feat(web): backend URL configuration

To point the frontend to a backend server, update the config.json
file in the website root.

The config.json is generated automatically in debug mode and when
running from a standalone jar.

15 files changed, 213 insertions, 131 deletions

diff --git a/subprojects/frontend/package.json b/subprojects/frontend/package.json
index 10de68ee..ed4b101b 100644
--- a/subprojects/frontend/package.json
+++ b/subprojects/frontend/package.json
@@ -29,21 +29,21 @@
     "@codemirror/lint": "^6.0.0",
     "@codemirror/search": "^6.2.2",
     "@codemirror/state": "^6.1.2",
-    "@codemirror/view": "^6.4.0",
+    "@codemirror/view": "^6.4.1",
     "@emotion/react": "^11.10.5",
     "@emotion/styled": "^11.10.5",
     "@fontsource/inter": "^4.5.14",
     "@fontsource/jetbrains-mono": "^4.5.11",
     "@lezer/common": "^1.0.1",
     "@lezer/highlight": "^1.1.2",
-    "@lezer/lr": "^1.2.3",
+    "@lezer/lr": "^1.2.4",
     "@material-icons/svg": "^1.0.33",
     "@mui/icons-material": "5.10.9",
-    "@mui/material": "5.10.12",
+    "@mui/material": "5.10.13",
     "ansi-styles": "^6.2.1",
     "escape-string-regexp": "^5.0.0",
     "lodash-es": "^4.17.21",
-    "loglevel": "^1.8.0",
+    "loglevel": "^1.8.1",
     "loglevel-plugin-prefix": "^0.8.4",
     "mobx": "^6.6.2",
     "mobx-react-lite": "^3.4.0",
@@ -56,7 +56,7 @@
     "zod": "^3.19.1"
   },
   "devDependencies": {
-    "@lezer/generator": "^1.1.1",
+    "@lezer/generator": "^1.1.3",
     "@types/eslint": "^8.4.10",
     "@types/html-minifier-terser": "^7.0.0",
     "@types/lodash-es": "^4.17.6",
@@ -65,12 +65,12 @@
     "@types/prettier": "^2.7.1",
     "@types/react": "^18.0.25",
     "@types/react-dom": "^18.0.8",
-    "@typescript-eslint/eslint-plugin": "^5.42.0",
-    "@typescript-eslint/parser": "^5.42.0",
+    "@typescript-eslint/eslint-plugin": "^5.42.1",
+    "@typescript-eslint/parser": "^5.42.1",
     "@vitejs/plugin-react": "^2.2.0",
     "@xstate/cli": "^0.3.3",
     "cross-env": "^7.0.3",
-    "eslint": "^8.26.0",
+    "eslint": "^8.27.0",
     "eslint-config-airbnb": "^19.0.4",
     "eslint-config-airbnb-typescript": "^17.0.0",
     "eslint-config-prettier": "^8.5.0",
@@ -84,9 +84,9 @@
     "html-minifier-terser": "^7.0.0",
     "prettier": "^2.7.1",
     "typescript": "4.8.4",
-    "vite": "^3.2.2",
+    "vite": "^3.2.3",
     "vite-plugin-inject-preload": "^1.1.0",
-    "vite-plugin-pwa": "^0.13.2",
+    "vite-plugin-pwa": "^0.13.3",
     "workbox-window": "^6.5.4"
   }
 }
diff --git a/subprojects/frontend/src/RootStore.ts b/subprojects/frontend/src/RootStore.ts
index 54a80501..2e76d66d 100644
--- a/subprojects/frontend/src/RootStore.ts
+++ b/subprojects/frontend/src/RootStore.ts
@@ -23,18 +23,17 @@ export default class RootStore {
       pwaStore: false,
       themeStore: false,
     });
-    import('./editor/EditorStore')
-      .then(({ default: EditorStore }) => {
-        runInAction(() => {
-          if (this.disposed) {
-            return;
-          }
-          this.editorStore = new EditorStore(initialValue, this.pwaStore);
-        });
-      })
-      .catch((error) => {
-        log.error('Failed to load EditorStore', error);
+    (async () => {
+      const { default: EditorStore } = await import('./editor/EditorStore');
+      runInAction(() => {
+        if (this.disposed) {
+          return;
+        }
+        this.editorStore = new EditorStore(initialValue, this.pwaStore);
       });
+    })().catch((error) => {
+      log.error('Failed to load EditorStore', error);
+    });
   }
 
