Fix ClassCastException caused by 2.x's filter in some condition

dubbo-compatible/src/main/java/com/alibaba/dubbo/rpc/Filter.java

@@ -17,6 +17,8 @@
 
 package com.alibaba.dubbo.rpc;
 
+import org.apache.dubbo.rpc.AsyncRpcResult;
+
 @Deprecated
 public interface Filter extends org.apache.dubbo.rpc.Filter {
 
@@ -26,8 +28,18 @@ public interface Filter extends org.apache.dubbo.rpc.Filter {
     default org.apache.dubbo.rpc.Result invoke(org.apache.dubbo.rpc.Invoker<?> invoker,
                                                org.apache.dubbo.rpc.Invocation invocation)
             throws org.apache.dubbo.rpc.RpcException {
-        Result.CompatibleResult result = (Result.CompatibleResult) invoke(new Invoker.CompatibleInvoker<>(invoker),
-                new Invocation.CompatibleInvocation(invocation));
-        return result.getDelegate();
+        Result invokeResult = invoke(new Invoker.CompatibleInvoker<>(invoker),
+            new Invocation.CompatibleInvocation(invocation));
+
+        if (invokeResult instanceof Result.CompatibleResult) {
+            return invokeResult;
+        }
+
+        AsyncRpcResult asyncRpcResult = AsyncRpcResult.newDefaultAsyncResult(invocation);
+        asyncRpcResult.setValue(invokeResult.getValue());
+        asyncRpcResult.setException(invokeResult.getException());
+        asyncRpcResult.setObjectAttachments(invokeResult.getObjectAttachments());
+
+        return asyncRpcResult;
     }
 }

dubbo-compatible/src/main/java/com/alibaba/dubbo/rpc/Invoker.java

@@ -17,6 +17,8 @@
 
 package com.alibaba.dubbo.rpc;
 
+import org.apache.dubbo.rpc.AsyncRpcResult;
+
 import com.alibaba.dubbo.common.URL;
 
 @Deprecated
@@ -54,9 +56,22 @@ public Class<T> getInterface() {
         public org.apache.dubbo.rpc.Result invoke(org.apache.dubbo.rpc.Invocation invocation) throws org.apache.dubbo.rpc.RpcException {
             return new Result.CompatibleResult(invoker.invoke(invocation));
         }
-        
+
         @Override
         public Result invoke(Invocation invocation) throws RpcException {
+            if (invoker instanceof Invoker) {
+                Result result = ((Invoker) invoker).invoke(invocation);
+                if (result instanceof Result.CompatibleResult) {
+                    return result;
+                } else {
+                    AsyncRpcResult asyncRpcResult = AsyncRpcResult.newDefaultAsyncResult(invocation.getOriginal());
+                    asyncRpcResult.setValue(result.getValue());
+                    asyncRpcResult.setException(result.getException());
+                    asyncRpcResult.setObjectAttachments(result.getObjectAttachments());
+
+                    return new Result.CompatibleResult(asyncRpcResult);
+                }
+            }
             return new Result.CompatibleResult(invoker.invoke(invocation.getOriginal()));
         }
 

dubbo-compatible/src/main/java/com/alibaba/dubbo/rpc/Result.java

@@ -64,35 +64,7 @@ default Object getObjectAttachment(String key, Object defaultValue) {
         return null;
     }
 
-    abstract class AbstractResult implements Result {
-
-        @Override
-        public void setValue(Object value) {
-
-        }
-
-        @Override
-        public org.apache.dubbo.rpc.Result whenCompleteWithContext(BiConsumer<org.apache.dubbo.rpc.Result, Throwable> fn) {
-            return null;
-        }
-
-        @Override
-        public <U> CompletableFuture<U> thenApply(Function<org.apache.dubbo.rpc.Result, ? extends U> fn) {
-            return null;
-        }
-
-        @Override
-        public org.apache.dubbo.rpc.Result get() throws InterruptedException, ExecutionException {
-            return null;
-        }
-
-        @Override
-        public org.apache.dubbo.rpc.Result get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
-            return null;
-        }
-    }
-
-    class CompatibleResult extends AbstractResult {
+    class CompatibleResult implements Result {
         private org.apache.dubbo.rpc.Result delegate;
 
         public CompatibleResult(org.apache.dubbo.rpc.Result result) {
@@ -177,5 +149,20 @@ public void setAttachment(String key, Object value) {
         public void setObjectAttachment(String key, Object value) {
             delegate.setObjectAttachment(key, value);
         }
+
+        @Override
+        public <U> CompletableFuture<U> thenApply(Function<org.apache.dubbo.rpc.Result, ? extends U> fn) {
+            return delegate.thenApply(fn);
+        }
+
+        @Override
+        public org.apache.dubbo.rpc.Result get() throws InterruptedException, ExecutionException {
+            return delegate.get();
+        }
+
+        @Override
+        public org.apache.dubbo.rpc.Result get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
+            return delegate.get(timeout, unit);
+        }
     }
 }

