用 Ruby 來尋找區網中的 Airplay、Chromecast

require 'resolv'

Resolv::DNS.new
           .each_resource('frost.tw', Resolv::DNS::Resource::IN::A) do |record|
             pp record
           end

require 'socket'

socket = UDPSocket.new
socket.bind('224.0.0.251', 5353)

membership = IPAddr.new('224.0.0.251').hton + IPAddr.new('0.0.0.0').hton
socket = UDPSocket.new

socket.setsockopt(:IPPROTO_IP, :IP_ADD_MEMBERSHIP, membership)
socket.setsockopt(:SOL_SOCKET, :SO_REUSEPORT, 1)

socket.bind('0.0.0.0', 5353)

# 略
if (setsockopt(fptr->fd, level, option, v, vlen) < 0)
        rsock_sys_fail_path("setsockopt(2)", fptr->pathv);

    return INT2FIX(0);

struct ip_mreq
{
        struct in_addr imr_multiaddr;   /* IP multicast address of group */
        struct in_addr imr_interface;   /* local IP address of interface */
};

setsockopt (socket, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));

irb(main):003:0> IPAddr.new('224.0.0.251').hton
=> "\xE0\x00\x00\xFB"

irb(main):004:0> IPAddr.new('224.0.0.251').hton + IPAddr.new('0.0.0.0').hton
=> "\xE0\x00\x00\xFB\x00\x00\x00\x00"

char *v;

# 略

    switch (TYPE(val)) {
      # 略
      default:
        StringValue(val);
        v = RSTRING_PTR(val);
        vlen = RSTRING_SOCKLEN(val);
        break;
    }

# C API 呼叫處

require 'socket'
require 'resolv'
require 'awesome_print'

MDNS_PORT = 5353
MDNS_ADDRESS = '224.0.0.251'.freeze
BIND_ADDRESS = '0.0.0.0'.freeze

M_MEMBERSHIP = IPAddr.new(MDNS_ADDRESS).hton + IPAddr.new(BIND_ADDRESS).hton

# :nodoc:
class MDNS
  include Enumerable

  def initialize
    @socket = UDPSocket.new
    @socket.setsockopt(:IPPROTO_IP, :IP_ADD_MEMBERSHIP, M_MEMBERSHIP)
    @socket.setsockopt(:SOL_SOCKET, :SO_REUSEPORT, 1)
    @socket.bind(BIND_ADDRESS, MDNS_PORT)
  end

  def each(&_block)
    loop do
      yield @socket.recvfrom(4096)
    end
  end
end

mdns = MDNS.new
mdns.each do |packet|
  ap packet
end

[
    [0] "\x00\x00\x84\x00\x00\x00\x00\x02\x00\x00\x00\x01\aAndroid\x05local\x00\x00\x01\x80\x01\x00\x00\x00x\x00\x04\xAC\x1F\x01\xC0\xC0\f\x00\x1C\x80\x01\x00\x00\x00x\x00\x10\xFE\x80\x00\x00\x00\x00\x00\x00\xAEc\xBE\xFF\xFE\xC21;\xC0\f\x00/\x80\x01\x00\x00\x00x\x00\b\xC0\f\x00\x04@\x00\x00\b",
    [1] [
        [0] "AF_INET",
        [1] 5353,
        [2] "172.31.1.192",
        [3] "172.31.1.192"
    ]
]

mdns = MDNS.new
mdns.each do |packet, _addr|
  ap Resolv::DNS::Message.decode(packet)
end

#<Resolv::DNS::Message:0x00007ff3dc0b8420 @id=0, @qr=0, @opcode=0, @aa=0, @tc=0, @rd=0, @ra=0, @rcode=0, @question=[[#<Resolv::DNS::Name: _airplay._tcp.local.>, Resolv::DNS::Resource::Generic::Type12_Class32769]], @answer=[[#<Resolv::DNS::Name: _airplay._tcp.local.>, 4487, #<Resolv::DNS::Resource::IN::PTR:0x00007ff3de822790 @name=#<Resolv::DNS::Name: \xE8\x87\xA5\xE5\xAE\xA4._airplay._tcp.local.>, @ttl=4487>]], @authority=[], @additional=[]>
#<Resolv::DNS::Message:0x00007ff3de820ff8 @id=0, @qr=0, @opcode=0, @aa=0, @tc=0, @rd=0, @ra=0, @rcode=0, @question=[[#<Resolv::DNS::Name: _airplay._tcp.local.>, Resolv::DNS::Resource::IN::PTR]], @answer=[[#<Resolv::DNS::Name: _airplay._tcp.local.>, 4486, #<Resolv::DNS::Resource::IN::PTR:0x00007ff3dc0e3198 @name=#<Resolv::DNS::Name: \xE8\x87\xA5\xE5\xAE\xA4._airplay._tcp.local.>, @ttl=4486>]], @authority=[], @additional=[]>

mdns = MDNS.new
mdns.each do |packet, _addr|
  message = Resolv::DNS::Message.decode(packet)
  next if message.qr.zero?

  ap message
end

_airplay._tcp_.local

# :nodoc:
class MDNS
  include Enumerable

  # 略

  def listen
    return if @thread

    @thread = Thread.new do
      loop do
        packet, = @socket.recvfrom(4096)
        reply = Resolv::DNS::Message.decode(packet)
        next if reply.qr.zero?
        next if ptr?(reply)

        @replies << reply
      end
    end
  end

  def each(&_block)
    loop do
      yield @replies.shift until @replies.empty?
      sleep 1
    end
  end

  private

  def ptr?(reply)
    reply.answer.reduce(true) do |prev, (_, _, data)|
      prev & data.is_a?(Resolv::DNS::Resource::IN::PTR)
    end
  end
end

mdns = MDNS.new
mdns.listen
mdns.each do |reply|
  reply.each_answer do |name, _, _|
    ap name
  end
end

#<Resolv::DNS::Name: 臥室._airplay._tcp.local.>
#<Resolv::DNS::Name: Sonos-7828CAC4542C.local.>
#<Resolv::DNS::Name: 7828CAC4542C@臥室._raop._tcp.local.>

# Airplay 有兩種
airplay = Resolv::DNS::Name.create('_airplay._tcp.local.')
raop = Resolv::DNS::Name.create('_raop._tcp.local.')
# Chromecast
chromecast = Resolv::DNS::Name.create('_googlecast._tcp.local.)

mdns.each do |reply|
  reply.each_answer do |name, _, _|
    next unless name.subdomain_of?(airplay)
    next unless name.subdomain_of?(raop)
    next unless name.subdomain_of?(chromecast)

    ap name
  end
end