apps/snmp/snmp_traps.c

/**
 * @file
 * SNMPv1 and SNMPv2 traps implementation.
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Martin Hentschel
 *         Christiaan Simons <christiaan.simons@axon.tv>
 *
 */

#include "lwip/apps/snmp_opts.h"

#if LWIP_SNMP /* don't build if not configured for use in lwipopts.h */

#include <string.h>

#include "lwip/snmp.h"
#include "lwip/sys.h"
#include "lwip/apps/snmp.h"
#include "lwip/apps/snmp_core.h"
#include "lwip/prot/iana.h"
#include "snmp_msg.h"
#include "snmp_asn1.h"
#include "snmp_core_priv.h"

#define SNMP_IS_INFORM                            1
#define SNMP_IS_TRAP                              0

struct snmp_msg_trap
{
  /* source enterprise ID (sysObjectID) */
  const struct snmp_obj_id *enterprise;
  /* source IP address, raw network order format */
  ip_addr_t sip;
  /* generic trap code */
  u32_t gen_trap;
  /* specific trap code */
  u32_t spc_trap;
  /* timestamp */
  u32_t ts;
  /* snmp_version */
  u32_t snmp_version;

  /* output trap lengths used in ASN encoding */
  /* encoding pdu length */
  u16_t pdulen;
  /* encoding community length */
  u16_t comlen;
  /* encoding sequence length */
  u16_t seqlen;
  /* encoding varbinds sequence length */
  u16_t vbseqlen;

  /* error status */
  s32_t error_status;
  /* error index */
  s32_t error_index;
  /* trap or inform? */
  u8_t trap_or_inform;
};

static u16_t snmp_trap_varbind_sum(struct snmp_msg_trap *trap, struct snmp_varbind *varbinds);
static u16_t snmp_trap_header_sum(struct snmp_msg_trap *trap, u16_t vb_len);
static err_t snmp_trap_header_enc(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream);
static err_t snmp_trap_varbind_enc(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream, struct snmp_varbind *varbinds);
static u16_t snmp_trap_header_sum_v1_specific(struct snmp_msg_trap *trap);
static u16_t snmp_trap_header_sum_v2c_specific(struct snmp_msg_trap *trap);
static err_t snmp_trap_header_enc_v1_specific(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream);
static err_t snmp_trap_header_enc_v2c_specific(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream);
static err_t snmp_prepare_trap_oid(struct snmp_obj_id *dest_snmp_trap_oid, const struct snmp_obj_id *eoid, s32_t generic_trap, s32_t specific_trap);
static void snmp_prepare_necessary_msg_fields(struct snmp_msg_trap *trap_msg, const struct snmp_obj_id *eoid, s32_t generic_trap, s32_t specific_trap, struct snmp_varbind *varbinds);
static err_t snmp_send_msg(struct snmp_msg_trap *trap_msg, struct snmp_varbind *varbinds, u16_t tot_len, ip_addr_t *dip);

#define BUILD_EXEC(code) \
  if ((code) != ERR_OK) { \
    LWIP_DEBUGF(SNMP_DEBUG, ("SNMP error during creation of outbound trap frame!\n")); \
    return ERR_ARG; \
  }

/** Agent community string for sending traps */
extern const char *snmp_community_trap;

void *snmp_traps_handle;

/**
 * @ingroup snmp_traps
 * @struct snmp_trap_dst
 */
struct snmp_trap_dst
{
  /* destination IP address in network order */
  ip_addr_t dip;
  /* set to 0 when disabled, >0 when enabled */
  u8_t enable;
};
static struct snmp_trap_dst trap_dst[SNMP_TRAP_DESTINATIONS];

static u8_t snmp_auth_traps_enabled = 0;

/* This is used in functions like snmp_coldstart_trap where user didn't specify which version of trap to use */
static u8_t snmp_default_trap_version = SNMP_VERSION_1;

/* This is used in trap messages v2c */
static s32_t req_id = 1;