dubbo-compatible/src/main/java/com/alibaba/dubbo/rpc/RpcResult.java

@@ -0,0 +1,35 @@
+/*
+ * 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
+ *
+ *     http://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.dubbo.rpc;
+
+import org.apache.dubbo.rpc.AppResponse;
+
+@Deprecated
+public class RpcResult extends AppResponse implements com.alibaba.dubbo.rpc.Result {
+
+    public RpcResult() {
+    }
+
+    public RpcResult(Object result) {
+        super(result);
+    }
+
+    public RpcResult(Throwable exception) {
+        super(exception);
+    }
+
+}

dubbo-compatible/src/test/java/org/apache/dubbo/filter/FilterTest.java

@@ -18,11 +18,11 @@
 package org.apache.dubbo.filter;
 
 import org.apache.dubbo.rpc.RpcException;
+import org.apache.dubbo.rpc.RpcInvocation;
 
 import com.alibaba.dubbo.rpc.Filter;
 import com.alibaba.dubbo.rpc.Invocation;
 import com.alibaba.dubbo.rpc.Invoker;
-import com.alibaba.dubbo.rpc.Result;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
@@ -46,15 +46,23 @@ void testInvokeException() {
     }
 
     @Test
-    void testDefault() {
+    void testDefault() throws Throwable {
         Invoker<FilterTest> invoker = new LegacyInvoker<FilterTest>(null);
-        Invocation invocation = new LegacyInvocation("bbb");
-        Result res = myFilter.invoke(invoker, invocation);
-        System.out.println(res);
+        org.apache.dubbo.rpc.Invocation invocation = new RpcInvocation(null, "echo", "DemoService", "DemoService", new Class[]{String.class}, new Object[]{"bbb"});
+        org.apache.dubbo.rpc.Result res = myFilter.invoke(invoker, invocation);
+        Assertions.assertEquals("alibaba", res.recreate());
+    }
+
+    @Test
+    void testRecreate() throws Throwable {
+        Invoker<FilterTest> invoker = new LegacyInvoker<FilterTest>(null);
+        org.apache.dubbo.rpc.Invocation invocation = new RpcInvocation(null, "echo", "DemoService", "DemoService", new Class[]{String.class}, new Object[]{"cc"});
+        org.apache.dubbo.rpc.Result res = myFilter.invoke(invoker, invocation);
+        Assertions.assertEquals("123test", res.recreate());
     }
 
     @AfterAll
     public static void tear() {
-        Assertions.assertEquals(2, MyFilter.count);
+        Assertions.assertEquals(3, MyFilter.count);
     }
 }

dubbo-compatible/src/test/java/org/apache/dubbo/filter/LegacyInvoker.java

@@ -17,14 +17,14 @@
 package org.apache.dubbo.filter;
 
 
-import org.apache.dubbo.rpc.AppResponse;
 import org.apache.dubbo.service.DemoService;
 
 import com.alibaba.dubbo.common.URL;
 import com.alibaba.dubbo.rpc.Invocation;
 import com.alibaba.dubbo.rpc.Invoker;
 import com.alibaba.dubbo.rpc.Result;
 import com.alibaba.dubbo.rpc.RpcException;
+import com.alibaba.dubbo.rpc.RpcResult;
 
 public class LegacyInvoker<T> implements Invoker<T> {
 
@@ -58,13 +58,13 @@ public boolean isAvailable() {
     }
 
     public Result invoke(Invocation invocation) throws RpcException {
-        AppResponse result = new AppResponse();
+        RpcResult result = new RpcResult();
         if (!hasException) {
             result.setValue("alibaba");
         } else {
             result.setException(new RuntimeException("mocked exception"));
         }
-        return new Result.CompatibleResult(result);
+        return result;
     }
 
     @Override

dubbo-compatible/src/test/java/org/apache/dubbo/filter/MyFilter.java

@@ -22,6 +22,7 @@
 import com.alibaba.dubbo.rpc.Invoker;
 import com.alibaba.dubbo.rpc.Result;
 import com.alibaba.dubbo.rpc.RpcException;
+import com.alibaba.dubbo.rpc.RpcResult;
 
 
 public class MyFilter implements Filter {
@@ -36,6 +37,10 @@ public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcExcept
             throw new RpcException(new IllegalArgumentException("arg0 illegal"));
         }
 
+        if (invocation.getArguments()[0].equals("cc")) {
+            return new RpcResult("123test");
+        }
+
         Result tmp = invoker.invoke(invocation);
         return tmp;
     }