mDNS-Cpp

This library provides a cross-platform mDNS and DNS-DS library in C++.

Currently this library is only a C++ wrapper around Mattias Jansson (@maniccoder) mdns.h file -> all feature credits go to him. His work is licensed with the The Unlicense license.

why does this exist:

• better integration in C++ projects
• better usage of modern C++ features
• higher level API
• pass logger function to library to use users logger

Features

The library does DNS-SD discovery and service as well as one-shot single record mDNS query and response.

Build

mkdir build
cd build
cmake ..
make -j
make install

Usage

you can either install the library, include the library as subdirectory or use conan: mdns_cpp/0.1.0@gocarlos/testing

# add subdirectory
add_subdirectory(vendor/mdns_cpp)
# or install / use conan
find_package(mdns_cpp)

add_executable(main main.cpp)
target_link_libraries(main PRIVATE mdns_cpp::mdns_cpp)

See the example folder for the different examples:

Service

#include <thread>
#include "mdns_cpp/mdns.hpp"

int main() {
  mdns_cpp::mDNS mdns;
  mdns.setServiceHostname("AirForce1");
  mdns.startService();
  while (true) {
    std::this_thread::sleep_for(std::chrono::seconds(1));
  }

  return 0;
}

To listen for incoming DNS-SD requests and mDNS queries the socket can be opened/setup on the default interface by passing 0 as socket address in the call to the socket open/setup functions (the socket will receive data from all network interfaces). 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.

Discovery

#include <thread>
#include "mdns_cpp/mdns.hpp"

int main() {
  mdns_cpp::mDNS mdns;
  mdns.executeDiscovery();
  while (true) {
    std::this_thread::sleep_for(std::chrono::seconds(1));
  }
  return 0;
}

To send a DNS-SD service discovery request use mdns_discovery_send. This will send a single multicast packet (single PTR question record for _services._dns-sd._udp.local.) requesting a unicast response.

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.

Query

#include <thread>
#include "mdns_cpp/mdns.hpp"

int main() {
  mdns_cpp::mDNS mdns;
  const std::string service = "_http._tcp.local.";
  mdns.executeQuery(service);
  while (true) {
    std::this_thread::sleep_for(std::chrono::seconds(1));
  }
  return 0;
}

To send a one-shot mDNS query for a single record use mdns_query_send. This will send a single multicast packet for the given record (single PTR question record, for example _http._tcp.local.). You can optionally pass in a query ID for the query for later filtering of responses (even though this is discouraged by the RFC), or pass 0 to be fully compliant. The function returns the query ID associated with this query, which if non-zero can be used to filter responses in mdns_query_recv. If the socket is bound to port 5353 a multicast response is requested, otherwise a unicast response.

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 query_id parameter is non-zero the function will filter out any response with a query ID that does not match the given query ID. The entry type will be one of MDNS_ENTRYTYPE_ANSWER, MDNS_ENTRYTYPE_AUTHORITY and MDNS_ENTRYTYPE_ADDITIONAL.