Custom Snmp PduRequestHandler

in Agent Toolkit Java Edition • 11 years ago

Greetings,
We do have compiled some predefined MIB to get the java handlers and they working fine with OIDs that already exists in the given MIB. (i.e. 1.2.3.4.5.1 ) such as below

public class XYZ extends SnmpAgent implements Runnable {
....
this.Enabler__HTTPListener = new Enabler__HTTPRequestHandler(this);
this.Enabler__HTTPListener.setEnabler__HTTPInterface(this.getEnabler__HTTPInstance());
this.Enabler__HTTPListener.addRegistrationListener(this.hdlr);
}

However this handler is created during the MIB Compilation and we need to introduce MIB changes that will not be available in the MIB.

I.e. if request oid STARTS WITH say 1.2.3.4.5.6 parse and respond it to programmatically.
the OID can extend to the depth even to 1.2.3.4.5.6.7.8.9 and I want to manage all of them myself programmatically without MIB code generation.

For this I introduced an extended version of PduRequestHandler (say PduRequestHandlerExtension) it
can catch the requests and I can parse the OID to find out if it needs special operation as below.

/*@Override
public void processSnmpPduRequest(final SnmpPduRequestEvent pduRequest) {
final SnmpPDU pdu = pduRequest.getSnmpPDU();
final Vector v = pdu.getVariableBindings();
final SnmpVarBind varb = (SnmpVarBind) v.firstElement();
SnmpOID oid=varb.getObjectID();
if(! oid.toString().equals("1.2.3.4.5.6")){
//Create my custom response
@SuppressWarnings("unchecked")
final long current = 15;
final SnmpInt var0 = new SnmpInt(current);
varb.setVariable(var0);
pdu.setVariable(0, var0);
pdu.setCommand(SnmpAPI.GET_RSP_MSG);
pdu.setErrindex(0);
pdu.setErrstat(0);
} else {
// Use the standart mechanism through the MIB compiler generated handlers ( Listeners)
super.processSnmpPduRequest(pduRequest);
}

I
The problem is even all the red code above is executed My Mib browser can not able to get a response for a request such as 1.2.3.4.5.6. The old blue code is working just fine and I can get responses appropriately.

What is missing above or can you suggest any direction for how we can introduce custom OID handlers ?

thanks
Onur Karadeli

Replies(4)

Guest

Custom Snmp PduRequestHandler

11 years ago

Dear Onur Karadeli,

Greetings.

Basically all your mib OIDs can be handled by instrumenting the generated source itself and we don't encourage/recommend api users to extend PduRequestHandler, as this is very critical place. However if you still wish to extend, please raise your query to support at agent-support@webnms.com with detailed requirement.

Thanks & Regards,
Pradheep

Guest

Custom Snmp PduRequestHandler

11 years ago

Greetings, we got the following solution.

For handling custom OIDs. (i.e. non-mib generated) we have devised the following method.
I cant share the source code, so here is the algorithm we used that can give you the idea and can help.

1- Create a base class i.e. MyCustomRequestHandler extending SimpleRequestHandler

2- Employ a field i.e. int[] myCustomOid to keep dynamic OIDs.

3- Dynamically create instances of MyCustomRequestHandler , where myCustomOid is based on
   i.e. new MyCustomRequestHandler ( ".1.2.3.4.5.6") and new MyCustomRequestHandler(".7.8.9.10.11")

4- Override the public int[] getOidRep() so that it returns the Oid you supply in the constructor.

5- Override the protected int[] getSubidList() so that it knows the number of Childs in the Oid group, otherwise you cant not able to intercept requests.

6- Override snmp methods per your needs , processGetRequest, processGetNextRequest...

7- In your SnmpAgent class. (i.e. MySnmpAgentWrapper) Add the following lines to register you new handler.

            final MyCustomRequestHandler handler = new MyCustomRequestHandler(myCustomOid);
            handler.addRegistrationListener(this.hdlr);

   Where hdlr = PduRequestHandler , automatically generated by MIB Generator.

8- That is it.!

The above algorithm is a generic one handling all Oid requests in the same way (i.e. in same processGetNext)
1.2.3.4.5.6
7.8.9.10.11
...
If you want to make a custom behaviour for each Oid request, enhance the constructor with a new Class such as MyCustomBehaviour and pass this parameter during creation.

thanks
Onur Karadeli



3- Each instance

For each OID family we need to handle dynamically.

Guest

Custom Snmp PduRequestHandler

11 years ago

Dear Onur karadeli,

We would like to inform you that you need not do all the work manually, We have already automated the above said(algorithm) list of tasks with a GUI tool known as MibCompiler, which will generate the XXXRequestHandler.java and XXXEntry/Instrument.java for each and every table and scalar group defined in the given MIB.

Kindly read of our help documentation for more details on source generation and instrumenting the generated code at

http://www.webnms.com/javaagent/help/snmp_agent/snmp/j_snmp_createagent.html

http://www.webnms.com/javaagent/help/snmp_agent/snmp/j_snmp_instrumentation.html

Also we recommend you to go through our complete help documentation at

http://www.webnms.com/javaagent/help/snmp_agent/index.html

as it will give you a clear idea of what all can be done with our product and how to achieve your requirement with our product.

Regards

Pradheep.V

Guest

Custom Snmp PduRequestHandler

11 years ago

No you dont address the case when OIDs or MIB definitions are not on hand during development.
That is dynamically ( by rules etc) deciding what to do with OIDs that are not known until runtime.
Say in another way , you dont have the chance to use the MIB compiler.

thanks

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