close connection explicitly before returning ErrBadConn for 1792 (#2)

packets.go

@@ -553,6 +553,16 @@ func (mc *mysqlConn) handleErrorPacket(data []byte) error {
 
 	// 1792: ER_CANT_EXECUTE_IN_READ_ONLY_TRANSACTION
 	if errno == 1792 && mc.cfg.RejectReadOnly {
+		// Oops; we are connected to a read-only connection, and won't be able
+		// to issue any write statements. Since RejectReadOnly is configured,
+		// we throw away this connection hoping this one would have write
+		// permission. This is specifically for an AWS Aurora behavior during
+		// failover. See README.md for more.
+		//
+		// We explicitly close the connection before returning
+		// driver.ErrBadConn to ensure that `database/sql` purges this
+		// connection and initiates a new one for next statement next time.
+		mc.Close()
 		return driver.ErrBadConn
 	}