Dubbo之telnet实现

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我们可以通过telnet来访问道对应dubbo服务的信息

比如

我们可以利用一些指令来访问。

我们知道，默认情况下，dubbo使用netty做transport。

那么dubbo是如何区分开正常业务请求和telnet请求呢？

首先来看一下netty的服务。

NettyServer在打开是会注册一些downStream和upStream的event

public class NettyServer extends AbstractServer implements Server {
            private static final Logger logger = LoggerFactory.getLogger(NettyServer.class);     private Map
    
       channels; // 
     
           private ServerBootstrap                 bootstrap;     private org.jboss.netty.channel.Channel channel;     public NettyServer(URL url, ChannelHandler handler) throws RemotingException{
           super(url, ChannelHandlers.wrap(handler, ExecutorUtil.setThreadName(url, SERVER_THREAD_POOL_NAME)));    }     @Override    protected void doOpen() throws Throwable {
           NettyHelper.setNettyLoggerFactory();        ExecutorService boss = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerBoss", true));        ExecutorService worker = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerWorker", true));        ChannelFactory channelFactory = new NioServerSocketChannelFactory(boss, worker, getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS));        bootstrap = new ServerBootstrap(channelFactory);                 final NettyHandler nettyHandler = new NettyHandler(getUrl(), this);        channels = nettyHandler.getChannels();        // https://issues.jboss.org/browse/NETTY-365        // https://issues.jboss.org/browse/NETTY-379        // final Timer timer = new HashedWheelTimer(new NamedThreadFactory("NettyIdleTimer", true));        bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
               public ChannelPipeline getPipeline() {
                   NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec() ,getUrl(), NettyServer.this);                ChannelPipeline pipeline = Channels.pipeline();                /*int idleTimeout = getIdleTimeout();                if (idleTimeout > 10000) {                    pipeline.addLast("timer", new IdleStateHandler(timer, idleTimeout / 1000, 0, 0));                }*/                pipeline.addLast("decoder", adapter.getDecoder());                pipeline.addLast("encoder", adapter.getEncoder());                pipeline.addLast("handler", nettyHandler);                return pipeline;            }        });        // bind        channel = bootstrap.bind(getBindAddress());    }

其中decoder和encoder对应加解码，这边也对应了之前调用异常时无法通过attachment传递信息

那么这边的nettyHandler最终通过层层包装委托的机制其实到了真正执行的应该是

HeaderExchangeHandler

public void received(Channel channel, Object message) throws RemotingException {
       channel.setAttribute(KEY_READ_TIMESTAMP, System.currentTimeMillis());    ExchangeChannel exchangeChannel = HeaderExchangeChannel.getOrAddChannel(channel);    try {
           if (message instanceof Request) {
               // handle request.            Request request = (Request) message;            if (request.isEvent()) {
                   handlerEvent(channel, request);            } else {
                   if (request.isTwoWay()) {
                       Response response = handleRequest(exchangeChannel, request);                    channel.send(response);                } else {
                       handler.received(exchangeChannel, request.getData());                }            }        } else if (message instanceof Response) {
               handleResponse(channel, (Response) message);        } else if (message instanceof String) {
               if (isClientSide(channel)) {
                   Exception e = new Exception("Dubbo client can not supported string message: " + message + " in channel: " + channel + ", url: " + channel.getUrl());                logger.error(e.getMessage(), e);            } else {
                   String echo = handler.telnet(channel, (String) message);                if (echo != null && echo.length() > 0) {
                       channel.send(echo);                }            }        } else {
               handler.received(exchangeChannel, message);        }    } finally {
           HeaderExchangeChannel.removeChannelIfDisconnected(channel);    }}

