fix running on ipv4-only systems

[OE1KHZ]

This simple fix makes running this fork of synapse-admin on ipv4-only systems possible.
Currently, running synapse-admin on non-ipv6 systems throws the following error:

synapse-admin  | 2025-11-20T15:42:48.214133Z ERROR static_web_server::server: server failed to start up: failed to bind to [::]:80 address
synapse-admin  | 
synapse-admin  | Caused by:
synapse-admin  |     Address family not supported by protocol (os error 97)

As mentioned in this issue in static-web-server passing the environment variable SERVER_HOST=0.0.0.0 overrides the default (SERVER_HOST=[::]) and therefore fixes this issue :)

[aine-etke]

Thank you for contribution!

Unfortunately, from the linked issue it sounds like such adjustment will break compatibility with IPv6-only systems, and may impact dual-stack systems as well.

Would you mind instead of setting the default value in the Dockerfile, mention that workaround in the readme?

[OE1KHZ]

Ahhh, yes sure. How have i not thought about that...

[OE1KHZ]

Ok sorry for the force pushes but everything i messed up is gone, since i squashed and pushed the commits.

[aine-etke]

Thank you! Added a few notes - please take a look whenever you have a chance

[OE1KHZ]

Sorry for the mess. I thought the only way to set environment variables was to set them during build time. That's why I chose to use an build argument which gets saved in a environment variable. I just found out that you can set environment variables after building via -e flag.

[aine-etke]

Thank you for handling it!

Yes, env vars can be set at run time with -e and --env-file args