   dispose(): void {
diff --git a/subprojects/frontend/src/xtext/XtextClient.ts b/subprojects/frontend/src/xtext/XtextClient.ts
index e7d26ae6..14fb2430 100644
--- a/subprojects/frontend/src/xtext/XtextClient.ts
+++ b/subprojects/frontend/src/xtext/XtextClient.ts
@@ -35,8 +35,7 @@ export default class XtextClient {
     this.webSocketClient = new XtextWebSocketClient(
       () => this.onReconnect(),
       () => this.onDisconnect(),
-      (resource, stateId, service, push) =>
-        this.onPush(resource, stateId, service, push),
+      this.onPush.bind(this),
     );
     this.updateService = new UpdateService(store, this.webSocketClient);
     this.contentAssistService = new ContentAssistService(this.updateService);
diff --git a/subprojects/frontend/src/xtext/XtextWebSocketClient.ts b/subprojects/frontend/src/xtext/XtextWebSocketClient.ts
index a39620cb..6b734546 100644
--- a/subprojects/frontend/src/xtext/XtextWebSocketClient.ts
+++ b/subprojects/frontend/src/xtext/XtextWebSocketClient.ts
@@ -7,7 +7,8 @@ import CancelledError from '../utils/CancelledError';
 import PendingTask from '../utils/PendingTask';
 import getLogger from '../utils/getLogger';
 
-import webSocketMachine, { isWebSocketURLLocal } from './webSocketMachine';
+import fetchBackendConfig from './fetchBackendConfig';
+import webSocketMachine from './webSocketMachine';
 import {
   type XtextWebPushService,
   XtextResponse,
@@ -42,26 +43,18 @@ export default class XtextWebSocketClient {
   private readonly pendingRequests = new Map<string, PendingTask<unknown>>();
 
   private readonly interpreter = interpret(
-    webSocketMachine
-      .withContext({
-        ...webSocketMachine.context,
-        webSocketURL: `${window.location.origin.replace(
-          /^http/,
-          'ws',
-        )}/xtext-service`,
-      })
-      .withConfig({
-        actions: {
-          openWebSocket: ({ webSocketURL }) => this.openWebSocket(webSocketURL),
-          closeWebSocket: () => this.closeWebSocket(),
-          notifyReconnect: () => this.onReconnect(),
-          notifyDisconnect: () => this.onDisconnect(),
-          cancelPendingRequests: () => this.cancelPendingRequests(),
-        },
-        services: {
-          pingService: () => this.sendPing(),
-        },
-      }),
+    webSocketMachine.withConfig({
+      actions: {
+        openWebSocket: () => this.openWebSocket(),
+        closeWebSocket: () => this.closeWebSocket(),
+        notifyReconnect: () => this.onReconnect(),
+        notifyDisconnect: () => this.onDisconnect(),
+        cancelPendingRequests: () => this.cancelPendingRequests(),
+      },
+      services: {
+        pingService: () => this.sendPing(),
+      },
+    }),
     {
       logger: log.log.bind(log),
     },
@@ -151,6 +144,7 @@ export default class XtextWebSocketClient {
       | 'webSocket'
       | 'interpreter'
       | 'openListener'
+      | 'openWebSocket'
       | 'errorListener'
       | 'closeListener'
       | 'messageListener'
@@ -160,6 +154,7 @@ export default class XtextWebSocketClient {
       webSocket: observable.ref,
       interpreter: false,
       openListener: false,
+      openWebSocket: false,
       errorListener: false,
       closeListener: false,
       messageListener: false,
@@ -221,9 +216,7 @@ export default class XtextWebSocketClient {
   get networkMissing(): boolean {
     return (
       this.state.matches('connection.temporarilyOffline') ||
-      (this.disconnectedByUser &&
-        this.state.matches('network.offline') &&
-        !isWebSocketURLLocal(this.state.context.webSocketURL))
+      (this.disconnectedByUser && this.state.matches('network.offline'))
     );
   }
 
@@ -275,17 +268,27 @@ export default class XtextWebSocketClient {
     this.interpreter.send(document.hidden ? 'TAB_HIDDEN' : 'TAB_VISIBLE');
   }
 
