refactor: decouple further response processing in exception resolving

Author: jdaugherty

grails-encoder/src/main/groovy/org/grails/buffer/GrailsResponseMutator.groovy

@@ -0,0 +1,31 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+
+package org.grails.buffer
+
+/**
+ * Interface to assign to a HttpServletResponse wrapper so on an error, it can be deactivated to not further
+ * change the response.
+ */
+interface GrailsResponseMutator {
+    /**
+     * Do not mutate the response & stop any processing of it.
+     */
+    void deactivateResponseMutator();
+}

grails-web-mvc/src/main/groovy/org/grails/web/errors/GrailsExceptionResolver.java

@@ -35,6 +35,7 @@
 import org.apache.commons.logging.LogFactory;
 import org.codehaus.groovy.control.CompilationFailedException;
 import grails.core.GrailsApplication;
+import org.grails.buffer.GrailsResponseMutator;
 import org.grails.exceptions.reporting.DefaultStackTraceFilterer;
 import org.grails.core.exceptions.GrailsRuntimeException;
 import org.grails.exceptions.reporting.StackTraceFilterer;
@@ -194,6 +195,10 @@ protected ModelAndView resolveViewOrForward(Exception ex, UrlMappingsHolder urlM
             else if (info != null && info.getControllerName() != null) {
                 String uri = determineUri(request);
                 if (!response.isCommitted()) {
+                    if (response instanceof GrailsResponseMutator) {
+                        // prevent further mutation of the request since an error page needs rendered instead
+                        ((GrailsResponseMutator) response).deactivateResponseMutator();
+                    }
                     forwardRequest(info, request, response, mv, uri);
                     // return an empty ModelAndView since the error handler has been processed
                     return new ModelAndView();