/**
 * @ingroup snmp_traps
 * Sets enable switch for this trap destination.
 * @param dst_idx index in 0 .. SNMP_TRAP_DESTINATIONS-1
 * @param enable switch if 0 destination is disabled >0 enabled.
 *
 */
void
snmp_trap_dst_enable(u8_t dst_idx, u8_t enable)
{
  LWIP_ASSERT_SNMP_LOCKED();
  if (dst_idx < SNMP_TRAP_DESTINATIONS) {
    trap_dst[dst_idx].enable = enable;
  }
}

/**
 * @ingroup snmp_traps
 * Sets IPv4 address for this trap destination.
 * @param dst_idx index in 0 .. SNMP_TRAP_DESTINATIONS-1
 * @param dst IPv4 address in host order.
 *
 */
void
snmp_trap_dst_ip_set(u8_t dst_idx, const ip_addr_t *dst)
{
  LWIP_ASSERT_SNMP_LOCKED();
  if (dst_idx < SNMP_TRAP_DESTINATIONS) {
    ip_addr_set(&trap_dst[dst_idx].dip, dst);
  }
}

/**
 * @ingroup snmp_traps
 * Enable/disable authentication traps
 *
 * @param enable enable SNMP traps
 *
 */
void
snmp_set_auth_traps_enabled(u8_t enable)
{
  snmp_auth_traps_enabled = enable;
}

/**
 * @ingroup snmp_traps
 * Get authentication traps enabled state
 *
 * @return TRUE if traps are enabled, FALSE if they aren't
 */
u8_t
snmp_get_auth_traps_enabled(void)
{
  return snmp_auth_traps_enabled;
}

/**
 * @ingroup snmp_traps
 * Choose default SNMP version for sending traps (if not specified, default version is SNMP_VERSION_1)
 * SNMP_VERSION_1  0
 * SNMP_VERSION_2c 1
 * SNMP_VERSION_3  3
 *
 * @param snmp_version version that will be used for sending traps
 *
 */
void
snmp_set_default_trap_version(u8_t snmp_version)
{
  snmp_default_trap_version = snmp_version;
}

/**
 * @ingroup snmp_traps
 * Get default SNMP version for sending traps
 *
 * @return selected default version:
 * 0 - SNMP_VERSION_1
 * 1 - SNMP_VERSION_2c
 * 3 - SNMP_VERSION_3
 */
u8_t
snmp_get_default_trap_version(void)
{
  return snmp_default_trap_version;
}

/**
 * @ingroup snmp_traps
 * Prepares snmpTrapOID for SNMP v2c
 * @param dest_snmp_trap_oid pointer to destination snmpTrapOID
 * @param eoid enterprise oid (can be NULL)
 * @param generic_trap SNMP v1 generic trap
 * @param specific_trap SNMP v1 specific trap
 * @return ERR_OK if completed successfully;
 *         ERR_MEM if there wasn't enough memory allocated for destination;
 *         ERR_VAL if value for generic trap was incorrect;
 */
static err_t
snmp_prepare_trap_oid(struct snmp_obj_id *dest_snmp_trap_oid, const struct snmp_obj_id *eoid, s32_t generic_trap, s32_t specific_trap)
{
  err_t err = ERR_OK;
  const u32_t snmpTrapOID[] = {1, 3, 6, 1, 6, 3, 1, 1, 5};     /* please see rfc3584 */

