = 0x02;
addr6.sin6_addr.s6_addr[15] = 0xFB;
addr6.sin6_port = htons((unsigned short)MDNS_PORT);
saddr = (struct sockaddr*)&addr6;
saddrlen = sizeof(addr6);
} else {
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
#ifdef __APPLE__
addr.sin_len = sizeof(addr);
#endif
addr.sin_addr.s_addr = htonl((((uint32_t)224U) << 24U) | ((uint32_t)251U));
addr.sin_port = htons((unsigned short)MDNS_PORT);
saddr = (struct sockaddr*)&addr;
saddrlen = sizeof(addr);
}
if (sendto(sock, (const char*)buffer, (mdns_size_t)size, 0, saddr, saddrlen) < 0)
return -1;
return 0;
}
static const uint8_t mdns_services_query[] = {
// Query ID
0x00, 0x00,
// Flags
0x00, 0x00,
// 1 question
0x00, 0x01,
// No answer, authority or additional RRs
0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
// _services._dns-sd._udp.local.
0x09, '_', 's', 'e', 'r', 'v', 'i', 'c', 'e', 's', 0x07, '_', 'd', 'n', 's', '-', 's', 'd',
0x04, '_', 'u', 'd', 'p', 0x05, 'l', 'o', 'c', 'a', 'l', 0x00,
// PTR record
0x00, MDNS_RECORDTYPE_PTR,
// QU (unicast response) and class IN
0x80, MDNS_CLASS_IN};
static int
mdns_discovery_send(int sock) {
return mdns_multicast_send(sock, mdns_services_query, sizeof(mdns_services_query));
}
static size_t
mdns_discovery_recv(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
void* user_data) {
struct sockaddr_in6 addr;
struct sockaddr* saddr = (struct sockaddr*)&addr;
socklen_t addrlen = sizeof(addr);
memset(&addr, 0, sizeof(addr));
#ifdef __APPLE__
saddr->sa_len = sizeof(addr);
#endif
int ret = recvfrom(sock, (char*)buffer, (mdns_size_t)capacity, 0, saddr, &addrlen);
if (ret <= 0)
return 0;
size_t data_size = (size_t)ret;
size_t records = 0;
uint16_t* data = (uint16_t*)buffer;
uint16_t query_id = ntohs(*data++);
uint16_t flags = ntohs(*data++);
uint16_t questions = ntohs(*data++);
uint16_t answer_rrs = ntohs(*data++);
uint16_t authority_rrs = ntohs(*data++);
uint16_t additional_rrs = ntohs(*data++);
// According to RFC 6762 the query ID MUST match the sent query ID (which is 0 in our case)
if (query_id || (flags != 0x8400))
return 0; // Not a reply to our question
// It seems some implementations do not fill the correct questions field,
// so ignore this check for now and only validate answer string
/*
if (questions != 1)
return 0;
*/
int i;
for (i = 0; i < questions; ++i) {
size_t ofs = (size_t)((char*)data - (char*)buffer);
size_t verify_ofs = 12;
// Verify it's our question, _services._dns-sd._udp.local.
if (!mdns_string_equal(buffer, data_size, &ofs, mdns_services_query,
sizeof(mdns_services_query), &verify_ofs))
return 0;
data = (uint16_t*)((char*)buffer + ofs);
uint16_t rtype = ntohs(*data++);
uint16_t rclass = ntohs(*data++);
// Make sure we get a reply based on our PTR question for class IN
if ((rtype != MDNS_RECORDTYPE_PTR) || ((rclass & 0x7FFF) != MDNS_CLASS_IN))
return 0;
}
int do_callback = 1;
for (i = 0; i < answer_rrs; ++i) {
size_t ofs = (size_t)((char*)data - (char*)buffer);
size_t verify_ofs = 12;
// Verify it's an answer to our question, _services._dns-sd._udp.local.
