Merge pull request #619 from ma-xiao-guang-64/dev

            log.debug("Read from client: \n {}", ByteBufUtil.prettyHexDump(in));

        }

        int payloadLength = in.markReaderIndex().readMediumLE();

        if (readableBytes < payloadLength) {

        //mysql协议包头 内容长度3字节 序号1字节 内容n字节

        //readableBytes的长度为3+1+payloadLength

        if (readableBytes - 4 < payloadLength) {

            in.resetReaderIndex();

            return;

        }

        if (readableBytes - 4 > payloadLength) {

            //frame长度为1+payloadLength

            ByteBuf frame = in.readRetainedSlice(payloadLength + 1);

            out.add(frame);

            return;

        }

        out.add(in);

    }