Prevent loading with rack 3

lib/puma.rb

@@ -10,9 +10,11 @@
 
 require 'thread'
 
+# extension files should not be loaded with `require_relative`
 require 'puma/puma_http11'
-require 'puma/detect'
-require 'puma/json_serialization'
+require_relative 'puma/detect'
+require_relative 'puma/json_serialization'
+require_relative 'rack/version_restriction'
 
 module Puma
   autoload :Const, 'puma/const'

lib/rack/version_restriction.rb

@@ -0,0 +1,15 @@
+begin
+  begin
+    # rack/version exists in Rack 2.2.0 and later, compatible with Ruby 2.3 and later
+    # we prefer to not load Rack
+    require 'rack/version'
+  rescue LoadError
+    require 'rack'
+  end
+
+  # Rack.release is needed for Rack v1, Rack::RELEASE was added in v2
+  if Gem::Version.new(Rack.release) >= Gem::Version.new("3.0.0")
+    raise StandardError.new "Puma 5 is not compatible with Rack 3, please upgrade to Puma 6 or higher."
+  end
+rescue LoadError
+end

test/bundle_rack_3/Gemfile

@@ -0,0 +1,4 @@
+source "https://rubygems.org"
+
+gem 'rack', '>= 3.0.0'
+gem 'puma', path: '../..'

test/bundle_rack_3/config.ru

@@ -0,0 +1 @@
+run lambda { |env| [200, {"Content-Type" => "text/plain"}, ["Hello World"]] }

test/helpers/integration.rb

@@ -54,11 +54,20 @@ def teardown
 
   private
 
+  def with_unbundled_env
+    bundler_ver = Gem::Version.new(Bundler::VERSION)
+    if bundler_ver < Gem::Version.new('2.1.0')
+      Bundler.with_clean_env { yield }
+    else
+      Bundler.with_unbundled_env { yield }
+    end
+  end
+
   def silent_and_checked_system_command(*args)
     assert(system(*args, out: File::NULL, err: File::NULL))
   end
 
-  def cli_server(argv, unix: false, config: nil, merge_err: false)
+  def cli_server(argv, unix: false, config: nil, merge_err: false, skip_waiting: false)
     if config
       config_file = Tempfile.new(%w(config .rb))
       config_file.write config
@@ -77,7 +86,7 @@ def cli_server(argv, unix: false, config: nil, merge_err: false)
     else
       @server = IO.popen(cmd, "r")
     end
-    wait_for_server_to_boot
+    wait_for_server_to_boot unless skip_waiting
     @pid = @server.pid
     @server
   end

test/test_rack_version_restriction.rb

@@ -0,0 +1,48 @@
+require_relative "helper"
+require_relative "helpers/integration"
+
+class TestRackVersionRestriction < TestIntegration
+  class PumaBooted < Timeout::Error; end
+
+  def setup
+    # Rack 3 minimum Ruby version is 2.4
+    skip if !::Puma::IS_MRI || RUBY_VERSION < '2.4'
+    super
+  end
+
+  def teardown
+    return if skipped?
+    FileUtils.rm_rf ["#{workdir}/vendor", "#{workdir}/Gemfile.lock"]
+    begin
+      # KILL works with all OS's
+      Process.kill(:KILL, @server.pid) if @server
+    rescue Errno::ESRCH
+    end
+  end
+
+  def test_prevent_booting_with_rack_3
+    msg = "Puma 5 is not compatible with Rack 3"
+    puma_crashed = false
+
+    Dir.chdir(workdir) do
+      with_unbundled_env do
+        silent_and_checked_system_command("bundle config --local path vendor/bundle")
+        silent_and_checked_system_command("bundle install")
+        Timeout.timeout(5, PumaBooted) do
+          cli_server './config.ru', merge_err: true, skip_waiting: true
+          sleep 0.1 until puma_crashed = @server.gets[msg]
+        end
+      end
+    end
+
+  rescue PumaBooted
+  ensure
+    assert puma_crashed, "Puma was expected to crash on boot, but it didn't! "
+  end
+
+  private
+
+  def workdir
+    File.expand_path("bundle_rack_3", __dir__)
+  end
+end

test/test_worker_gem_independence.rb

@@ -133,13 +133,4 @@ def start_phased_restart
 
     true while @server.gets !~ /booted in [.0-9]+s, phase: 1/
   end
-
-  def with_unbundled_env
-    bundler_ver = Gem::Version.new(Bundler::VERSION)
-    if bundler_ver < Gem::Version.new('2.1.0')
-      Bundler.with_clean_env { yield }
-    else
-      Bundler.with_unbundled_env { yield }
-    end
-  end
 end