# From: http://www.net-snmp.org/wiki/index.php/FAQ:Agent_17
# send v1 traps
trapsink   127.0.0.1:162
# also send v2 traps
trap2sink  127.0.0.1:162
informsink 127.0.0.1:162

sudo snmptrapd –d –f –Lo

 sudo snmpd -f -L

Received 64 bytes from UDP: [127.0.0.1]:56929
0000: 30 3E 02 01  00 04 06 70  75 62 6C 69  63 A4 31 06    0>.....public.1.
0016: 09 2B 06 01  04 01 BF 08  02 03 40 04  AC 10 81 01    .+........@.....
0032: 02 01 06 02  01 01 43 03  03 CC BC 30  13 30 11 06    ......C....0.0..
0048: 0C 2B 06 01  04 01 BF 08  02 03 02 01  00 02 01 1E    .+..............

2008-11-11 15:43:11 172.16.129.1(via UDP: [127.0.0.1]:56929) TRAP, SNMP v1, community public
        NET-SNMP-EXAMPLES-MIB::netSnmpExampleNotifications Enterprise Specific Trap (NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification) Uptime: 0:41:30.20
        NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatRate.0 = INTEGER: 30

/** @example 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:
 *
 *   可以通过 --with-mib-modules="examples/notification" 把这个模块
 * 编译到agent模块中，snmptrapd可以接收到他发送的traps, 接收到的信息
 * 如下:
 *
 *  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 初始化
 * (to get called, the function name must match init_FILENAME()
 * 函数的名字必须是 init_FILENAME() 这种格式
 */
void
init_notification(void)
{
    DEBUGMSGTL(("example_notification",
                "initializing (setting callback alarm)\n"));
    snmp_alarm_register(30,     /* seconds, 秒 */
                        SA_REPEAT,      /* repeat (every 30 seconds). 每隔30秒发送一个trap*/
                        send_example_notification,      /* our callback 我们的回调函数 */
                        NULL    /* no callback data needed */
        );
}

/** here we send a SNMP v2 trap (which can be sent through snmpv3 and
 *  snmpv1 as well) and send it out.
 *
 *     The various "send_trap()" calls allow you to specify traps in different
 *  formats.  And the various "trapsink" directives allow you to specify
 *  destinations to receive different formats.
 *  But *all* traps are sent to *all* destinations, regardless of how they
 *  were specified.
 * 
 * 
 *  I.e. it's
 * @verbatim
 *                                           ___  trapsink
 *                                          /
 *      send_easy_trap \___  [  Trap      ] ____  trap2sink
 *                      ___  [ Generator  ]
 *      send_v2trap    /     [            ] ----- informsink
 *                                          \____
 *                                                trapsess
 * 
 *  *Not*
 *       send_easy_trap  ------------------->  trapsink
 *       send_v2trap     ------------------->  trap2sink
 *       ????            ------------------->  informsink
 *       ????            ------------------->  trapsess
 * @endverbatim
 */
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); // 发送snmpv2的trap

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