fixes reconnect problem when mysql is restarted

Author: tomponline

AUTHORS

@@ -60,6 +60,7 @@ Runrioter Wung <runrioter at gmail.com>
 Soroush Pour <me at soroushjp.com>
 Stan Putrya <root.vagner at gmail.com>
 Stanley Gunawan <gunawan.stanley at gmail.com>
+Thomas Parrott <tomp at tomp.uk>
 Xiangyu Hu <xiangyu.hu at outlook.com>
 Xiaobing Jiang <s7v7nislands at gmail.com>
 Xiuming Chen <cc at cxm.cc>

packets.go

@@ -46,8 +46,15 @@ func (mc *mysqlConn) readPacket() ([]byte, error) {
 			if data[3] > mc.sequence {
 				return nil, ErrPktSyncMul
 			}
-			return nil, ErrPktSync
+
+			// The MariaDB server sends an error packet with sequence numer 0 during
+			// server shutdown. Continue to process it so the specific error can be
+			// detected.
+			if data[3] != 0 {
+				return nil, ErrPktSync
+			}
 		}
+
 		mc.sequence++
 
 		// packets with length 0 terminate a previous packet which is a
@@ -585,6 +592,13 @@ func (mc *mysqlConn) handleErrorPacket(data []byte) error {
 		pos = 9
 	}
 
+	// If error code is for ER_CONNECTION_KILLED, then mark connection as bad.
+	// https://mariadb.com/kb/en/mariadb/mariadb-error-codes/
+	if errno == 1927 {
+		errLog.Print("Error ", errno, ": ", string(data[pos:]))
+		return driver.ErrBadConn
+	}
+
 	// Error Message [string]
 	return &MySQLError{
 		Number:  errno,