size_t name_offset = ofs;
int is_answer = mdns_string_equal(buffer, data_size, &ofs, mdns_services_query,
sizeof(mdns_services_query), &verify_ofs);
size_t name_length = ofs - name_offset;
data = (uint16_t*)((char*)buffer + ofs);
uint16_t rtype = ntohs(*data++);
uint16_t rclass = ntohs(*data++);
uint32_t ttl = ntohl(*(uint32_t*)(void*)data);
data += 2;
uint16_t length = ntohs(*data++);
if (length >= (data_size - ofs))
return 0;
if (is_answer && do_callback) {
++records;
ofs = (size_t)((char*)data - (char*)buffer);
if (callback(sock, saddr, addrlen, MDNS_ENTRYTYPE_ANSWER, query_id, rtype, rclass, ttl,
buffer, data_size, name_offset, name_length, ofs, length, user_data))
do_callback = 0;
}
data = (uint16_t*)((char*)data + length);
}
size_t offset = (size_t)((char*)data - (char*)buffer);
records +=
mdns_records_parse(sock, saddr, addrlen, buffer, data_size, &offset,
MDNS_ENTRYTYPE_AUTHORITY, query_id, authority_rrs, callback, user_data);
records += mdns_records_parse(sock, saddr, addrlen, buffer, data_size, &offset,
MDNS_ENTRYTYPE_ADDITIONAL, query_id, additional_rrs, callback,
user_data);
return records;
}
static size_t
mdns_socket_listen(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
void* user_data) {
struct sockaddr_in6 addr;
struct sockaddr* saddr = (struct sockaddr*)&addr;
socklen_t addrlen = sizeof(addr);
memset(&addr, 0, sizeof(addr));
#ifdef __APPLE__
saddr->sa_len = sizeof(addr);
#endif
int ret = recvfrom(sock, (char*)buffer, (mdns_size_t)capacity, 0, saddr, &addrlen);
if (ret <= 0)
return 0;
size_t data_size = (size_t)ret;
uint16_t* data = (uint16_t*)buffer;
uint16_t query_id = ntohs(*data++);
uint16_t flags = ntohs(*data++);
uint16_t questions = ntohs(*data++);
/*
This data is unused at the moment, skip
uint16_t answer_rrs = ntohs(*data++);
uint16_t authority_rrs = ntohs(*data++);
uint16_t additional_rrs = ntohs(*data++);
*/
data += 3;
size_t parsed = 0;
for (int iquestion = 0; iquestion < questions; ++iquestion) {
size_t question_offset = (size_t)((char*)data - (char*)buffer);
size_t offset = question_offset;
size_t verify_ofs = 12;
if (mdns_string_equal(buffer, data_size, &offset, mdns_services_query,
sizeof(mdns_services_query), &verify_ofs)) {
if (flags || (questions != 1))
return 0;
} else {
offset = question_offset;
if (!mdns_string_skip(buffer, data_size, &offset))
break;
}
size_t length = offset - question_offset;
data = (uint16_t*)((char*)buffer + offset);
uint16_t rtype = ntohs(*data++);
uint16_t rclass = ntohs(*data++);
// Make sure we get a question of class IN
if ((rclass & 0x7FFF) != MDNS_CLASS_IN)
return 0;
if (callback)
callback(sock, saddr, addrlen, MDNS_ENTRYTYPE_QUESTION, query_id, rtype, rclass, 0,
buffer, data_size, question_offset, length, question_offset, length,
user_data);
++parsed;
}
return parsed;
}
static int
mdns_discovery_answer(int sock, const void* address, size_t address_size, void* buffer,
size_t capacity, const char* record, size_t length) {
if (capacity < (sizeof(mdns_services_query) + 32 + length))
return -1;
uint16_t* data = (uint16_t*)buffer;
// Basic reply structure
memcpy(data, mdns_services_query, sizeof(mdns_services_query));
// Flags
uint16_t* flags = data + 1;
*flags = htons(0x8400U);
// One answer
uint16_t* answers = data + 3;
*answers = htons(1);
// Fill in answer PTR record
data = (uint16_t*)((char*)buffer + sizeof(mdns_services_query));
// Reference _services._dns-sd._udp.local. string in question
*data++ = htons(0xC000U | 12U);
// Type
*data++ = htons(MDNS_RECORDTYPE_PTR);
// Rclass
*data++ = htons(MDNS_CLASS_IN);
// TTL
*(uint32_t*)data = htonl(10);
data += 2;
// Record string length
uint16_t* record_length = data++;
uint8_t* record_data = (uint8_t*)data;
size_t remain = capacity - (sizeof(mdns_services_query) + 10);
record_data = (uint8_t*)mdns_string_make(record_data, remain, record, length);
*record_length = htons((uint16_t)(record_data - (uint8_t*)data));
*record_data++ = 0;
ptrdiff_t tosend = (char*)record_data - (char*)buffer;
