notification.c

This example shows how to send a notification from inside the agent. In this case we do something really boring to decide whether to send a notification or not: we simply sleep for 30 seconds and send it, then we sleep for 30 more and send it again. We do this through the snmp_alarm mechanisms (which are safe to use within the agent. Don't use the system alarm() call, it won't work properly). Normally, you would probably want to do something to test whether or not to send an alarm, based on the type of mib module you were creating.

When this module is compiled into the agent (run configure with --with-mib-modules="examples/notification") then it should send out traps, which when received by the snmptrapd demon will look roughly like:

2002-05-08 08:57:05 localhost.localdomain [udp:127.0.0.1:32865]: sysUpTimeInstance = Timeticks: (3803) 0:00:38.03 snmpTrapOID.0 = OID: netSnmpExampleNotification

/*
 * start be including the appropriate header files 
 */
#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-includes.h>
#include <net-snmp/agent/net-snmp-agent-includes.h>

/*
 * contains prototypes 
 */
#include "notification.h"

/*
 * our initialization routine
 * (to get called, the function name must match init_FILENAME() 
 */
void
init_notification(void)
{
    DEBUGMSGTL(("example_notification",
                "initializing (setting callback alarm)\n"));
    snmp_alarm_register(30,     /* seconds */
                        SA_REPEAT,      /* repeat (every 30 seconds). */
                        send_example_notification,      /* our callback */
                        NULL    /* no callback data needed */
        );
}

void
send_example_notification(unsigned int clientreg, void *clientarg)
{
    /*
     * define the OID for the notification we're going to send
     * NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification 
     */
    oid             notification_oid[] =
        { 1, 3, 6, 1, 4, 1, 8072, 2, 3, 0, 1 };
    size_t          notification_oid_len = OID_LENGTH(notification_oid);
    static u_long count = 0;

    /*
     * In the notification, we have to assign our notification OID to
     * the snmpTrapOID.0 object. Here is it's definition. 
     */
    oid             objid_snmptrap[] = { 1, 3, 6, 1, 6, 3, 1, 1, 4, 1, 0 };
    size_t          objid_snmptrap_len = OID_LENGTH(objid_snmptrap);

    /*
     * define the OIDs for the varbinds we're going to include
     *  with the notification -
     * NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatRate  and
     * NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatName 
     */
    oid      hbeat_rate_oid[]   = { 1, 3, 6, 1, 4, 1, 8072, 2, 3, 2, 1, 0 };
    size_t   hbeat_rate_oid_len = OID_LENGTH(hbeat_rate_oid);
    oid      hbeat_name_oid[]   = { 1, 3, 6, 1, 4, 1, 8072, 2, 3, 2, 2, 0 };
    size_t   hbeat_name_oid_len = OID_LENGTH(hbeat_name_oid);

    /*
     * here is where we store the variables to be sent in the trap 
     */
    netsnmp_variable_list *notification_vars = NULL;
    const char *heartbeat_name = "A girl named Maria";
#ifdef  RANDOM_HEARTBEAT
    int  heartbeat_rate = rand() % 60;
#else
    int  heartbeat_rate = 30;
#endif

    DEBUGMSGTL(("example_notification", "defining the trap\n"));

    /*
     * add in the trap definition object 
     */
    snmp_varlist_add_variable(&notification_vars,
                              /*
                               * the snmpTrapOID.0 variable 
                               */
                              objid_snmptrap, objid_snmptrap_len,
                              /*
                               * value type is an OID 
                               */
                              ASN_OBJECT_ID,
                              /*
                               * value contents is our notification OID 
                               */
                              (u_char *) notification_oid,
                              /*
                               * size in bytes = oid length * sizeof(oid) 
                               */
                              notification_oid_len * sizeof(oid));

    /*
     * add in the additional objects defined as part of the trap
     */

    snmp_varlist_add_variable(&notification_vars,
                               hbeat_rate_oid, hbeat_rate_oid_len,
                               ASN_INTEGER,
                              (u_char *)&heartbeat_rate,
                                  sizeof(heartbeat_rate));

    /*
     * if we want to insert additional objects, we do it here 
     */
    if (heartbeat_rate < 30 ) {
        snmp_varlist_add_variable(&notification_vars,
                               hbeat_name_oid, hbeat_name_oid_len,
                               ASN_OCTET_STR,
                               heartbeat_name, strlen(heartbeat_name));
    }

    /*
     * send the trap out.  This will send it to all registered
     * receivers (see the "SETTING UP TRAP AND/OR INFORM DESTINATIONS"
     * section of the snmpd.conf manual page. 
     */
    ++count;
    DEBUGMSGTL(("example_notification", "sending trap %ld\n",count));
    send_v2trap(notification_vars);

    /*
     * free the created notification variable list 
     */
    DEBUGMSGTL(("example_notification", "cleaning up\n"));
    snmp_free_varbind(notification_vars);
}