  if (generic_trap == SNMP_GENTRAP_ENTERPRISE_SPECIFIC) {
    if (eoid == NULL) {
      MEMCPY(dest_snmp_trap_oid, snmp_get_device_enterprise_oid(), sizeof(*dest_snmp_trap_oid));
    } else {
      MEMCPY(dest_snmp_trap_oid, eoid, sizeof(*dest_snmp_trap_oid));
    }
    if (dest_snmp_trap_oid->len + 2 < SNMP_MAX_OBJ_ID_LEN) {
      dest_snmp_trap_oid->id[dest_snmp_trap_oid->len++] = 0;
      dest_snmp_trap_oid->id[dest_snmp_trap_oid->len++] = specific_trap;
    } else {
      err = ERR_MEM;
    }
  } else if ((generic_trap >= SNMP_GENTRAP_COLDSTART) && (generic_trap < SNMP_GENTRAP_ENTERPRISE_SPECIFIC)) {
    if (sizeof(dest_snmp_trap_oid->id) >= sizeof(snmpTrapOID)) {
      MEMCPY(&dest_snmp_trap_oid->id, snmpTrapOID , sizeof(snmpTrapOID));
      dest_snmp_trap_oid->len = LWIP_ARRAYSIZE(snmpTrapOID);
      dest_snmp_trap_oid->id[dest_snmp_trap_oid->len++] = specific_trap + 1;
    } else {
      err = ERR_MEM;
    }
  } else {
    err = ERR_VAL;
  }
  return err;
}

/**
 * @ingroup snmp_traps
 * Prepare the rest of the necessary fields for trap/notification/inform message.
 * @param trap_msg message that should be set
 * @param eoid enterprise oid (can be NULL)
 * @param generic_trap SNMP v1 generic trap
 * @param specific_trap SNMP v1 specific trap
 * @param varbinds list of varbinds
 */
static void
snmp_prepare_necessary_msg_fields(struct snmp_msg_trap *trap_msg, const struct snmp_obj_id *eoid, s32_t generic_trap, s32_t specific_trap, struct snmp_varbind *varbinds)
{
  if (trap_msg->snmp_version == SNMP_VERSION_1) {
    trap_msg->enterprise = (eoid == NULL) ? snmp_get_device_enterprise_oid() : eoid;
    trap_msg->gen_trap = generic_trap;
    trap_msg->spc_trap = (generic_trap == SNMP_GENTRAP_ENTERPRISE_SPECIFIC) ? specific_trap : 0;
    MIB2_COPY_SYSUPTIME_TO(&trap_msg->ts);
  } else if (trap_msg->snmp_version == SNMP_VERSION_2c) {
    /* Copy sysUpTime into the first varbind */
    MIB2_COPY_SYSUPTIME_TO((u32_t *)varbinds[0].value);
  }
}

/**
 * @ingroup snmp_traps
 * Copy trap message structure to pbuf and sends it
 * @param trap_msg contains the data that should be sent
 * @param varbinds list of varbinds
 * @param tot_len total length of encoded data
 * @param dip destination IP address
 * @return ERR_OK if sending was successful
 */
static err_t
snmp_send_msg(struct snmp_msg_trap *trap_msg, struct snmp_varbind *varbinds, u16_t tot_len, ip_addr_t *dip)
{
  err_t err = ERR_OK;
  struct pbuf *p = NULL;
  /* allocate pbuf(s) */
  p = pbuf_alloc(PBUF_TRANSPORT, tot_len, PBUF_RAM);
  if (p != NULL) {
    struct snmp_pbuf_stream pbuf_stream;
    snmp_pbuf_stream_init(&pbuf_stream, p, 0, tot_len);

    /* pass 1, encode packet ino the pbuf(s) */
    BUILD_EXEC( snmp_trap_header_enc(trap_msg, &pbuf_stream) );
    BUILD_EXEC( snmp_trap_varbind_enc(trap_msg, &pbuf_stream, varbinds) );

    snmp_stats.outtraps++;
    snmp_stats.outpkts++;

    /** send to the TRAP destination */
    err = snmp_sendto(snmp_traps_handle, p, dip, LWIP_IANA_PORT_SNMP_TRAP);
    pbuf_free(p);
  } else {
    err = ERR_MEM;
  }
  return err;
}

