snmp_core.c

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/*
 * 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>
 *         Martin Hentschel <info@cl-soft.de>
*/
 
#include "lwip/apps/snmp_opts.h"
 
#if LWIP_SNMP /* don't build if not configured for use in lwipopts.h */
 
#include "lwip/apps/snmp.h"
#include "lwip/apps/snmp_core.h"
#include "snmp_core_priv.h"
#include "lwip/netif.h"
#include <string.h>
 
 
#if (LWIP_SNMP && (SNMP_TRAP_DESTINATIONS<=0))
#error "If you want to use SNMP, you have to define SNMP_TRAP_DESTINATIONS>=1 in your lwipopts.h"
#endif
#if (!LWIP_UDP && LWIP_SNMP)
#error "If you want to use SNMP, you have to define LWIP_UDP=1 in your lwipopts.h"
#endif
#if SNMP_MAX_OBJ_ID_LEN > 255
#error "SNMP_MAX_OBJ_ID_LEN must fit into an u8_t"
#endif
 
struct snmp_statistics snmp_stats;
static const struct snmp_obj_id  snmp_device_enterprise_oid_default = {SNMP_DEVICE_ENTERPRISE_OID_LEN, SNMP_DEVICE_ENTERPRISE_OID};
static const struct snmp_obj_id *snmp_device_enterprise_oid         = &snmp_device_enterprise_oid_default;
 
const u32_t snmp_zero_dot_zero_values[] = { 0, 0 };
const struct snmp_obj_id_const_ref snmp_zero_dot_zero = { LWIP_ARRAYSIZE(snmp_zero_dot_zero_values), snmp_zero_dot_zero_values };
 
#if SNMP_LWIP_MIB2 && LWIP_SNMP_V3
#include "lwip/apps/snmp_mib2.h"
#include "lwip/apps/snmp_snmpv2_framework.h"
#include "lwip/apps/snmp_snmpv2_usm.h"
static const struct snmp_mib *const default_mibs[] = { &mib2, &snmpframeworkmib, &snmpusmmib };
static u8_t snmp_num_mibs                          = LWIP_ARRAYSIZE(default_mibs);
#elif SNMP_LWIP_MIB2
#include "lwip/apps/snmp_mib2.h"
static const struct snmp_mib *const default_mibs[] = { &mib2 };
static u8_t snmp_num_mibs                          = LWIP_ARRAYSIZE(default_mibs);
#else
static const struct snmp_mib *const default_mibs[] = { NULL };
static u8_t snmp_num_mibs                          = 0;
#endif
 
/* List of known mibs */
static struct snmp_mib const *const *snmp_mibs = default_mibs;
 
void
snmp_set_mibs(const struct snmp_mib **mibs, u8_t num_mibs)
{
  LWIP_ASSERT_SNMP_LOCKED();
  LWIP_ASSERT("mibs pointer must be != NULL", (mibs != NULL));
  LWIP_ASSERT("num_mibs pointer must be != 0", (num_mibs != 0));
  snmp_mibs     = mibs;
  snmp_num_mibs = num_mibs;
}
 
void snmp_set_device_enterprise_oid(const struct snmp_obj_id *device_enterprise_oid)
{
  LWIP_ASSERT_SNMP_LOCKED();
  if (device_enterprise_oid == NULL) {
    snmp_device_enterprise_oid = &snmp_device_enterprise_oid_default;
  } else {
    snmp_device_enterprise_oid = device_enterprise_oid;
  }
}
 
const struct snmp_obj_id *snmp_get_device_enterprise_oid(void)
{
  LWIP_ASSERT_SNMP_LOCKED();
  return snmp_device_enterprise_oid;
}
 
#if LWIP_IPV4
u8_t
snmp_oid_to_ip4(const u32_t *oid, ip4_addr_t *ip)
{
  if ((oid[0] > 0xFF) ||
      (oid[1] > 0xFF) ||
      (oid[2] > 0xFF) ||
      (oid[3] > 0xFF)) {
    ip4_addr_copy(*ip, *IP4_ADDR_ANY4);
    return 0;
  }
 
  IP4_ADDR(ip, oid[0], oid[1], oid[2], oid[3]);
  return 1;
}
 
void
snmp_ip4_to_oid(const ip4_addr_t *ip, u32_t *oid)
{
  oid[0] = ip4_addr1(ip);
  oid[1] = ip4_addr2(ip);
  oid[2] = ip4_addr3(ip);
  oid[3] = ip4_addr4(ip);
}
#endif /* LWIP_IPV4 */
 
