support intercept specified command handler

sentinel-transport/sentinel-transport-common/src/main/java/com/alibaba/csp/sentinel/command/CommandHandlerInterceptor.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 1999-2022 Alibaba Group Holding Ltd.
+ *
+ * Licensed 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 com.alibaba.csp.sentinel.command;
+
+/**
+ * intercept specified command, and can be extended using SPI
+ *
+ * @author icodening
+ * @date 2022.03.03
+ * @see com.alibaba.csp.sentinel.spi.SpiLoader
+ * @see com.alibaba.csp.sentinel.spi.Spi
+ */
+public interface CommandHandlerInterceptor<R> {
+
+    /**
+     * whether to intercept the specified command
+     *
+     * @param commandName command name, eg. getRules
+     * @return "true" means intercept, "false" means skip
+     */
+    boolean shouldIntercept(String commandName);
+
+    /**
+     * intercept the given command request, and return a command response
+     *
+     * @param request   commandRequest
+     * @param execution interceptor chain execution
+     * @return command response
+     */
+    CommandResponse<R> intercept(CommandRequest request, CommandRequestExecution<R> execution);
+
+}

sentinel-transport/sentinel-transport-common/src/main/java/com/alibaba/csp/sentinel/command/CommandHandlerProvider.java

@@ -15,12 +15,13 @@
  */
 package com.alibaba.csp.sentinel.command;
 
-import java.util.*;
-
 import com.alibaba.csp.sentinel.command.annotation.CommandMapping;
+import com.alibaba.csp.sentinel.command.handler.InterceptingCommandHandler;
 import com.alibaba.csp.sentinel.spi.SpiLoader;
 import com.alibaba.csp.sentinel.util.StringUtil;
 
+import java.util.*;
+
 /**
  * Provides and filters command handlers registered via SPI.
  *
@@ -38,8 +39,18 @@ public class CommandHandlerProvider implements Iterable<CommandHandler> {
     public Map<String, CommandHandler> namedHandlers() {
         Map<String, CommandHandler> map = new HashMap<String, CommandHandler>();
         List<CommandHandler> handlers = spiLoader.loadInstanceList();
+        List<CommandHandlerInterceptor> commandHandlerInterceptors = SpiLoader.of(CommandHandlerInterceptor.class).loadInstanceListSorted();
         for (CommandHandler handler : handlers) {
             String name = parseCommandName(handler);
+            if (!commandHandlerInterceptors.isEmpty()) {
+                List<CommandHandlerInterceptor> interceptors = new ArrayList<>();
+                for (CommandHandlerInterceptor commandHandlerInterceptor : commandHandlerInterceptors) {
+                    if (commandHandlerInterceptor.shouldIntercept(name)) {
+                        interceptors.add(commandHandlerInterceptor);
+                    }
+                }
+               handler = new InterceptingCommandHandler(handler, interceptors);
+            }
             if (!StringUtil.isEmpty(name)) {
                 map.put(name, handler);
             }

sentinel-transport/sentinel-transport-common/src/main/java/com/alibaba/csp/sentinel/command/CommandRequestExecution.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright 1999-2022 Alibaba Group Holding Ltd.
+ *
+ * Licensed 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 com.alibaba.csp.sentinel.command;
+
+/**
+ * @author icodening
+ * @date 2022.03.03
+ */
+public interface CommandRequestExecution<R> {
+
+    /**
+     * execute the command request and return the command response.
+     *
+     * @param request command request
+     * @return command response
+     */
+    CommandResponse<R> execute(CommandRequest request);
+}

sentinel-transport/sentinel-transport-common/src/main/java/com/alibaba/csp/sentinel/command/handler/InterceptingCommandHandler.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 1999-2022 Alibaba Group Holding Ltd.
+ *
+ * Licensed 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 com.alibaba.csp.sentinel.command.handler;
+
+import com.alibaba.csp.sentinel.command.*;
+import com.alibaba.csp.sentinel.util.AssertUtil;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Function;
+
+/**
+ * intercept specified command handler
+ *
+ * @author icodening
+ * @date 2022.03.03
+ */
+public class InterceptingCommandHandler<R> implements CommandHandler<R> {
+
+    private final CommandHandler<R> delegate;
+
+    private final List<CommandHandlerInterceptor<R>> commandHandlerInterceptors;
+
+    public InterceptingCommandHandler(CommandHandler<R> delegate, List<CommandHandlerInterceptor<R>> commandHandlerInterceptors) {
+        AssertUtil.notNull(delegate, "delegate cannot be null");
+        AssertUtil.notNull(commandHandlerInterceptors, "commandHandlerInterceptors cannot be null");
+        this.delegate = delegate;
+        this.commandHandlerInterceptors = commandHandlerInterceptors;
+    }
+
+    @Override
+    public CommandResponse<R> handle(CommandRequest request) {
+        return new InterceptingRequestExecution<>(commandHandlerInterceptors.iterator(), delegate::handle).execute(request);
+    }
+
+    private static class InterceptingRequestExecution<R> implements CommandRequestExecution<R> {
+
+        private final Iterator<CommandHandlerInterceptor<R>> iterator;
+
+        private final Function<CommandRequest, CommandResponse<R>> commandResponseFunction;
+
+        public InterceptingRequestExecution(Iterator<CommandHandlerInterceptor<R>> iterator,
+                                            Function<CommandRequest, CommandResponse<R>> commandResponseFunction) {
+            this.iterator = iterator;
+            this.commandResponseFunction = commandResponseFunction;
+        }
+
+        @Override
+        public CommandResponse<R> execute(CommandRequest request) {
+            if (this.iterator.hasNext()) {
+                CommandHandlerInterceptor<R> nextInterceptor = this.iterator.next();
+                return nextInterceptor.intercept(request, this);
+            }
+            return commandResponseFunction.apply(request);
+        }
+    }
+}