This library provides a cross-platform mDNS and DNS-DS library in C.
This library is put in the public domain; you can redistribute it and/or modify it without any restrictions.
The upstream implementation is created by Mattias Jansson (@maniccoder).
The latest source code is always available at https://github.com/mjansson/mdns
The library does DNS-SD discovery and service as well as single record mDNS query and response. There are no memory allocations done by the library, all buffers used must be passed in by the caller. Custom data for use in processing can be passed along using a user data opaque pointer.
The mdns-test.c test executable file demostrates the use of all features, including discovery, query and service response.
Socket for mDNS communication can either be opened by the library by using mdns_socket_open_ipv4 or mdns_socket_open_ipv6, or by initializing an existing socket with mdns_socket_setup_ipv4 or mdns_socket_setup_ipv6.
If you want to do only discovery and send queries you can pass in 0 as port in the socket create/setup functions. This will bind the socket to a random free port in user range.
If you want to do mDNS service response to incoming queries, you need to pass in MDNS_PORT to the socket create/setup functions to allow the socket to receive incoming query packets.
The socket is initialized with multicast membership (including loopback) and set to non-blocking mode.
Call mdns_socket_close to close a socket opened with mdns_socket_open_ipv4 or mdns_socket_open_ipv6.
To send a DNS-SD service discovery request use mdns_discovery_send. This will send a single multicast packet (single question record for _services._dns-sd._udp.local.).
To read discovery responses use mdns_discovery_recv. All records received since last call will be piped to the callback supplied in the function call. The entry type will be one of MDNS_ENTRYTYPE_ANSWER, MDNS_ENTRYTYPE_AUTHORITY and MDNS_ENTRYTYPE_ADDITIONAL.
To send a mDNS query for a single record use mdns_query_send. This will send a single multicast packet for the given record (since question record, for example _http._tcp.local.).
To read query responses use mdns_query_recv. All records received since last call will be piped to the callback supplied in the function call. If only_last_query parameter is non-zero the function will filter out any response with a transaction id that does not match the last query sent. The entry type will be one of MDNS_ENTRYTYPE_ANSWER, MDNS_ENTRYTYPE_AUTHORITY and MDNS_ENTRYTYPE_ADDITIONAL.
To listen for incoming DNS-SD requests and mDNS queries the socket should be opened on port 5353 (defined in header as MDNS_PORT) in call to the socket open/setup functions. Then call mdns_socket_listen either on notification of incoming data, or by setting blocking mode and calling mdns_socket_listen to block until data is available and parsed.
The entry type passed to the callback will be MDNS_ENTRYTYPE_QUESTION and record type MDNS_RECORDTYPE_PTR. Use the mdns_record_parse_ptr function to get the name string of the service record that was asked for.
If service record name is _services._dns-sd._udp.local. you should use mdns_discovery_answer to send the records of the services you provide (DNS-SD).
If the service record name is a service you provide, use mdns_query_answer to send the service details back in response to the query.
See the test executable implementation for more details on how to handle the parameters to the given functions.
The mdns-test.c file contains a test executable implementation using the library to do DNS-SD and mDNS queries. Compile into an executable and run to see command line options for discovery, query and service modes.