Bug #8067: Checking a network connection in a loop never succeeds even if the connection is available.

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.0.0p0 (2013-02-24 revision 39474) [x86_64-linux]

[l0x (Markus Lux)]

=begin
I want to check for a connection to a specific server with Ruby. So I just wrap the HTTP request into a begin/rescue construct and try again in a few seconds if the connection is not available.

((Problem)): If I start the program with no connection available (link down) it will never succeed in finding a connection even if at some time the connection is available (e.g. via ping, browser request).

((Test case:))

require 'net/http'

loop do

begin
	uri = URI.parse 'http://www.example.com'
	resp = Net::HTTP.get uri
rescue SocketError => se
	puts se
	sleep 3
	next
rescue Exception => e
	puts e
	break	
end

puts 'It works!'
break

end

((Steps to reproduce:))

(1) Take network link down
(2) Start program
(3) -> getaddrinfo: Name or service not known
(4) -> ...
(5) Turn network link on again
(6) Still no connection, same error

((Expected behavior:)) Don't throw SocketException as soon as a connection is available.

((Ruby versions tested:))

ruby 1.9.3p392 (2013-02-22 revision 39386) [x86_64-linux]

ruby 2.0.0p0 (2013-02-24 revision 39474) [x86_64-linux]

This may only affect Linux since there exist reports on [1] where people commented that the program works as expected on Windows and Mac.

[1] http://stackoverflow.com/questions/15321260/checking-a-network-connection-in-a-loop-never-succeeds-even-if-the-connection-is

=end

[steakknife (Barry Allard)]

Modified a bit for interactive looping:

#!/usr/bin/env ruby
require 'net/http'

loop do
sleep 1
begin
uri = URI.parse 'http://www.example.com'
resp = Net::HTTP.get uri
puts 'It works!'
rescue SocketError => se
puts se
next
rescue Exception => e
puts e
next
end
end

Mac 10.7.5 + 1.9.3-p392 output:

It works! # network on here
It works!
It works!
It works!
It works!
No route to host - connect(2) # network off here
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known # network on here
It works!
It works!
It works!
It works! # network off here
No route to host - connect(2)
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known
getaddrinfo: nodename nor servname provided, or not known # network on here
It works!
It works!
It works!
^C
It works!
It works!
^C./net_test.rb:5:in sleep': Interrupt from ./net_test.rb:5:in block in '
from ./net_test.rb:4:in loop' from ./net_test.rb:4:in '

Haven't tried Linux or FreeBSD yet.

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Feedback

The script runs as expected on OpenBSD with ruby 2.6. I expect the issue you are experiencing is probably specific to your environment. Can you recreate this issue with a supported version of Ruby, and if so provide more details regarding your environment?

[jeremyevans0 (Jeremy Evans)]

• Status changed from Feedback to Closed