/**
 * @ingroup snmp_traps
 * Prepare and sends a generic or enterprise specific trap message, notification or inform.
 *
 * @param trap_msg defines msg type
 * @param eoid points to enterprise object identifier
 * @param generic_trap is the trap code
 * @param specific_trap used for enterprise traps when generic_trap == 6
 * @param varbinds linked list of varbinds to be sent
 * @return ERR_OK when success, ERR_MEM if we're out of memory
 *
 * @note the use of the enterprise identifier field
 * is per RFC1215.
 * Use .iso.org.dod.internet.mgmt.mib-2.snmp for generic traps
 * and .iso.org.dod.internet.private.enterprises.yourenterprise
 * (sysObjectID) for specific traps.
 */
static err_t
snmp_send_trap_or_notification_or_inform_generic(struct snmp_msg_trap *trap_msg, const struct snmp_obj_id *eoid, s32_t generic_trap, s32_t specific_trap, struct snmp_varbind *varbinds)
{
  struct snmp_trap_dst *td = NULL;
  u16_t i = 0;
  u16_t tot_len = 0;
  err_t err = ERR_OK;
  u32_t timestamp = 0;
  struct snmp_obj_id snmp_trap_oid = { 0 };  /* used for converting SNMPv1 generic/specific trap parameter to SNMPv2 snmpTrapOID */
  struct snmp_varbind snmp_v2_special_varbinds[] = {
                                                     /* First varbind is used to store sysUpTime */
                                                     {
                                                       NULL,                            /* *next */
                                                       {                                /* oid */
                                                         8,                             /* oid len */
                                                         {1, 3, 6, 1, 2, 1, 1, 3}       /* oid for sysUpTime */
                                                       },
                                                       SNMP_ASN1_TYPE_TIMETICKS,        /* type */
                                                       sizeof(u32_t),                   /* value_len */
                                                       NULL                             /* value */
                                                     },
                                                     /* Second varbind is used to store snmpTrapOID */
                                                     {
                                                       NULL,                            /* *next */
                                                       {                                /* oid */
                                                         10,                            /* oid len */
                                                         {1, 3, 6, 1, 6, 3, 1, 1, 4, 1} /* oid for snmpTrapOID */
                                                       },
                                                       SNMP_ASN1_TYPE_OBJECT_ID,        /* type */
                                                       0,                               /* value_len */
                                                       NULL                             /* value */
                                                     }
   };

  LWIP_ASSERT_SNMP_LOCKED();

  snmp_v2_special_varbinds[0].next = &snmp_v2_special_varbinds[1];

  snmp_v2_special_varbinds[0].value = &timestamp;

  snmp_v2_special_varbinds[1].next = varbinds;

  /* see rfc3584 */
  if (trap_msg->snmp_version == SNMP_VERSION_2c) {
    err = snmp_prepare_trap_oid(&snmp_trap_oid, eoid, generic_trap, specific_trap);
    if (err == ERR_OK) {
      snmp_v2_special_varbinds[1].value_len = snmp_trap_oid.len * sizeof(snmp_trap_oid.id[0]);
      snmp_v2_special_varbinds[1].value = snmp_trap_oid.id;
      varbinds = snmp_v2_special_varbinds;  /* After inserting two varbinds at the beginning of the list, make sure that pointer is pointing to the first element  */
    }
  }

  for (i = 0, td = &trap_dst[0]; (i < SNMP_TRAP_DESTINATIONS) && (err == ERR_OK); i++, td++) {
    if ((td->enable != 0) && !ip_addr_isany(&td->dip)) {
      /* lookup current source address for this dst */
      if (snmp_get_local_ip_for_dst(snmp_traps_handle, &td->dip, &trap_msg->sip)) {
        snmp_prepare_necessary_msg_fields(trap_msg, eoid, generic_trap, specific_trap, varbinds);

        /* pass 0, calculate length fields */
        tot_len = snmp_trap_varbind_sum(trap_msg, varbinds);
        tot_len = snmp_trap_header_sum(trap_msg, tot_len);

        /* allocate pbuf, fill it and send it */
        err = snmp_send_msg(trap_msg, varbinds, tot_len, &td->dip);
      } else {
        /* routing error */
        err = ERR_RTE;
      }
    }
  }
  req_id++;
  return err;
}

