mdns.h

/* 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
#define IMPORT __declspec(dllimport)
#define EXPORT __declspec(dllexport)
#ifndef PUBLIC
#define PUBLIC (IMPORT)
#else
#define PUBLIC (EXPORT)
#endif
#include <Winsock2.h>
#include <Ws2tcpip.h>
#else
#define PUBLIC
#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_ARGS(s) s.str, s.length
#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
#define MDNS_MAX_SUBSTRINGS 64

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,
	// Any available records
	MDNS_RECORDTYPE_ANY = 255
};

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_string_table_item_t mdns_string_table_item_t;
typedef struct mdns_string_table_t mdns_string_table_t;
typedef struct mdns_record_t mdns_record_t;
typedef struct mdns_record_srv_t mdns_record_srv_t;
typedef struct mdns_record_ptr_t mdns_record_ptr_t;
typedef struct mdns_record_a_t mdns_record_a_t;
typedef struct mdns_record_aaaa_t mdns_record_aaaa_t;
typedef struct mdns_record_txt_t mdns_record_txt_t;

#ifdef _WIN32
typedef int mdns_size_t;
typedef int mdns_ssize_t;
#else
typedef size_t mdns_size_t;
typedef ssize_t mdns_ssize_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_string_table_t {
	size_t offset[16];
	size_t count;
	size_t next;
};

struct mdns_record_srv_t {
	uint16_t priority;
	uint16_t weight;
	uint16_t port;
	mdns_string_t name;
};

struct mdns_record_ptr_t {
	mdns_string_t name;
};

struct mdns_record_a_t {
	struct sockaddr_in addr;
};

struct mdns_record_aaaa_t {
	struct sockaddr_in6 addr;
};

struct mdns_record_txt_t {
	mdns_string_t key;
	mdns_string_t value;
};

struct mdns_record_t {
	mdns_string_t name;
	mdns_record_type_t type;
	union mdns_record_data {
		mdns_record_ptr_t ptr;
		mdns_record_srv_t srv;
		mdns_record_a_t a;
		mdns_record_aaaa_t aaaa;
		mdns_record_txt_t txt;
	} data;
};

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.
PUBLIC
int
mdns_socket_open_ipv4(const 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.
PUBLIC
int
mdns_socket_setup_ipv4(int sock, const 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.
PUBLIC
int
mdns_socket_open_ipv6(const 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.
PUBLIC
int
mdns_socket_setup_ipv6(int sock, const struct sockaddr_in6* saddr);

//! Close a socket opened with mdns_socket_open_ipv4 and mdns_socket_open_ipv6.
PUBLIC
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. Buffer must be 32 bit
//! aligned. Parsing is stopped when callback function returns non-zero. Returns the number of
//! queries parsed.
PUBLIC
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.
PUBLIC
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. Buffer must be 32 bit aligned. Parsing is stopped when callback
//! function returns non-zero. Returns the number of responses parsed.
PUBLIC
size_t
mdns_discovery_recv(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
                    void* user_data);

//! 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 and must be 32 bit aligned. 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.
PUBLIC
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. Buffer must be 32 bit aligned. Parsing is stopped when callback
//! function returns non-zero. Returns the number of responses parsed.
PUBLIC
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 variable unicast mDNS query answer to any question with variable number of records to the
//! given address. Use the top bit of the query class field (MDNS_UNICAST_RESPONSE) in the query
//! recieved to determine if the answer should be sent unicast (bit set) or multicast (bit not set).
//! Buffer must be 32 bit aligned. The record type and name should match the data from the query
//! recieved. Returns 0 if success, or <0 if error.
PUBLIC
int
mdns_query_answer_unicast(int sock, const void* address, size_t address_size, void* buffer,
                          size_t capacity, uint16_t query_id, mdns_record_type_t record_type,
                          const char* name, size_t name_length, mdns_record_t answer,
                          mdns_record_t* authority, size_t authority_count,
                          mdns_record_t* additional, size_t additional_count);

//! Send a variable multicast mDNS query answer to any question with variable number of records. Use
//! the top bit of the query class field (MDNS_UNICAST_RESPONSE) in the query recieved to determine
//! if the answer should be sent unicast (bit set) or multicast (bit not set). Buffer must be 32 bit
//! aligned. Returns 0 if success, or <0 if error.
PUBLIC
int
mdns_query_answer_multicast(int sock, void* buffer, size_t capacity, mdns_record_t answer,
                            mdns_record_t* authority, size_t authority_count,
                            mdns_record_t* additional, size_t additional_count);

//! Send a variable multicast mDNS announcement (as an unsolicited answer) with variable number of
//! records.Buffer must be 32 bit aligned. Returns 0 if success, or <0 if error. Use this on service
//! startup to announce your instance to the local network.
PUBLIC
int
mdns_announce_multicast(int sock, void* buffer, size_t capacity, mdns_record_t answer,
                        mdns_record_t* authority, size_t authority_count, mdns_record_t* additional,
                        size_t additional_count);

//! Send a variable multicast mDNS announcement. Use this on service end for removing the resource
//! from the local network. The records must be identical to the according announcement.
PUBLIC
int
mdns_goodbye_multicast(int sock, void* buffer, size_t capacity, mdns_record_t answer,
                       mdns_record_t* authority, size_t authority_count, mdns_record_t* additional,
                       size_t additional_count);

// Parse records functions

//! Parse a PTR record, returns the name in the record
PUBLIC
mdns_string_t
mdns_record_parse_ptr(const void* buffer, size_t size, size_t offset, size_t length,
                      char* strbuffer, size_t capacity);

//! Parse a SRV record, returns the priority, weight, port and name in the record
PUBLIC
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);

//! Parse an A record, returns the IPv4 address in the record
PUBLIC
struct sockaddr_in*
mdns_record_parse_a(const void* buffer, size_t size, size_t offset, size_t length,
                    struct sockaddr_in* addr);

//! Parse an AAAA record, returns the IPv6 address in the record
PUBLIC
struct sockaddr_in6*
mdns_record_parse_aaaa(const void* buffer, size_t size, size_t offset, size_t length,
                       struct sockaddr_in6* addr);

//! Parse a TXT record, returns the number of key=value records parsed and stores the key-value
//! pairs in the supplied buffer
PUBLIC
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);

// Internal functions

PUBLIC
mdns_string_t
mdns_string_extract(const void* buffer, size_t size, size_t* offset, char* str, size_t capacity);

PUBLIC
int
mdns_string_skip(const void* buffer, size_t size, size_t* offset);

PUBLIC
size_t
mdns_string_find(const char* str, size_t length, char c, size_t offset);

PUBLIC
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);

PUBLIC
void*
mdns_string_make(void* buffer, size_t capacity, void* data, const char* name, size_t length,
                 mdns_string_table_t* string_table);

PUBLIC
size_t
mdns_string_table_find(mdns_string_table_t* string_table, const void* buffer, size_t capacity,
                       const char* str, size_t first_length, size_t total_length);

#ifdef __cplusplus
}
#endif