-  private openWebSocket(webSocketURL: string | undefined): void {
+  private openWebSocket(): void {
     if (this.webSocket !== undefined) {
       throw new Error('WebSocket already open');
     }
 
-    if (webSocketURL === undefined) {
-      throw new Error('URL not configured');
-    }
-
     log.debug('Creating WebSocket');
 
+    (async () => {
+      const { webSocketURL } = await fetchBackendConfig();
+      this.openWebSocketWithURL(webSocketURL);
+    })().catch((error) => {
+      log.error('Error while initializing connection', error);
+      const message = error instanceof Error ? error.message : String(error);
+      this.interpreter.send({
+        type: 'ERROR',
+        message,
+      });
+    });
+  }
+
+  private openWebSocketWithURL(webSocketURL: string): void {
     this.webSocket = new WebSocket(webSocketURL, XTEXT_SUBPROTOCOL_V1);
     this.webSocket.addEventListener('open', this.openListener);
     this.webSocket.addEventListener('close', this.closeListener);
@@ -295,7 +298,9 @@ export default class XtextWebSocketClient {
 
   private closeWebSocket() {
     if (this.webSocket === undefined) {
-      throw new Error('WebSocket already closed');
+      // We might get here when there is a network error before the socket is initialized
+      // and we don't have to do anything to close it.
+      return;
     }
 
     log.debug('Closing WebSocket');
diff --git a/subprojects/frontend/src/xtext/fetchBackendConfig.ts b/subprojects/frontend/src/xtext/fetchBackendConfig.ts
new file mode 100644
index 00000000..f8087a70
--- /dev/null
+++ b/subprojects/frontend/src/xtext/fetchBackendConfig.ts
@@ -0,0 +1,16 @@
+/* eslint-disable @typescript-eslint/no-redeclare -- Declare types with their companion objects */
+
+import { z } from 'zod';
+
+export const BackendConfig = z.object({
+  webSocketURL: z.string().url(),
+});
+
+export type BackendConfig = z.infer<typeof BackendConfig>;
+
+export default async function fetchBackendConfig(): Promise<BackendConfig> {
+  const configURL = `${import.meta.env.BASE_URL}config.json`;
+  const response = await fetch(configURL);
+  const rawConfig = (await response.json()) as unknown;
+  return BackendConfig.parse(rawConfig);
+}
diff --git a/subprojects/frontend/src/xtext/webSocketMachine.ts b/subprojects/frontend/src/xtext/webSocketMachine.ts
index b5b40d11..5f6bc604 100644
--- a/subprojects/frontend/src/xtext/webSocketMachine.ts
+++ b/subprojects/frontend/src/xtext/webSocketMachine.ts
@@ -6,12 +6,10 @@ const { raise } = actions;
 const ERROR_WAIT_TIMES = ['200', '1s', '5s', '30s'].map(ms);
 
 export interface WebSocketContext {
-  webSocketURL: string | undefined;
   errors: string[];
 }
 
 export type WebSocketEvent =
-  | { type: 'CONFIGURE'; webSocketURL: string }
   | { type: 'CONNECT' }
   | { type: 'DISCONNECT' }
   | { type: 'OPENED' }
@@ -25,24 +23,6 @@ export type WebSocketEvent =
   | { type: 'OFFLINE' }
   | { type: 'ERROR'; message: string };
 
