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lib/em/dns_cache.rb
Ruby
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# $Id: dns_cache.rb 5040 2007-10-05 17:31:04Z francis $
#
#
 
require 'rubygems'
require 'eventmachine'
require 'resolv'
 
 
module EventMachine
module DnsCache
 
class Cache
def initialize
@hash = {}
end
def add domain, value, expiration
ex = ((expiration < 0) ? :none : (Time.now + expiration))
@hash[domain] = [ex, value]
end
def retrieve domain
if @hash.has_key?(domain)
d = @hash[domain]
if d.first != :none and d.first < Time.now
@hash.delete(domain)
nil
else
d.last
end
end
end
end
 
@a_cache = Cache.new
@mx_cache = Cache.new
@nameservers = []
@message_ix = 0
 
def self.add_nameserver ns
@nameservers << ns unless @nameservers.include?(ns)
end
 
def self.verbose v=true
@verbose = v
end
 
 
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
 
# Needs to be DRYed up with resolve_mx.
#
def self.resolve domain
if d = @a_cache.retrieve(domain)
d
else
=begin
d = @a_cache[domain]
if d.first < Time.now
$>.puts "Expiring stale cache entry for #{domain}" if @verbose
@a_cache.delete domain
resolve domain
else
$>.puts "Fulfilled #{domain} from cache" if @verbose
d.last
end
else
=end
$>.puts "Fulfilling #{domain} from network" if @verbose
d = EM::DefaultDeferrable.new
d.timeout(5)
@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
@nameservers.each {|ns|
@message_ix = (@message_ix + 1) % 60000
Request.new d, @message_ix
msg = m.dup
msg[0,2] = [@message_ix].pack("n")
@u.send_datagram msg, ns, 53
}
 
d.callback {|resp|
r = []
resp.each_answer {|name,ttl,data|
r << data.address.to_s
}
 
# 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
d.succeed r
}
 
 
d
end
end
 
 
# Needs to be DRYed up with resolve.
#
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
$>.puts "Expiring stale cache entry for #{domain}" if @verbose
@mx_cache.delete domain
resolve_mx domain
else
$>.puts "Fulfilled #{domain} from cache" if @verbose
d.last
end
else
=end
$>.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
 
 
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
 
 
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
 
 
class MxQuery
include EM::Deferrable
 
def initialize rslt
@result = rslt # Deferrable
@n_a_lookups = 0
 
self.callback {|resp|
addrs = {}
resp.each_additional {|name,ttl,data|
addrs.has_key?(name) ? (addrs[name] << data.address.to_s) : (addrs[name] = [data.address.to_s])
}
 
@addresses = resp.answer.
sort {|a,b| a[2].preference <=> b[2].preference}.
map {|name,ttl,data|
ex = data.exchange
addrs[ex] or EM::DnsCache.resolve(ex.to_s)
}
 
@addresses.each_with_index {|a,ix|
if a.respond_to?(:set_deferred_status)
@n_a_lookups += 1
a.callback {|r|
@addresses[ix] = r
@n_a_lookups -= 1
succeed_result if @n_a_lookups == 0
}
end
}
 
succeed_result if @n_a_lookups == 0
}
end
 
def succeed_result
# Questionable whether we should uniq if it perturbs the sort order.
# Also freeze it so some user can't wipe it out on us.
@result.succeed @addresses.flatten.uniq.freeze
end
 
end
 
class Request
include EM::Deferrable
 
@@outstanding = {}
 
def self.post response
if r = @@outstanding.delete(response.id)
r.succeed response
end
end
 
def initialize rslt, m_id
@result = rslt
@msgid = m_id
raise "request-queue overflow" if @@outstanding.has_key?(@msgid)
@@outstanding[@msgid] = self
 
self.timeout(10)
self.errback { @@outstanding.delete(@msgid) }
self.callback {|resp| @result.succeed resp }
end
end
 
class Socket < EM::Connection
attr_accessor :unbind_signaller
 
def receive_data dg
m = nil
begin
m = Resolv::DNS::Message.decode dg
rescue
end
Request.post(m) if m
end
 
def unbind
@unbind_signaller.call if @unbind_signaller
end
end
 
end
end
test/test_basic.rb
Ruby
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# $Id: test_basic.rb 5040 2007-10-05 17:31:04Z francis $
#
#
 
$:.unshift(File.dirname(__FILE__) + '/../lib')
require 'dns_cache'
 
 
 
 
#--------------------------------------
 
 
class TestBasic < Test::Unit::TestCase
 
TestNameserver = "151.202.0.85"
TestNameserver2 = "151.202.0.86"
 
