Module: EventMachine::DnsCache

Defined in:
lib/em/dns_cache.rb

Defined Under Namespace

Classes: Cache, MxQuery, Request, Socket

Constant Summary collapse

MAX_WAITING = 
100

Class Method Summary collapse

Class Method Details

.add_cache_entry(cache_type, domain, value, expiration) ⇒ Object 



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# File 'lib/em/dns_cache.rb', line 61

def self.add_cache_entry cache_type, domain, value, expiration
  cache = if cache_type == :mx
            @mx_cache
          elsif cache_type == :a
            @a_cache
          else
            raise "bad cache type"
          end

  v = EM::DefaultDeferrable.new
  v.succeed( value.dup.freeze )
  cache.add domain, v, expiration
end

.add_nameserver(ns) ⇒ Object 



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# File 'lib/em/dns_cache.rb', line 42

def self.add_nameserver ns
  @nameservers << ns unless @nameservers.include?(ns)
end

.add_nameservers_from_file(file = '/etc/resolv.conf') ⇒ Object 



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# File 'lib/em/dns_cache.rb', line 46

def self.add_nameservers_from_file file='/etc/resolv.conf'
  IO::readlines(file).each do |line|
    if line =~ /^nameserver (.+)$/
      $1.split(/\s+/).each { |ns|
        @nameservers << ns unless ns.empty?
      }
    end
  end
end

.lazy_initialize ⇒ Object 



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# File 'lib/em/dns_cache.rb', line 218

def self.lazy_initialize
  # Will throw an exception if EM is not running.
  # We wire a signaller into the socket handler to tell us when that socket
  # goes away. (Which can happen, among other things, if the reactor
  # stops and restarts.)
  #
  raise "EventMachine reactor not running" unless EM.reactor_running?

  unless @u
    us = proc {@u = nil}
    @u = EM::open_datagram_socket( "0.0.0.0", 0, Socket ) {|c|
      c.unbind_signaller = us
    }
  end

end

.look_pending ⇒ Object 



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# File 'lib/em/dns_cache.rb', line 120

def self.look_pending
  EM.next_tick {
    while @waiting < MAX_WAITING && !@pending.empty?
      pending1 = @pending.shift
      pending1.call
      puts "#{@pending.size} pending requests now" if @verbose
    end
  }
end

.parse_local_mx_records(txt) ⇒ Object 



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# File 'lib/em/dns_cache.rb', line 236

def self.parse_local_mx_records txt
  domain = nil
  addrs = []

  add_it = proc {
    a = addrs.sort {|m,n| m.last <=> n.last}.map {|y| y.first}
    add_cache_entry :mx, domain, a, -1
  }

  txt = StringIO.new( txt ) if txt.is_a?(String)
  txt.each_line {|ln|
    if ln =~ /\A\s*([\d\w\.\-\_]+)\s+(\d+)\s*\Z/
      if domain
        addrs << [$1.dup, $2.dup.to_i]
      end
    elsif ln =~ /\A\s*([^\s\:]+)\s*\:\s*\Z/
      add_it.call if domain
      domain = $1.dup
      addrs.clear
    end
  }

  add_it.call if domain
end

.resolve(domain) ⇒ Object

Needs to be DRYed up with resolve_mx.



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# File 'lib/em/dns_cache.rb', line 77

def self.resolve domain
  if d = @a_cache.retrieve(domain)
    puts "Cache hit for #{domain}" if @verbose
    look_pending
    d
  else
=begin
    d = @a_cache[domain]
    if d.first < Time.now
      STDOUT.puts "Expiring stale cache entry for #{domain}" if @verbose
      @a_cache.delete domain
      resolve domain
    else
      STDOUT.puts "Fulfilled #{domain} from cache" if @verbose
      d.last
    end
  else
=end
    if @waiting >= MAX_WAITING
      puts "Postponing #{domain} because already waiting for #{@waiting} queries" if @verbose
      d = EM::DefaultDeferrable.new
      @pending << lambda {
        d_inner = resolve domain
        d_inner.callback &d.method(:succeed)
        d_inner.errback &d.method(:fail)
      }
      puts "#{@pending.size} pending requests now" if @verbose
      d
    else
      d = resolve_do domain
      @waiting += 1
      STDOUT.puts "Now waiting for #{@waiting}" if @verbose
      on_one_done = lambda {
        @waiting -= 1
        look_pending
      }
      d.callback &on_one_done
      d.errback &on_one_done
      d
    end
  end
end

.resolve_do(domain) ⇒ Object 



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# File 'lib/em/dns_cache.rb', line 130

def self.resolve_do domain
  STDOUT.puts "Fulfilling #{domain} from network" if @verbose
  d = EM::DefaultDeferrable.new
  #d.timeout(5)
  d.callback { d.cancel_timeout }
  d.errback { d.cancel_timeout }
  @a_cache.add domain, d, 300 # Hard-code a 5 minute expiration
  #@a_cache[domain] = [Time.now+120, d] # Hard code a 120-second expiration.

  lazy_initialize
  m = Resolv::DNS::Message.new
  m.rd = 1
  m.add_question domain, Resolv::DNS::Resource::IN::A
  m = m.encode
  d_inner = EM::DefaultDeferrable.new
  @nameservers.each {|ns|
    @message_ix = (@message_ix + 1) % 60000
    Request.new d_inner, @message_ix
    msg = m.dup
    msg[0,2] = [@message_ix].pack("n")
    @u.send_datagram msg, ns, 53
  }

  d_inner.callback {|resp|
    r = []
    resp.each_answer {|name,ttl,data|
      r << data.address.to_s if data.kind_of?(Resolv::DNS::Resource::IN::A)
    }

    # Freeze the array since we'll be keeping it in cache and passing it
    # around to multiple users. And alternative would have been to dup it.
    r.freeze
    puts "Succeeding with #{r.inspect}"
    d.succeed r
  }
  d_inner.errback &d.method(:fail)


  d
end

.resolve_mx(domain) ⇒ Object

Needs to be DRYed up with resolve.



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# File 'lib/em/dns_cache.rb', line 174

def self.resolve_mx domain
  if d = @mx_cache.retrieve(domain)
    d
  else
=begin
       if @mx_cache.has_key?(domain)
         d = @mx_cache[domain]
         if d.first < Time.now
           STDOUT.puts "Expiring stale cache entry for #{domain}" if @verbose
           @mx_cache.delete domain
           resolve_mx domain
         else
           STDOUT.puts "Fulfilled #{domain} from cache" if @verbose
           d.last
         end
       else
=end
    STDOUT.puts "Fulfilling #{domain} from network" if @verbose
    d = EM::DefaultDeferrable.new
    d.timeout(5)
    #@mx_cache[domain] = [Time.now+120, d] # Hard code a 120-second expiration.
    @mx_cache.add domain, d, 300 # Hard-code a 5 minute expiration

    mx_query = MxQuery.new d

    lazy_initialize
    m = Resolv::DNS::Message.new
    m.rd = 1
    m.add_question domain, Resolv::DNS::Resource::IN::MX
    m = m.encode
    @nameservers.each {|ns|
      @message_ix = (@message_ix + 1) % 60000
      Request.new mx_query, @message_ix
      msg = m.dup
      msg[0,2] = [@message_ix].pack("n")
      @u.send_datagram msg, ns, 53
    }


    d
  end
end

.verbose(v = true) ⇒ Object 



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# File 'lib/em/dns_cache.rb', line 56

def self.verbose v=true
  @verbose = v
end