-export function isWebSocketURLLocal(webSocketURL: string | undefined): boolean {
-  if (webSocketURL === undefined) {
-    return false;
-  }
-  let hostname: string;
-  try {
-    ({ hostname } = new URL(webSocketURL));
-  } catch {
-    return false;
-  }
-  // https://stackoverflow.com/a/57949518
-  return (
-    hostname === 'localhost' ||
-    hostname === '[::1]' ||
-    hostname.match(/^127(?:\.(?:25[0-5]|2[0-4]\d|[01]?\d\d?)){3}$/) !== null
-  );
-}
-
 export default createMachine(
   {
     id: 'webSocket',
@@ -53,7 +33,6 @@ export default createMachine(
     },
     tsTypes: {} as import('./webSocketMachine.typegen').Typegen0,
     context: {
-      webSocketURL: undefined,
       errors: [],
     },
     type: 'parallel',
@@ -65,16 +44,12 @@ export default createMachine(
           disconnected: {
             id: 'disconnected',
             entry: ['clearErrors', 'notifyDisconnect'],
-            on: {
-              CONFIGURE: { actions: 'configure' },
-            },
           },
           timedOut: {
             id: 'timedOut',
             always: [
               {
                 target: 'temporarilyOffline',
-                cond: 'needsNetwork',
                 in: '#offline',
               },
               { target: 'socketCreated', in: '#tabVisible' },
@@ -89,7 +64,6 @@ export default createMachine(
             always: [
               {
                 target: 'temporarilyOffline',
-                cond: 'needsNetwork',
                 in: '#offline',
               },
             ],
@@ -183,7 +157,7 @@ export default createMachine(
           },
         },
         on: {
-          CONNECT: { target: '.timedOut', cond: 'hasWebSocketURL' },
+          CONNECT: '.timedOut',
           DISCONNECT: '.disconnected',
         },
       },
@@ -224,10 +198,6 @@ export default createMachine(
     },
   },
   {
-    guards: {
-      hasWebSocketURL: ({ webSocketURL }) => webSocketURL !== undefined,
-      needsNetwork: ({ webSocketURL }) => !isWebSocketURLLocal(webSocketURL),
-    },
     delays: {
       IDLE_TIMEOUT: ms('5m'),
       OPEN_TIMEOUT: ms('10s'),
@@ -239,10 +209,6 @@ export default createMachine(
       },
     },
     actions: {
-      configure: assign((context, { webSocketURL }) => ({
-        ...context,
-        webSocketURL,
-      })),
       pushError: assign((context, { message }) => ({
         ...context,
         errors: [...context.errors, message],
diff --git a/subprojects/frontend/types/ImportMeta.d.ts b/subprojects/frontend/types/ImportMeta.d.ts
index 2008e268..c32b48f5 100644
--- a/subprojects/frontend/types/ImportMeta.d.ts
+++ b/subprojects/frontend/types/ImportMeta.d.ts
@@ -1,5 +1,6 @@
 interface ImportMeta {
   env: {
+    BASE_URL: string;
     DEV: boolean;
     MODE: string;
     PROD: boolean;
diff --git a/subprojects/frontend/vite.config.ts b/subprojects/frontend/vite.config.ts
index e690d005..526ea541 100644
--- a/subprojects/frontend/vite.config.ts
+++ b/subprojects/frontend/vite.config.ts
@@ -30,6 +30,7 @@ const apiPort = portNumberOrElse('API_PORT', 1312);
 const apiSecure = apiPort === 443;
 const publicHost = process.env.PUBLIC_HOST || listenHost;
 const publicPort = portNumberOrElse('PUBLIC_PORT', listenPort);
+const publicSecure = publicPort === 443;
 
 const { name: packageName, version: packageVersion } = JSON.parse(
   readFileSync(path.join(thisDir, 'package.json'), 'utf8'),
@@ -56,6 +57,23 @@ const minifyPlugin: PluginOption = {
   },
 };
 
+const backendConfigPlugin: PluginOption = {
+  name: 'backend-config',
+  configureServer(server) {
+    const protocol = publicSecure ? 'wss' : 'ws';
+    const webSocketURL = `${protocol}://${publicHost}:${publicPort}/xtext-service`;
+    const config = JSON.stringify({ webSocketURL });
+    server.middlewares.use((req, res, next) => {
+      if (req.url === '/config.json') {
+        res.setHeader('Content-Type', 'application/json');
+        res.end(config);
+      } else {
+        next();
+      }
+    });
+  },
+};
+
 export default defineConfig({
   logLevel: 'info',
   mode,
@@ -63,6 +81,7 @@ export default defineConfig({
   cacheDir: path.join(thisDir, 'build/vite/cache'),
   plugins: [
     minifyPlugin,
+    backendConfigPlugin,
     react(),
     injectPreload({
       files: [
@@ -90,6 +109,12 @@ export default defineConfig({
         ],
         dontCacheBustURLsMatching: /\.(?:css|js|woff2?)$/,
         navigateFallbackDenylist: [/^\/xtext-service/],
+        runtimeCaching: [
+          {
+            urlPattern: 'config.json',
+            handler: 'StaleWhileRevalidate',
+          },
+        ],
       },
       includeAssets: ['apple-touch-icon.png', 'favicon.svg', 'mask-icon.svg'],
       manifest: {
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/CacheControlFilter.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/CacheControlFilter.java
index fbce62c1..fd2af1b2 100644
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/CacheControlFilter.java
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/CacheControlFilter.java
@@ -13,8 +13,9 @@ import java.util.regex.Pattern;
 public class CacheControlFilter implements Filter {
         private static final Pattern CACHE_URI_PATTERN = Pattern.compile(".*\\.(css|gif|js|map|png|svg|woff2?)");
 
