Ensure isolation level is applied to subsequent transactions after setting (#202)

Motivation:

Aligning Connection#setTransactionIsolationLevel Behavior with r2dbc-spi
Specification. See #192
for more.

Modification:

Change session isolation level as well after invoking
`Connection#setTransactionIsolationLevel`.

Result:

All subsequent transactions will be applied the isolation level set by
`Connection#setTransactionIsolationLevel`.

Author: JohnNiang

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

@@ -124,7 +124,7 @@ public final class MySqlConnection implements Connection, Lifecycle, ConnectionS
 
     private final MySqlConnectionMetadata metadata;
 
-    private final IsolationLevel sessionLevel;
+    private volatile IsolationLevel sessionLevel;
 
     private final QueryCache queryCache;
 
@@ -298,13 +298,27 @@ public IsolationLevel getTransactionIsolationLevel() {
         return currentLevel;
     }
 
+    /**
+     * Gets session transaction isolation level(Only for testing).
+     *
+     * @return session transaction isolation level.
+     */
+    IsolationLevel getSessionTransactionIsolationLevel() {
+        return sessionLevel;
+    }
+
     @Override
     public Mono<Void> setTransactionIsolationLevel(IsolationLevel isolationLevel) {
         requireNonNull(isolationLevel, "isolationLevel must not be null");
 
-        // Set next transaction isolation level.
-        return QueryFlow.executeVoid(client, "SET TRANSACTION ISOLATION LEVEL " + isolationLevel.asSql())
-            .doOnSuccess(ignored -> setIsolationLevel(isolationLevel));
+        // Set subsequent transaction isolation level.
+        return QueryFlow.executeVoid(client, "SET SESSION TRANSACTION ISOLATION LEVEL " + isolationLevel.asSql())
+            .doOnSuccess(ignored -> {
+                this.sessionLevel = isolationLevel;
+                if (!this.isInTransaction()) {
+                    this.currentLevel = isolationLevel;
+                }
+            });
     }
 
     @Override

src/main/java/io/asyncer/r2dbc/mysql/message/client/TextQueryMessage.java

@@ -19,6 +19,7 @@
 import io.asyncer.r2dbc.mysql.ConnectionContext;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufAllocator;
+import java.util.Objects;
 import reactor.core.publisher.Mono;
 
 import java.nio.charset.Charset;
@@ -67,6 +68,23 @@ public Mono<ByteBuf> encode(ByteBufAllocator allocator, ConnectionContext contex
         });
     }
 
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        TextQueryMessage that = (TextQueryMessage) o;
+        return Objects.equals(sql, that.sql);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(sql);
+    }
+
     @Override
     public String toString() {
         return "TextQueryMessage{sql=REDACTED}";

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

@@ -139,6 +139,51 @@ void transactionDefinitionIsolationLevel() {
             }));
     }
 
+    @Test
+    void setTransactionLevelNotInTransaction() {
+        complete(connection ->
+            // check initial session isolation level
+            Mono.fromSupplier(connection::getTransactionIsolationLevel)
+                .doOnSuccess(it -> assertThat(it).isEqualTo(REPEATABLE_READ))
+                .then(connection.beginTransaction())
+                .doOnSuccess(ignored -> assertThat(connection.isInTransaction()).isTrue())
+                .then(Mono.fromSupplier(connection::getTransactionIsolationLevel))
+                .doOnSuccess(it -> assertThat(it).isEqualTo(REPEATABLE_READ))
+                .then(connection.rollbackTransaction())
+                .then(connection.setTransactionIsolationLevel(READ_COMMITTED))
+                // ensure that session isolation level is changed
+                .then(Mono.fromSupplier(connection::getTransactionIsolationLevel))
+                .doOnSuccess(it -> assertThat(it).isEqualTo(READ_COMMITTED))
+                .then(connection.beginTransaction())
+                .doOnSuccess(ignored -> assertThat(connection.isInTransaction()).isTrue())
+                // ensure transaction isolation level applies to subsequent transactions
+                .then(Mono.fromSupplier(connection::getTransactionIsolationLevel))
+                .doOnSuccess(it -> assertThat(it).isEqualTo(READ_COMMITTED))
+        );
+    }
+
+    @Test
+    void setTransactionLevelInTransaction() {
+        complete(connection ->
+            // check initial session transaction isolation level
+            Mono.fromSupplier(connection::getTransactionIsolationLevel)
+                .doOnSuccess(it -> assertThat(it).isEqualTo(REPEATABLE_READ))
+                .then(connection.beginTransaction())
+                .then(connection.setTransactionIsolationLevel(READ_COMMITTED))
+                // ensure that current transaction isolation level is not changed
+                .then(Mono.fromSupplier(connection::getTransactionIsolationLevel))
+                .doOnSuccess(it -> assertThat(it).isNotEqualTo(READ_COMMITTED))
+                .then(connection.rollbackTransaction())
+                .doOnSuccess(ignored -> assertThat(connection.isInTransaction()).isFalse())
+                // ensure that session isolation level is changed after rollback
+                .then(Mono.fromSupplier(connection::getTransactionIsolationLevel))
+                .doOnSuccess(it -> assertThat(it).isEqualTo(READ_COMMITTED))
+                // ensure transaction isolation level applies to subsequent transactions
+                .then(connection.beginTransaction())
+                .doOnSuccess(ignored -> assertThat(connection.isInTransaction()).isTrue())
+        );
+    }
+
     @Test
     void transactionDefinition() {
         // The WITH CONSISTENT SNAPSHOT phrase can only be used with the REPEATABLE READ isolation level.

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

@@ -19,13 +19,20 @@
 import io.asyncer.r2dbc.mysql.cache.Caches;
 import io.asyncer.r2dbc.mysql.client.Client;
 import io.asyncer.r2dbc.mysql.codec.Codecs;
+import io.asyncer.r2dbc.mysql.message.client.ClientMessage;
+import io.asyncer.r2dbc.mysql.message.client.TextQueryMessage;
 import io.r2dbc.spi.IsolationLevel;
 import org.assertj.core.api.ThrowableTypeAssert;
 import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Flux;
+import reactor.test.StepVerifier;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 /**
  * Unit tests for {@link MySqlConnection}.
@@ -125,6 +132,18 @@ void badSetTransactionIsolationLevel() {
         assertThatIllegalArgumentException().isThrownBy(() -> noPrepare.setTransactionIsolationLevel(null));
     }
 
+    @Test
+    void shouldSetTransactionIsolationLevelSuccessfully() {
+        ClientMessage message = new TextQueryMessage("SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE");
+        when(client.exchange(eq(message), any())).thenReturn(Flux.empty());
+
+        noPrepare.setTransactionIsolationLevel(IsolationLevel.SERIALIZABLE)
+            .as(StepVerifier::create)
+            .verifyComplete();
+
+        assertThat(noPrepare.getSessionTransactionIsolationLevel()).isEqualTo(IsolationLevel.SERIALIZABLE);
+    }
+
     @SuppressWarnings("ConstantConditions")
     @Test
     void badValidate() {