Method readPacket

packets.go:41–123

Read packet to buffer 'data'

()

// Read packet to buffer 'data'
func (mc *mysqlConn) readPacket() ([]byte, error) {
	var prevData []byte
	invalidSequence := false

	readNext := mc.readNext
	if mc.compress {
		readNext = mc.compIO.readNext
	}

	for {
		// read packet header
		data, err := readNext(4)
		if err != nil {
			mc.close()
			if cerr := mc.canceled.Value(); cerr != nil {
				return nil, cerr
			}
			mc.log(err)
			return nil, ErrInvalidConn
		}

		// packet length [24 bit]
		pktLen := getUint24(data[:3])
		seq := data[3]

		// check packet sync [8 bit]
		if seq != mc.sequence {
			mc.log(fmt.Sprintf("[warn] unexpected sequence nr: expected %v, got %v", mc.sequence, seq))
			// MySQL and MariaDB doesn't check packet nr in compressed packet.
			if !mc.compress {
				// For large packets, we stop reading as soon as sync error.
				if len(prevData) > 0 {
					mc.close()
					return nil, ErrPktSyncMul
				}
				invalidSequence = true
			}
		}
		mc.sequence = seq + 1

		// packets with length 0 terminate a previous packet which is a
		// multiple of (2^24)-1 bytes long
		if pktLen == 0 {
			// there was no previous packet
			if prevData == nil {
				mc.log(ErrMalformPkt)
				mc.close()
				return nil, ErrInvalidConn
			}
			return prevData, nil
		}

		// read packet body [pktLen bytes]
		data, err = readNext(pktLen)
		if err != nil {
			mc.close()
			if cerr := mc.canceled.Value(); cerr != nil {
				return nil, cerr