canal 源码解析（2）-数据流转篇（2）

最新推荐文章于 2025-10-17 20:02:12 发布

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最新推荐文章于 2025-10-17 20:02:12 发布 · 1.6k 阅读

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本文详细介绍了Canal在接收到MySQL内部指令和日常DML、DDL操作时的数据处理流程。从解析MySQL报文头部、获取body、到根据不同事件类型进行过滤和分发，如binlog事件的确认、格式描述等。文中还列出了不同event类型的过滤规则，如插入、更新、删除等。

一、msyql内部指令操作

1)接收msyql发送过来的报文，先获取头部。

header = PacketManager.readHeader(connector.getChannel(), 4);

public static HeaderPacket readHeader(SocketChannel ch, int len) throws IOException {
    HeaderPacket header = new HeaderPacket();
    header.fromBytes(ch.read(len));
    return header;
}

public void fromBytes(byte[] data) {
    if (data == null || data.length != 4) {
        throw new IllegalArgumentException("invalid header data. It can't be null and the length must be 4 byte.");
    }
    this.packetBodyLength = (data[0] & 0xFF) | ((data[1] & 0xFF) << 8) | ((data[2] & 0xFF) << 16);
    this.setPacketSequenceNumber(data[3]);
}

只取了data的前四个字节

2）根据头部大小判断body长度

开始获取body

byte[] body = PacketManager.readBytes(connector.getChannel(), header.getPacketBodyLength());

public static byte[] readBytes(SocketChannel ch, int len) throws IOException {
    return ch.read(len);
}

若body长度为7，则从input里获取0-7字节放入data

public byte[] read(int readSize) throws IOException {
    InputStream input = this.input;
    byte[] data = new byte[readSize];
    int remain = readSize;
    if (input == null) {
        throw new SocketException("Socket already closed.");
    }
    while (remain > 0) {
        try {
            int read = input.read(data, readSize - remain, remain);
            if (read > -1) {
                remain -= read;
            } else {
                throw new IOException("EOF encountered.");
            }
        } catch (SocketTimeoutException te) {
            if (Thread.interrupted()) {
                throw new ClosedByInterruptException();
            }
        }
    }
    return data;
}

3）获得data为，根据msyql协议里ok报文的特性（如下，）

4）获得ok后，进行下一步操作

二、msyql 日常指令（dml，ddl）操作：

1）先初始化一个buff，new buffer（32）和chanel，

接收msyql发送过来的data

public boolean fetch() throws IOException {
    try {
        // Fetching packet header from input.
        if (!fetch0(0, NET_HEADER_SIZE)) {
            logger.warn("Reached end of input stream while fetching header");
            return false;
        }

        // Fetching the first packet(may a multi-packet).
        int netlen = getUint24(PACKET_LEN_OFFSET);//body长度
        int netnum = getUint8(PACKET_SEQ_OFFSET);//
        if (!fetch0(NET_HEADER_SIZE, netlen)) {//获取body
            logger.warn("Reached end of input stream: packet #" + netnum + ", len = " + netlen);
            return false;
        }

        // Detecting error code.
        final int mark = getUint8(NET_HEADER_SIZE);
        if (mark != 0) {
            if (mark == 255) // error from master
            {

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