#if LWIP_IPV6
u8_t
snmp_oid_to_ip6(const u32_t *oid, ip6_addr_t *ip)
{
  if ((oid[0]  > 0xFF) ||
      (oid[1]  > 0xFF) ||
      (oid[2]  > 0xFF) ||
      (oid[3]  > 0xFF) ||
      (oid[4]  > 0xFF) ||
      (oid[5]  > 0xFF) ||
      (oid[6]  > 0xFF) ||
      (oid[7]  > 0xFF) ||
      (oid[8]  > 0xFF) ||
      (oid[9]  > 0xFF) ||
      (oid[10] > 0xFF) ||
      (oid[11] > 0xFF) ||
      (oid[12] > 0xFF) ||
      (oid[13] > 0xFF) ||
      (oid[14] > 0xFF) ||
      (oid[15] > 0xFF)) {
    ip6_addr_set_any(ip);
    return 0;
  }
 
  ip->addr[0] = (oid[0]  << 24) | (oid[1]  << 16) | (oid[2]  << 8) | (oid[3]  << 0);
  ip->addr[1] = (oid[4]  << 24) | (oid[5]  << 16) | (oid[6]  << 8) | (oid[7]  << 0);
  ip->addr[2] = (oid[8]  << 24) | (oid[9]  << 16) | (oid[10] << 8) | (oid[11] << 0);
  ip->addr[3] = (oid[12] << 24) | (oid[13] << 16) | (oid[14] << 8) | (oid[15] << 0);
  return 1;
}
 
void
snmp_ip6_to_oid(const ip6_addr_t *ip, u32_t *oid)
{
  oid[0]  = (ip->addr[0] & 0xFF000000) >> 24;
  oid[1]  = (ip->addr[0] & 0x00FF0000) >> 16;
  oid[2]  = (ip->addr[0] & 0x0000FF00) >>  8;
  oid[3]  = (ip->addr[0] & 0x000000FF) >>  0;
  oid[4]  = (ip->addr[1] & 0xFF000000) >> 24;
  oid[5]  = (ip->addr[1] & 0x00FF0000) >> 16;
  oid[6]  = (ip->addr[1] & 0x0000FF00) >>  8;
  oid[7]  = (ip->addr[1] & 0x000000FF) >>  0;
  oid[8]  = (ip->addr[2] & 0xFF000000) >> 24;
  oid[9]  = (ip->addr[2] & 0x00FF0000) >> 16;
  oid[10] = (ip->addr[2] & 0x0000FF00) >>  8;
  oid[11] = (ip->addr[2] & 0x000000FF) >>  0;
  oid[12] = (ip->addr[3] & 0xFF000000) >> 24;
  oid[13] = (ip->addr[3] & 0x00FF0000) >> 16;
  oid[14] = (ip->addr[3] & 0x0000FF00) >>  8;
  oid[15] = (ip->addr[3] & 0x000000FF) >>  0;
}
#endif /* LWIP_IPV6 */
 
#if LWIP_IPV4 || LWIP_IPV6
u8_t
snmp_ip_port_to_oid(const ip_addr_t *ip, u16_t port, u32_t *oid)
{
  u8_t idx;
 
  idx = snmp_ip_to_oid(ip, oid);
  oid[idx] = port;
  idx++;
 
  return idx;
}
 
u8_t
snmp_ip_to_oid(const ip_addr_t *ip, u32_t *oid)
{
  if (IP_IS_ANY_TYPE_VAL(*ip)) {
    oid[0] = 0; /* any */
    oid[1] = 0; /* no IP OIDs follow */
    return 2;
  } else if (IP_IS_V6(ip)) {
#if LWIP_IPV6
    oid[0] = 2; /* ipv6 */
    oid[1] = 16; /* 16 InetAddressIPv6 OIDs follow */
    snmp_ip6_to_oid(ip_2_ip6(ip), &oid[2]);
    return 18;
#else /* LWIP_IPV6 */
    return 0;
#endif /* LWIP_IPV6 */
  } else {
#if LWIP_IPV4
    oid[0] = 1; /* ipv4 */
    oid[1] = 4; /* 4 InetAddressIPv4 OIDs follow */
    snmp_ip4_to_oid(ip_2_ip4(ip), &oid[2]);
    return 6;
#else /* LWIP_IPV4 */
    return 0;
#endif /* LWIP_IPV4 */
  }
}
 
u8_t
snmp_oid_to_ip(const u32_t *oid, u8_t oid_len, ip_addr_t *ip)
{
  /* InetAddressType */
  if (oid_len < 1) {
    return 0;
  }
 
  if (oid[0] == 0) { /* any */
    /* 1x InetAddressType, 1x OID len */
    if (oid_len < 2) {
      return 0;
    }
    if (oid[1] != 0) {
      return 0;
    }
 
    memset(ip, 0, sizeof(*ip));
    IP_SET_TYPE(ip, IPADDR_TYPE_ANY);
 
    return 2;
  } else if (oid[0] == 1) { /* ipv4 */
#if LWIP_IPV4
    /* 1x InetAddressType, 1x OID len, 4x InetAddressIPv4 */
    if (oid_len < 6) {
      return 0;
    }
 
    /* 4x ipv4 OID */
    if (oid[1] != 4) {
      return 0;
    }
 
    IP_SET_TYPE(ip, IPADDR_TYPE_V4);
    if (!snmp_oid_to_ip4(&oid[2], ip_2_ip4(ip))) {
      return 0;
    }
 
    return 6;
#else /* LWIP_IPV4 */
    return 0;
#endif /* LWIP_IPV4 */
  } else if (oid[0] == 2) { /* ipv6 */
#if LWIP_IPV6
    /* 1x InetAddressType, 1x OID len, 16x InetAddressIPv6 */
    if (oid_len < 18) {
      return 0;
    }
 
    /* 16x ipv6 OID */
    if (oid[1] != 16) {
      return 0;
    }
 
    IP_SET_TYPE(ip, IPADDR_TYPE_V6);
    if (!snmp_oid_to_ip6(&oid[2], ip_2_ip6(ip))) {
      return 0;
    }
 
    return 18;
#else /* LWIP_IPV6 */
    return 0;
#endif /* LWIP_IPV6 */
  } else { /* unsupported InetAddressType */
    return 0;
  }
}
 
u8_t
snmp_oid_to_ip_port(const u32_t *oid, u8_t oid_len, ip_addr_t *ip, u16_t *port)
{
  u8_t idx;
 
  /* InetAddressType + InetAddress */
  idx = snmp_oid_to_ip(&oid[0], oid_len, ip);
  if (idx == 0) {
    return 0;
  }
 
  /* InetPortNumber */
  if (oid_len < (idx + 1)) {
    return 0;
  }
  if (oid[idx] > 0xffff) {
    return 0;
  }
  *port = (u16_t)oid[idx];
  idx++;
 
  return idx;
}
 
#endif /* LWIP_IPV4 || LWIP_IPV6 */
 
void
snmp_oid_assign(struct snmp_obj_id *target, const u32_t *oid, u8_t oid_len)
{
  LWIP_ASSERT("oid_len <= SNMP_MAX_OBJ_ID_LEN", oid_len <= SNMP_MAX_OBJ_ID_LEN);
 
  target->len = oid_len;
 
  if (oid_len > 0) {
    MEMCPY(target->id, oid, oid_len * sizeof(u32_t));
  }
}
 
void
snmp_oid_prefix(struct snmp_obj_id *target, const u32_t *oid, u8_t oid_len)
{
  LWIP_ASSERT("target->len + oid_len <= SNMP_MAX_OBJ_ID_LEN", (target->len + oid_len) <= SNMP_MAX_OBJ_ID_LEN);
 
  if (oid_len > 0) {
    /* move existing OID to make room at the beginning for OID to insert */
    int i;
    for (i = target->len - 1; i >= 0; i--) {
      target->id[i + oid_len] = target->id[i];
    }
 
    /* paste oid at the beginning */
    MEMCPY(target->id, oid, oid_len * sizeof(u32_t));
  }
}
 
void
snmp_oid_combine(struct snmp_obj_id *target, const u32_t *oid1, u8_t oid1_len, const u32_t *oid2, u8_t oid2_len)
{
  snmp_oid_assign(target, oid1, oid1_len);
  snmp_oid_append(target, oid2, oid2_len);
}
 
void
snmp_oid_append(struct snmp_obj_id *target, const u32_t *oid, u8_t oid_len)
{
  LWIP_ASSERT("offset + oid_len <= SNMP_MAX_OBJ_ID_LEN", (target->len + oid_len) <= SNMP_MAX_OBJ_ID_LEN);
 
  if (oid_len > 0) {
    MEMCPY(&target->id[target->len], oid, oid_len * sizeof(u32_t));
    target->len = (u8_t)(target->len + oid_len);
  }
}
 
s8_t
snmp_oid_compare(const u32_t *oid1, u8_t oid1_len, const u32_t *oid2, u8_t oid2_len)
{
  u8_t level = 0;
  LWIP_ASSERT("'oid1' param must not be NULL or 'oid1_len' param be 0!", (oid1 != NULL) || (oid1_len == 0));
  LWIP_ASSERT("'oid2' param must not be NULL or 'oid2_len' param be 0!", (oid2 != NULL) || (oid2_len == 0));
 
  while ((level < oid1_len) && (level < oid2_len)) {
    if (*oid1 < *oid2) {
      return -1;
    }
    if (*oid1 > *oid2) {
      return 1;
    }
 
    level++;
    oid1++;
    oid2++;
  }
 
  /* common part of both OID's is equal, compare length */
  if (oid1_len < oid2_len) {
    return -1;
  }
  if (oid1_len > oid2_len) {
    return 1;
  }
 
  /* they are equal */
  return 0;
}
 
 
u8_t
snmp_oid_equal(const u32_t *oid1, u8_t oid1_len, const u32_t *oid2, u8_t oid2_len)
{
  return (snmp_oid_compare(oid1, oid1_len, oid2, oid2_len) == 0) ? 1 : 0;
}
 
u8_t
netif_to_num(const struct netif *netif)
{
  return netif_get_index(netif);
}
 
static const struct snmp_mib *
snmp_get_mib_from_oid(const u32_t *oid, u8_t oid_len)
{
  const u32_t *list_oid;
  const u32_t *searched_oid;
  u8_t i, l;
 
  u8_t max_match_len = 0;
  const struct snmp_mib *matched_mib = NULL;
 
  LWIP_ASSERT("'oid' param must not be NULL!", (oid != NULL));
 
  if (oid_len == 0) {
    return NULL;
  }
 
  for (i = 0; i < snmp_num_mibs; i++) {
    LWIP_ASSERT("MIB array not initialized correctly", (snmp_mibs[i] != NULL));
    LWIP_ASSERT("MIB array not initialized correctly - base OID is NULL", (snmp_mibs[i]->base_oid != NULL));
 
    if (oid_len >= snmp_mibs[i]->base_oid_len) {
      l            = snmp_mibs[i]->base_oid_len;
      list_oid     = snmp_mibs[i]->base_oid;
      searched_oid = oid;
 
      while (l > 0) {
        if (*list_oid != *searched_oid) {
          break;
        }
 
        l--;
        list_oid++;
        searched_oid++;
      }
 
      if ((l == 0) && (snmp_mibs[i]->base_oid_len > max_match_len)) {
        max_match_len = snmp_mibs[i]->base_oid_len;
        matched_mib = snmp_mibs[i];
      }
    }
  }
 
  return matched_mib;
}
 
static const struct snmp_mib *
snmp_get_next_mib(const u32_t *oid, u8_t oid_len)
{
  u8_t i;
  const struct snmp_mib *next_mib = NULL;
 
  LWIP_ASSERT("'oid' param must not be NULL!", (oid != NULL));
 
  if (oid_len == 0) {
    return NULL;
  }
 
  for (i = 0; i < snmp_num_mibs; i++) {
    if (snmp_mibs[i]->base_oid != NULL) {
      /* check if mib is located behind starting point */
      if (snmp_oid_compare(snmp_mibs[i]->base_oid, snmp_mibs[i]->base_oid_len, oid, oid_len) > 0) {
        if ((next_mib == NULL) ||
            (snmp_oid_compare(snmp_mibs[i]->base_oid, snmp_mibs[i]->base_oid_len,
                              next_mib->base_oid, next_mib->base_oid_len) < 0)) {
          next_mib = snmp_mibs[i];
        }
      }
    }
  }
 
  return next_mib;
}
 
static const struct snmp_mib *
snmp_get_mib_between(const u32_t *oid1, u8_t oid1_len, const u32_t *oid2, u8_t oid2_len)
{
  const struct snmp_mib *next_mib = snmp_get_next_mib(oid1, oid1_len);
 
  LWIP_ASSERT("'oid2' param must not be NULL!", (oid2 != NULL));
  LWIP_ASSERT("'oid2_len' param must be greater than 0!", (oid2_len > 0));
 
  if (next_mib != NULL) {
    if (snmp_oid_compare(next_mib->base_oid, next_mib->base_oid_len, oid2, oid2_len) < 0) {
      return next_mib;
    }
  }
 
  return NULL;
}
 
u8_t
snmp_get_node_instance_from_oid(const u32_t *oid, u8_t oid_len, struct snmp_node_instance *node_instance)
{
  u8_t result = SNMP_ERR_NOSUCHOBJECT;
  const struct snmp_mib *mib;
  const struct snmp_node *mn = NULL;
 
  mib = snmp_get_mib_from_oid(oid, oid_len);
  if (mib != NULL) {
    u8_t oid_instance_len;
 
    mn = snmp_mib_tree_resolve_exact(mib, oid, oid_len, &oid_instance_len);
    if ((mn != NULL) && (mn->node_type != SNMP_NODE_TREE)) {
      /* get instance */
      const struct snmp_leaf_node *leaf_node = (const struct snmp_leaf_node *)(const void *)mn;
 
      node_instance->node = mn;
      snmp_oid_assign(&node_instance->instance_oid, oid + (oid_len - oid_instance_len), oid_instance_len);
 
      result = leaf_node->get_instance(
                 oid,
                 oid_len - oid_instance_len,
                 node_instance);
 
#ifdef LWIP_DEBUG
      if (result == SNMP_ERR_NOERROR) {
        if (((node_instance->access & SNMP_NODE_INSTANCE_ACCESS_READ) != 0) && (node_instance->get_value == NULL)) {
          LWIP_DEBUGF(SNMP_DEBUG, ("SNMP inconsistent access: node is readable but no get_value function is specified\n"));
        }
        if (((node_instance->access & SNMP_NODE_INSTANCE_ACCESS_WRITE) != 0) && (node_instance->set_value == NULL)) {
          LWIP_DEBUGF(SNMP_DEBUG, ("SNMP inconsistent access: node is writable but no set_value and/or set_test function is specified\n"));
        }
      }
#endif
    }
  }
 
  return result;
}
 
u8_t
snmp_get_next_node_instance_from_oid(const u32_t *oid, u8_t oid_len, snmp_validate_node_instance_method validate_node_instance_method, void *validate_node_instance_arg, struct snmp_obj_id *node_oid, struct snmp_node_instance *node_instance)
{
  const struct snmp_mib      *mib;
  const struct snmp_node *mn = NULL;
  const u32_t *start_oid     = NULL;
  u8_t         start_oid_len = 0;
 
  /* resolve target MIB from passed OID */
  mib = snmp_get_mib_from_oid(oid, oid_len);
  if (mib == NULL) {
    /* passed OID does not reference any known MIB, start at the next closest MIB */
    mib = snmp_get_next_mib(oid, oid_len);
 
    if (mib != NULL) {
      start_oid     = mib->base_oid;
      start_oid_len = mib->base_oid_len;
    }
  } else {
    start_oid     = oid;
    start_oid_len = oid_len;
  }
 
  /* resolve target node from MIB, skip to next MIB if no suitable node is found in current MIB */
  while ((mib != NULL) && (mn == NULL)) {
    u8_t oid_instance_len;
 
    /* check if OID directly references a node inside current MIB, in this case we have to ask this node for the next instance */
    mn = snmp_mib_tree_resolve_exact(mib, start_oid, start_oid_len, &oid_instance_len);
    if (mn != NULL) {
      snmp_oid_assign(node_oid, start_oid, start_oid_len - oid_instance_len); /* set oid to node */
      snmp_oid_assign(&node_instance->instance_oid, start_oid + (start_oid_len - oid_instance_len), oid_instance_len); /* set (relative) instance oid */
    } else {
      /* OID does not reference a node, search for the next closest node inside MIB; set instance_oid.len to zero because we want the first instance of this node */
      mn = snmp_mib_tree_resolve_next(mib, start_oid, start_oid_len, node_oid);
      node_instance->instance_oid.len = 0;
    }
 
    /* validate the node; if the node has no further instance or the returned instance is invalid, search for the next in MIB and validate again */
    node_instance->node = mn;
    while (mn != NULL) {
      u8_t result;
 
      /* clear fields which may have values from previous loops */
      node_instance->asn1_type        = 0;
      node_instance->access           = SNMP_NODE_INSTANCE_NOT_ACCESSIBLE;
      node_instance->get_value        = NULL;
      node_instance->set_test         = NULL;
      node_instance->set_value        = NULL;
      node_instance->release_instance = NULL;
      node_instance->reference.ptr    = NULL;
      node_instance->reference_len    = 0;
 
      result = ((const struct snmp_leaf_node *)(const void *)mn)->get_next_instance(
                 node_oid->id,
                 node_oid->len,
                 node_instance);
 
      if (result == SNMP_ERR_NOERROR) {
#ifdef LWIP_DEBUG
        if (((node_instance->access & SNMP_NODE_INSTANCE_ACCESS_READ) != 0) && (node_instance->get_value == NULL)) {
          LWIP_DEBUGF(SNMP_DEBUG, ("SNMP inconsistent access: node is readable but no get_value function is specified\n"));
        }
        if (((node_instance->access & SNMP_NODE_INSTANCE_ACCESS_WRITE) != 0) && (node_instance->set_value == NULL)) {
          LWIP_DEBUGF(SNMP_DEBUG, ("SNMP inconsistent access: node is writable but no set_value function is specified\n"));
        }
#endif
 
        /* validate node because the node may be not accessible for example (but let the caller decide what is valid */
        if ((validate_node_instance_method == NULL) ||
            (validate_node_instance_method(node_instance, validate_node_instance_arg) == SNMP_ERR_NOERROR)) {
          /* node_oid "returns" the full result OID (including the instance part) */
          snmp_oid_append(node_oid, node_instance->instance_oid.id, node_instance->instance_oid.len);
          break;
        }
 
        if (node_instance->release_instance != NULL) {
          node_instance->release_instance(node_instance);
        }
        /*
        the instance itself is not valid, ask for next instance from same node.
        we don't have to change any variables because node_instance->instance_oid is used as input (starting point)
        as well as output (resulting next OID), so we have to simply call get_next_instance method again
        */
      } else {
        if (node_instance->release_instance != NULL) {
          node_instance->release_instance(node_instance);
        }
 
        /* the node has no further instance, skip to next node */
        mn = snmp_mib_tree_resolve_next(mib, node_oid->id, node_oid->len, &node_instance->instance_oid); /* misuse node_instance->instance_oid as tmp buffer */
        if (mn != NULL) {
          /* prepare for next loop */
          snmp_oid_assign(node_oid, node_instance->instance_oid.id, node_instance->instance_oid.len);
          node_instance->instance_oid.len = 0;
          node_instance->node = mn;
        }
      }
    }
 
    if (mn != NULL) {
      /*
      we found a suitable next node,
      now we have to check if a inner MIB is located between the searched OID and the resulting OID.
      this is possible because MIB's may be located anywhere in the global tree, that means also in
      the subtree of another MIB (e.g. if searched OID is .2 and resulting OID is .4, then another
      MIB having .3 as root node may exist)
      */
      const struct snmp_mib *intermediate_mib;
      intermediate_mib = snmp_get_mib_between(start_oid, start_oid_len, node_oid->id, node_oid->len);
 
      if (intermediate_mib != NULL) {
        /* search for first node inside intermediate mib in next loop */
        if (node_instance->release_instance != NULL) {
          node_instance->release_instance(node_instance);
        }
 
        mn            = NULL;
        mib           = intermediate_mib;
        start_oid     = mib->base_oid;
        start_oid_len = mib->base_oid_len;
      }
      /* else { we found out target node } */
    } else {
      /*
      there is no further (suitable) node inside this MIB, search for the next MIB with following priority
      1. search for inner MIB's (whose root is located inside tree of current MIB)
      2. search for surrounding MIB's (where the current MIB is the inner MIB) and continue there if any
      3. take the next closest MIB (not being related to the current MIB)
      */
      const struct snmp_mib *next_mib;
      next_mib = snmp_get_next_mib(start_oid, start_oid_len); /* returns MIB's related to point 1 and 3 */
 
      /* is the found MIB an inner MIB? (point 1) */
      if ((next_mib != NULL) && (next_mib->base_oid_len > mib->base_oid_len) &&
          (snmp_oid_compare(next_mib->base_oid, mib->base_oid_len, mib->base_oid, mib->base_oid_len) == 0)) {
        /* yes it is -> continue at inner MIB */
        mib = next_mib;
        start_oid     = mib->base_oid;
        start_oid_len = mib->base_oid_len;
      } else {
        /* check if there is a surrounding mib where to continue (point 2) (only possible if OID length > 1) */
        if (mib->base_oid_len > 1) {
          mib = snmp_get_mib_from_oid(mib->base_oid, mib->base_oid_len - 1);
 
          if (mib == NULL) {
            /* no surrounding mib, use next mib encountered above (point 3) */
            mib = next_mib;
 
            if (mib != NULL) {
              start_oid     = mib->base_oid;
              start_oid_len = mib->base_oid_len;
            }
          }
          /* else { start_oid stays the same because we want to continue from current offset in surrounding mib (point 2) } */
        }
      }
    }
  }
 
  if (mib == NULL) {
    /* loop is only left when mib == null (error) or mib_node != NULL (success) */
    return SNMP_ERR_ENDOFMIBVIEW;
  }
 
  return SNMP_ERR_NOERROR;
}
 
const struct snmp_node *
snmp_mib_tree_resolve_exact(const struct snmp_mib *mib, const u32_t *oid, u8_t oid_len, u8_t *oid_instance_len)
{
  const struct snmp_node *const *node = &mib->root_node;
  u8_t oid_offset = mib->base_oid_len;
 
  while ((oid_offset < oid_len) && ((*node)->node_type == SNMP_NODE_TREE)) {
    /* search for matching sub node */
    u32_t subnode_oid = *(oid + oid_offset);
 
    u32_t i = (*(const struct snmp_tree_node * const *)node)->subnode_count;
    node    = (*(const struct snmp_tree_node * const *)node)->subnodes;
    while ((i > 0) && ((*node)->oid != subnode_oid)) {
      node++;
      i--;
    }
 
    if (i == 0) {
      /* no matching subnode found */
      return NULL;
    }
 
    oid_offset++;
  }
 
  if ((*node)->node_type != SNMP_NODE_TREE) {
    /* we found a leaf node */
    *oid_instance_len = oid_len - oid_offset;
    return (*node);
  }
 
  return NULL;
}
 
const struct snmp_node *
snmp_mib_tree_resolve_next(const struct snmp_mib *mib, const u32_t *oid, u8_t oid_len, struct snmp_obj_id *oidret)
{
  u8_t  oid_offset = mib->base_oid_len;
  const struct snmp_node *const *node;
  const struct snmp_tree_node *node_stack[SNMP_MAX_OBJ_ID_LEN];
  s32_t nsi = 0; /* NodeStackIndex */
  u32_t subnode_oid;
 
  if (mib->root_node->node_type != SNMP_NODE_TREE) {
    /* a next operation on a mib with only a leaf node will always return NULL because there is no other node */
    return NULL;
  }
 
