Awesome
Crystal Lang mDNS Support
- Discover services using DNS-SD
DNS-SD is used where there might be multiple devices implementing a service.
- Lookup devices using mDNS
mDNS is used to find the IP address of device, like a Raspberry Pi
Installation
-
Add the dependency to your
shard.yml
:dependencies: mDNS: github: spider-gazelle/mdns
-
Run
shards install
Single Shot usage
As described in the rfc
mDNS query
If we are looking for the IP address of a device for instance.
# We're requesting the IPv4 address of the phone (A record)
# We could also do a multi-request and get the IPv6 address too (AAAA record)
results = MDNS.one_shot "Steves-iPhone.local", type: MDNS::Type::A
if address_response = results.first?
# NOTE:: the `_address` here is the device that responded, it might not be an
# authoritative answer (i.e. something replying on behalf of the device) so
# extract the IP address from the payload (mDNS only, for DNS-SD use the `_address`)
_address, response = address_response
# This is assuming answers[0] is an A or AAAA record
response.answers[0].payload.as(Socket::IPAddress).address # => "192.168.40.150"
end
Another common request, if you want the port of the service, is the SRV query. Use the SRV query in tandem with the DNS-SD request described below
Simple DNS-SD query
To perform a simple query for a service on the network
require "mdns"
# Look up homekit devices on the network
results = MDNS.one_shot "_hap._tcp.local"
results.each do |(address, response)|
address # => Socket::IPAddress
response # => MDNS::Message
response.is_response # => true
response.authoritative_answer # => true / false
response.response_code # => ResponseCode::NoError
response.answer_count # => 1
response.answers # => Array(MDNS::Resource)
# The answers will most likely be PTRs to the devices local domain names
# Then you can perform a SRV query for the service details of the pointer
end
Multiple service queries
In a single request
# Look up homekit devices and hubs on the network
results = MDNS.one_shot do |message|
message.query "_hap._tcp.local"
message.query "_homekit._tcp.local"
end
# You will need to inspect the answers to differentiate between devices and hubs
results.each do |(address, response)|
is_hap = false
is_kit = false
response.answers.each do |answer|
domain_name = answer.domain_name
if domain_name == "_hap._tcp.local"
is_hap = true
elsif domain_name == "_homekit._tcp.local"
is_kit = true
end
end
end
Continuous Multicast DNS Querying
This is only the most basic of servers implementing the transport layer. It could definitely be used as the basis for a DNS cache as described by the RFC
require "mdns"
server = MDNS::Server.new(MDNS::IPv4)
loop do
break if server.closed?
address, message = server.receive
if message.query?
# process a query here
else
# process responses here
end
# This code prints the details of the message
puts Time.utc.to_s("%X")
puts "QUERY:"
puts message.queries.map(&.domain_name).join("\n")
puts "ANSWERS:"
puts message.answers.map { |answer|
String.build do |str|
str << answer.domain_name
str << " => (#{answer.type}) "
str << answer.payload.inspect
end
}.join("\n")
puts "\n\n\n"
end
See the example for how to register a service on your local network.