Ruby TCPServer always delay on dns reverse lookup? - how to disable?

Question

I created a TCPServer with ruby gserver.

Everytime I connect remotly to the server, it takes 2-4 seconds until connection is established.

This is only happen if I connect from remote machine.

Connection from same machine has running the service will send immidiate response.

For the connection on same machine there is no difference if I connect via localhost or via the machines ip.

I think delay depends on reverse lookup but can not localize why.

in gserver.rb it is line 263

client = @tcpServer.accept

Here the delay occurs, I do not know what is in this method.

I added all machines which are used during tests to the local hosts file. But that changed nothing.

Same happens when using Webrick, I tried to set also

BasicSocket.do_not_reverse_lookup = true

as well as direct on the resulting server socket

Socket.do_not_reverse_lookup = true

as well as on client connection socket

client.do_not_reverse_lookup = true

But that also changed nothing on delay.

Whenever connection is established, the values of remote_host and remote_ip are resolved and as defined in hosts file.

I tried that running ruby 2.2.1 on ubuntu 14.04 as well as ruby 1.9.3 running debian wheezy.

Same behavior - (long) delay on connecting service.

Q: How to fix that / disable lookup on TCPServer?

I made same test with webrick - same behavior, when connecting from remote it has 2-4 seconds delay. — Tom Freudenberg, Jun 29 '14 at 19:44
I also configured my systems nsswitch.conf once to only use files, but again no effect - still delay — Tom Freudenberg, Jun 29 '14 at 19:53

Tom Freudenberg · Accepted Answer · 2014-07-03T23:34:14.263

The problem depends on my client machine where I run on MAC OSX Mav.

The used telnet client tries to open IPv6 connection and afterwards IPv4.

To solve the delay, just open connection with

telnet -4 my-server 3333

I have build a small connect echo servive where you can check resolves and timings.

If you change NO_REVERSE_LOOKUP you will get IPs or ADDRESSes and if not resolveable, different response times.

require 'socket'

NO_REVERSE_LOOKUP = true
CONNECT_PORT = 3333

puts "#{Time.now} Starting service on port: #{CONNECT_PORT}"

# the full hell - just to test if anything meets what we want
TCPServer.do_not_reverse_lookup = NO_REVERSE_LOOKUP
BasicSocket.do_not_reverse_lookup = NO_REVERSE_LOOKUP
Socket.do_not_reverse_lookup = NO_REVERSE_LOOKUP

srv = TCPServer.open(CONNECT_PORT)

puts "#{Time.now} Waiting for client"

client = srv.accept

puts "#{Time.now} Client connected"

client.do_not_reverse_lookup = NO_REVERSE_LOOKUP

client.print "Hello connected\n"

# in case that we disabled reverse lookup, we should only receive IP Adresses

puts "#{Time.now} Getting server address infos" 

puts "SERVER INFO:"
puts NO_REVERSE_LOOKUP ? client.addr(:numeric) : client.addr(:hostname)

puts ""

puts "#{Time.now} Getting remote client infos"

puts "REMOTE INFO:"
puts NO_REVERSE_LOOKUP ? client.peeraddr(:numeric) : client.peeraddr(:hostname)

###

puts "#{Time.now} Closing connection"

client.close

puts "#{Time.now} End"

Thanks to drbrain from #ruby-lang irc for pointing me to the IPv6 problem.

Ruby TCPServer always delay on dns reverse lookup? - how to disable?

1 Answers1