/**
 * @ingroup snmp_traps
 * This function is a wrapper function for preparing and sending generic or specific traps.
 *
 * @param oid points to enterprise object identifier
 * @param generic_trap is the trap code
 * @param specific_trap used for enterprise traps when generic_trap == 6
 * @param varbinds linked list of varbinds to be sent
 * @return ERR_OK when success, ERR_MEM if we're out of memory
 *
 * @note the use of the enterprise identifier field
 * is per RFC1215.
 * Use .iso.org.dod.internet.mgmt.mib-2.snmp for generic traps
 * and .iso.org.dod.internet.private.enterprises.yourenterprise
 * (sysObjectID) for specific traps.
 */
err_t
snmp_send_trap(const struct snmp_obj_id* oid, s32_t generic_trap, s32_t specific_trap, struct snmp_varbind *varbinds)
{
  struct snmp_msg_trap trap_msg = {0};
  trap_msg.snmp_version = snmp_default_trap_version;
  trap_msg.trap_or_inform = SNMP_IS_TRAP;
  return snmp_send_trap_or_notification_or_inform_generic(&trap_msg, oid, generic_trap, specific_trap, varbinds);
}

/**
 * @ingroup snmp_traps
 * Send generic SNMP trap
 * @param generic_trap is the trap code
 * return ERR_OK when success
 */
err_t
snmp_send_trap_generic(s32_t generic_trap)
{
  err_t err = ERR_OK;
  struct snmp_msg_trap trap_msg = {0};
  trap_msg.snmp_version = snmp_default_trap_version;
  trap_msg.trap_or_inform = SNMP_IS_TRAP;

  if(snmp_default_trap_version == SNMP_VERSION_1) {
    static const struct snmp_obj_id oid = { 7, { 1, 3, 6, 1, 2, 1, 11 } };
    err = snmp_send_trap_or_notification_or_inform_generic(&trap_msg, &oid, generic_trap, 0, NULL);
  } else if (snmp_default_trap_version == SNMP_VERSION_2c) {
    err = snmp_send_trap_or_notification_or_inform_generic(&trap_msg, NULL, generic_trap, 0, NULL);
  } else {
    err = ERR_VAL;
  }
  return err;
}

/**
 * @ingroup snmp_traps
 * Send specific SNMP trap with variable bindings
 * @param specific_trap used for enterprise traps (generic_trap = 6)
 * @param varbinds linked list of varbinds to be sent
 * @return ERR_OK when success
 */
err_t
snmp_send_trap_specific(s32_t specific_trap, struct snmp_varbind *varbinds)
{
  struct snmp_msg_trap trap_msg = {0};
  trap_msg.snmp_version = snmp_default_trap_version;
  trap_msg.trap_or_inform = SNMP_IS_TRAP;
  return snmp_send_trap_or_notification_or_inform_generic(&trap_msg, NULL, SNMP_GENTRAP_ENTERPRISE_SPECIFIC, specific_trap, varbinds);
}

/**
 * @ingroup snmp_traps
 * Send coldstart trap
 */
void
snmp_coldstart_trap(void)
{
  snmp_send_trap_generic(SNMP_GENTRAP_COLDSTART);
}

/**
 * @ingroup snmp_traps
 * Send authentication failure trap (used internally by agent)
 */
void
snmp_authfail_trap(void)
{
  if (snmp_auth_traps_enabled != 0) {
    snmp_send_trap_generic(SNMP_GENTRAP_AUTH_FAILURE);
  }
}

/**
 * @ingroup snmp_traps
 * Sums trap varbinds
 *
 * @param trap Trap message
 * @param varbinds linked list of varbinds
 * @return the required length for encoding of this part of the trap header
 */
static u16_t
snmp_trap_varbind_sum(struct snmp_msg_trap *trap, struct snmp_varbind *varbinds)
{
  struct snmp_varbind *varbind;
  u16_t tot_len;
  u8_t tot_len_len;

  tot_len = 0;
  varbind = varbinds;
  while (varbind != NULL) {
    struct snmp_varbind_len len;

    if (snmp_varbind_length(varbind, &len) == ERR_OK) {
      tot_len += 1 + len.vb_len_len + len.vb_value_len;
    }

