DATAREDIS-988 - Discard transactions when releasing pooled connections.

We now check on connection release whether a connection is in MULTI state. If so, then we discard (rollback) the transaction to reset the connection to a fresh state.

Original Pull Request: #453

src/main/java/org/springframework/data/redis/connection/lettuce/LettuceConnection.java

@@ -1281,6 +1281,13 @@ public class LettuceConnection extends AbstractRedisConnection {
 		public void release(StatefulConnection<?, ?> connection) {
 
 			if (connection.isOpen()) {
+
+				if (connection instanceof StatefulRedisConnection) {
+					StatefulRedisConnection<?, ?> redisConnection = (StatefulRedisConnection<?, ?>) connection;
+					if (redisConnection.isMulti()) {
+						redisConnection.async().discard();
+					}
+				}
 				pool.returnResource((StatefulConnection<byte[], byte[]>) connection);
 			} else {
 				pool.returnBrokenResource((StatefulConnection<byte[], byte[]>) connection);

src/main/java/org/springframework/data/redis/connection/lettuce/LettucePoolingConnectionProvider.java

@@ -17,6 +17,7 @@ package org.springframework.data.redis.connection.lettuce;
 
 import io.lettuce.core.AbstractRedisClient;
 import io.lettuce.core.api.StatefulConnection;
+import io.lettuce.core.api.StatefulRedisConnection;
 import io.lettuce.core.support.AsyncConnectionPoolSupport;
 import io.lettuce.core.support.AsyncPool;
 import io.lettuce.core.support.BoundedPoolConfig;
@@ -109,7 +110,7 @@ class LettucePoolingConnectionProvider implements LettuceConnectionProvider, Red
 		}
 	}
 
-	/* 
+	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.redis.connection.lettuce.LettuceConnectionProvider#getConnectionAsync(java.lang.Class)
 	 */
@@ -170,14 +171,27 @@ class LettucePoolingConnectionProvider implements LettuceConnectionProvider, Red
 						+ " was either previously returned or does not belong to this connection provider");
 			}
 
+			discardIfNecessary(connection);
 			asyncPool.release(connection).join();
 			return;
 		}
 
+		discardIfNecessary(connection);
 		pool.returnObject(connection);
 	}
 
-	/* 
+	private void discardIfNecessary(StatefulConnection<?, ?> connection) {
+
+		if (connection instanceof StatefulRedisConnection) {
+
+			StatefulRedisConnection<?, ?> redisConnection = (StatefulRedisConnection<?, ?>) connection;
+			if (redisConnection.isMulti()) {
+				redisConnection.async().discard();
+			}
+		}
+	}
+
+	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.redis.connection.lettuce.LettuceConnectionProvider#releaseAsync(io.lettuce.core.api.StatefulConnection)
 	 */

src/test/java/org/springframework/data/redis/connection/lettuce/LettucePoolingConnectionProviderUnitTests.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * 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 org.springframework.data.redis.connection.lettuce;
+
+import static org.mockito.Mockito.*;
+
+import io.lettuce.core.api.StatefulRedisConnection;
+import io.lettuce.core.api.async.RedisAsyncCommands;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
+
+/**
+ * Unit tests for {@link LettucePoolingConnectionProvider}.
+ *
+ * @author Mark Paluch
+ */
+@RunWith(MockitoJUnitRunner.class)
+public class LettucePoolingConnectionProviderUnitTests {
+
+	@Mock LettuceConnectionProvider connectionProviderMock;
+	@Mock StatefulRedisConnection<byte[], byte[]> connectionMock;
+	@Mock RedisAsyncCommands<byte[], byte[]> commandsMock;
+
+	LettucePoolingClientConfiguration config = LettucePoolingClientConfiguration.defaultConfiguration();
+
+	@Before
+	public void before() {
+
+		when(connectionMock.async()).thenReturn(commandsMock);
+		when(connectionProviderMock.getConnection(any())).thenReturn(connectionMock);
+	}
+
+	@Test // DATAREDIS-988
+	public void shouldReturnConnectionOnRelease() {
+
+		LettucePoolingConnectionProvider provider = new LettucePoolingConnectionProvider(connectionProviderMock, config);
+
+		provider.release(provider.getConnection(StatefulRedisConnection.class));
+
+		verifyZeroInteractions(commandsMock);
+	}
+
+	@Test // DATAREDIS-988
+	public void shouldDiscardTransactionOnReleaseOnActiveTransaction() {
+
+		LettucePoolingConnectionProvider provider = new LettucePoolingConnectionProvider(connectionProviderMock, config);
+		when(connectionMock.isMulti()).thenReturn(true);
+
+		provider.release(provider.getConnection(StatefulRedisConnection.class));
+
+		verify(commandsMock).discard();
+	}
+}