SNMP4J服务端连接超时问题解决方案

Z时代
2024-01-10
分类：综合

我们的网络管理中心作为管理中心，是服务端！各个被管设备通过交换机作为客户端与网管中心进行通信，使用的TCP/IP协议！

SNMP只是一种协议包，SNMP4J作为SNMP使用的Java工具包，提供了方便安全的工具包功能！

但是在使用中发现一个问题就是，服务端与客户端发送消息时，发送数次后就不再发送数据了！网络抓包也抓不到，跟踪断点到SNMP4J的代码中发现了这样一个问题！


	/**
	 * Sends a SNMP message to the supplied address.
	 * 
	 * @param address
	 *      an <code>TcpAddress</code>. A
	 *      <code>ClassCastException</code> is thrown if
	 *      <code>address</code> is not a <code>TcpAddress</code>
	 *      instance.
	 * @param message
	 *      byte[] the message to sent.
	 * @throws IOException
	 */
	public void sendMessage(Address address, byte[] message)
			throws java.io.IOException {
		if (server == null) {
			listen();
		}
		serverThread.sendMessage(address, message);
	}

我们可以看到，他与UDP的不同是，使用了一个服务的线程！


	public void sendMessage(Address address, byte[] message)
			throws java.io.IOException {
		Socket s = null;
		SocketEntry entry = (SocketEntry) sockets.get(address);
		if (logger.isDebugEnabled()) {
			logger.debug("Looking up connection for destination '"
					+ address + "' returned: " + entry);
			logger.debug(sockets.toString());
		}
		if (entry != null) {
			s = entry.getSocket();
		}
		if ((s == null) || (s.isClosed()) || (!s.isConnected())) {
			if (logger.isDebugEnabled()) {
				logger.debug("Socket for address '" + address
						+ "' is closed, opening it...");
			}
			pending.remove(entry);
			SocketChannel sc = null;
			try {
				// Open the channel, set it to non-blocking, initiate
				// connect
				sc = SocketChannel.open();
				sc.configureBlocking(false);
				sc
						.connect(new InetSocketAddress(
								((TcpAddress) address).getInetAddress(),
								((TcpAddress) address).getPort()));
				s = sc.socket();
				entry = new SocketEntry((TcpAddress) address, s);
				entry.addMessage(message);
				sockets.put(address, entry);
				synchronized (pending) {
					pending.add(entry);
				}
				selector.wakeup();
				logger.debug("Trying to connect to " + address);
			} catch (IOException iox) {
				logger.error(iox);
				throw iox;
			}
		} else {
			entry.addMessage(message);
			synchronized (pending) {
				pending.add(entry);
			}
			selector.wakeup();
		}
	}

他从一个Map中去获得连接 SocketEntry ，然后得到连接对象Socket！

判断Socket是否有效，有效则直接发送，无效则创建连接后再发送！

然后我找到这样一段代码


private synchronized void timeoutSocket(SocketEntry entry) { 
  if (connectionTimeout > 0) { 
    socketCleaner.schedule(new SocketTimeout(entry), connectionTimeout); 
  } 
}

也就是说服务端会自己检查的连接并且去清除他！

我尝试设置 connectionTimeout 的值


private void init() throws UnknownHostException, IOException { 
  threadPool = ThreadPool.create("Trap", 2); 
  dispatcher = new MultiThreadedMessageDispatcher(threadPool,new MessageDispatcherImpl()); 
  // 本地IP与监听端口 
  listenAddress = GenericAddress.parse(System.getProperty("snmp4j.listenAddress", "tcp:192.168.9.69/5055")); 
  DefaultTcpTransportMapping transport; 
  transport = new DefaultTcpTransportMapping((TcpAddress) listenAddress); 
  transport.setConnectionTimeout(0); 
  snmp = new Snmp(dispatcher, transport); 
  snmp.getMessageDispatcher().addMessageProcessingModel(new MPv1()); 
  snmp.getMessageDispatcher().addMessageProcessingModel(new MPv2c()); 
  snmp.getMessageDispatcher().addMessageProcessingModel(new MPv3()); 
  USM usm = new USM(SecurityProtocols.getInstance(), new OctetString(MPv3.createLocalEngineID()), 0); 
  SecurityModels.getInstance().addSecurityModel(usm); 
  snmp.listen(); 
}