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.

7 files changed, 114 insertions, 43 deletions

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);
                 }
         }