new config file option 'maxWorkQueueSize' that lets you set the maxim…

…um size of the request queue - if it gets larger than this, requests will be rejected (503 Service unavailable)

languagetool-server/src/main/java/org/languagetool/server/HTTPSServer.java

@@ -79,6 +79,7 @@ public HTTPSServer(HTTPSServerConfig config, boolean runInternally, String host,
         httpHandler.setAfterTheDeadlineMode(config.getAfterTheDeadlineLanguage());
       }
       httpHandler.setLanguageModel(config.getLanguageModelDir());
+      httpHandler.setMaxWorkQueueSize(config.getMaxWorkQueueSize());
       server.createContext("/", httpHandler);
       executorService = getExecutorService(workQueue, config);
       server.setExecutor(executorService);

languagetool-server/src/main/java/org/languagetool/server/HTTPServer.java

@@ -105,6 +105,7 @@ public HTTPServer(HTTPServerConfig config, boolean runInternally, String host, S
         httpHandler.setAfterTheDeadlineMode(config.getAfterTheDeadlineLanguage());
       }
       httpHandler.setLanguageModel(config.getLanguageModelDir());
+      httpHandler.setMaxWorkQueueSize(config.getMaxWorkQueueSize());
       server.createContext("/", httpHandler);
       executorService = getExecutorService(workQueue, config);
       server.setExecutor(executorService);

languagetool-server/src/main/java/org/languagetool/server/HTTPServerConfig.java

@@ -52,6 +52,7 @@ enum Mode { LanguageTool, AfterTheDeadline }
   protected int requestLimit;
   protected int requestLimitPeriodInSeconds;
   protected boolean trustXForwardForHeader;
+  protected int maxWorkQueueSize;
 
   /**
    * Create a server configuration for the default port ({@link #DEFAULT_PORT}).
@@ -114,6 +115,7 @@ private void parseConfigFile(File file) {
         requestLimit = Integer.parseInt(getOptionalProperty(props, "requestLimit", "0"));
         requestLimitPeriodInSeconds = Integer.parseInt(getOptionalProperty(props, "requestLimitPeriodInSeconds", "0"));
         trustXForwardForHeader = Boolean.valueOf(getOptionalProperty(props, "trustXForwardForHeader", "false"));
+        maxWorkQueueSize = Integer.parseInt(getOptionalProperty(props, "maxWorkQueueSize", "0"));
         String langModel = getOptionalProperty(props, "languageModel", null);
         if (langModel != null) {
           languageModelDir = new File(langModel);
@@ -239,6 +241,11 @@ boolean getTrustXForwardForHeader() {
     return trustXForwardForHeader;
   }
 
+  /** @since 2.9 */
+  int getMaxWorkQueueSize() {
+    return maxWorkQueueSize;
+  }
+
   /**
    * @throws IllegalConfigurationException if property is not set 
    */

languagetool-server/src/main/java/org/languagetool/server/LanguageToolHttpHandler.java

@@ -65,6 +65,7 @@ class LanguageToolHttpHandler implements HttpHandler {
   private boolean afterTheDeadlineMode;
   private Language afterTheDeadlineLanguage;
   private File languageModelDir;
+  private int maxWorkQueueSize;
   private boolean trustXForwardForHeader = false;
 
   /**
@@ -133,6 +134,17 @@ void setLanguageModel(File languageModelDir) {
     this.languageModelDir = languageModelDir;
   }
 
+  /**
+   * @param size maximum queue size - if the queue is larger, the user will get an error. Use {@code 0} for no limit.
+   * @since 2.9
+   */
+  void setMaxWorkQueueSize(int size) {
+    if (size < 0) {
+      throw new IllegalArgumentException("Max queue size must be >= 0: " + size);
+    }
+    this.maxWorkQueueSize = size;
+  }
+
   @Override
   public void handle(HttpExchange httpExchange) throws IOException {
     synchronized (this) {
@@ -156,6 +168,12 @@ public void handle(HttpExchange httpExchange) throws IOException {
         print(errorMessage);
         return;
       }
+      if (maxWorkQueueSize != 0 && workQueue.size() > maxWorkQueueSize) {
+        String response = "Error: There are currently too many parallel requests. Please try again later.";
+        print(response + " Queue size: " + workQueue.size() + ", maximum size: " + maxWorkQueueSize);
+        sendError(httpExchange, HttpURLConnection.HTTP_UNAVAILABLE, "Error: " + response);
+        return;
+      }
       if (allowedIps == null || allowedIps.contains(origAddress)) {
         if (requestedUri.getRawPath().endsWith("/Languages")) {
           // request type: list known languages
@@ -259,13 +277,13 @@ private String getLastIpIgnoringOwn(List<String> forwardedIps) {
     return lastIp;
   }
 
-  private void sendError(HttpExchange httpExchange, int returnCode, String response) throws IOException {
+  private void sendError(HttpExchange httpExchange, int httpReturnCode, String response) throws IOException {
     if (afterTheDeadlineMode) {
       String xmlResponse = "<results><message>" + escapeForXmlContent(response) + "</message></results>";
-      httpExchange.sendResponseHeaders(returnCode, xmlResponse.getBytes(ENCODING).length);
+      httpExchange.sendResponseHeaders(httpReturnCode, xmlResponse.getBytes(ENCODING).length);
       httpExchange.getResponseBody().write(xmlResponse.getBytes(ENCODING));
     } else {
-      httpExchange.sendResponseHeaders(returnCode, response.getBytes(ENCODING).length);
+      httpExchange.sendResponseHeaders(httpReturnCode, response.getBytes(ENCODING).length);
       httpExchange.getResponseBody().write(response.getBytes(ENCODING));
     }
   }

languagetool-server/src/main/java/org/languagetool/server/Server.java

@@ -111,6 +111,7 @@ protected static void printCommonConfigFileOptions() {
     System.out.println("                 'requestLimitPeriodInSeconds' - time period to which requestLimit applies (optional)");
     System.out.println("                 'languageModel' - a directory with a '3grams' sub directory with a Lucene index that");
     System.out.println("                  contains ngram occurrence counts; activates the confusion rule if supported (optional)");
+    System.out.println("                 'maxWorkQueueSize' - reject request if request queue gets larger than this (optional)");
   }
 
   protected static void printCommonOptions() {

languagetool-standalone/CHANGES.txt

@@ -71,6 +71,9 @@ LanguageTool Change Log
 -Embedded server:
     -XML escaping has been fixed, this could cause invalid XML documents
      to be returned
+    -new config file option 'maxWorkQueueSize' that lets you set the maximum
+     size of the request queue - if it gets larger than this, requests will
+     be rejected (503 Service unavailable)
 
 -Rule syntax:
     -A rule may now have a single example sentence as long as it has a 'correction'