return mdns_unicast_send(sock, address, address_size, buffer, (size_t)tosend);
}
static int
mdns_query_send(int sock, mdns_record_type_t type, const char* name, size_t length, void* buffer,
size_t capacity, uint16_t query_id) {
if (capacity < (17 + length))
return -1;
uint16_t rclass = MDNS_CLASS_IN | MDNS_UNICAST_RESPONSE;
struct sockaddr_storage addr_storage;
struct sockaddr* saddr = (struct sockaddr*)&addr_storage;
socklen_t saddrlen = sizeof(addr_storage);
if (getsockname(sock, saddr, &saddrlen) == 0) {
if ((saddr->sa_family == AF_INET) &&
(ntohs(((struct sockaddr_in*)saddr)->sin_port) == MDNS_PORT))
rclass &= ~MDNS_UNICAST_RESPONSE;
else if ((saddr->sa_family == AF_INET6) &&
(ntohs(((struct sockaddr_in6*)saddr)->sin6_port) == MDNS_PORT))
rclass &= ~MDNS_UNICAST_RESPONSE;
}
uint16_t* data = (uint16_t*)buffer;
// Query ID
*data++ = htons(query_id);
// Flags
*data++ = 0;
// Questions
*data++ = htons(1);
// No answer, authority or additional RRs
*data++ = 0;
*data++ = 0;
*data++ = 0;
// Fill in question
// Name string
data = (uint16_t*)mdns_string_make(data, capacity - 17, name, length);
if (!data)
return -1;
// Record type
*data++ = htons(type);
//! Optional unicast response based on local port, class IN
*data++ = htons(rclass);
ptrdiff_t tosend = (char*)data - (char*)buffer;
if (mdns_multicast_send(sock, buffer, (size_t)tosend))
return -1;
return query_id;
}
static size_t
mdns_query_recv(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
void* user_data, int only_query_id) {
struct sockaddr_in6 addr;
struct sockaddr* saddr = (struct sockaddr*)&addr;
socklen_t addrlen = sizeof(addr);
memset(&addr, 0, sizeof(addr));
#ifdef __APPLE__
saddr->sa_len = sizeof(addr);
#endif
int ret = recvfrom(sock, (char*)buffer, (mdns_size_t)capacity, 0, saddr, &addrlen);
if (ret <= 0)
return 0;
size_t data_size = (size_t)ret;
uint16_t* data = (uint16_t*)buffer;
uint16_t query_id = ntohs(*data++);
uint16_t flags = ntohs(*data++);
uint16_t questions = ntohs(*data++);
uint16_t answer_rrs = ntohs(*data++);
uint16_t authority_rrs = ntohs(*data++);
uint16_t additional_rrs = ntohs(*data++);
(void)sizeof(flags);
if ((only_query_id > 0) && (query_id != only_query_id))
return 0; // Not a reply to the wanted one-shot query
if (questions > 1)
return 0;
// Skip questions part
int i;
for (i = 0; i < questions; ++i) {
size_t ofs = (size_t)((char*)data - (char*)buffer);
if (!mdns_string_skip(buffer, data_size, &ofs))
return 0;
data = (uint16_t*)((char*)buffer + ofs);
uint16_t rtype = ntohs(*data++);
uint16_t rclass = ntohs(*data++);
(void)sizeof(rtype);
(void)sizeof(rclass);
}
size_t records = 0;
size_t offset = MDNS_POINTER_DIFF(data, buffer);
records += mdns_records_parse(sock, saddr, addrlen, buffer, data_size, &offset,
MDNS_ENTRYTYPE_ANSWER, query_id, answer_rrs, callback, user_data);
records +=
mdns_records_parse(sock, saddr, addrlen, buffer, data_size, &offset,
MDNS_ENTRYTYPE_AUTHORITY, query_id, authority_rrs, callback, user_data);
records += mdns_records_parse(sock, saddr, addrlen, buffer, data_size, &offset,
MDNS_ENTRYTYPE_ADDITIONAL, query_id, additional_rrs, callback,
user_data);
return records;
}
static int
mdns_query_answer(int sock, const void* address, size_t address_size, void* buffer, size_t capacity,
uint16_t query_id, const char* service, size_t service_length,
const char* hostname, size_t hostname_length, uint32_t ipv4, const uint8_t* ipv6,
uint16_t port, const char* txt, size_t txt_length) {
if (capacity < (sizeof(struct mdns_header_t) + 32 + service_length + hostname_length))
return -1;
int unicast = (address_size ? 1 : 0);
int use_ipv4 = (ipv4 != 0);
int use_ipv6 = (ipv6 != 0);
int use_txt = (txt && txt_length && (txt_length <= 255));
uint16_t question_rclass = (unicast ? MDNS_UNICAST_RESPONSE : 0) | MDNS_CLASS_IN;
uint16_t rclass = (unicast ? MDNS_CACHE_FLUSH : 0) | MDNS_CLASS_IN;
uint32_t ttl = (unicast ? 10 : 60);
uint32_t a_ttl = ttl;
// Basic answer structure
