Can't make EMQX listen to both IPv4 and IPv6 on the same port

[bjanders]

Problem/Motivation

I'm trying to make the EMQX addon to listen to both IPv4 and IPV6 on port 1883. The default settings listen to IPv4 0.0.0.0:1883. In the EMQX web UI in Cluster Settings -> Listeners, I tried to add a new listener for '[::]:1883', but get the error

400 BAD_REQUEST: {failed_to_start,"tcp:IPv6([::]:1883) : {shutdown,{failed_to_start_child,listener,eaddrinuse}}"}

("IPv6" in the message above is the name of listener I created.)

I can replace '0.0.0.0:1883' with '[::]:1883' but then I don't have IPv4.

When configuring the EMQX config file directly, I believe you can set:

listeners.tcp.default {
    bind = "0.0.0.0:1883"
    bind = "[::]:1883"
}

But AFAIK I cannot edit the config file directly in Home Assistant.

Expected behavior

I should be able to add an IPv6 listener on port 1883 along with the IPv4 listener on the same port.

Actual behavior

I get the error:

400 BAD_REQUEST: {failed_to_start,"tcp:IPv6([::]:1883) : {shutdown,{failed_to_start_child,listener,eaddrinuse}}"}

Steps to reproduce

• Go to Cluster Settings -> Listeners, click "Add Listener" and add a lister for "[::]:1883"
• An error is displayed, and the listener is not added.

Proposed changes

Probably an issue in the upstream web UI, and should be fixed there.

This add-on could provide direct access to the config file, or then the default config should listen to IPv6 as well.

[bjanders]

I also tried to set

env_vars:
  - name: EMQX_LISTENERS__TCP__IPV6__BIND 
    value: "[::]:1883"

but it logs:

 tcp:ipv6 failed to listen on 1883 - eaddrinuse (address already in use)

Then when I try to remove env_vars in the add-on configuration, I get the error:

Failed to save add-on configuration, Invalid list for option 'env_vars' in EMQX (a0d7b954_emqx). Got {'env_vars': {}}

which is another issue.

Btw, the link to https://www.emqx.io/docs/en/v5.0/admin/cfg.html in https://github.com/hassio-addons/addon-emqx/blob/main/emqx/DOCS.md does not work. I found the documentation here: https://docs.emqx.com/en/emqx/latest/configuration/configuration.html#environment-variables