    varbind = varbind->next;
  }

  trap->vbseqlen = tot_len;
  snmp_asn1_enc_length_cnt(trap->vbseqlen, &tot_len_len);
  tot_len += 1 + tot_len_len;

  return tot_len;
}

/**
 * @ingroup snmp_traps
 * Sums trap header fields that are specific for SNMP v1
 *
 * @param trap Trap message
 * @return the required length for encoding of this part of the trap header
 */
static u16_t
snmp_trap_header_sum_v1_specific(struct snmp_msg_trap *trap)
{
  u16_t tot_len = 0;
  u16_t len = 0;
  u8_t lenlen = 0;

  snmp_asn1_enc_u32t_cnt(trap->ts, &len);
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;

  snmp_asn1_enc_s32t_cnt(trap->spc_trap, &len);
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;

  snmp_asn1_enc_s32t_cnt(trap->gen_trap, &len);
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;

  if (IP_IS_V6_VAL(trap->sip)) {
#if LWIP_IPV6
    len = sizeof(ip_2_ip6(&trap->sip)->addr);
#endif
  } else {
#if LWIP_IPV4
    len = sizeof(ip_2_ip4(&trap->sip)->addr);
#endif
  }
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;

  snmp_asn1_enc_oid_cnt(trap->enterprise->id, trap->enterprise->len, &len);
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;

  return tot_len;
}

/**
 * @ingroup snmp_traps
 * Sums trap header fields that are specific for SNMP v2c
 *
 * @param trap Trap message
 * @return the required length for encoding of this part of the trap header
 */
static u16_t
snmp_trap_header_sum_v2c_specific(struct snmp_msg_trap *trap)
{
  u16_t tot_len = 0;
  u16_t len = 0;
  u8_t lenlen = 0;

  snmp_asn1_enc_u32t_cnt(req_id, &len);
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;
  snmp_asn1_enc_u32t_cnt(trap->error_status, &len);
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;
  snmp_asn1_enc_u32t_cnt(trap->error_index, &len);
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;

  return tot_len;
}

/**
 * @ingroup snmp_traps
 * Sums trap header field lengths from tail to head and
 * returns trap_header_lengths for second encoding pass.
 *
 * @param trap Trap message
 * @param vb_len varbind-list length
 * @return the required length for encoding the trap header
 */
static u16_t
snmp_trap_header_sum(struct snmp_msg_trap *trap, u16_t vb_len)
{
  u16_t tot_len = vb_len;
  u16_t len = 0;
  u8_t lenlen = 0;

  if (trap->snmp_version == SNMP_VERSION_1) {
    tot_len += snmp_trap_header_sum_v1_specific(trap);
  } else if (trap->snmp_version == SNMP_VERSION_2c) {
    tot_len += snmp_trap_header_sum_v2c_specific(trap);
  }
  trap->pdulen = tot_len;
  snmp_asn1_enc_length_cnt(trap->pdulen, &lenlen);
  tot_len += 1 + lenlen;

  trap->comlen = (u16_t)LWIP_MIN(strlen(snmp_community_trap), 0xFFFF);
  snmp_asn1_enc_length_cnt(trap->comlen, &lenlen);
  tot_len += 1 + lenlen + trap->comlen;

  snmp_asn1_enc_s32t_cnt(trap->snmp_version, &len);
  snmp_asn1_enc_length_cnt(len, &lenlen);
  tot_len += 1 + len + lenlen;

  trap->seqlen = tot_len;
  snmp_asn1_enc_length_cnt(trap->seqlen, &lenlen);
  tot_len += 1 + lenlen;

  return tot_len;
}

/**
 * @ingroup snmp_traps
 * Encodes varbinds.
 * @param trap Trap message
 * @param pbuf_stream stream used for storing data inside pbuf
 * @param varbinds linked list of varbinds
 * @retval err_t ERR_OK if successful, ERR_ARG otherwise
 */
static err_t
snmp_trap_varbind_enc(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream, struct snmp_varbind *varbinds)
{
  struct snmp_asn1_tlv tlv;
  struct snmp_varbind *varbind;

  varbind = varbinds;

