Return proper exit code for TERM signal (#1337)

Attempt at returning the proper exit code (128+15) when TERM signal
is sent to the server, for both single and clustered mode.

The changes are achieved by restoring signal from within the trap
and accordingly killing the process using TERM event.

Added plus, stopping single mode gracefully now.

lib/puma/cluster.rb

@@ -375,7 +375,10 @@ def setup_signals
           log "Early termination of worker"
           exit! 0
         else
+          stop_workers
           stop
+
+          raise SignalException, "SIGTERM"
         end
       end
     end

lib/puma/launcher.rb

@@ -392,7 +392,9 @@ def setup_signals
 
       begin
         Signal.trap "SIGTERM" do
-          stop
+          graceful_stop
+
+          raise SignalException, "SIGTERM"
         end
       rescue Exception
         log "*** SIGTERM not implemented, signal based gracefully stopping unavailable!"

test/test_integration.rb

@@ -53,6 +53,21 @@ def server(argv)
     @server
   end
 
+  def start_forked_server(argv)
+    pid = fork do
+      exec "#{Gem.ruby} -I lib/ bin/puma -b tcp://127.0.0.1:#{@tcp_port} #{argv}"
+    end
+
+    sleep 5
+    pid
+  end
+
+  def stop_forked_server(pid)
+    Process.kill(:TERM, pid)
+    sleep 1
+    Process.wait2(pid)
+  end
+
   def restart_server_and_listen(argv)
     skip_on_appveyor
     server(argv)
@@ -218,4 +233,22 @@ def test_restart_restores_environment
     assert_includes new_reply, "Hello RAND"
     refute_equal initial_reply, new_reply
   end
+
+  def test_term_signal_exit_code_in_single_mode
+    skip if Puma.jruby? || Puma.windows?
+
+    pid = start_forked_server("test/rackup/hello.ru")
+    _, status = stop_forked_server(pid)
+
+    assert_equal 15, status
+  end
+
+  def test_term_signal_exit_code_in_clustered_mode
+    skip if Puma.jruby? || Puma.windows?
+
+    pid = start_forked_server("-w 2 test/rackup/hello.ru")
+    _, status = stop_forked_server(pid)
+
+    assert_equal 15, status
+  end
 end