[Fix #11984] Add configurable server idle timeout

changelog/new_add_configurable_server_idle_timeout.md

@@ -0,0 +1 @@
+* [#11984](https://github.com/rubocop/rubocop/issues/11984): Add configurable server idle timeout via the `RUBOCOP_SERVER_IDLE_TIMEOUT` environment variable. ([@Palladinium][])

docs/modules/ROOT/pages/usage/server.adoc

@@ -116,8 +116,12 @@ environment variables.
 * `$RUBOCOP_SERVER_HOST`
 * `$RUBOCOP_SERVER_PORT`
 
-The following is an example:
+You can configure the server process to automatically shut down after a period of not receiving connections. The option takes a number in seconds.
+
+* `$RUBOCOP_SERVER_IDLE_TIMEOUT`
+
+The following is an example that listens on port 98989 and shuts down after one minute without receiving connections:
 
 ```console
-$ RUBOCOP_SERVER_PORT=98989 rubocop --start-server
+$ RUBOCOP_SERVER_PORT=98989 RUBOCOP_SERVER_IDLE_TIMEOUT=60 rubocop --start-server
 ```

lib/rubocop/options.rb

@@ -623,7 +623,11 @@ module OptionsHelp
                                          'Default is false.',
                                          'You can specify the server host and port with the',
                                          '$RUBOCOP_SERVER_HOST and the $RUBOCOP_SERVER_PORT',
-                                         'environment variables.'],
+                                         'environment variables.',
+                                         'You can set a timeout in seconds with the',
+                                         '$RUBOCOP_SERVER_IDLE_TIMEOUT environment variable,',
+                                         'after which the server will shut down if no connections',
+                                         'are made.'],
       restart_server:                   'Restart server process.',
       start_server:                     'Start server process.',
       stop_server:                      'Stop server process.',

lib/rubocop/server/client_command/start.rb

@@ -20,6 +20,7 @@ def initialize(detach: true)
           super()
         end
 
+        # rubocop:disable Metrics/MethodLength
         def run
           if Server.running?
             warn "RuboCop server (#{Cache.pid_path.read}) is already running."
@@ -38,10 +39,12 @@ def run
 
             host = ENV.fetch('RUBOCOP_SERVER_HOST', '127.0.0.1')
             port = ENV.fetch('RUBOCOP_SERVER_PORT', 0)
+            idle_timeout = ENV.fetch('RUBOCOP_SERVER_IDLE_TIMEOUT', nil)&.to_i
 
-            Server::Core.new.start(host, port, detach: @detach)
+            Server::Core.new.start(host, port, detach: @detach, idle_timeout: idle_timeout)
           end
         end
+        # rubocop:enable Metrics/MethodLength
       end
     end
   end

lib/rubocop/server/core.rb

@@ -27,7 +27,8 @@ def token
         self.class.token
       end
 
-      def start(host, port, detach: true)
+      def start(host, port, detach: true, idle_timeout: nil)
+        @idle_timeout = idle_timeout
         $PROGRAM_NAME = "rubocop --server #{Cache.project_dir}"
 
         require_relative '../../rubocop'
@@ -58,7 +59,20 @@ def write_port_and_token_files
 
       def process_input
         Cache.write_pid_file do
-          read_socket(@server.accept) until @server.closed?
+          until @server.closed?
+            begin
+              socket = @server.accept_nonblock
+            rescue IO::WaitReadable, Errno::EINTR
+              if @server.wait_readable(@idle_timeout).nil?
+                output_stream&.puts 'RuboCop server terminating due to idle timeout.'
+                break
+              end
+
+              retry
+            end
+
+            read_socket(socket)
+          end
         end
       end
 
@@ -71,15 +85,18 @@ def server_mode?
         true
       end
 
-      def start_server(host, port)
-        @server = TCPServer.open(host, port)
-
+      def output_stream
         # JSON format does not expected output message when IDE integration with server mode.
         # See: https://github.com/rubocop/rubocop/issues/11164
-        return if use_json_format?
+        return nil if use_json_format?
+
+        ARGV.include?('--stderr') ? $stderr : $stdout
+      end
+
+      def start_server(host, port)
+        @server = TCPServer.open(host, port)
 
-        output_stream = ARGV.include?('--stderr') ? $stderr : $stdout
-        output_stream.puts "RuboCop server starting on #{@server.addr[3]}:#{@server.addr[1]}."
+        output_stream&.puts "RuboCop server starting on #{@server.addr[3]}:#{@server.addr[1]}."
       end
 
       def read_socket(socket)

spec/rubocop/options_spec.rb

@@ -97,6 +97,10 @@ def abs(path)
                                                You can specify the server host and port with the
                                                $RUBOCOP_SERVER_HOST and the $RUBOCOP_SERVER_PORT
                                                environment variables.
+                                               You can set a timeout in seconds with the
+                                               $RUBOCOP_SERVER_IDLE_TIMEOUT environment variable,
+                                               after which the server will shut down if no connections
+                                               are made.
                   --restart-server             Restart server process.
                   --start-server               Start server process.
                   --stop-server                Stop server process.