struct mdns_header_t* header = (struct mdns_header_t*)buffer;
header->query_id = (address_size ? htons(query_id) : 0);
header->flags = htons(0x8400);
header->questions = htons(unicast ? 1 : 0);
header->answer_rrs = htons(1);
header->authority_rrs = 0;
header->additional_rrs = htons((unsigned short)(1 + use_ipv4 + use_ipv6 + use_txt));
void* data = MDNS_POINTER_OFFSET(buffer, sizeof(struct mdns_header_t));
uint16_t* udata;
size_t remain, service_offset = 0, local_offset = 0, full_offset, host_offset;
// Fill in question if unicast
if (unicast) {
service_offset = MDNS_POINTER_DIFF(data, buffer);
remain = capacity - service_offset;
data = mdns_string_make(data, remain, service, service_length);
local_offset = MDNS_POINTER_DIFF(data, buffer) - 7;
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
if (!data || (remain <= 4))
return -1;
udata = (uint16_t*)data;
*udata++ = htons(MDNS_RECORDTYPE_PTR);
*udata++ = htons(question_rclass);
data = udata;
}
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
// Fill in answers
// PTR record for service
if (unicast) {
data = mdns_string_make_ref(data, remain, service_offset);
} else {
service_offset = MDNS_POINTER_DIFF(data, buffer);
remain = capacity - service_offset;
data = mdns_string_make(data, remain, service, service_length);
local_offset = MDNS_POINTER_DIFF(data, buffer) - 7;
}
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
if (!data || (remain <= 10))
return -1;
udata = (uint16_t*)data;
*udata++ = htons(MDNS_RECORDTYPE_PTR);
*udata++ = htons(rclass);
*(uint32_t*)udata = htonl(ttl);
udata += 2;
uint16_t* record_length = udata++; // length
data = udata;
// Make a string <hostname>.<service>.local.
full_offset = MDNS_POINTER_DIFF(data, buffer);
remain = capacity - full_offset;
data = mdns_string_make_with_ref(data, remain, hostname, hostname_length, service_offset);
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
if (!data || (remain <= 10))
return -1;
*record_length = htons((uint16_t)MDNS_POINTER_DIFF(data, record_length + 1));
// Fill in additional records
// SRV record for <hostname>.<service>.local.
data = mdns_string_make_ref(data, remain, full_offset);
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
if (!data || (remain <= 10))
return -1;
udata = (uint16_t*)data;
*udata++ = htons(MDNS_RECORDTYPE_SRV);
*udata++ = htons(rclass);
*(uint32_t*)udata = htonl(ttl);
udata += 2;
record_length = udata++; // length
*udata++ = htons(0); // priority
*udata++ = htons(0); // weight
*udata++ = htons(port); // port
// Make a string <hostname>.local.
data = udata;
host_offset = MDNS_POINTER_DIFF(data, buffer);
remain = capacity - host_offset;
data = mdns_string_make_with_ref(data, remain, hostname, hostname_length, local_offset);
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
if (!data || (remain <= 10))
return -1;
*record_length = htons((uint16_t)MDNS_POINTER_DIFF(data, record_length + 1));
// A record for <hostname>.local.
if (use_ipv4) {
data = mdns_string_make_ref(data, remain, host_offset);
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
if (!data || (remain <= 14))
return -1;
udata = (uint16_t*)data;
*udata++ = htons(MDNS_RECORDTYPE_A);
*udata++ = htons(rclass);
*(uint32_t*)udata = htonl(a_ttl);
udata += 2;
*udata++ = htons(4); // length
*(uint32_t*)udata = ipv4; // ipv4 address
udata += 2;
data = udata;
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
}
// AAAA record for <hostname>.local.
if (use_ipv6) {
data = mdns_string_make_ref(data, remain, host_offset);
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
if (!data || (remain <= 26))
return -1;
udata = (uint16_t*)data;
*udata++ = htons(MDNS_RECORDTYPE_AAAA);
*udata++ = htons(rclass);
*(uint32_t*)udata = htonl(a_ttl);
udata += 2;
*udata++ = htons(16); // length
memcpy(udata, ipv6, 16); // ipv6 address
data = MDNS_POINTER_OFFSET(udata, 16);
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
}
// TXT record for <hostname>.<service>.local.
