Fixed SetReadDeadline before connCheck (go-sql-driver#1299)

there's no need to set conn's readline if CheckConnLiveness is false,
and the ReadTimeout shall work with rawConn.Read inside conncheck.
buffer.fill will do SetReadDeadline if needed

packets.go

@@ -110,14 +110,13 @@ func (mc *mysqlConn) writePacket(data []byte) error {
  conn = mc.rawConn
  }
  var err error
- // If this connection has a ReadTimeout which we've been setting on
- // reads, reset it to its default value before we attempt a non-blocking
- // read, otherwise the scheduler will just time us out before we can read
- if mc.cfg.ReadTimeout != 0 {
- err = conn.SetReadDeadline(time.Time{})
- }
- if err == nil && mc.cfg.CheckConnLiveness {
- err = connCheck(conn)
+ if mc.cfg.CheckConnLiveness {
+ if mc.cfg.ReadTimeout != 0 {
+ err = conn.SetReadDeadline(time.Now().Add(mc.cfg.ReadTimeout))
+ }
+ if err == nil {
+ err = connCheck(conn)
+ }
  }
  if err != nil {
  errLog.Print("closing bad idle connection: ", err)