url.hostport() joined the host and port without brackets. For an IPv6 host that gives ::1:8080 which is ambiguous and not a valid Host value or URL authority.

This showed up in a few places:

• mitmdump --mode reverse:http://[::1]:8000 rewrote the Host header of every forwarded request to ::1:8000.
• Changing request.host, request.port or request.url in a script rewrote the Host header or :authority the same way.
• request.url and request.pretty_url returned http://::1:8080/a for IPv6 targets.

hostport() now wraps an unbracketed IPv6 literal in brackets. A host that is already bracketed is left alone. unparse() uses hostport() so it is fixed too.

#8284 has the same change in hostport(). That PR has had no review since June. This one also covers the Request url and Host header paths and the reverse proxy case with tests. I am happy to close this one if you would rather use #8284.

Tests: five new tests across test_url.py, test_http.py and test_modes.py (reverse proxy to [::1]:8000). They fail without the change. ruff and mypy pass. A broader run of the proxy, net, http and addon tests passes except for a few load dependent tests that fail the same way on unmodified main here.