Option to enable/disable IPv6

[orlandothoeny]

Description
We cannot use the library since version 3.6.1, because of #1145.

We use https://github.com/cloudamqp/amqproxy which only listens on IPv4. Our application connects to this proxy via localhost, which has the default ::1 localhost ip6-localhost ip6-loopback entry in the server's /etc/hosts file.

Possible fixes:

• Either make it that IPv6 support must be explicitly enabled or add an option that allows disabling IPv6
• Have some sort of check that validates that IPv6 is actually working, not sure though if that would be too expensive performance-wise

Example
We get the following error:

In SocketIO.php line 82:
                                                        
  [PhpAmqpLib\Exception\AMQPIOException (111)]          
  Error Connecting to server (111): Connection refused

[lukebakken]

Hello, thanks for using this library.

You should fix your /etc/hosts file. It is quite unusual for localhost to be an ipv6 address.

We would also accept a PR that addresses this issue without breaking existing behavior.

[ramunasd]

Just use 127.0.0.1 for connection if proxy is listening on local loopback.

[orlandothoeny]

We're using the default /etc/hosts of Ubuntu.

Yes, changing to an IP (127.0.0.1) would probably be the easiest fix.

[lukebakken]

Hmm, I'm surprised the ipv6 address is picked up first.

$ docker run --pull always --tty --interactive ubuntu:latest
latest: Pulling from library/ubuntu
bccd10f490ab: Already exists
Digest: sha256:77906da86b60585ce12215807090eb327e7386c8fafb5402369e421f44eff17e
Status: Downloaded newer image for ubuntu:latest
root@0e7320e07973:/# cat /etc/hosts
127.0.0.1       localhost
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.2      0e7320e07973

[orlandothoeny]

Yes it's strange, the 127.0.0.1 localhost record is also the first one on our servers:

cat /etc/hosts
127.0.0.1	localhost
127.0.1.1	my-ubuntu-user

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

[orlandothoeny]

Oh no, wait a second..
That was my local one. There localhost doesn't even point to ::1.

Seems like this changed in some Ubuntu version or is different on the Ubuntu Server version.
That's the actual one from the server:

127.0.0.1	localhost

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters