Diff: lwip/core/snmp/msg_out.c

Revision:

0:2a53a4c3238c

Child:

2:25e12a7fe0aa

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lwip/core/snmp/msg_out.c	Mon Aug 13 15:07:40 2012 +0000
@@ -0,0 +1,853 @@
+/*****************************************************************************
+*                     Copyright Field Electronics Ltd
+* File:             msg_out.c
+* Reference:        3000-A3600-HDR-msg_out
+* Content:          Builds SNMP output messages
+* Version:          0.5
+* System:           mbed gnu compiler
+* Target Hardware:  mbed LPC1768                                  
+* Amendment Record:    
+* Author:      L. Smith for all versions unless otherwise specified 
+* Initial release
+* 0.1         26/04/12: L. Smith
+  Derived from msg_out.c by Christiaan Simons <christiaan.simons@axon.tv>
+  Allow variable length snmp_publiccommunity up to 20 characters 
+* 0.2         08/06/12: L. Smith
+  Define snmp_linkdown_trap() & snmp_linkup_trap()
+* 0.3         19/06/12: L. Smith
+  Define snmp_SPIdown_trap() & snmp_SPIup_trap() and f3kIOchange_trap()
+* 0.4         25/07/12: L. Smith
+  Declare struct snmp_varbind io_var for sending f3kIOchange_trap() 
+* 0.5         03/08/12: L. Smith
+  Add f3kIOalarm_trap() and struct snmp_varbind io_alarm for IO alarm messages
+*******************************************************************************/
+/**
+ * @file
+ * SNMP output message processing (RFC1157).
+ *
+ * Output responses and traps are build in two passes:
+ *
+ * Pass 0: iterate over the output message backwards to determine encoding lengths
+ * Pass 1: the actual forward encoding of internal form into ASN1
+ *
+ * The single-pass encoding method described by Comer & Stevens
+ * requires extra buffer space and copying for reversal of the packet.
+ * The buffer requirement can be prohibitively large for big payloads
+ * (>= 484) therefore we use the two encoding passes.
+ */
+
+/*
+ * Copyright (c) 2006 Axon Digital Design B.V., The Netherlands.
+ * 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.
+ *
+ * Author: Christiaan Simons <christiaan.simons@axon.tv>
+ */
+
+#include "lwip/opt.h"
+
+#if LWIP_SNMP /* don't build if not configured for use in lwipopts.h */
+
+#include "lwip/udp.h"
+#include "lwip/netif.h"
+#include "lwip/snmp.h"
+#include "lwip/snmp_asn1.h"
+#include "lwip/snmp_msg.h"
+#include "private_mib.h"
+
+/** v0.5: enterprise ID for enterprise specific TRAPs */
+const struct snmp_obj_id snmptrap_id = {7,{1,3,6,1,4,1,SNMP_ENTERPRISE_ID}};
+
+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;
+};
+struct snmp_trap_dst trap_dst[SNMP_TRAP_DESTINATIONS];
+
+/** TRAP message structure */
+struct snmp_msg_trap trap_msg;
+
+/** v0.4: TRAP IO variable structure */
+struct snmp_varbind io_var;
+/** v0.5: TRAP IO alarm message variable structures */
+struct snmp_varbind al_var;
+struct snmp_varbind io_alarm;
+
+static u16_t snmp_resp_header_sum(struct snmp_msg_pstat *m_stat, u16_t vb_len);
+static u16_t snmp_trap_header_sum(struct snmp_msg_trap *m_trap, u16_t vb_len);
+static u16_t snmp_varbind_list_sum(struct snmp_varbind_root *root);
+
+static u16_t snmp_resp_header_enc(struct snmp_msg_pstat *m_stat, struct pbuf *p);
+static u16_t snmp_trap_header_enc(struct snmp_msg_trap *m_trap, struct pbuf *p);
+static u16_t snmp_varbind_list_enc(struct snmp_varbind_root *root, struct pbuf *p, u16_t ofs);
+
+/**
+ * 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)
+{
+  if (dst_idx < SNMP_TRAP_DESTINATIONS)
+  {
+printf("Trap %d enabled", dst_idx);
+    trap_dst[dst_idx].enable = enable;
+  }
+}
+
+/**
+ * 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, ip_addr_t *dst)
+{
+  if (dst_idx < SNMP_TRAP_DESTINATIONS)
+  {
+    ip_addr_set(&trap_dst[dst_idx].dip, dst);
+  }
+}
+
+/**
+ * Sends a 'getresponse' message to the request originator.
+ *
+ * @param m_stat points to the current message request state source
+ * @return ERR_OK when success, ERR_MEM if we're out of memory
+ *
+ * @note the caller is responsible for filling in outvb in the m_stat
+ * and provide error-status and index (except for tooBig errors) ...
+ */
+err_t
+snmp_send_response(struct snmp_msg_pstat *m_stat)
+{
+  struct snmp_varbind_root emptyvb = {NULL, NULL, 0, 0, 0};
+  struct pbuf *p;
+  u16_t tot_len;
+  err_t err;
+
+  /* pass 0, calculate length fields */
+  tot_len = snmp_varbind_list_sum(&m_stat->outvb);
+  tot_len = snmp_resp_header_sum(m_stat, tot_len);
+
+  /* try allocating pbuf(s) for complete response */
+  p = pbuf_alloc(PBUF_TRANSPORT, tot_len, PBUF_POOL);
+  if (p == NULL)
+  {
+    LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_snd_response() tooBig\n"));
+
+    /* can't construct reply, return error-status tooBig */
+    m_stat->error_status = SNMP_ES_TOOBIG;
+    m_stat->error_index = 0;
+    /* pass 0, recalculate lengths, for empty varbind-list */
+    tot_len = snmp_varbind_list_sum(&emptyvb);
+    tot_len = snmp_resp_header_sum(m_stat, tot_len);
+    /* retry allocation once for header and empty varbind-list */
+    p = pbuf_alloc(PBUF_TRANSPORT, tot_len, PBUF_POOL);
+  }
+  if (p != NULL)
+  {
+    /* first pbuf alloc try or retry alloc success */
+    u16_t ofs;
+
+    LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_snd_response() p != NULL\n"));
+
+    /* pass 1, size error, encode packet ino the pbuf(s) */
+    ofs = snmp_resp_header_enc(m_stat, p);
+    if (m_stat->error_status == SNMP_ES_TOOBIG)
+    {
+      snmp_varbind_list_enc(&emptyvb, p, ofs);
+    }
+    else
+    {
+      snmp_varbind_list_enc(&m_stat->outvb, p, ofs);
+    }
+
+    switch (m_stat->error_status)
+    {
+      case SNMP_ES_TOOBIG:
+        snmp_inc_snmpouttoobigs();
+        break;
+      case SNMP_ES_NOSUCHNAME:
+        snmp_inc_snmpoutnosuchnames();
+        break;
+      case SNMP_ES_BADVALUE:
+        snmp_inc_snmpoutbadvalues();
+        break;
+      case SNMP_ES_GENERROR:
+        snmp_inc_snmpoutgenerrs();
+        break;
+    }
+    snmp_inc_snmpoutgetresponses();
+    snmp_inc_snmpoutpkts();
+
+    /** @todo do we need separate rx and tx pcbs for threaded case? */
+    /** connect to the originating source */
+    udp_connect(m_stat->pcb, &m_stat->sip, m_stat->sp);
+    err = udp_send(m_stat->pcb, p);
+    if (err == ERR_MEM)
+    {
+      /** @todo release some memory, retry and return tooBig? tooMuchHassle? */
+      err = ERR_MEM;
+    }
+    else
+    {
+      err = ERR_OK;
+    }
+    /** disassociate remote address and port with this pcb */
+    udp_disconnect(m_stat->pcb);
+
+    pbuf_free(p);
+    LWIP_DEBUGF(SNMP_MSG_DEBUG, ("snmp_snd_response() done\n"));
+    return err;
+  }
+  else
+  {
+    /* first pbuf alloc try or retry alloc failed
+       very low on memory, couldn't return tooBig */
+    return ERR_MEM;
+  }
+}
+
+
+/**
+ * Sends an generic or enterprise specific trap message.
+ *
+ * @param generic_trap is the trap code
+ * @param eoid points to enterprise object identifier
+ * @param specific_trap used for enterprise traps when generic_trap == 6
+ * @return ERR_OK when success, ERR_MEM if we're out of memory
+ *
+ * @note the caller is responsible for filling in outvb in the trap_msg
+ * @note the use of the enterpise 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(s8_t generic_trap, struct snmp_obj_id *eoid, s32_t specific_trap)
+{
+  struct snmp_trap_dst *td;
+  struct netif *dst_if;
+  ip_addr_t dst_ip;
+  struct pbuf *p;
+  u16_t i,tot_len;
+
+  for (i=0, td = &trap_dst[0]; i<SNMP_TRAP_DESTINATIONS; i++, td++)
+  {
+printf("\r\nsnmp_send_trap: generic trap %d, %d \r\n", generic_trap, specific_trap );
+    if ((td->enable != 0) && !ip_addr_isany(&td->dip))
+    {
+      /* network order trap destination */
+      ip_addr_copy(trap_msg.dip, td->dip);
+printf("trap_msg.dip %d.%d.%d.%d\r\n", ip4_addr1(&trap_msg.dip), ip4_addr2(&trap_msg.dip), ip4_addr3(&trap_msg.dip), ip4_addr4(&trap_msg.dip));
+      /* lookup current source address for this dst */
+      dst_if = ip_route(&td->dip);
+      ip_addr_copy(dst_ip, dst_if->ip_addr);
+      /* @todo: what about IPv6? */
+      trap_msg.sip_raw[0] = ip4_addr1(&dst_ip);
+      trap_msg.sip_raw[1] = ip4_addr2(&dst_ip);
+      trap_msg.sip_raw[2] = ip4_addr3(&dst_ip);
+      trap_msg.sip_raw[3] = ip4_addr4(&dst_ip);
+//printf("snmp_send_trap: source ip %d.%d.%d.%d\r\n", trap_msg.sip_raw[0], trap_msg.sip_raw[1], trap_msg.sip_raw[2], trap_msg.sip_raw[3]);
+      trap_msg.gen_trap = generic_trap;
+      trap_msg.spc_trap = specific_trap;
+      if (generic_trap == SNMP_GENTRAP_ENTERPRISESPC)
+      {
+        /* enterprise-Specific trap */
+        trap_msg.enterprise = eoid;
+      }
+      else
+      {
+        /* generic (MIB-II) trap */
+        snmp_get_snmpgrpid_ptr(&trap_msg.enterprise);
+      }
+      snmp_get_sysuptime(&trap_msg.ts);
+
+      /* pass 0, calculate length fields */
+      tot_len = snmp_varbind_list_sum(&trap_msg.outvb);
+      tot_len = snmp_trap_header_sum(&trap_msg, tot_len);
+//printf("\r\nsnmp_send_trap: tot_len inc header %d", tot_len);
+
+      /* allocate pbuf(s) */
+      p = pbuf_alloc(PBUF_TRANSPORT, tot_len, PBUF_POOL);
+      if (p != NULL)
+      {
+        u16_t ofs;
+
+        /* pass 1, encode packet ino the pbuf(s) */
+        ofs = snmp_trap_header_enc(&trap_msg, p);
+        snmp_varbind_list_enc(&trap_msg.outvb, p, ofs);
+printf("\r\nsnmp_send_trap: ofs %d tot_len % d\r\n", ofs, tot_len);
+
+        snmp_inc_snmpouttraps();
+        snmp_inc_snmpoutpkts();
+
+//    udp_connect(trap_msg.pcb, (ip_addr_t *)&trap_msg.sip_raw[0], SNMP_TRAP_PORT); // added here
+    /** LS: udp_connect to destination not required */ 
+        udp_sendto(trap_msg.pcb, p, &trap_msg.dip, SNMP_TRAP_PORT); 
+//    udp_disconnect(trap_msg.pcb);  
+
+        pbuf_free(p);
+      }
+      else
+      {
+        return ERR_MEM;
+      }
+    }
+  }
+  return ERR_OK;
+}
+
+void
+snmp_coldstart_trap(void)
+{
+  trap_msg.outvb.head = NULL;
+  trap_msg.outvb.tail = NULL;
+  trap_msg.outvb.count = 0;
+  snmp_send_trap(SNMP_GENTRAP_COLDSTART, NULL, 0);
+}
+
+/****************************************************************************/ 
+/*              snmp_linkdown_trap: v0.2
+* Description:  sends linkdown trap message with no OID for source
+* Globals used: trap_msg
+* Parameters:   NONE
+* Returns:      NONE
+*/
+/****************************************************************************/ 
+void
+snmp_linkdown_trap(void)
+{
+  trap_msg.outvb.head = NULL;
+  trap_msg.outvb.tail = NULL;
+  trap_msg.outvb.count = 0;
+  snmp_send_trap(SNMP_GENTRAP_LINK_DOWN, NULL, 0);
+}
+
+/****************************************************************************/ 
+/*              snmp_linkup_trap: v0.2
+* Description:  sends linkup trap message with no OID for source
+* Globals used: trap_msg
+* Parameters:   NONE
+* Returns:      NONE
+*/
+/****************************************************************************/ 
+void
+snmp_linkup_trap(void)
+{
+  trap_msg.outvb.head = NULL;
+  trap_msg.outvb.tail = NULL;
+  trap_msg.outvb.count = 0;
+  snmp_send_trap(SNMP_GENTRAP_LINK_UP, NULL, 0);
+}
+
+void
+snmp_authfail_trap(void)
+{
+  u8_t enable;
+  snmp_get_snmpenableauthentraps(&enable);
+  if (enable == 1)
+  {
+    trap_msg.outvb.head = NULL;
+    trap_msg.outvb.tail = NULL;
+    trap_msg.outvb.count = 0;
+    snmp_send_trap(SNMP_GENTRAP_AUTHFAIL, NULL, 0);
+  }
+}
+
+
+/****************************************************************************/ 
+/*              f3kIOchange_trap: v0.3
+* Description:  sends general IO changed trap message
+* Globals used: trap_msg
+* Parameters:   NONE
+* Returns:      NONE
+*/
+/****************************************************************************/ 
+void f3kIOchange_trap( void )
+{
+  trap_msg.outvb.head = &io_var;
+  trap_msg.outvb.tail = &io_var;
+  trap_msg.outvb.count = 1;
+  snmp_send_trap(SNMP_GENTRAP_ENTERPRISESPC, (snmp_obj_id *)&snmptrap_id, SNMP_SPCTRAP_IO_CHANGE);
+}
+
+/****************************************************************************/ 
+/*              snmp_SPIdown_trap: v0.3
+* Description:  sends SPIdown trap message
+* Globals used: trap_msg
+* Parameters:   NONE
+* Returns:      NONE
+*/
+/****************************************************************************/ 
+void snmp_SPIdown_trap( void )
+{
+  trap_msg.outvb.head = NULL;
+  trap_msg.outvb.tail = NULL;
+  trap_msg.outvb.count = 0;
+  snmp_send_trap(SNMP_GENTRAP_ENTERPRISESPC, (snmp_obj_id *)&snmptrap_id, SNMP_SPCTRAP_SPI_DOWN);
+}
+
+/****************************************************************************/ 
+/*              snmp_SPIup_trap: v0.3
+* Description:  sends SPI up trap message
+* Globals used: trap_msg
+* Parameters:   NONE
+* Returns:      NONE
+*/
+/****************************************************************************/ 
+void snmp_SPIup_trap( void )
+{
+  trap_msg.outvb.head = NULL;
+  trap_msg.outvb.tail = NULL;
+  trap_msg.outvb.count = 0;
+  snmp_send_trap(SNMP_GENTRAP_ENTERPRISESPC, (snmp_obj_id *)&snmptrap_id, SNMP_SPCTRAP_SPI_UP);
+}
+
+/****************************************************************************/ 
+/*              f3kIOalarm_trap: v0.5
+* Description:  sends alarm trap message
+* Globals used: trap_msg
+* Parameters:   NONE
+* Returns:      NONE
+*/
+/****************************************************************************/ 
+void f3kIOalarm_trap( void )
+{
+  trap_msg.outvb.head = &al_var;
+  trap_msg.outvb.tail = &io_alarm;
+  trap_msg.outvb.count = 1;
+  snmp_send_trap(SNMP_GENTRAP_ENTERPRISESPC, (snmp_obj_id *)&snmptrap_id, SNMP_SPCTRAP_IO_ALARM);
+}
+
+
+/**
+ * Sums response header field lengths from tail to head and
+ * returns resp_header_lengths for second encoding pass.
+ *
+ * @param vb_len varbind-list length
+ * @param rhl points to returned header lengths
+ * @return the required lenght for encoding the response header
+ */
+static u16_t
+snmp_resp_header_sum(struct snmp_msg_pstat *m_stat, u16_t vb_len)
+{
+  u16_t tot_len;
+  struct snmp_resp_header_lengths *rhl;
+
+  rhl = &m_stat->rhl;
+  tot_len = vb_len;
+  snmp_asn1_enc_s32t_cnt(m_stat->error_index, &rhl->erridxlen);
+  snmp_asn1_enc_length_cnt(rhl->erridxlen, &rhl->erridxlenlen);
+  tot_len += 1 + rhl->erridxlenlen + rhl->erridxlen;
+
+  snmp_asn1_enc_s32t_cnt(m_stat->error_status, &rhl->errstatlen);
+  snmp_asn1_enc_length_cnt(rhl->errstatlen, &rhl->errstatlenlen);
+  tot_len += 1 + rhl->errstatlenlen + rhl->errstatlen;
+
+  snmp_asn1_enc_s32t_cnt(m_stat->rid, &rhl->ridlen);
+  snmp_asn1_enc_length_cnt(rhl->ridlen, &rhl->ridlenlen);
+  tot_len += 1 + rhl->ridlenlen + rhl->ridlen;
+
+  rhl->pdulen = tot_len;
+  snmp_asn1_enc_length_cnt(rhl->pdulen, &rhl->pdulenlen);
+  tot_len += 1 + rhl->pdulenlen;
+
+//printf("\r\n community length %d\r\n", m_stat->com_strlen); // debug
+
+  rhl->comlen = m_stat->com_strlen;
+  snmp_asn1_enc_length_cnt(rhl->comlen, &rhl->comlenlen);
+  tot_len += 1 + rhl->comlenlen + rhl->comlen;
+
+  snmp_asn1_enc_s32t_cnt(snmp_version, &rhl->verlen);
+  snmp_asn1_enc_length_cnt(rhl->verlen, &rhl->verlenlen);
+  tot_len += 1 + rhl->verlen + rhl->verlenlen;
+
+  rhl->seqlen = tot_len;
+  snmp_asn1_enc_length_cnt(rhl->seqlen, &rhl->seqlenlen);
+  tot_len += 1 + rhl->seqlenlen;
+
+  return tot_len;
+}
+
+/**
+ * Sums trap header field lengths from tail to head and
+ * returns trap_header_lengths for second encoding pass.
+ *
+ * @param vb_len varbind-list length
+ * @param thl points to returned header lengths
+ * @return the required lenght for encoding the trap header
+ */
+static u16_t
+snmp_trap_header_sum(struct snmp_msg_trap *m_trap, u16_t vb_len)
+{
+  u16_t tot_len;
+  struct snmp_trap_header_lengths *thl;
+
+  thl = &m_trap->thl;
+  tot_len = vb_len;
+
+  snmp_asn1_enc_u32t_cnt(m_trap->ts, &thl->tslen);
+  snmp_asn1_enc_length_cnt(thl->tslen, &thl->tslenlen);
+  tot_len += 1 + thl->tslen + thl->tslenlen;
+
+  snmp_asn1_enc_s32t_cnt(m_trap->spc_trap, &thl->strplen);
+  snmp_asn1_enc_length_cnt(thl->strplen, &thl->strplenlen);
+  tot_len += 1 + thl->strplen + thl->strplenlen;
+
+  snmp_asn1_enc_s32t_cnt(m_trap->gen_trap, &thl->gtrplen);
+  snmp_asn1_enc_length_cnt(thl->gtrplen, &thl->gtrplenlen);
+  tot_len += 1 + thl->gtrplen + thl->gtrplenlen;
+
+  thl->aaddrlen = 4;
+  snmp_asn1_enc_length_cnt(thl->aaddrlen, &thl->aaddrlenlen);
+  tot_len += 1 + thl->aaddrlen + thl->aaddrlenlen;
+
+  snmp_asn1_enc_oid_cnt(m_trap->enterprise->len, &m_trap->enterprise->id[0], &thl->eidlen);
+  snmp_asn1_enc_length_cnt(thl->eidlen, &thl->eidlenlen);
+  tot_len += 1 + thl->eidlen + thl->eidlenlen;
+
+  thl->pdulen = tot_len;
+  snmp_asn1_enc_length_cnt(thl->pdulen, &thl->pdulenlen);
+  tot_len += 1 + thl->pdulenlen;
+
+// v0.1:  thl->comlen = sizeof(snmp_publiccommunity) - 1;
+  thl->comlen = strlen(snmp_publiccommunity);   // v0.1: user-defined community of variable length
+  snmp_asn1_enc_length_cnt(thl->comlen, &thl->comlenlen);
+  tot_len += 1 + thl->comlenlen + thl->comlen;
+
+  snmp_asn1_enc_s32t_cnt(snmp_version, &thl->verlen);
+  snmp_asn1_enc_length_cnt(thl->verlen, &thl->verlenlen);
+  tot_len += 1 + thl->verlen + thl->verlenlen;
+
+  thl->seqlen = tot_len;
+  snmp_asn1_enc_length_cnt(thl->seqlen, &thl->seqlenlen);
+  tot_len += 1 + thl->seqlenlen;
+
+  return tot_len;
+}
+
+/**
+ * Sums varbind lengths from tail to head and
+ * annotates lengths in varbind for second encoding pass.
+ *
+ * @param root points to the root of the variable binding list
+ * @return the required lenght for encoding the variable bindings
+ */
+static u16_t
+snmp_varbind_list_sum(struct snmp_varbind_root *root)
+{
+  struct snmp_varbind *vb;
+  u32_t *uint_ptr;
+  s32_t *sint_ptr;
+  u16_t tot_len;
+
+  tot_len = 0;
+  vb = root->tail;
+  while ( vb != NULL )
+  {
+    /* encoded value length depends on type */
+    switch (vb->value_type)
+    {
+      case (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG):
+        sint_ptr = (s32_t*)vb->value;
+        snmp_asn1_enc_s32t_cnt(*sint_ptr, &vb->vlen);
+        break;
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_COUNTER):
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_GAUGE):
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_TIMETICKS):
+        uint_ptr = (u32_t*)vb->value;
+        snmp_asn1_enc_u32t_cnt(*uint_ptr, &vb->vlen);
+        break;
+      case (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OC_STR):
+      case (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_NUL):
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_IPADDR):
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_OPAQUE):
+        vb->vlen = vb->value_len;
+        break;
+      case (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OBJ_ID):
+        sint_ptr = (s32_t*)vb->value;
+        snmp_asn1_enc_oid_cnt(vb->value_len / sizeof(s32_t), sint_ptr, &vb->vlen);
+        break;
+      default:
+        /* unsupported type */
+        vb->vlen = 0;
+        break;
+    };
+    /* encoding length of value length field */
+    snmp_asn1_enc_length_cnt(vb->vlen, &vb->vlenlen);
+    snmp_asn1_enc_oid_cnt(vb->ident_len, vb->ident, &vb->olen);
+    snmp_asn1_enc_length_cnt(vb->olen, &vb->olenlen);
+
+    vb->seqlen = 1 + vb->vlenlen + vb->vlen;
+    vb->seqlen += 1 + vb->olenlen + vb->olen;
+    snmp_asn1_enc_length_cnt(vb->seqlen, &vb->seqlenlen);
+
+    /* varbind seq */
+    tot_len += 1 + vb->seqlenlen + vb->seqlen;
+
+    vb = vb->prev;
+  }
+
+  /* varbind-list seq */
+  root->seqlen = tot_len;
+  snmp_asn1_enc_length_cnt(root->seqlen, &root->seqlenlen);
+  tot_len += 1 + root->seqlenlen;
+
+  return tot_len;
+}
+
+/**
+ * Encodes response header from head to tail.
+ */
+static u16_t
+snmp_resp_header_enc(struct snmp_msg_pstat *m_stat, struct pbuf *p)
+{
+  u16_t ofs;
+
+  ofs = 0;
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_CONSTR | SNMP_ASN1_SEQ));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_stat->rhl.seqlen);
+  ofs += m_stat->rhl.seqlenlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_stat->rhl.verlen);
+  ofs += m_stat->rhl.verlenlen;
+  snmp_asn1_enc_s32t(p, ofs, m_stat->rhl.verlen, snmp_version);
+  ofs += m_stat->rhl.verlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OC_STR));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_stat->rhl.comlen);
+  ofs += m_stat->rhl.comlenlen;
+  snmp_asn1_enc_raw(p, ofs, m_stat->rhl.comlen, m_stat->community);
+  ofs += m_stat->rhl.comlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_CONTXT | SNMP_ASN1_CONSTR | SNMP_ASN1_PDU_GET_RESP));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_stat->rhl.pdulen);
+  ofs += m_stat->rhl.pdulenlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_stat->rhl.ridlen);
+  ofs += m_stat->rhl.ridlenlen;
+  snmp_asn1_enc_s32t(p, ofs, m_stat->rhl.ridlen, m_stat->rid);
+  ofs += m_stat->rhl.ridlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_stat->rhl.errstatlen);
+  ofs += m_stat->rhl.errstatlenlen;
+  snmp_asn1_enc_s32t(p, ofs, m_stat->rhl.errstatlen, m_stat->error_status);
+  ofs += m_stat->rhl.errstatlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_stat->rhl.erridxlen);
+  ofs += m_stat->rhl.erridxlenlen;
+  snmp_asn1_enc_s32t(p, ofs, m_stat->rhl.erridxlen, m_stat->error_index);
+  ofs += m_stat->rhl.erridxlen;
+
+  return ofs;
+}
+
+/**
+ * Encodes trap header from head to tail.
+ */
+static u16_t
+snmp_trap_header_enc(struct snmp_msg_trap *m_trap, struct pbuf *p)
+{
+  u16_t ofs = 0;
+
+/* DEBUG variable added */
+u16_t dbug_ofs = ofs;
+u8_t *raw_ptr;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_CONSTR | SNMP_ASN1_SEQ));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.seqlen);
+  ofs += m_trap->thl.seqlenlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.verlen);
+  ofs += m_trap->thl.verlenlen;
+  snmp_asn1_enc_s32t(p, ofs, m_trap->thl.verlen, snmp_version);
+  ofs += m_trap->thl.verlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OC_STR));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.comlen);
+  ofs += m_trap->thl.comlenlen;
+  snmp_asn1_enc_raw(p, ofs, m_trap->thl.comlen, (u8_t *)&snmp_publiccommunity[0]);
+  ofs += m_trap->thl.comlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_CONTXT | SNMP_ASN1_CONSTR | SNMP_ASN1_PDU_TRAP));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.pdulen);
+  ofs += m_trap->thl.pdulenlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OBJ_ID));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.eidlen);
+  ofs += m_trap->thl.eidlenlen;
+  snmp_asn1_enc_oid(p, ofs, m_trap->enterprise->len, &m_trap->enterprise->id[0]);
+  ofs += m_trap->thl.eidlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_IPADDR));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.aaddrlen);
+  ofs += m_trap->thl.aaddrlenlen;
+  snmp_asn1_enc_raw(p, ofs, m_trap->thl.aaddrlen, &m_trap->sip_raw[0]);
+  ofs += m_trap->thl.aaddrlen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.gtrplen);
+  ofs += m_trap->thl.gtrplenlen;
+  snmp_asn1_enc_u32t(p, ofs, m_trap->thl.gtrplen, m_trap->gen_trap);
+  ofs += m_trap->thl.gtrplen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.strplen);
+  ofs += m_trap->thl.strplenlen;
+  snmp_asn1_enc_u32t(p, ofs, m_trap->thl.strplen, m_trap->spc_trap);
+  ofs += m_trap->thl.strplen;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_TIMETICKS));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, m_trap->thl.tslen);
+  ofs += m_trap->thl.tslenlen;
+  snmp_asn1_enc_u32t(p, ofs, m_trap->thl.tslen, m_trap->ts);
+  ofs += m_trap->thl.tslen;
+
+/* DEBUG code */
+//printf("\r\nsnmp_trap_header_enc: ");
+  raw_ptr = (u8_t*)p->payload;
+  raw_ptr += dbug_ofs;
+  while ( dbug_ofs < ofs )
+  {
+//printf("%d.", *raw_ptr);
+    raw_ptr++;
+    dbug_ofs++;
+  }
+//printf("\r\nsnmp_trap_header_enc: ofs %d\r\n", ofs);
+  return ofs;
+}
+
+/**
+ * Encodes varbind list from head to tail.
