# Integrating Language Servers

In order to integrate a language server with GNOME Builder you have to create an `Ide.SubprocessLauncher` to startup the language server.

This subprocess should be restarted if it breaks therefore we have to wrap this `Ide.SubprocessLauncher` in a `Ide.SubprocessSupervisor` to monitor the external process. After the subprocess is started we connect `stdin` and `stdout` to our `Ide.LspClient` for dispatching of messages between client and server.

    class LSPService(Ide.Object):
       _has_started = False
       _client = None

       @GObject.Property(type=Ide.LspClient)
       def client(self):
          return self._client = value

       @client.setter
       def client(self, value):
          self._client = value
          self.notify('client')

       def start(self):
          if not self._has_started:
             self._has_started = True
             launcher = Ide.SubprocessLauncher()
             launcher.set_flags(Gio.SubprocessFlags.STDIN_PIPE | Gio.SubprocessFlags.STDOUT_PIPE)
             launcher.push_argv("my_language_server_executable")

             supervisor = Ide.SubprocessSupervisor()
             supervisor.connect('spawned', lsp_spawned)
             supervisor.set_launcher(launcher)
             supervisor.start()

       def lsp_spawned(self, supervisor, subprocess):
          stdin = subprocess.get_stdin_pipe()
          stdout = subprocess.get_stdout_pipe()
          io_stream = Gio.SimpleIOStream.new(stdout, stdin)

          client = Ide.LspClient.new(io_stream)
          self.append(client)
          client.add_language('my_language')
          client.start()
          self.client(client)

As a language server handles several parts of an IDE we have to create according extensions for code completion, diagnostics or hover content. As we want to make sure that the corresponding service is only started once we use the builtin object system (`Ide.Context.ensure_child_type(type)`.

    class MyLspCompletionProvider(Ide.LspCompletionProvider, Ide.CompletionProvider):

       def do_load(self, context):
          service = context.ensure_child_typed(LSPService)
          service.start()
          service.bind_property('client', self, 'client', GObject.BindingFlags.SYNC_CREATE)

       def do_get_priority(self, context):
          return 0

    class MyLspDiagnosticProvider(Ide.LspDiagnosticProvider, Ide.DiagnosticProvider):

       def do_load(self):
          context = self.get_context()
          service = context.ensure_child_typed(LSPService)
          service.start()
          service.bind_property('client', self, 'client', GObject.BindingFlags.SYNC_CREATE)