  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 0, trap->vbseqlen);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );

  while (varbind != NULL) {
    BUILD_EXEC( snmp_append_outbound_varbind(pbuf_stream, varbind) );

    varbind = varbind->next;
  }

  return ERR_OK;
}

/**
 * @ingroup snmp_traps
 * Encodes trap header PDU part.
 * @param trap Trap message
 * @param pbuf_stream stream used for storing data inside pbuf
 * @retval err_t ERR_OK if successful, ERR_ARG otherwise
 */
static err_t
snmp_trap_header_enc_pdu(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream)
{
  struct snmp_asn1_tlv tlv;
  /* 'PDU' sequence */
  if (trap->snmp_version == SNMP_VERSION_1) {
    /* TRAP V1 */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_TRAP), 0, trap->pdulen);
    BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  } else if ((trap->snmp_version == SNMP_VERSION_2c) && (trap->trap_or_inform == SNMP_IS_INFORM)) {
    /* TRAP v2 - INFORM */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_INFORM_REQ), 0, trap->pdulen);
    BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  } else if (trap->snmp_version == SNMP_VERSION_2c) {
    /* TRAP v2 - NOTIFICATION*/
    SNMP_ASN1_SET_TLV_PARAMS(tlv, (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_V2_TRAP), 0, trap->pdulen);
    BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  }

  return ERR_OK;
}

/**
 * @ingroup snmp_traps
 * Encodes trap header part that is SNMP v1 header specific.
 * @param trap Trap message
 * @param pbuf_stream stream used for storing data inside pbuf
 */
static err_t
snmp_trap_header_enc_v1_specific(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream)
{
  struct snmp_asn1_tlv tlv;
  /* object ID */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OBJECT_ID, 0, 0);
  snmp_asn1_enc_oid_cnt(trap->enterprise->id, trap->enterprise->len, &tlv.value_len);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_oid(pbuf_stream, trap->enterprise->id, trap->enterprise->len) );

  /* IP addr */
  if (IP_IS_V6_VAL(trap->sip)) {
#if LWIP_IPV6
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_IPADDR, 0, sizeof(ip_2_ip6(&trap->sip)->addr));
    BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
    BUILD_EXEC( snmp_asn1_enc_raw(pbuf_stream, (const u8_t *)&ip_2_ip6(&trap->sip)->addr, sizeof(ip_2_ip6(&trap->sip)->addr)) );
#endif
  } else {
#if LWIP_IPV4
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_IPADDR, 0, sizeof(ip_2_ip4(&trap->sip)->addr));
    BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
    BUILD_EXEC( snmp_asn1_enc_raw(pbuf_stream, (const u8_t *)&ip_2_ip4(&trap->sip)->addr, sizeof(ip_2_ip4(&trap->sip)->addr)) );
#endif
  }

  /* generic trap */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
  snmp_asn1_enc_s32t_cnt(trap->gen_trap, &tlv.value_len);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, trap->gen_trap) );

  /* specific trap */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
  snmp_asn1_enc_s32t_cnt(trap->spc_trap, &tlv.value_len);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, trap->spc_trap) );

  /* timestamp */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_TIMETICKS, 0, 0);
  snmp_asn1_enc_s32t_cnt(trap->ts, &tlv.value_len);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, trap->ts) );

  return ERR_OK;
}

/**
 * @ingroup snmp_traps
 * Encodes trap header part that is SNMP v2c header specific.
 *
 * @param trap Trap message
 * @param pbuf_stream stream used for storing data inside pbuf
 */
static err_t
snmp_trap_header_enc_v2c_specific(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream)
{
  struct snmp_asn1_tlv tlv;
  /* request id */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
  snmp_asn1_enc_s32t_cnt(req_id, &tlv.value_len);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, req_id) );

  /* error status */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
  snmp_asn1_enc_s32t_cnt(trap->error_status, &tlv.value_len);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, trap->error_status) );