+ */
+static u16_t
+snmp_varbind_list_enc(struct snmp_varbind_root *root, struct pbuf *p, u16_t ofs)
+{
+  struct snmp_varbind *vb;
+  s32_t *sint_ptr;
+  u32_t *uint_ptr;
+  u8_t *raw_ptr;
+  
+/* DEBUG variable added */
+u16_t dbug_ofs = ofs;
+
+  snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_CONSTR | SNMP_ASN1_SEQ));
+  ofs += 1;
+  snmp_asn1_enc_length(p, ofs, root->seqlen);
+  ofs += root->seqlenlen;
+
+  vb = root->head;
+  while ( vb != NULL )
+  {
+printf("\r\nsnmp_varbind_list_enc: start offset %d\r\n", ofs);
+    snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_CONSTR | SNMP_ASN1_SEQ));
+    ofs += 1;
+    snmp_asn1_enc_length(p, ofs, vb->seqlen);
+    ofs += vb->seqlenlen;
+
+    snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OBJ_ID));
+    ofs += 1;
+    snmp_asn1_enc_length(p, ofs, vb->olen);
+    ofs += vb->olenlen;
+    snmp_asn1_enc_oid(p, ofs, vb->ident_len, &vb->ident[0]);
+    ofs += vb->olen;
+
+    snmp_asn1_enc_type(p, ofs, vb->value_type);
+    ofs += 1;
+    snmp_asn1_enc_length(p, ofs, vb->vlen);
+    ofs += vb->vlenlen;
+
+    switch (vb->value_type)
+    {
+      case (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_INTEG):
+        sint_ptr = (s32_t*)vb->value;
+        snmp_asn1_enc_s32t(p, ofs, vb->vlen, *sint_ptr);
+        break;
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_COUNTER):
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_GAUGE):
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_TIMETICKS):
+        uint_ptr = (u32_t*)vb->value;
+        snmp_asn1_enc_u32t(p, ofs, vb->vlen, *uint_ptr);
+        break;
+      case (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OC_STR):
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_IPADDR):
+      case (SNMP_ASN1_APPLIC | SNMP_ASN1_PRIMIT | SNMP_ASN1_OPAQUE):
+        raw_ptr = (u8_t*)vb->value;
+        snmp_asn1_enc_raw(p, ofs, vb->vlen, raw_ptr);
+        break;
+      case (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_NUL):
+        break;
+      case (SNMP_ASN1_UNIV | SNMP_ASN1_PRIMIT | SNMP_ASN1_OBJ_ID):
+        sint_ptr = (s32_t*)vb->value;
+        snmp_asn1_enc_oid(p, ofs, vb->value_len / sizeof(s32_t), sint_ptr);
+        break;
+      default:
+        /* unsupported type */
+        break;
+    };
+    ofs += vb->vlen;
+    vb = vb->next;
+  }
+/* DEBUG code */
+//printf("\r\nsnmp_varbind_list_enc: ");
+  raw_ptr = (u8_t*)p->payload;
+  raw_ptr += dbug_ofs;
+  while ( dbug_ofs < ofs )
+  {
+//printf("%d.", *raw_ptr);
+    raw_ptr++;
+    dbug_ofs++;
+  }
+  return ofs;
+}
+
+#endif /* LWIP_SNMP */