-        private static final Set<String> CACHE_URI_DENYLIST = Set.of("apple-touch-icon.png", "favicon.png", "favicon.svg",
-                        "favicon-96x96.png", "icon-any.svg", "icon-192x192.png", "icon-512x512.png", "mask-icon.svg", "sw.js");
+        private static final Set<String> CACHE_URI_DENYLIST = Set.of("apple-touch-icon.png", "config.json", "favicon.png",
+                        "favicon.svg", "favicon-96x96.png", "icon-any.svg", "icon-192x192.png", "icon-512x512.png", "mask-icon.svg",
+                        "sw.js");
 
         private static final Duration EXPIRY = Duration.ofDays(365);
 
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/ServerLauncher.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/ServerLauncher.java
index ffa61321..58c8ea4e 100644
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/ServerLauncher.java
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/ServerLauncher.java
@@ -14,6 +14,7 @@ import org.eclipse.jetty.util.resource.Resource;
 import org.eclipse.jetty.websocket.server.config.JettyWebSocketServletContainerInitializer;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import tools.refinery.language.web.config.BackendConfigServlet;
 import tools.refinery.language.web.xtext.servlet.XtextWebSocketServlet;
 
 import java.io.File;
@@ -41,11 +42,13 @@ public class ServerLauncher {
 
         private final Server server;
 
-        public ServerLauncher(InetSocketAddress bindAddress, Resource baseResource, String[] allowedOrigins) {
+        public ServerLauncher(InetSocketAddress bindAddress, Resource baseResource, String[] allowedOrigins,
+                                                  String webSocketUrl) {
                 server = new Server(bindAddress);
                 var handler = new ServletContextHandler();
                 addSessionHandler(handler);
                 addProblemServlet(handler, allowedOrigins);
+                addBackendConfigServlet(handler, webSocketUrl);
                 if (baseResource != null) {
                         handler.setBaseResource(baseResource);
                         handler.setWelcomeFiles(new String[]{"index.html"});
@@ -76,6 +79,12 @@ public class ServerLauncher {
                 JettyWebSocketServletContainerInitializer.configure(handler, null);
         }
 
