Class: Celluloid::IO::DNSResolver

Inherits:
Object
  • Object
show all
Defined in:
lib/celluloid/io/dns_resolver.rb

Overview

Asynchronous DNS resolver using Celluloid::IO::UDPSocket

Constant Summary collapse

RESOLV_CONF = 
'/etc/resolv.conf'
HOSTS = 
'/etc/hosts'
DNS_PORT = 
53

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ DNSResolver

Returns a new instance of DNSResolver.



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# File 'lib/celluloid/io/dns_resolver.rb', line 35

def initialize
  @nameservers, @hosts = self.class.nameservers, self.class.hosts
  
  # TODO: fall back on other nameservers if the first one is unavailable
  @server = @nameservers.first

  # The non-blocking secret sauce is here, as this is actually a
  # Celluloid::IO::UDPSocket
  @socket = UDPSocket.new
end

Class Method Details

.generate_id ⇒ Object 



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# File 'lib/celluloid/io/dns_resolver.rb', line 14

def self.generate_id
  @mutex.synchronize { @identifier = (@identifier + 1) & 0xFFFF }
end

.hosts(hostfile = HOSTS) ⇒ Object

FIXME: Y U NO Resolv::Hosts?



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# File 'lib/celluloid/io/dns_resolver.rb', line 23

def self.hosts(hostfile = HOSTS)
  hosts = {}
  File.open(hostfile) do |f|
    f.each_line do |host_entry|
      entries = host_entry.gsub(/#.*$/, '').gsub(/\s+/, ' ').split(' ')
      addr = entries.shift
      entries.each { |e| hosts[e] ||= addr }
    end
  end
  hosts
end

.nameservers(config = RESOLV_CONF) ⇒ Object 



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# File 'lib/celluloid/io/dns_resolver.rb', line 18

def self.nameservers(config = RESOLV_CONF)
  File.read(config).scan(/^\s*nameserver\s+([0-9.:]+)/).flatten
end

Instance Method Details

#resolve(hostname) ⇒ Object 



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# File 'lib/celluloid/io/dns_resolver.rb', line 46

def resolve(hostname)
  host = @hosts[hostname]
  if host
    begin
      return Resolv::IPv4.create(host)
    rescue ArgumentError
    end

    begin
      return Resolv::IPv6.create(host)
    rescue ArgumentError
    end
    
    raise Resolv::ResolvError, "invalid entry in hosts file: #{host}"
  end
  
  query = Resolv::DNS::Message.new
  query.id = self.class.generate_id
  query.rd = 1
  query.add_question hostname, Resolv::DNS::Resource::IN::A
  
  @socket.send query.encode, 0, @server, DNS_PORT
  data, _ = @socket.recvfrom(512)
  response = Resolv::DNS::Message.decode(data)
  
  addrs = []
  # The answer might include IN::CNAME entries so filters them out
  # to include IN::A & IN::AAAA entries only.
  response.each_answer { |name, ttl, value| addrs << (value.respond_to?(:address) ? value.address : nil) }
  addrs.compact!
  
  return if addrs.empty?
  return addrs.first if addrs.size == 1
  addrs
end