need check error when read from mysql

[zeast]

Issue description

The function readUntilEOF of struct mysqlConn did not check if data[0] is 0xff.
If I exec a lock command like ' select id from foo for update ', mysql maybe return a timeout error. Without check, program will wait for read forever.

Example code

// Reads Packets until EOF-Packet or an Error appears. Returns count of Packets read
func (mc *mysqlConn) readUntilEOF() error {
    for {
        data, err := mc.readPacket()
        if err != nil {
            return err
        }

        //check if a error packet
        if data[0] == iERR {
            //read the error code and error message
            //https://dev.mysql.com/doc/refman/5.5/en/error-messages-server.html
        }

        // No Err and no EOF Packet
        if err == nil && data[0] != iEOF {
            continue
        }
        if err == nil && data[0] == iEOF && len(data) == 5 {
            mc.status = readStatus(data[3:])
        }

        return nil // Err or EOF
    }
}

Configuration

go version go1.6.2 darwin/amd64

mysql Ver 14.14 Distrib 5.7.12, for osx10.11 (x86_64) using EditLine wrapper

OS X EI Capitan 10.11.5

[qbig]

I encounter a very similar issue. In my case, mc.buf was corrupted. So in

func (rows *mysqlRows) Close() error {
    mc := rows.mc
    if mc == nil {
        return nil
    }
    if mc.netConn == nil {
        return ErrInvalidConn
    }

    // Remove unread packets from stream
    err := mc.readUntilEOF()
    rows.mc = nil
    return err
}

which calls readUntilEOF()

mc.readPacket(), pktLen would actually come from garbage and return a huge number. And as a result it would wait forever.

go1.6.2 darwin/amd64
OS X EI Capitan 10.11.5

[qbig]

related to golang/go#8874 ?