Fixes #13931 - Introduce ConditionalHandler.NextElseReject.

Signed-off-by: Simone Bordet <[email protected]>

Author: sbordet

documentation/jetty/modules/programming-guide/pages/server/http.adoc

@@ -874,14 +874,17 @@ Alternatively, you can use the following `ConditionalHandler` subclasses that im
 ** When conditions are met, you have to write the implementation.
 ** When conditions are not met, the handling of the request is forwarded to the next `Handler`.
 * `ConditionalHandler.Reject`:
-** When conditions are met, a response is written with a configurable, non-2xx, HTTP status code.
+** When conditions are met, a response is written with a configurable HTTP status code.
 ** When conditions are not met, the handling of the request is forwarded to the next `Handler`.
 * `ConditionalHandler.SkipNext`:
 ** When conditions are met, the handling of the request is forwarded to the next-next `Handler`, skipping the next `Handler`.
 ** When conditions are not met, the handling of the request is forwarded to the next `Handler`.
 * `ConditionalHandler.DontHandle`:
 ** When conditions are met, the request is not handled.
 ** When conditions are not met, the handling of the request is forwarded to the next `Handler`.
+* `ConditionalHandler.NextElseReject`:
+** When conditions are met, the handling of the request is forwarded to the next `Handler`.
+** When conditions are not met, a response is written with a configurable HTTP status code.
 
 Conditions can be specified using an include/exclude mechanism, where a condition match if it is not excluded, and either it is included or the include set is empty.
 
@@ -894,7 +897,7 @@ For example, you can specify to match only the specific HTTP request method `DEL
 * The request remote address.
 * Custom predicates that receive the request to match a custom condition.
 
-Notable subclasses of `ConditionalHandler` are, for example, <<handler-use-qos,`QoSHandler`>> and <<handler-use-thread-limit,`ThreadLimitHandler`>>.
+Notable subclasses of `ConditionalHandler` are, for example, <<handler-use-qos,`QoSHandler`>>, <<handler-use-thread-limit,`ThreadLimitHandler`>> and <<handler-use-dos,`DoSHandler`>>.
 
 [[handler-use-compression]]
 ==== CompressionHandler

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/handler/ConditionalHandler.java

@@ -851,4 +851,62 @@ protected boolean onConditionsMet(Request request, Response response, Callback c
             return nextNext != null && nextNext.handle(request, response, callback);
         }
     }
+
+    /**
+     * <p>An implementation of {@link ConditionalHandler} that, if conditions are met,
+     * calls {@link #nextHandler(Request, Response, Callback)}, otherwise sends an
+     * error response with a configurable HTTP status code, by default {@code 403}
+     * (Forbidden).</p>
+     * <p>Websites that want to allow only certain HTTP methods, can configure an
+     * instance of this class allowing only {@code GET}, {@code HEAD} and {@code POST},
+     * so that other HTTP methods such as {@code DELETE}, {@code TRACE}, etc. are
+     * not allowed.</p>
+     * <p>Similarly, websites can configure HTTP URI path patterns to allow or
+     * disallow specific request paths.</p>
+     */
+    public static class NextElseReject extends ConditionalHandler
+    {
+        private final int _status;
+
+        public NextElseReject()
+        {
+            this(HttpStatus.FORBIDDEN_403);
+        }
+
+        public NextElseReject(int status)
+        {
+            this(null, status);
+        }
+
+        public NextElseReject(Handler nextHandler, int status)
+        {
+            this(false, nextHandler, status);
+        }
+
+        public NextElseReject(boolean dynamic, Handler nextHandler, int status)
+        {
+            super(dynamic, nextHandler);
+            if (status < 200 || status > 999)
+                throw new IllegalArgumentException("bad status");
+            _status = status;
+        }
+
+        public int getStatusCode()
+        {
+            return _status;
+        }
+
+        @Override
+        protected boolean onConditionsMet(Request request, Response response, Callback callback) throws Exception
+        {
+            return nextHandler(request, response, callback);
+        }
+
+        @Override
+        protected boolean onConditionsNotMet(Request request, Response response, Callback callback)
+        {
+            Response.writeError(request, response, callback, getStatusCode());
+            return true;
+        }
+    }
 }