  /* error index */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
  snmp_asn1_enc_s32t_cnt(trap->error_index, &tlv.value_len);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, trap->error_index) );

  return ERR_OK;
}

/**
 * @ingroup snmp_traps
 * Encodes trap header from head to tail.
 *
 * @param trap Trap message
 * @param pbuf_stream stream used for storing data inside pbuf
 */
static err_t
snmp_trap_header_enc(struct snmp_msg_trap *trap, struct snmp_pbuf_stream *pbuf_stream)
{
  struct snmp_asn1_tlv tlv;

  /* 'Message' sequence */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 0, trap->seqlen);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );

  /* version */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
  snmp_asn1_enc_s32t_cnt(trap->snmp_version, &tlv.value_len);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, trap->snmp_version) );

  /* community */
  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, trap->comlen);
  BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
  BUILD_EXEC( snmp_asn1_enc_raw(pbuf_stream,  (const u8_t *)snmp_community_trap, trap->comlen) );

  /* PDU */
  BUILD_EXEC( snmp_trap_header_enc_pdu(trap, pbuf_stream) );
  if (trap->snmp_version == SNMP_VERSION_1) {
    /* object ID, IP addr, generic trap, specific trap, timestamp */
    BUILD_EXEC( snmp_trap_header_enc_v1_specific(trap, pbuf_stream) );
  } else if (SNMP_VERSION_2c == trap->snmp_version) {
    /* request id, error status, error index */
    BUILD_EXEC( snmp_trap_header_enc_v2c_specific(trap, pbuf_stream) );
  }

  return ERR_OK;
}

/**
 * @ingroup snmp_traps
 * Wrapper function for sending informs
 * @param specific_trap will be appended to enterprise oid [see RFC 3584]
 * @param varbinds linked list of varbinds (at the beginning of this list function will insert 2 special purpose varbinds [see RFC 3584])
 * @param ptr_request_id [out] variable in which to store request_id needed to verify acknowledgement
 * @return ERR_OK if successful
 */
err_t
snmp_send_inform_specific(s32_t specific_trap, struct snmp_varbind *varbinds, s32_t *ptr_request_id)
{
  return snmp_send_inform(NULL, SNMP_GENTRAP_ENTERPRISE_SPECIFIC, specific_trap, varbinds, ptr_request_id);
}

/**
 * @ingroup snmp_traps
 * Wrapper function for sending informs
 * @param generic_trap is the trap code
 * @param varbinds linked list of varbinds (at the beginning of this list function will insert 2 special purpose varbinds [see RFC 3584])
 * @param ptr_request_id [out] variable in which to store request_id needed to verify acknowledgement
 * @return ERR_OK if successful
 */
err_t
snmp_send_inform_generic(s32_t generic_trap, struct snmp_varbind *varbinds, s32_t *ptr_request_id)
{
  return snmp_send_inform(NULL, generic_trap, 0, varbinds, ptr_request_id);
}

/**
 * @ingroup snmp_traps
 * Generic function for sending informs
 * @param oid points to object identifier
 * @param generic_trap is the trap code
 * @param specific_trap used for enterprise traps when generic_trap == 6
 * @param varbinds linked list of varbinds (at the beginning of this list function will insert 2 special purpose varbinds [see RFC 3584])
 * @param ptr_request_id [out] variable in which to store request_id needed to verify acknowledgement
 * @return ERR_OK if successful
 */
err_t
snmp_send_inform(const struct snmp_obj_id* oid, s32_t generic_trap, s32_t specific_trap, struct snmp_varbind *varbinds, s32_t *ptr_request_id)
{
  struct snmp_msg_trap trap_msg = {0};
  trap_msg.snmp_version = SNMP_VERSION_2c;
  trap_msg.trap_or_inform = SNMP_IS_INFORM;
  *ptr_request_id = req_id;
  return snmp_send_trap_or_notification_or_inform_generic(&trap_msg, oid, generic_trap, specific_trap, varbinds);
}

#endif /* LWIP_SNMP */