if (use_txt) {
data = mdns_string_make_ref(data, remain, full_offset);
remain = capacity - MDNS_POINTER_DIFF(data, buffer);
if (!data || (remain <= (11 + txt_length)))
return -1;
udata = (uint16_t*)data;
*udata++ = htons(MDNS_RECORDTYPE_TXT);
*udata++ = htons(rclass);
*(uint32_t*)udata = htonl(ttl);
udata += 2;
*udata++ = htons((unsigned short)(txt_length + 1)); // length
char* txt_record = (char*)udata;
*txt_record++ = (char)txt_length;
memcpy(txt_record, txt, txt_length); // txt record
data = MDNS_POINTER_OFFSET(txt_record, txt_length);
// Unused until multiple txt records are supported
// remain = capacity - MDNS_POINTER_DIFF(data, buffer);
}
size_t tosend = MDNS_POINTER_DIFF(data, buffer);
if (address_size)
return mdns_unicast_send(sock, address, address_size, buffer, tosend);
return mdns_multicast_send(sock, buffer, tosend);
}
static mdns_string_t
mdns_record_parse_ptr(const void* buffer, size_t size, size_t offset, size_t length,
char* strbuffer, size_t capacity) {
// PTR record is just a string
if ((size >= offset + length) && (length >= 2))
return mdns_string_extract(buffer, size, &offset, strbuffer, capacity);
mdns_string_t empty = {0, 0};
return empty;
}
static mdns_record_srv_t
mdns_record_parse_srv(const void* buffer, size_t size, size_t offset, size_t length,
char* strbuffer, size_t capacity) {
mdns_record_srv_t srv;
memset(&srv, 0, sizeof(mdns_record_srv_t));
// Read the priority, weight, port number and the discovery name
// SRV record format (http://www.ietf.org/rfc/rfc2782.txt):
// 2 bytes network-order unsigned priority
// 2 bytes network-order unsigned weight
// 2 bytes network-order unsigned port
// string: discovery (domain) name, minimum 2 bytes when compressed
if ((size >= offset + length) && (length >= 8)) {
const uint16_t* recorddata = (const uint16_t*)((const char*)buffer + offset);
srv.priority = ntohs(*recorddata++);
srv.weight = ntohs(*recorddata++);
srv.port = ntohs(*recorddata++);
offset += 6;
srv.name = mdns_string_extract(buffer, size, &offset, strbuffer, capacity);
}
return srv;
}
static struct sockaddr_in*
mdns_record_parse_a(const void* buffer, size_t size, size_t offset, size_t length,
struct sockaddr_in* addr) {
memset(addr, 0, sizeof(struct sockaddr_in));
addr->sin_family = AF_INET;
#ifdef __APPLE__
addr->sin_len = sizeof(struct sockaddr_in);
#endif
if ((size >= offset + length) && (length == 4))
addr->sin_addr.s_addr = *(const uint32_t*)((const char*)buffer + offset);
return addr;
}
static struct sockaddr_in6*
mdns_record_parse_aaaa(const void* buffer, size_t size, size_t offset, size_t length,
struct sockaddr_in6* addr) {
memset(addr, 0, sizeof(struct sockaddr_in6));
addr->sin6_family = AF_INET6;
#ifdef __APPLE__
addr->sin6_len = sizeof(struct sockaddr_in6);
#endif
if ((size >= offset + length) && (length == 16))
addr->sin6_addr = *(const struct in6_addr*)((const char*)buffer + offset);
return addr;
}
static size_t
mdns_record_parse_txt(const void* buffer, size_t size, size_t offset, size_t length,
mdns_record_txt_t* records, size_t capacity) {
size_t parsed = 0;
const char* strdata;
size_t separator, sublength;
size_t end = offset + length;
if (size < end)
end = size;
while ((offset < end) && (parsed < capacity)) {
strdata = (const char*)buffer + offset;
sublength = *(const unsigned char*)strdata;
++strdata;
offset += sublength + 1;
separator = 0;
for (size_t c = 0; c < sublength; ++c) {
// DNS-SD TXT record keys MUST be printable US-ASCII, [0x20, 0x7E]
if ((strdata[c] < 0x20) || (strdata[c] > 0x7E))
break;
if (strdata[c] == '=') {
separator = c;
break;
}
}
if (!separator)
continue;
if (separator < sublength) {
records[parsed].key.str = strdata;
records[parsed].key.length = separator;
records[parsed].value.str = strdata + separator + 1;
records[parsed].value.length = sublength - (separator + 1);
} else {
records[parsed].key.str = strdata;
records[parsed].key.length = sublength;
}
++parsed;
}
return parsed;
}
#ifdef _WIN32
#undef strncasecmp
#endif
#ifdef __cplusplus
}
#endif