LocalMxRecords = %Q(
boondoggle.zzz:
65.66.67.68 10
55.56.57.58 5
esmtp.someone.zzz 4
 
boondoggle.yyy:
)
 
def test_a
EM::DnsCache.add_nameserver TestNameserver
EM::DnsCache.verbose
 
out = nil
 
EM.run {
d = EM::DnsCache.resolve "bayshorenetworks.com"
d.errback {EM.stop}
d.callback {|r|
d = EM::DnsCache.resolve "bayshorenetworks.com"
d.errback { EM.stop }
d.callback {|r| puts r; out = r; EM.stop }
}
}
 
assert out
end
 
def test_a_pair
EM::DnsCache.add_nameserver TestNameserver
EM::DnsCache.verbose
 
out = nil
 
EM.run {
d = EM::DnsCache.resolve "maila.microsoft.com"
d.errback {EM.stop}
d.callback {|r|
out = r
EM.stop
}
}
 
assert_equal( Array, out.class )
assert_equal( 2, out.length )
end
 
 
# This test causes each request to hit the network because they're all scheduled
# before the first one can come back and load the cache. Although a nice mis-feature for
# stress testing, it would be nice to fix it someday, perhaps by not kicking off a
# request for a particular domain if one is already pending.
# Without epoll, this test gets really slow and usually doesn't complete.
def test_lots_of_a
EM.epoll
EM::DnsCache.add_nameserver TestNameserver
EM::DnsCache.add_nameserver TestNameserver2
EM::DnsCache.verbose
 
n = 250
e = 0
s = 0
EM.run {
n.times {
d = EM::DnsCache.resolve "ibm.com"
d.errback {e+=1; n -= 1; EM.stop if n == 0}
d.callback {s+=1; n -= 1; EM.stop if n == 0}
}
}
assert_equal( 0, n)
assert_equal( 250, s)
end
 
 
 
 
def test_mx
EM::DnsCache.add_nameserver TestNameserver
EM::DnsCache.verbose
 
out = nil
 
EM.run {
d = EM::DnsCache.resolve_mx "steamheat.net"
d.errback {EM.stop}
d.callback {|r|
p r
d = EM::DnsCache.resolve_mx "steamheat.net"
d.errback {EM.stop}
d.callback {|r|
out = r
p r
EM.stop
}
}
}
 
assert out
end
 
 
# The arrays of addresses we get back from the DnsCache are FROZEN.
# That's because the same objects get passed around to any caller that
# asks for them. If you need to modify the array, dup it.
#
def test_freeze
EM::DnsCache.add_nameserver TestNameserver
EM::DnsCache.verbose
 
out = nil
 
EM.run {
d = EM::DnsCache.resolve_mx "steamheat.net"
d.errback {EM.stop}
d.callback {|r|
out = r
EM.stop
}
}
 
assert out
assert( out.length > 0)
assert_raise( TypeError ) {
out.clear
}
end
 
 
def test_local_defs
EM::DnsCache.add_nameserver TestNameserver
EM::DnsCache.verbose
 
EM::DnsCache.add_cache_entry( :mx, "example.zzz", ["1.2.3.4"], -1 )
out = nil
EM.run {
d = EM::DnsCache.resolve_mx "example.zzz"
d.errback {EM.stop}
d.callback {|r|
out = r
EM.stop
}
}
assert_equal( ["1.2.3.4"], out )
end
 
def test_multiple_local_defs
EM::DnsCache.verbose
 
EM::DnsCache.add_cache_entry( :mx, "example.zzz", ["1.2.3.4", "5.6.7.8"], -1 )
out = nil
EM.run {
d = EM::DnsCache.resolve_mx "example.zzz"
d.errback {EM.stop}
d.callback {|r|
out = r
EM.stop
}
}
assert_equal( ["1.2.3.4","5.6.7.8"], out )
end
 
# Adding cache entries where they already exist causes them to be REPLACED.
#
def test_replace
EM::DnsCache.verbose
 
EM::DnsCache.add_cache_entry( :mx, "example.zzz", ["1.2.3.4", "5.6.7.8"], -1 )
EM::DnsCache.add_cache_entry( :mx, "example.zzz", ["10.11.12.13"], -1 )
out = nil
EM.run {
d = EM::DnsCache.resolve_mx "example.zzz"
d.errback {EM.stop}
d.callback {|r|
out = r
EM.stop
}
}
assert_equal( ["10.11.12.13"], out )
end
 
# We have a facility for storing locally-defined MX records.
# The DNS cache has a way to parse and process these values.
#
def test_external_mx_defs
EM::DnsCache.verbose
 
EM::DnsCache.parse_local_mx_records LocalMxRecords
 
out = nil
EM.run {
d = EM::DnsCache.resolve_mx "boondoggle.zzz"
d.errback {EM.stop}
d.callback {|r|
out = r
EM.stop
}
}
assert_equal( ["esmtp.someone.zzz", "55.56.57.58", "65.66.67.68"], out )
end
 
end

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