  /* first build node stack related to passed oid (as far as possible), then go backwards to determine the next node */
  node_stack[nsi] = (const struct snmp_tree_node *)(const void *)mib->root_node;
  while (oid_offset < oid_len) {
    /* search for matching sub node */
    u32_t i = node_stack[nsi]->subnode_count;
    node    = node_stack[nsi]->subnodes;
 
    subnode_oid = *(oid + oid_offset);
 
    while ((i > 0) && ((*node)->oid != subnode_oid)) {
      node++;
      i--;
    }
 
    if ((i == 0) || ((*node)->node_type != SNMP_NODE_TREE)) {
      /* no (matching) tree-subnode found */
      break;
    }
    nsi++;
    node_stack[nsi] = (const struct snmp_tree_node *)(const void *)(*node);
 
    oid_offset++;
  }
 
 
  if (oid_offset >= oid_len) {
    /* passed oid references a tree node -> return first usable sub node of it */
    subnode_oid = 0;
  } else {
    subnode_oid = *(oid + oid_offset) + 1;
  }
 
  while (nsi >= 0) {
    const struct snmp_node *subnode = NULL;
 
    /* find next node on current level */
    s32_t i        = node_stack[nsi]->subnode_count;
    node           = node_stack[nsi]->subnodes;
    while (i > 0) {
      if ((*node)->oid == subnode_oid) {
        subnode = *node;
        break;
      } else if (((*node)->oid > subnode_oid) && ((subnode == NULL) || ((*node)->oid < subnode->oid))) {
        subnode = *node;
      }
 
      node++;
      i--;
    }
 
    if (subnode == NULL) {
      /* no further node found on this level, go one level up and start searching with index of current node*/
      subnode_oid = node_stack[nsi]->node.oid + 1;
      nsi--;
    } else {
      if (subnode->node_type == SNMP_NODE_TREE) {
        /* next is a tree node, go into it and start searching */
        nsi++;
        node_stack[nsi] = (const struct snmp_tree_node *)(const void *)subnode;
        subnode_oid = 0;
      } else {
        /* we found a leaf node -> fill oidret and return it */
        snmp_oid_assign(oidret, mib->base_oid, mib->base_oid_len);
        i = 1;
        while (i <= nsi) {
          oidret->id[oidret->len] = node_stack[i]->node.oid;
          oidret->len++;
          i++;
        }
 
        oidret->id[oidret->len] = subnode->oid;
        oidret->len++;
 
        return subnode;
      }
    }
  }
 
  return NULL;
}
 
void
snmp_next_oid_init(struct snmp_next_oid_state *state,
                   const u32_t *start_oid, u8_t start_oid_len,
                   u32_t *next_oid_buf, u8_t next_oid_max_len)
{
  state->start_oid        = start_oid;
  state->start_oid_len    = start_oid_len;
  state->next_oid         = next_oid_buf;
  state->next_oid_len     = 0;
  state->next_oid_max_len = next_oid_max_len;
  state->status           = SNMP_NEXT_OID_STATUS_NO_MATCH;
}
 
u8_t
snmp_next_oid_precheck(struct snmp_next_oid_state *state, const u32_t *oid, u8_t oid_len)
{
  if (state->status != SNMP_NEXT_OID_STATUS_BUF_TO_SMALL) {
    u8_t start_oid_len = (oid_len < state->start_oid_len) ? oid_len : state->start_oid_len;
 
    /* check passed OID is located behind start offset */
    if (snmp_oid_compare(oid, oid_len, state->start_oid, start_oid_len) >= 0) {
      /* check if new oid is located closer to start oid than current closest oid */
      if ((state->status == SNMP_NEXT_OID_STATUS_NO_MATCH) ||
          (snmp_oid_compare(oid, oid_len, state->next_oid, state->next_oid_len) < 0)) {
        return 1;
      }
    }
  }
 
