Clear MySQL prepared statements cache on connection reset (#1428)

* Clear MySQL prepared statements cache on connection reset

See #1424

Otherwise, the client emits an error such as:

io.vertx.mysqlclient.MySQLException: {errorMessage=Unknown prepared statement handler (1) given to mysql_stmt_precheck, errorCode=1243, sqlState=HY000}

Signed-off-by: Thomas Segismont <tsegismont@gmail.com>

* Add LruCacheTest#testCacheCleared

Signed-off-by: Thomas Segismont <tsegismont@gmail.com>

---------

Signed-off-by: Thomas Segismont <tsegismont@gmail.com>

vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/MySQLSocketConnection.java

@@ -30,6 +30,7 @@
 import io.vertx.mysqlclient.MySQLAuthenticationPlugin;
 import io.vertx.mysqlclient.MySQLConnectOptions;
 import io.vertx.mysqlclient.SslMode;
+import io.vertx.mysqlclient.impl.codec.ClearCachedStatementsEvent;
 import io.vertx.mysqlclient.impl.codec.MySQLCodec;
 import io.vertx.mysqlclient.impl.codec.MySQLPacketDecoder;
 import io.vertx.mysqlclient.impl.command.InitialHandshakeCommand;
@@ -114,6 +115,21 @@ protected <R> void doSchedule(CommandBase<R> cmd, Handler<AsyncResult<R>> handle
     }
   }
 
+  @Override
+  protected void handleMessage(Object msg) {
+    if (msg == ClearCachedStatementsEvent.INSTANCE) {
+      clearCachedStatements();
+    } else {
+      super.handleMessage(msg);
+    }
+  }
+
+  private void clearCachedStatements() {
+    if (this.psCache != null) {
+      this.psCache.clear();
+    }
+  }
+
   public Future<Void> upgradeToSsl(ClientSSLOptions sslOptions) {
     return socket.upgradeToSsl(sslOptions);
   }

vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/codec/ClearCachedStatementsEvent.java

@@ -0,0 +1,13 @@
+package io.vertx.mysqlclient.impl.codec;
+
+/**
+ * An event that signals all cached statements must be cleared from the cache.
+ */
+public class ClearCachedStatementsEvent {
+
+  public static final ClearCachedStatementsEvent INSTANCE = new ClearCachedStatementsEvent();
+
+  private ClearCachedStatementsEvent() {
+    // Singleton
+  }
+}

vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/codec/ResetConnectionCommandCodec.java

@@ -30,6 +30,7 @@ void encode(MySQLEncoder encoder) {
 
   @Override
   void decodePayload(ByteBuf payload, int payloadLength) {
+    encoder.chctx.fireChannelRead(ClearCachedStatementsEvent.INSTANCE);
     handleOkPacketOrErrorPacketPayload(payload);
   }
 

vertx-mysql-client/src/test/java/io/vertx/mysqlclient/MySQLUtilityCommandTest.java

@@ -17,6 +17,7 @@
 import io.vertx.ext.unit.junit.VertxUnitRunner;
 import io.vertx.sqlclient.Row;
 import io.vertx.sqlclient.RowSet;
+import io.vertx.sqlclient.Tuple;
 import org.junit.After;
 import org.junit.Assume;
 import org.junit.Before;
@@ -160,6 +161,19 @@ public void testResetConnection(TestContext ctx) {
     }));
   }
 
+  @Test
+  public void testResetConnectionClearsPreparedStatementCache(TestContext ctx) {
+    Assume.assumeFalse(rule.isUsingMySQL5_6());
+    MySQLConnectOptions connectOptions = new MySQLConnectOptions(options).setCachePreparedStatements(true);
+    MySQLConnection.connect(vertx, connectOptions).onComplete(ctx.asyncAssertSuccess(conn -> {
+      conn.preparedQuery("SELECT 1").execute(Tuple.tuple()).onComplete(ctx.asyncAssertSuccess(res1 -> {
+        conn.resetConnection().onComplete(ctx.asyncAssertSuccess(rst -> {
+          conn.preparedQuery("SELECT 1").execute(Tuple.tuple()).onComplete(ctx.asyncAssertSuccess());
+        }));
+      }));
+    }));
+  }
+
   @Test
   public void testChangeUser(TestContext ctx) {
     MySQLConnection.connect(vertx, options).onComplete( ctx.asyncAssertSuccess(conn -> {

vertx-sql-client/src/main/java/io/vertx/sqlclient/impl/cache/LruCache.java

@@ -11,19 +11,10 @@
 
 package io.vertx.sqlclient.impl.cache;
 
-import io.vertx.core.AsyncResult;
-import io.vertx.core.Handler;
-import io.vertx.sqlclient.impl.PreparedStatement;
-
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.Iterator;
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 
 /**
- * A LRU replacement strategy cache based on {@link java.util.LinkedHashMap} for prepared statements.
+ * An LRU replacement strategy cache based on {@link java.util.LinkedHashMap} for prepared statements.
  */
 public class LruCache<K, V> extends LinkedHashMap<K, V> {
 
@@ -75,4 +66,10 @@ protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
       return false;
     }
   }
+
+  @Override
+  public void clear() {
+    super.clear();
+    removed = null;
+  }
 }

vertx-sql-client/src/main/java/io/vertx/sqlclient/impl/cache/PreparedStatementCache.java

@@ -65,4 +65,13 @@ public boolean isFull() {
   public int size() {
     return cache.size();
   }
+
+  /**
+   * Clears the cache.
+   * <p>
+   * This method must be called only when the cached prepared statements have been released (e.g. with a connection reset).
+   */
+  public void clear() {
+    cache.clear();
+  }
 }

vertx-sql-client/src/test/java/io/vertx/sqlclient/impl/LruCacheTest.java

@@ -5,7 +5,7 @@
 
 import java.util.List;
 
-import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.*;
 
 public class LruCacheTest {
 
@@ -37,4 +37,14 @@ public void testEvict() {
     assertEquals("value-0", evicted);
     assertEquals(1023, cache.size());
   }
+
+  @Test
+  public void testCacheCleared() {
+    LruCache<String, String> cache = new LruCache<>(42);
+    List<String> evicted = cache.cache("foo", "bar");
+    assertTrue(evicted.isEmpty());
+    assertNotNull(cache.get("foo"));
+    cache.clear();
+    assertNull(cache.get("foo"));
+  }
 }