+        private void addBackendConfigServlet(ServletContextHandler handler, String webSocketUrl) {
+                var backendConfigServletHolder = new ServletHolder(BackendConfigServlet.class);
+                backendConfigServletHolder.setInitParameter(BackendConfigServlet.WEBSOCKET_URL_INIT_PARAM, webSocketUrl);
+                handler.addServlet(backendConfigServletHolder, "/config.json");
+        }
+
         private void addDefaultServlet(ServletContextHandler handler) {
                 var defaultServletHolder = new ServletHolder(DefaultServlet.class);
                 var isWindows = System.getProperty("os.name").toLowerCase().contains("win");
@@ -97,7 +106,8 @@ public class ServerLauncher {
                         var bindAddress = getBindAddress();
                         var baseResource = getBaseResource();
                         var allowedOrigins = getAllowedOrigins();
-                        var serverLauncher = new ServerLauncher(bindAddress, baseResource, allowedOrigins);
+                        var webSocketUrl = getWebSocketUrl();
+                        var serverLauncher = new ServerLauncher(bindAddress, baseResource, allowedOrigins, webSocketUrl);
                         serverLauncher.start();
                 } catch (Exception exception) {
                         LOG.error("Fatal server error", exception);
@@ -190,4 +200,19 @@ public class ServerLauncher {
                 }
                 return new String[]{urlWithPort};
         }
+
+        private static String getWebSocketUrl() {
+                String host;
+                int port;
+                var publicHost = getPublicHost();
+                if (publicHost == null) {
+                        host = getListenAddress();
+                        port = getListenPort();
+                } else {
+                        host = publicHost;
+                        port = getPublicPort();
+                }
+                var scheme = port == HTTPS_DEFAULT_PORT ? "wss" : "ws";
+                return String.format("%s://%s:%d/xtext-service", scheme, host, port);
+        }
 }
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/config/BackendConfig.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/config/BackendConfig.java
new file mode 100644
index 00000000..2e864998
--- /dev/null
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/config/BackendConfig.java
@@ -0,0 +1,20 @@
+package tools.refinery.language.web.config;
+
+import com.google.gson.annotations.SerializedName;
+
+public class BackendConfig {
+        @SerializedName("webSocketURL")
+        private String webSocketUrl;
+
+        public BackendConfig(String webSocketUrl) {
+                this.webSocketUrl = webSocketUrl;
+        }
+
+        public String getWebSocketUrl() {
+                return webSocketUrl;
+        }
+
+        public void setWebSocketUrl(String webSocketUrl) {
+                this.webSocketUrl = webSocketUrl;
+        }
+}
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/config/BackendConfigServlet.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/config/BackendConfigServlet.java
new file mode 100644
index 00000000..f314a9fa
--- /dev/null
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/config/BackendConfigServlet.java
@@ -0,0 +1,39 @@
+package tools.refinery.language.web.config;
+
+import com.google.gson.Gson;
+import jakarta.servlet.ServletConfig;
+import jakarta.servlet.ServletException;
+import jakarta.servlet.http.HttpServlet;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+import org.eclipse.jetty.http.HttpStatus;
+
+import java.io.IOException;
+
+public class BackendConfigServlet extends HttpServlet {
+        public static final String WEBSOCKET_URL_INIT_PARAM = "tools.refinery.language.web.config.BackendConfigServlet" +
+                        ".webSocketUrl";
+
+        private String serializedConfig;
+
+        @Override
+        public void init(ServletConfig config) throws ServletException {
+                super.init(config);
+                var webSocketUrl = config.getInitParameter(WEBSOCKET_URL_INIT_PARAM);
+                if (webSocketUrl == null) {
+                        throw new IllegalArgumentException("Init parameter " + WEBSOCKET_URL_INIT_PARAM + " is mandatory");
+                }
+                var backendConfig = new BackendConfig(webSocketUrl);
+                var gson = new Gson();
+                serializedConfig = gson.toJson(backendConfig);
+        }
+
+        @Override
+        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+                resp.setStatus(HttpStatus.OK_200);
+                resp.setContentType("application/json");
+                var writer = resp.getWriter();
+                writer.write(serializedConfig);
+                writer.flush();
+        }
+}
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/ResponseHandlerException.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/ResponseHandlerException.java
index 34fcb546..b686d33a 100644
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/ResponseHandlerException.java
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/ResponseHandlerException.java
@@ -1,7 +1,10 @@
 package tools.refinery.language.web.xtext.server;
 
+import java.io.Serial;
+
 public class ResponseHandlerException extends Exception {
 
+        @Serial
         private static final long serialVersionUID = 3589866922420268164L;
 
         public ResponseHandlerException(String message, Throwable cause) {
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java
index 0b417b06..7bb11d2e 100644
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java
@@ -1,35 +1,25 @@
 package tools.refinery.language.web.xtext.server;
 
-import java.lang.ref.WeakReference;
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-
+import com.google.common.base.Strings;
+import com.google.inject.Injector;
 import org.eclipse.emf.common.util.URI;
 import org.eclipse.xtext.resource.IResourceServiceProvider;
 import org.eclipse.xtext.util.IDisposable;
-import org.eclipse.xtext.web.server.IServiceContext;
-import org.eclipse.xtext.web.server.IServiceResult;
-import org.eclipse.xtext.web.server.ISession;
-import org.eclipse.xtext.web.server.InvalidRequestException;
+import org.eclipse.xtext.web.server.*;
 import org.eclipse.xtext.web.server.InvalidRequestException.UnknownLanguageException;
-import org.eclipse.xtext.web.server.XtextServiceDispatcher;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
-import com.google.common.base.Strings;
-import com.google.inject.Injector;
-
-import tools.refinery.language.web.xtext.server.message.XtextWebErrorKind;
-import tools.refinery.language.web.xtext.server.message.XtextWebErrorResponse;
-import tools.refinery.language.web.xtext.server.message.XtextWebOkResponse;
-import tools.refinery.language.web.xtext.server.message.XtextWebPushMessage;
-import tools.refinery.language.web.xtext.server.message.XtextWebRequest;
+import tools.refinery.language.web.xtext.server.message.*;
 import tools.refinery.language.web.xtext.server.push.PrecomputationListener;
 import tools.refinery.language.web.xtext.server.push.PushWebDocument;
 import tools.refinery.language.web.xtext.servlet.SimpleServiceContext;
 
