Add ProcessClient and ProcessServer classes for addon framework

This commit introduces two new classes to enhance the addon framework:

1. ProcessClient: Manages communication with addon servers, handling
   initialization, message sending/receiving, and shutdown.

2. ProcessServer: Provides a base class for addon servers to handle
   requests and responses.

These classes facilitate better separation of concerns and provide a
structured approach for addons to communicate with the Ruby LSP server.

lib/ruby_lsp/addon/process_client.rb

@@ -0,0 +1,171 @@
+# typed: strict
+# frozen_string_literal: true
+
+module RubyLsp
+  class Addon
+    class ProcessClient
+      class InitializationError < StandardError; end
+      class IncompleteMessageError < StandardError; end
+      class EmptyMessageError < StandardError; end
+
+      MAX_RETRIES = 5
+
+      extend T::Sig
+      extend T::Generic
+
+      abstract!
+
+      sig { returns(Addon) }
+      attr_reader :addon
+
+      sig { returns(IO) }
+      attr_reader :stdin
+
+      sig { returns(IO) }
+      attr_reader :stdout
+
+      sig { returns(IO) }
+      attr_reader :stderr
+
+      sig { returns(Process::Waiter) }
+      attr_reader :wait_thread
+
+      sig { params(addon: Addon, command: String).void }
+      def initialize(addon, command)
+        @addon = T.let(addon, Addon)
+        @mutex = T.let(Mutex.new, Mutex)
+        # Spring needs a Process session ID. It uses this ID to "attach" itself to the parent process, so that when the
+        # parent ends, the spring process ends as well. If this is not set, Spring will throw an error while trying to
+        # set its own session ID
+        begin
+          Process.setpgrp
+          Process.setsid
+        rescue Errno::EPERM
+          # If we can't set the session ID, continue
+        rescue NotImplementedError
+          # setpgrp() may be unimplemented on some platform
+          # https://github.com/Shopify/ruby-lsp-rails/issues/348
+        end
+
+        stdin, stdout, stderr, wait_thread = Bundler.with_original_env do
+          Open3.popen3(command)
+        end
+
+        @stdin = T.let(stdin, IO)
+        @stdout = T.let(stdout, IO)
+        @stderr = T.let(stderr, IO)
+        @wait_thread = T.let(wait_thread, Process::Waiter)
+
+        # for Windows compatibility
+        @stdin.binmode
+        @stdout.binmode
+        @stderr.binmode
+
+        log_output("booting server")
+        count = 0
+
+        begin
+          count += 1
+          handle_initialize_response(T.must(read_response))
+        rescue EmptyMessageError
+          log_output("is retrying initialize (#{count})")
+          retry if count < MAX_RETRIES
+        end
+
+        log_output("finished booting server")
+
+        register_exit_handler
+      rescue Errno::EPIPE, IncompleteMessageError
+        raise InitializationError, stderr.read
+      end
+
+      sig { void }
+      def shutdown
+        log_output("shutting down server")
+        send_message("shutdown")
+        sleep(0.5) # give the server a bit of time to shutdown
+        [stdin, stdout, stderr].each(&:close)
+      rescue IOError
+        # The server connection may have died
+        force_kill
+      end
+
+      sig { returns(T::Boolean) }
+      def stopped?
+        [stdin, stdout, stderr].all?(&:closed?) && !wait_thread.alive?
+      end
+
+      sig { params(message: String).void }
+      def log_output(message)
+        $stderr.puts("#{@addon.name} - #{message}")
+      end
+
+      # Notifications are like messages, but one-way, with no response sent back.
+      sig { params(request: String, params: T.nilable(T::Hash[Symbol, T.untyped])).void }
+      def send_notification(request, params = nil) = send_message(request, params)
+
+      private
+
+      sig do
+        params(
+          request: String,
+          params: T.nilable(T::Hash[Symbol, T.untyped]),
+        ).returns(T.nilable(T::Hash[Symbol, T.untyped]))
+      end
+      def make_request(request, params = nil)
+        send_message(request, params)
+        read_response
+      end
+
+      sig { overridable.params(request: String, params: T.nilable(T::Hash[Symbol, T.untyped])).void }
+      def send_message(request, params = nil)
+        message = { method: request }
+        message[:params] = params if params
+        json = message.to_json
+
+        @mutex.synchronize do
+          @stdin.write("Content-Length: #{json.length}\r\n\r\n", json)
+        end
+      rescue Errno::EPIPE
+        # The server connection died
+      end
+
+      sig { overridable.returns(T.nilable(T::Hash[Symbol, T.untyped])) }
+      def read_response
+        raw_response = @mutex.synchronize do
+          headers = @stdout.gets("\r\n\r\n")
+          raise IncompleteMessageError unless headers
+
+          content_length = headers[/Content-Length: (\d+)/i, 1].to_i
+          raise EmptyMessageError if content_length.zero?
+
+          @stdout.read(content_length)
+        end
+
+        response = JSON.parse(T.must(raw_response), symbolize_names: true)
+
+        if response[:error]
+          log_output("error: " + response[:error])
+          return
+        end
+
+        response.fetch(:result)
+      rescue Errno::EPIPE
+        # The server connection died
+        nil
+      end
+
+      sig { void }
+      def force_kill
+        # Windows does not support the `TERM` signal, so we're forced to use `KILL` here
+        Process.kill(T.must(Signal.list["KILL"]), @wait_thread.pid)
+      end
+
+      sig { abstract.void }
+      def register_exit_handler; end
+
+      sig { abstract.params(response: T::Hash[Symbol, T.untyped]).void }
+      def handle_initialize_response(response); end
+    end
+  end
+end

