datagramclient.java

这是一个以JAVA编写的程序,本人还没有试过,是一个简单的温度控制系统

package net.sf.dz.pnp.custom;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.util.StringTokenizer;

import org.freehold.jukebox.logger.LogChannel;
import net.sf.dz.pnp.MulticastClient;
import net.sf.dz.pnp.MulticastEvent;
import net.sf.dz.util.MessageDigestFactory;

/**
 * @author Copyright &copy; <a href="mailto:[e-mail]">Vadim Tkachenko</a> 2004
 * @version $Id: DatagramClient.java,v 1.2 2004/06/28 20:35:49 vtt Exp $
 */
abstract public class DatagramClient extends MulticastClient {

    public static final LogChannel CH_DC = new LogChannel("DatagramClient");

    abstract protected void receive(DatagramPacket packet) throws IOException;
    
    protected final MulticastEvent receive() throws Throwable {
    
        byte data[] = new byte[1000];
        DatagramPacket packet = new DatagramPacket(data, data.length);
        
        while ( true ) {
        
            receive(packet);
            
            byte received[] = packet.getData();
            String message = new String(received);
            InetAddress source = packet.getAddress();
            
            // VT: IMPORTANT: Unless the following step is performed, a bug
            // somewhere deep in JVM is triggered, and even though the
            // string will look the same on debug console, .equals will
            // return false, and message digest will be different!
            
            message = message.substring(0, packet.getLength());
            
            if ( message == null ) {
            
                complain(LOG_WARNING, CH_DC, "Null packet received");
                continue;
            }
            
            if ( message.startsWith("SHA") ) {
            
                // VT: FIXME: SHA should have a fixed length, but since I don't
                // remember it now, I'll calculate it
                
                int offset = message.indexOf("}");
                
                if ( offset == -1 ) {
                
                    throw new IllegalStateException("Can't find SHA end offset in '" + message + "'");
                }

                String md = message.substring(4, offset);
                String payload = message.substring(offset + 2);
                
                complain(LOG_DEBUG, CH_DC, "Source: " + packet.getAddress());
                complain(LOG_DEBUG, CH_DC, "SHA: " + md);
                complain(LOG_DEBUG, CH_DC, "Payload: '" + payload + "'");
                
                String md2 = new MessageDigestFactory().getSHA(payload);
                
                if ( !md.equals(md2) ) {
                
                    complain(LOG_WARNING, CH_DC, "SHA mismatch: " + md2);
                    
                    // Have to discard the packet, it's garbled
                    // Let's receive another

                } else {
                
                    // We have a good packet
                    
                    return createEvent(source, payload);
                }
            
            } else {
            
                // This means that we don't have the message digest. Too
                // bad, but let's allow this so far.
                
                //return new MulticastEvent(source, buf[0], buf[1]);
                
                // VT: FIXME: Unlike the previous case, there's no guarantee
                // we won't screw up here, so better check any exceptions...
                
                return createEvent(source, message);
            }
        }
    }
    
    private MulticastEvent createEvent(InetAddress source, String payload) {
    
        StringTokenizer st = new StringTokenizer(payload, "/");
        
        // This *must* be present
        
        String serviceSignature = st.nextToken();

        int port = Integer.parseInt(st.nextToken());
        boolean secure = "secure".equals(st.nextToken());
        
        // If nothing else is available, the hell with it
        
        String message = "";
        
        if ( st.hasMoreTokens() ) {
        
            // If there's more than one slash, we'll have to reassemble the
            // message
            
            if ( !"".equals(message) ) {
            
                message += "/";
            }
            
            message += st.nextToken();
        }
        
        return new MulticastEvent(source, serviceSignature, port, secure, message.trim());
    }
}