2024-01-18  阅读(44)
原文作者:hashcon 原文地址: https://zhanghaoxin.blog.csdn.net/article/details/50828003

3. 连接模块

3.5 后端连接

对于后端连接,我们只关心MySQL的。
从后端连接工厂开始MySQLConnectionFactory.java:

202401182020309171.png

    public MySQLConnection make(MySQLDataSource pool, ResponseHandler handler,
                String schema) throws IOException {
            //DBHost配置
            DBHostConfig dsc = pool.getConfig();
            //根据是否为NIO返回SocketChannel或者AIO的AsynchronousSocketChannel
            NetworkChannel channel = openSocketChannel(MycatServer.getInstance()
                    .isAIO());
            //新建MySQLConnection
            MySQLConnection c = new MySQLConnection(channel, pool.isReadNode());
            //根据配置初始化MySQLConnection
            MycatServer.getInstance().getConfig().setSocketParams(c, false);
            c.setHost(dsc.getIp());
            c.setPort(dsc.getPort());
            c.setUser(dsc.getUser());
            c.setPassword(dsc.getPassword());
            c.setSchema(schema);
            //目前实际连接还未建立,handler为MySQL连接认证MySQLConnectionAuthenticator
            c.setHandler(new MySQLConnectionAuthenticator(c, handler));
            c.setPool(pool);
            c.setIdleTimeout(pool.getConfig().getIdleTimeout());
            //AIO和NIO连接方式建立实际的MySQL连接
            if (channel instanceof AsynchronousSocketChannel) {
                ((AsynchronousSocketChannel) channel).connect(
                        new InetSocketAddress(dsc.getIp(), dsc.getPort()), c,
                        (CompletionHandler) MycatServer.getInstance()
                                .getConnector());
            } else {
                //通过NIOConnector建立连接
                ((NIOConnector) MycatServer.getInstance().getConnector())
                        .postConnect(c);
    
            }
            return c;
        }

通过NIOConnector建立实际连接的过程与前端连接的建立相似,也是先放在队列中,之后由NIOConnector去建立连接。

    public void postConnect(AbstractConnection c) {
        connectQueue.offer(c);
        selector.wakeup();
    }
    public void run() {
        final Selector tSelector = this.selector;
        for (;;) {
            ++connectCount;
            try {
                //查看有无连接就绪
                tSelector.select(1000L);
                connect(tSelector);
                Set<SelectionKey> keys = tSelector.selectedKeys();
                try {
                    for (SelectionKey key : keys) {
                        Object att = key.attachment();
                        if (att != null && key.isValid() && key.isConnectable()) {
                            finishConnect(key, att);
                        } else {
                            key.cancel();
                        }
                    }
                } finally {
                    keys.clear();
                }
            } catch (Exception e) {
                LOGGER.warn(name, e);
            }
        }
    }
    
    private void connect(Selector selector) {
        AbstractConnection c = null;
        while ((c = connectQueue.poll()) != null) {
            try {
                SocketChannel channel = (SocketChannel) c.getChannel();
                //注册OP_CONNECT监听与后端连接是否真正建立
                channel.register(selector, SelectionKey.OP_CONNECT, c);
                   //主动连接
                channel.connect(new InetSocketAddress(c.host, c.port));
            } catch (Exception e) {
                c.close(e.toString());
            }
        }
    }
    
    private void finishConnect(SelectionKey key, Object att) {
        BackendAIOConnection c = (BackendAIOConnection) att;
        try {
            if (finishConnect(c, (SocketChannel) c.channel)) { //做原生NIO连接是否完成的判断和操作
                clearSelectionKey(key);
                c.setId(ID_GENERATOR.getId());
                   //绑定特定的NIOProcessor以作idle清理
                NIOProcessor processor = MycatServer.getInstance()
                        .nextProcessor();
                c.setProcessor(processor);
                   //与特定NIOReactor绑定监听读写
                NIOReactor reactor = reactorPool.getNextReactor();
                reactor.postRegister(c);
            }
        } catch (Exception e) {
            //如有异常,将key清空
               clearSelectionKey(key);
               c.close(e.toString());
            c.onConnectFailed(e);
        }
    }
    
    private boolean finishConnect(AbstractConnection c, SocketChannel channel)
            throws IOException {
        if (channel.isConnectionPending()) {
            channel.finishConnect();
            c.setLocalPort(channel.socket().getLocalPort());
            return true;
        } else {
            return false;
        }
    }
    
    private void clearSelectionKey(SelectionKey key) {
        if (key.isValid()) {
            key.attach(null);
            key.cancel();
        }
    }

绑定到具体的NIOReactor之后,监听读事件。和之前讲的前端连接建立过程类似。这次是后端MySQL主动发握手包。这时,读事件就绪,NIOReactor中的RW线程会调用对应AbstractConnection(这里是MySQLConnection)的handler的处理方法处理。这里MySQLConnection中的handler参考工厂方法发现是MySQLConnectionAuthenticator。查看handle方法:

