Detecting a doi collision

[robert bouwens]

hi,
when the bacnet4j app monitors other bacnet devices (notifications and cov) then detecting a doi collision gets important.
when two davices do have the same doi then one device will miss event data.

the iamrequest.java has to be modified as follows:

   /**
     * see if the address is my own local echo
     * 
     * @param from
     * @return
     */
    private boolean localEcho(Address from, Address[] localAddresses)
    {
    	for ( Address addr : localAddresses)
    	{
    		boolean equal = addr.equals(from);
    		if (equal)
    		{
    			return true;
    		}
    	}
    	return false;
    }
    
   // modified
    @Override
    public void handle(LocalDevice localDevice, Address from, Network network) {
        // Make sure we're not hearing from ourselves.
    	
    	int myDoi = localDevice.getConfiguration().getInstanceId();
    	int remoteDoi = iAmDeviceIdentifier.getInstanceNumber();
        if (remoteDoi == myDoi)
        {
        	// get my bacnet address and compare the addresses
        	Address[] myAddresses = localDevice.getAllLocalAddresses();
        	boolean lEcho = localEcho(from, myAddresses);
        	if ( lEcho)
        	{
        		return;
         	}
        	else
        	{
        		System.out.println("another instance with my doi found!");
        	}
        }

        // Register the device in the list of known devices.
        RemoteDevice d = localDevice.getRemoteDeviceCreate(remoteDoi, from, network);
        d.setMaxAPDULengthAccepted(maxAPDULengthAccepted.intValue());
        d.setSegmentationSupported(segmentationSupported);
        d.setVendorId(vendorId.intValue());

        // Fire the appropriate event.
        localDevice.getEventHandler().fireIAmReceived(d);
    }

in localdevice.java is the function getLocalIPAdress, but we have multihomed linux boxes - a pain for java developers :wink:
so we need to add a new function:

    public Address[] getAllLocalAddresses()
    {
        try 
        {
	    	ArrayList<Address> lAddr = new ArrayList<Address>();
	        for (NetworkInterface iface : Collections.list(NetworkInterface.getNetworkInterfaces())) {
	            for (InetAddress addr : Collections.list(iface.getInetAddresses())) 
	            {
	                if (!addr.isLoopbackAddress() && addr.isSiteLocalAddress())
	                {
	                	byte[] addrBytes = addr.getAddress();
	                	Address address = new Address(addrBytes, messageControl.getPort());
	                	lAddr.add(address);
	                }
	             }
	        }
	  	    	
	    	int elems = lAddr.size();
	    	Address[] retVal = new Address[elems];
	    	lAddr.toArray(retVal);
	    	return retVal;
        }
        catch (Exception e) 
        {
            // Should never happen, so just wrap in a RuntimeException
            throw new RuntimeException(e);
        }
   }

now you can easily detect if there is another device wioth the same doi:

	public boolean isUniqueInstanceNumber()
	{
		int deviceID = getConfiguration().getInstanceId();
		RemoteDevice rd = getRemoteDevice(deviceID);
		if (null != rd)
		{
			return false;
		}
		else
		{
			return true;
		}
	}

some functionality which is needed in our daily work.

robert

[mlohbihler]

Thanks Robert. This is been added in similar form to the code base. It imposed a difference to the public interface in LocalDevice though, in that the getAddress method now take an InetAddress parameter. The equivalent code is now:

d.getAddress(d.getDefaultLocalInetAddress())

All code changes have been checked into CVS.