weird Socket.getaddrinfo result for localhost

Question

I have a problem with a ruby application connecting to a data base. After some hours of poking around, my problem boiled down to Socket.getaddrinfo 'localhost', nil returns unexpected addresses:

ruby -e "require \"socket\"; puts Socket.getaddrinfo('localhost', nil).inspect"

[["AF_INET", nil, "10.10.1.37", "10.10.1.37", 2, 2, 17], 
 ["AF_INET", nil, "10.10.1.37", "10.10.1.37", 2, 1, 6], 
 ["AF_INET", nil, "fe80:0:0:0:5e96:9dff:fe94:fce3%5", "fe80:0:0:0:5e96:9dff:fe94:fce3%5", 2, 2, 17], 
 ["AF_INET", nil, "fe80:0:0:0:5e96:9dff:fe94:fce3%5", "fe80:0:0:0:5e96:9dff:fe94:fce3%5", 2, 1, 6]]

10.10.1.37 is the address of the network adapter.

I'm using rvm and this strange behavior just happens, when I use a jruby. If I use a regular ruby version, the result is what I expect ('127.0.0.1' for example).

According to wikipedia, localhost should refer to the local loop back interface. What could cause this behavior, it this a Java thingy?

JRuby versions I've tried are: 1.7.2, 1.7.4 and 1.7.9

The more expected output (when using a regular ruby-1.9.3) is:

ruby -e "require \"socket\"; puts Socket.getaddrinfo('localhost', nil).inspect"

[["AF_INET6", 0, "::1", "::1", 30, 2, 17], 
 ["AF_INET6", 0, "::1", "::1", 30, 1, 6], 
 ["AF_INET", 0, "127.0.0.1", "127.0.0.1", 2, 2, 17], 
 ["AF_INET", 0, "127.0.0.1", "127.0.0.1", 2, 1, 6], 
 ["AF_INET6", 0, "fe80::1%lo0", "fe80::1%lo0", 30, 2, 17], 
 ["AF_INET6", 0, "fe80::1%lo0", "fe80::1%lo0", 30, 1, 6]]

Answer 1

This looks like a bug in jruby. They try to maintain compatibility with MRI as much as possible, and when that doesn't happen, it is considered a bug unless otherwise noted. You should open an issue with them over at Github

EDIT

I was not able to reproduce this on Linux running jruby 1.7.10 or on OS X using 1.7.8, but it still seems like a bug to me.