Internal Server Error 500 when Empty Host Header Sent

Tái hiện request bằng thiết lập config.ru được hiển thị và header Host trống, sau đó lần theo request qua httpserver.rb của WEBrick và rackup handler được đề cập trong stack trace. Xác nhận rằng request không hợp lệ hiện đến Rack với SERVER_NAME bị thiếu và hành vi hoàn chỉnh là phản hồi HTTP 400 thay vì 500.

Overview

When sent a GET request with an empty host header, WEBrick responds with error code 500, but it should respond with Error Code 400, for an invalid request.

Reproducing the Bug

1. Clone, build, and install WEBrick. (Tested on ea124002ee5ff43b6cf846931b2cb898b3f47819)
2. Set up a config.ru file with the following contents:

class Server
  def call(env)
    [200, {}, []]
  end
end

run Server.new

3. Run rackup.
4. Send a GET request with an empty host header, and observe WEBrick's response as follows:

printf 'GET / HTTP/1.1\r\nHost: \r\n\r\n' | ncat localhost 9292

Rack::Lint::LintError: env missing required key SERVER_NAME (Rack::Lint::LintError)
	/usr/share/rubygems-integration/all/gems/rack-3.1.16/lib/rack/lint.rb:283:in `block in check_environment'
	/usr/share/rubygems-integration/all/gems/rack-3.1.16/lib/rack/lint.rb:282:in `each'
	/usr/share/rubygems-integration/all/gems/rack-3.1.16/lib/rack/lint.rb:282:in `check_environment'
	/usr/share/rubygems-integration/all/gems/rack-3.1.16/lib/rack/lint.rb:63:in `response'
	/usr/share/rubygems-integration/all/gems/rack-3.1.16/lib/rack/lint.rb:41:in `call'
	/usr/share/rubygems-integration/all/gems/rack-3.1.16/lib/rack/show_exceptions.rb:31:in `call'
	/usr/share/rubygems-integration/all/gems/rack-3.1.16/lib/rack/common_logger.rb:43:in `call'
	/usr/share/rubygems-integration/all/gems/rack-3.1.16/lib/rack/content_length.rb:20:in `call'
	/usr/share/rubygems-integration/all/gems/rackup-2.1.0/lib/rackup/handler/webrick.rb:111:in `service'
	/var/lib/gems/3.3.0/gems/webrick-1.9.1/lib/webrick/httpserver.rb:140:in `service'
	/var/lib/gems/3.3.0/gems/webrick-1.9.1/lib/webrick/httpserver.rb:96:in `run'
	/var/lib/gems/3.3.0/gems/webrick-1.9.1/lib/webrick/server.rb:310:in `block in start_thread'
::1 - - [27/Aug/2025:18:40:52 +0000] "GET / HTTP/1.1" 500 1183 0.0002