get_request called twice

[Guy.HINDELL____opentrade.co.uk]

Hi

I've recently implemented a leaf derived from MibLeaf which overrides the
get_value() method with some code which performs rather more processing than
the simple return of a varbind. I noticed whilst debugging this code that it
was being invoked twice for each get request I sent to the agent, which is
an overhead I don't want.

The reason for this is that the MibTable::get_request() method uses the
MibTable::find() method to locate the right leaf and then calls the
get_value() method of that leaf. The resulting varbind is tested using its
valid() method, before the request is serviced using a call to the leaf's
get_request() method. This call itself calls the the get_value() method!

I fiddled with altering the code in MibTable::get_request to avoid this
second call by using the varbind produced by the first get_value() call to
complete the request as follows...

void MibTable::get_request(Request *req, int ind)
{
   ...
	Vbx leaf_val(o->get_value());

	if (leaf_val.valid()) {
		// call get request-method of
		// the MibLeaf Object
		// o->get_request(req, ind);   // Don't do this
		// response has been sent by the above call,
		// so we could leave here
		// return;				// Don't return here

		// Just do what MibLeaf->GetRequest was doing.
		if (o->get_access() >= READONLY) {
			Mib::instance->done(req->get_transaction_id(), ind,
				leaf_val);
		}
		else {
			Mib::instance->done(req->get_transaction_id(), ind,
				SNMP_ERROR_NO_ACCESS);
		}
		return;
	else {
	...


One problem with this is that get_request can't be overridden in derived
leaf classes (I don't do this anyway), but maybe another approach is an
additional get_reqest method which can take a varbind as an argument rather
than call get_value.


Guy Hindell
OpenTrade Technologies Ltd.
(guy.hindell at opentrade.co.uk)

	


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