其中根据请求message的类型进行了区分，如果是request则进行正常的业务调用，如果是String则进行telnet的回复。

这边的handler类型是ExchangeHandlerAdapter及其对应的子类。

可以确认调用telnet时继续根据spi的方法来查找对应的实现

public String telnet(Channel channel, String message) throws RemotingException {
       String prompt = channel.getUrl().getParameterAndDecoded(Constants.PROMPT_KEY, Constants.DEFAULT_PROMPT);    boolean noprompt = message.contains("--no-prompt");    message = message.replace("--no-prompt", "");    StringBuilder buf = new StringBuilder();    message = message.trim();    String command;    if (message.length() > 0) {
           int i = message.indexOf(' ');        if (i > 0) {
               command = message.substring(0, i).trim();            message = message.substring(i + 1).trim();        } else {
               command = message;            message = "";        }    } else {
           command = "";    }    if (command.length() > 0) {
           if (extensionLoader.hasExtension(command)) {
               try {
                   String result = extensionLoader.getExtension(command).telnet(channel, message);                if (result == null) {
                       return null;                }                buf.append(result);            } catch (Throwable t) {
                   buf.append(t.getMessage());            }        } else {
               buf.append("Unsupported command: ");            buf.append(command);        }    }    if (buf.length() > 0) {
           buf.append("\r\n");    }    if (prompt != null && prompt.length() > 0 && ! noprompt) {
           buf.append(prompt);    }    return buf.toString();}

可想而知spi在dubbo服务中完全是非常大规模的使用，可以在项目中借鉴，这也是一种很典型的控制反转详细查看filter一级的说明

回到TelnetHandler的spi文件

clear=com.alibaba.dubbo.remoting.telnet.support.command.ClearTelnetHandlerexit=com.alibaba.dubbo.remoting.telnet.support.command.ExitTelnetHandlerhelp=com.alibaba.dubbo.remoting.telnet.support.command.HelpTelnetHandlerstatus=com.alibaba.dubbo.remoting.telnet.support.command.StatusTelnetHandlerlog=com.alibaba.dubbo.remoting.telnet.support.command.LogTelnetHandlerls=com.alibaba.dubbo.rpc.protocol.dubbo.telnet.ListTelnetHandlerps=com.alibaba.dubbo.rpc.protocol.dubbo.telnet.PortTelnetHandlercd=com.alibaba.dubbo.rpc.protocol.dubbo.telnet.ChangeTelnetHandlerpwd=com.alibaba.dubbo.rpc.protocol.dubbo.telnet.CurrentTelnetHandlerinvoke=com.alibaba.dubbo.rpc.protocol.dubbo.telnet.InvokeTelnetHandlertrace=com.alibaba.dubbo.rpc.protocol.dubbo.telnet.TraceTelnetHandlercount=com.alibaba.dubbo.rpc.protocol.dubbo.telnet.CountTelnetHandler

很明显这些就是telnet所提供的具体的指令。

这边以Help为例

@Activate@Help(parameter = "[command]", summary = "Show help.", detail = "Show help.")public class HelpTelnetHandler implements TelnetHandler {
            private final ExtensionLoader
    
      extensionLoader = ExtensionLoader.getExtensionLoader(TelnetHandler.class);     public String telnet(Channel channel, String message) {
           if (message.length() > 0) {
               if (! extensionLoader.hasExtension(message)) {
                   return "No such command " + message;            }            TelnetHandler handler = extensionLoader.getExtension(message);            Help help = handler.getClass().getAnnotation(Help.class);            StringBuilder buf = new StringBuilder();            buf.append("Command:\r\n    ");            buf.append(message + " " + help.parameter().replace("\r\n", " ").replace("\n", " "));            buf.append("\r\nSummary:\r\n    ");            buf.append(help.summary().replace("\r\n", " ").replace("\n", " "));            buf.append("\r\nDetail:\r\n    ");            buf.append(help.detail().replace("\r\n", "    \r\n").replace("\n", "    \n"));            return buf.toString();        } else {
               List
     
      
       > table = new ArrayList
       
        
         >();            List
         
           handlers = extensionLoader.getActivateExtension(channel.getUrl(), "telnet"); if (handlers != null && handlers.size() > 0) { for (TelnetHandler handler : handlers) { Help help = handler.getClass().getAnnotation(Help.class); List
          
            row = new ArrayList
           
            (); String parameter = " " + extensionLoader.getExtensionName(handler) + " " + (help != null ? help.parameter().replace("\r\n", " ").replace("\n", " ") : ""); row.add(parameter.length() > 50 ? parameter.substring(0, 50) + "..." : parameter); String summary = help != null ? help.summary().replace("\r\n", " ").replace("\n", " ") : ""; row.add(summary.length() > 50 ? summary.substring(0, 50) + "..." : summary); table.add(row); } } return "Please input \"help [command]\" show detail.\r\n" + TelnetUtils.toList(table); } } }