lib/ruby_lsp/addon/process_server.rb

@@ -0,0 +1,48 @@
+# typed: strict
+# frozen_string_literal: true
+
+module RubyLsp
+  class Addon
+    class ProcessServer
+      extend T::Sig
+      extend T::Generic
+
+      abstract!
+
+      VOID = Object.new
+
+      sig { void }
+      def initialize
+        $stdin.sync = true
+        $stdout.sync = true
+        $stdin.binmode
+        $stdout.binmode
+        @running = T.let(true, T.nilable(T::Boolean))
+      end
+
+      sig { void }
+      def start
+        initialize_result = generate_initialize_response
+        $stdout.write("Content-Length: #{initialize_result.length}\r\n\r\n#{initialize_result}")
+
+        while @running
+          headers = $stdin.gets("\r\n\r\n")
+          json = $stdin.read(headers[/Content-Length: (\d+)/i, 1].to_i)
+
+          request = JSON.parse(json, symbolize_names: true)
+          response = execute(request.fetch(:method), request[:params])
+          next if response == VOID
+
+          json_response = response.to_json
+          $stdout.write("Content-Length: #{json_response.length}\r\n\r\n#{json_response}")
+        end
+      end
+
+      sig { abstract.returns(String) }
+      def generate_initialize_response; end
+
+      sig { abstract.params(request: String, params: T.untyped).returns(T.untyped) }
+      def execute(request, params); end
+    end
+  end
+end

test/addon/fake_process_server.rb

@@ -0,0 +1,30 @@
+# typed: true
+# frozen_string_literal: true
+
+require "sorbet-runtime"
+require "json"
+require "ruby_lsp/addon/process_server"
+
+module RubyLsp
+  class Addon
+    class FakeProcessServer < ProcessServer
+      def generate_initialize_response
+        JSON.dump({ result: { initialized: true } })
+      end
+
+      def execute(request, params)
+        case request
+        when "echo"
+          { result: { echo_result: params[:message] } }
+        when "shutdown"
+          @running = false
+          { result: {} }
+        else
+          VOID
+        end
+      end
+    end
+  end
+end
+
+RubyLsp::Addon::FakeProcessServer.new.start

test/addon/process_client_server_test.rb

@@ -0,0 +1,81 @@
+# typed: true
+# frozen_string_literal: true
+
+require "test_helper"
+require "ruby_lsp/addon/process_client"
+
+module RubyLsp
+  class Addon
+    class ProcessClientServerTest < Minitest::Test
+      class FakeAddon < Addon
+        def name
+          "FakeAddon"
+        end
+
+        def activate(global_state, outgoing_queue)
+          # No-op for testing
+        end
+
+        def deactivate
+          # No-op for testing
+        end
+      end
+
+      class FakeClient < ProcessClient
+        def initialize(addon)
+          server_path = File.expand_path("../fake_process_server.rb", __FILE__)
+          super(addon, "bundle exec ruby #{server_path}")
+        end
+
+        def echo(message)
+          make_request("echo", { message: message })
+        end
+
+        def send_unknown_request
+          send_message("unknown_request")
+        end
+
+        def log_output(message)
+          # No-op for testing to reduce noise
+        end
+
+        private
+
+        def handle_initialize_response(response)
+          raise InitializationError, "Server not initialized" unless response[:initialized]
+        end
+
+        def register_exit_handler
+          # No-op for testing
+        end
+      end
+
+      def setup
+        @addon = FakeAddon.new
+        @client = FakeClient.new(@addon)
+      end
+
+      def teardown
+        @client.shutdown
+        assert_predicate(@client, :stopped?, "Client should be stopped after shutdown")
+        RubyLsp::Addon.addons.clear
+      end
+
+      def test_client_server_communication
+        response = @client.echo("Hello, World!")
+        assert_equal({ echo_result: "Hello, World!" }, response)
+      end
+
+      def test_server_initialization
+        # The server is already initialized in setup, so we just need to verify it didn't raise an error
+        assert_instance_of(FakeClient, @client)
+      end
+
+      def test_server_ignores_unknown_request
+        @client.send_unknown_request
+        response = @client.echo("Hey!")
+        assert_equal({ echo_result: "Hey!" }, response)
+      end
+    end
+  end
+end