    /**
     * MySQL 4.1版本之前是MySQL323加密,MySQL 4.1和之后的版本都是MySQLSHA1加密,在MySQL5.5的版本之后可以客户端插件式加密(这个MyCat实现)
     * @see @http://dev.mysql.com/doc/internals/en/determining-authentication-method.html
     */
    @Override
    public void handle(byte[] data) {
        try {
            switch (data[4]) {
            //如果是OkPacket,检查是否认证成功
            case OkPacket.FIELD_COUNT:
                HandshakePacket packet = source.getHandshake();
                if (packet == null) {
                    //如果为null,证明链接第一次建立,处理
                    processHandShakePacket(data);
                    // 发送认证数据包
                    source.authenticate();
                    break;
                }
                // 如果packet不为null,处理认证结果
                //首先将连接设为已验证并将handler改为MySQLConnectionHandler
                source.setHandler(new MySQLConnectionHandler(source));
                source.setAuthenticated(true);
                //判断是否用了压缩协议
                boolean clientCompress = Capabilities.CLIENT_COMPRESS==(Capabilities.CLIENT_COMPRESS & packet.serverCapabilities);
                boolean usingCompress= MycatServer.getInstance().getConfig().getSystem().getUseCompression()==1 ;
                if(clientCompress&&usingCompress)
                {
                    source.setSupportCompress(true);
                }
                //设置ResponseHandler
                if (listener != null) {
                    listener.connectionAcquired(source);
                }
                break;
            //如果为ErrorPacket,则认证失败
            case ErrorPacket.FIELD_COUNT:
                ErrorPacket err = new ErrorPacket();
                err.read(data);
                String errMsg = new String(err.message);
                LOGGER.warn("can't connect to mysql server ,errmsg:"+errMsg+" "+source);
                //source.close(errMsg);
                throw new ConnectionException(err.errno, errMsg);
            //如果是EOFPacket,则为MySQL 4.1版本,是MySQL323加密
            case EOFPacket.FIELD_COUNT:
                auth323(data[3]);
                break;
            default:
                packet = source.getHandshake();
                if (packet == null) {
                    processHandShakePacket(data);
                    // 发送认证数据包
                    source.authenticate();
                    break;
                } else {
                    throw new RuntimeException("Unknown Packet!");
                }
    
            }
    
        } catch (RuntimeException e) {
            if (listener != null) {
                listener.connectionError(e, source);
                return;
            }
            throw e;
        }
    }

在连接建立并认证后,MySQLConnectionHandler来处理这个连接的请求和相应。
MySQL服务端响应客户端查询请求的流程如下:

202401182020312402.png
可以分为三个阶段:
(第一阶段)客户端发送查询请求包COM_QUERY (command query packet),如果有结果集返回,且结果集不为空,则返回FieldCount(列数量)包;如果结果集为空,则返回OKPacket;如果命令有错,则返回ERRPacket;如果是Load file data命令,则返回LOCAL_INFILE_Request。
(第二阶段)如果有结果集返回,则先返回列集合,所有列返回完了之后,会返回EOFPacket;如果过程中出现错误,则返回错误包。
(第三阶段)之后返回行记录,返回全部行记录之后,返回EOFPacket。如果有错误,回错误包。
MyCat实现源代码如下:

    protected void handleData(byte[] data) {
        switch (resultStatus) {
            //第一阶段
            case RESULT_STATUS_INIT:
                switch (data[4]) {
                    //返回OKPacket
                    case OkPacket.FIELD_COUNT:
                        handleOkPacket(data);
                        break;
                    //返回错误包
                    case ErrorPacket.FIELD_COUNT:
                        handleErrorPacket(data);
                        break;
                    //返回Load Data进一步操作
                    case RequestFilePacket.FIELD_COUNT:
                        handleRequestPacket(data);
                        break;
                    //返回结果集列数量
                    default:
                        //记录列数量并进入第二阶段
                        resultStatus = RESULT_STATUS_HEADER;
                        header = data;
                        fields = new ArrayList<byte[]>((int) ByteUtil.readLength(data,
                                4));
                }
                break;
            //第二阶段
            case RESULT_STATUS_HEADER:
                switch (data[4]) {
                    //返回错误包
                    case ErrorPacket.FIELD_COUNT:
                        resultStatus = RESULT_STATUS_INIT;
                        handleErrorPacket(data);
                        break;
                    //返回EOF,证明列集合返回完毕,进入第三阶段
                    case EOFPacket.FIELD_COUNT:
                        resultStatus = RESULT_STATUS_FIELD_EOF;
                        handleFieldEofPacket(data);
                        break;
                    //返回的是列集合,记录
                    default:
                        fields.add(data);
                }
                break;
            //第三阶段
            case RESULT_STATUS_FIELD_EOF:
                switch (data[4]) {
                    //返回错误包
                    case ErrorPacket.FIELD_COUNT:
                        resultStatus = RESULT_STATUS_INIT;
                        handleErrorPacket(data);
                        break;
                    //返回EOF,证明结果集返回完毕,回到第一阶段等待下一个请求的响应
                    case EOFPacket.FIELD_COUNT:
                        resultStatus = RESULT_STATUS_INIT;
                        handleRowEofPacket(data);
                        break;
                    //返回结果集包
                    default:
                        handleRowPacket(data);
                }
                break;
            default:
                throw new RuntimeException("unknown status!");
        }
    }
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