Problem

Rack::Request#host returns unexpected host when the domain starts with a number.

Rack v2.1.2 returns host correctly.

gem 'rack', '2.1.2'
require 'rack'

p Rack::Request.new({'HTTP_HOST' => '123foo.example.com'}).host
# => "123foo.example.com"

But Rack v2.2.0 (and v2.2.1) returns a part of the host unexpectedly.

gem 'rack', '2.2.0'
require 'rack'


p Rack::Request.new({'HTTP_HOST' => '123foo.example.com'}).host
# => "123"

I guess the cause is the following pull request. #1561