Implement Lifecycle for MySqlConnection (#171)

Motivation:

Implement `Lifecycle` for `MySqlConnection`. See also #64 

Modification:

The `MySqlConnection`.

Result:

The `MySqlConnection` implements `Lifecycle` and will rollback in
`preRelease`.

Author: mirromutth

src/main/java/io/asyncer/r2dbc/mysql/MySqlConnection.java

@@ -31,6 +31,7 @@
 import io.netty.util.internal.logging.InternalLoggerFactory;
 import io.r2dbc.spi.Connection;
 import io.r2dbc.spi.IsolationLevel;
+import io.r2dbc.spi.Lifecycle;
 import io.r2dbc.spi.TransactionDefinition;
 import io.r2dbc.spi.ValidationDepth;
 import org.jetbrains.annotations.Nullable;
@@ -52,7 +53,7 @@
 /**
  * An implementation of {@link Connection} for connecting to the MySQL database.
  */
-public final class MySqlConnection implements Connection, ConnectionState {
+public final class MySqlConnection implements Connection, Lifecycle, ConnectionState {
 
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(MySqlConnection.class);
 
@@ -278,6 +279,17 @@ public MySqlStatement createStatement(String sql) {
         return new PrepareParametrizedStatement(client, codecs, query, context, prepareCache);
     }
 
+    @Override
+    public Mono<Void> postAllocate() {
+        return Mono.empty();
+    }
+
+    @Override
+    public Mono<Void> preRelease() {
+        // Rollback if the connection is in transaction.
+        return rollbackTransaction();
+    }
+
     @Override
     public Mono<Void> releaseSavepoint(String name) {
         requireValidName(name, "Savepoint name must not be empty and not contain backticks");

src/test/java/io/asyncer/r2dbc/mysql/ConnectionIntegrationTest.java

@@ -22,6 +22,7 @@
 
 import java.time.Duration;
 import java.util.Arrays;
+import java.util.Collections;
 
 import static io.r2dbc.spi.IsolationLevel.READ_COMMITTED;
 import static io.r2dbc.spi.IsolationLevel.READ_UNCOMMITTED;
@@ -52,6 +53,54 @@ void isInTransaction() {
             .doOnSuccess(ignored -> assertThat(connection.isInTransaction()).isFalse()));
     }
 
+    @Test
+    void autoRollbackPreRelease() {
+        // Mock pool allocate/release.
+        complete(conn -> conn.postAllocate()
+            .thenMany(conn.createStatement("CREATE TEMPORARY TABLE test (id INT NOT NULL PRIMARY KEY)")
+                .execute())
+            .flatMap(MySqlResult::getRowsUpdated)
+            .then(conn.beginTransaction())
+            .thenMany(conn.createStatement("INSERT INTO test VALUES (1)")
+                .execute())
+            .flatMap(MySqlResult::getRowsUpdated)
+            .single()
+            .doOnNext(it -> assertThat(it).isEqualTo(1))
+            .doOnSuccess(ignored -> assertThat(conn.isInTransaction()).isTrue())
+            .then(conn.preRelease())
+            .doOnSuccess(ignored -> assertThat(conn.isInTransaction()).isFalse())
+            .then(conn.postAllocate())
+            .thenMany(conn.createStatement("SELECT * FROM test")
+                .execute())
+            .flatMap(it -> it.map((row, metadata) -> row.get(0, Integer.class)))
+            .count()
+            .doOnNext(it -> assertThat(it).isZero()));
+    }
+
+    @Test
+    void shouldNotRollbackCommittedPreRelease() {
+        // Mock pool allocate/release.
+        complete(conn -> conn.postAllocate()
+            .thenMany(conn.createStatement("CREATE TEMPORARY TABLE test (id INT NOT NULL PRIMARY KEY)")
+                .execute())
+            .flatMap(MySqlResult::getRowsUpdated)
+            .then(conn.beginTransaction())
+            .thenMany(conn.createStatement("INSERT INTO test VALUES (1)")
+                .execute())
+            .flatMap(MySqlResult::getRowsUpdated)
+            .single()
+            .doOnNext(it -> assertThat(it).isEqualTo(1))
+            .then(conn.commitTransaction())
+            .then(conn.preRelease())
+            .doOnSuccess(ignored -> assertThat(conn.isInTransaction()).isFalse())
+            .then(conn.postAllocate())
+            .thenMany(conn.createStatement("SELECT * FROM test")
+                .execute())
+            .flatMap(it -> it.map((row, metadata) -> row.get(0, Integer.class)))
+            .collectList()
+            .doOnNext(it -> assertThat(it).isEqualTo(Collections.singletonList(1))));
+    }
+
     @Test
     void transactionDefinitionLockWaitTimeout() {
         complete(connection -> connection.beginTransaction(MySqlTransactionDefinition.builder()