Add experimental support for Puma

This allows us (and others) to test drive Puma without it affecting all
users. Puma can be enabled by setting the environment variable
"EXPERIMENTAL_PUMA" to a non empty value.

spec/rack_servers/puma_spec.rb

+# frozen_string_literal: true
+
+require 'fileutils'
+
+require 'excon'
+
+require 'spec_helper'
+
+describe 'Puma' do
+  before(:all) do
+    config_lines = File.read('spec/rack_servers/configs/puma.rb')
+      .gsub('$WORKING_DIR', Dir.pwd)
+
+    config_path = 'tmp/tests/puma.rb'
+    @socket_path = File.join(Dir.pwd, 'tmp/tests/puma.socket')
+
+    File.write(config_path, config_lines)
+
+    cmd = %W[puma -e test -C #{config_path} spec/rack_servers/configs/config.ru]
+    @puma_master_pid = spawn(*cmd)
+    wait_puma_boot!(@puma_master_pid, 'tmp/tests/puma-worker-ready')
+    WebMock.allow_net_connect!
+  end
+
+  %w[SIGQUIT SIGTERM SIGKILL].each do |signal|
+    it "has a worker that self-terminates on signal #{signal}" do
+      response = Excon.get('unix://', socket: @socket_path)
+      expect(response.status).to eq(200)
+
+      worker_pid = response.body.to_i
+      expect(worker_pid).to be > 0
+
+      begin
+        Excon.post("unix://?#{signal}", socket: @socket_path)
+      rescue Excon::Error::Socket
+        # The connection may be closed abruptly
+      end
+
+      expect(pid_gone?(worker_pid)).to eq(true)
+    end
+  end
+
+  after(:all) do
+    begin
+      WebMock.disable_net_connect!(allow_localhost: true)
+      Process.kill('TERM', @puma_master_pid)
+    rescue Errno::ESRCH
+    end
+  end
+
+  def wait_puma_boot!(master_pid, ready_file)
+    # We have seen the boot timeout after 2 minutes in CI so let's set it to 5 minutes.
+    timeout = 5 * 60
+    timeout.times do
+      return if File.exist?(ready_file)
+
+      pid = Process.waitpid(master_pid, Process::WNOHANG)
+      raise "puma failed to boot: #{$?}" unless pid.nil?
+
+      sleep 1
+    end
+
+    raise "puma boot timed out after #{timeout} seconds"
+  end
+
+  def pid_gone?(pid)
+    # Worker termination should take less than a second. That makes 10
+    # seconds a generous timeout.
+    10.times do
+      begin
+        Process.kill(0, pid)
+      rescue Errno::ESRCH
+        return true
+      end
+
+      sleep 1
+    end
+
+    false
+  end
+end

spec/unicorn/unicorn_spec.rb → spec/rack_servers/unicorn_spec.rb

+# frozen_string_literal: true
+
 require 'fileutils'
 require 'excon'