+import java.lang.ref.WeakReference;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
 public class TransactionExecutor implements IDisposable, PrecomputationListener {
         private static final Logger LOG = LoggerFactory.getLogger(TransactionExecutor.class);
 
@@ -41,11 +31,11 @@ public class TransactionExecutor implements IDisposable, PrecomputationListener
 
         private ResponseHandler responseHandler;
 
-        private Object callPendingLock = new Object();
+        private final Object callPendingLock = new Object();
 
         private boolean callPending;
 
-        private List<XtextWebPushMessage> pendingPushMessages = new ArrayList<>();
+        private final List<XtextWebPushMessage> pendingPushMessages = new ArrayList<>();
 
         public TransactionExecutor(ISession session, IResourceServiceProvider.Registry resourceServiceProviderRegistry) {
                 this.session = session;
@@ -132,10 +122,9 @@ public class TransactionExecutor implements IDisposable, PrecomputationListener
 
         /**
          * Get the injector to satisfy the request in the {@code serviceContext}.
-         * 
          * Based on {@link org.eclipse.xtext.web.servlet.XtextServlet#getInjector}.
-         * 
-         * @param serviceContext the Xtext service context of the request
+         *
+         * @param context the Xtext service context of the request
          * @return the injector for the Xtext language in the request
          * @throws UnknownLanguageException if the Xtext language cannot be determined
          */
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/servlet/XtextWebSocket.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/servlet/XtextWebSocket.java
index fd41f213..82391d8b 100644
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/servlet/XtextWebSocket.java
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/servlet/XtextWebSocket.java
@@ -1,31 +1,25 @@
 package tools.refinery.language.web.xtext.servlet;
 
-import java.io.IOException;
-import java.io.Reader;
-
+import com.google.gson.Gson;
+import com.google.gson.JsonIOException;
+import com.google.gson.JsonParseException;
 import org.eclipse.jetty.websocket.api.Session;
 import org.eclipse.jetty.websocket.api.StatusCode;
 import org.eclipse.jetty.websocket.api.WriteCallback;
-import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
-import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
-import org.eclipse.jetty.websocket.api.annotations.OnWebSocketError;
-import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
-import org.eclipse.jetty.websocket.api.annotations.WebSocket;
+import org.eclipse.jetty.websocket.api.annotations.*;
 import org.eclipse.xtext.resource.IResourceServiceProvider;
 import org.eclipse.xtext.web.server.ISession;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
-import com.google.gson.Gson;
-import com.google.gson.JsonIOException;
-import com.google.gson.JsonParseException;
-
 import tools.refinery.language.web.xtext.server.ResponseHandler;
 import tools.refinery.language.web.xtext.server.ResponseHandlerException;
 import tools.refinery.language.web.xtext.server.TransactionExecutor;
 import tools.refinery.language.web.xtext.server.message.XtextWebRequest;
 import tools.refinery.language.web.xtext.server.message.XtextWebResponse;
 
+import java.io.IOException;
+import java.io.Reader;
+
 @WebSocket
 public class XtextWebSocket implements WriteCallback, ResponseHandler {
         private static final Logger LOG = LoggerFactory.getLogger(XtextWebSocket.class);
@@ -118,7 +112,7 @@ public class XtextWebSocket implements WriteCallback, ResponseHandler {
                         webSocketSession.getRemote().sendPartialString(responseString, true, this);
                 } catch (IOException e) {
                         throw new ResponseHandlerException(
-                                        "Cannot initiaite async write to websocket " + webSocketSession.getRemoteAddress(), e);
+                                        "Cannot initiate async write to websocket " + webSocketSession.getRemoteAddress(), e);
                 }
         }