Simple method of parsing HTTP_HOST in normalize_env breaks on IPv6 addresses.

[kaorihinata]

Describe the bug

Currently, normalize_env (in lib/puma/request.rb line 231) splits HTTP_HOST into SERVER_NAME and SERVER_PORT by finding the colon using String.index (if there is one.) This works fine for IPv4 addresses, but with IPv6 addresses this results in improperly split values being stored in SERVER_NAME and SERVER_PORT.

For example, an HTTP_HOST value of [::1]:9292 would result in SERVER_NAME being set to [ and SERVER_PORT being set to :1]:9292. Further up the stack, Rack catches this and panics.

Puma config:

A "hello world" config.ru:

run lambda { |env| [200, {"content-type" => "text/plain"}, [""]] }

...then just run rackup.

To Reproduce

Open a browser and navigate to the application using the IPv6 loopback address ([::1]:9292). I'd create a link, but GitHub seems to choke on the bracketing.

Alternatively, use curl:

curl 'http://[::1]:9292/'

I won't dump the entire HTML result in here, but you should receive a backtrace from Rack starting with:

Rack::Lint::LintError at /
env[SERVER_PORT] is not an Integer

Expected behavior

The "hello world" application above returns an empty response, so you should see nothing at all. Just a blank page. You can confirm this by replacing lib/puma/request.rb line 233:

        if colon = host.index(":")

...with:

        if colon = host.index(/:\d+$/)

Desktop (please complete the following information):

• OS: macOS Big Sur (11.2.3)
• Puma Version: 5.2.2, though I've confirmed the offending line still exists in HEAD.