  return 0;
}
 
u8_t
snmp_next_oid_check(struct snmp_next_oid_state *state, const u32_t *oid, u8_t oid_len, void *reference)
{
  /* do not overwrite a fail result */
  if (state->status != SNMP_NEXT_OID_STATUS_BUF_TO_SMALL) {
    /* check passed OID is located behind start offset */
    if (snmp_oid_compare(oid, oid_len, state->start_oid, state->start_oid_len) > 0) {
      /* check if new oid is located closer to start oid than current closest oid */
      if ((state->status == SNMP_NEXT_OID_STATUS_NO_MATCH) ||
          (snmp_oid_compare(oid, oid_len, state->next_oid, state->next_oid_len) < 0)) {
        if (oid_len <= state->next_oid_max_len) {
          MEMCPY(state->next_oid, oid, oid_len * sizeof(u32_t));
          state->next_oid_len = oid_len;
          state->status       = SNMP_NEXT_OID_STATUS_SUCCESS;
          state->reference    = reference;
          return 1;
        } else {
          state->status = SNMP_NEXT_OID_STATUS_BUF_TO_SMALL;
        }
      }
    }
  }
 
  return 0;
}
 
u8_t
snmp_oid_in_range(const u32_t *oid_in, u8_t oid_len, const struct snmp_oid_range *oid_ranges, u8_t oid_ranges_len)
{
  u8_t i;
 
  if (oid_len != oid_ranges_len) {
    return 0;
  }
 
  for (i = 0; i < oid_ranges_len; i++) {
    if ((oid_in[i] < oid_ranges[i].min) || (oid_in[i] > oid_ranges[i].max)) {
      return 0;
    }
  }
 
  return 1;
}
 
snmp_err_t
snmp_set_test_ok(struct snmp_node_instance *instance, u16_t value_len, void *value)
{
  LWIP_UNUSED_ARG(instance);
  LWIP_UNUSED_ARG(value_len);
  LWIP_UNUSED_ARG(value);
 
  return SNMP_ERR_NOERROR;
}
 
err_t
snmp_decode_bits(const u8_t *buf, u32_t buf_len, u32_t *bit_value)
{
  u8_t b;
  u8_t bits_processed = 0;
  *bit_value = 0;
 
  while (buf_len > 0) {
    /* any bit set in this byte? */
    if (*buf != 0x00) {
      if (bits_processed >= 32) {
        /* accept more than 4 bytes, but only when no bits are set */
        return ERR_VAL;
      }
 
      b = *buf;
      do {
        if (b & 0x80) {
          *bit_value |= (1 << bits_processed);
        }
        bits_processed++;
        b <<= 1;
      } while ((bits_processed & 0x07) != 0); /* &0x07 -> % 8 */
    } else {
      bits_processed += 8;
    }
 
    buf_len--;
    buf++;
  }
 
  return ERR_OK;
}
 
err_t
snmp_decode_truthvalue(const s32_t *asn1_value, u8_t *bool_value)
{
  /* defined by RFC1443:
   TruthValue ::= TEXTUAL-CONVENTION
    STATUS       current
    DESCRIPTION
     "Represents a boolean value."
    SYNTAX       INTEGER { true(1), false(2) }
  */
 
  if ((asn1_value == NULL) || (bool_value == NULL)) {
    return ERR_ARG;
  }
 
  if (*asn1_value == 1) {
    *bool_value = 1;
  } else if (*asn1_value == 2) {
    *bool_value = 0;
  } else {
    return ERR_VAL;
  }
 
  return ERR_OK;
}
 
u8_t
snmp_encode_bits(u8_t *buf, u32_t buf_len, u32_t bit_value, u8_t bit_count)
{
  u8_t len = 0;
  u8_t min_bytes = (bit_count + 7) >> 3; /* >>3 -> / 8 */
 
  while ((buf_len > 0) && (bit_value != 0x00)) {
    s8_t i = 7;
    *buf = 0x00;
    while (i >= 0) {
      if (bit_value & 0x01) {
        *buf |= 0x01;
      }
 
      if (i > 0) {
        *buf <<= 1;
      }
 
      bit_value >>= 1;
      i--;
    }
 
    buf++;
    buf_len--;
    len++;
  }
 
  if (len < min_bytes) {
    buf     += len;
    buf_len -= len;
 
    while ((len < min_bytes) && (buf_len > 0)) {
      *buf = 0x00;
      buf++;
      buf_len--;
      len++;
    }
  }
 
  return len;
}
 
u8_t
snmp_encode_truthvalue(s32_t *asn1_value, u32_t bool_value)
{
  /* defined by RFC1443:
   TruthValue ::= TEXTUAL-CONVENTION
    STATUS       current
    DESCRIPTION
     "Represents a boolean value."
    SYNTAX       INTEGER { true(1), false(2) }
  */
 
  if (asn1_value == NULL) {
    return 0;
  }
 
  if (bool_value) {
    *asn1_value = 1; /* defined by RFC1443 */
  } else {
    *asn1_value = 2; /* defined by RFC1443 */
  }
 
  return sizeof(s32_t);
}
 
#endif /* LWIP_SNMP */