bind fails for localhost on system without IPv6 DNS

[bertsky]

Probably a regression from #827:

If I do

echo 'from starlette.applications import Starlette; app = Starlette()' > server.py
uvicorn --host localhost --port 7000 server:app

that yields:

INFO:     Started server process [12]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
ERROR:    [Errno 99] error while attempting to bind on address ('::1', 7000, 0, 0): cannot assign requested address
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.

The system in question does not resolve localhost to IPv6, only IPv4:

> host localhost
localhost.localdomain has address 127.0.0.1
> host -6 localhost
;; connection timed out; no servers could be reached

Version is uvicorn 0.22.0 with CPython 3.11.3 on Linux.

[asdorsey]

Also seeing this in a Docker container without IPv6.

Version is uvicorn 0.24.0 with CPython 3.11.6 on Linux.

[martin-schulze-e2m]

Still seems to be an issue in docker with uvicorn 0.30.6 with CPython 3.11.6 on Linux. We found that docker (pre v26.0) has a bug regarding IPv6.