msg_out.c

《嵌入式网络系统设计-基于Atmel ARM7 系列》这个本书的光盘资料

/**
 * @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 <[e-mail]>
 */

#include "lwip/opt.h"

#if LWIP_SNMP
#include "arch/cc.h"
#include "lwip/udp.h"
#include "lwip/netif.h"

#include "lwip/snmp.h"
#include "lwip/snmp_asn1.h"
#include "lwip/snmp_msg.h"

struct snmp_trap_dst
{
  /* destination IP address in network order */
  struct ip_addr dip;
  /* set to 0 when disabled, >0 when enabled */
  u8_t enable;
};
#if (SNMP_TRAP_DESTINATIONS == 0)
#error "need at least one trap destination"
#endif
struct snmp_trap_dst trap_dst[SNMP_TRAP_DESTINATIONS];

/** TRAP message structure */
struct snmp_msg_trap trap_msg;

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)
  {
    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, struct ip_addr *dst)
{
  if (dst_idx < SNMP_TRAP_DESTINATIONS)
  {
    trap_dst[dst_idx].dip.addr = htonl(dst->addr);
  }
}

/**
 * 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;
  struct ip_addr dst_ip;
  struct pbuf *p;
  u16_t i,tot_len;

  for (i=0, td = &trap_dst[0]; i<SNMP_TRAP_DESTINATIONS; i++, td++)
  {
    if ((td->enable != 0) && (td->dip.addr != 0))
    {
      /* network order trap destination */
      trap_msg.dip.addr = td->dip.addr;
      /* lookup current source address for this dst */
      dst_if = ip_route(&td->dip);
      dst_ip.addr = ntohl(dst_if->ip_addr.addr);
      trap_msg.sip_raw[0] = dst_ip.addr >> 24;
      trap_msg.sip_raw[1] = dst_ip.addr >> 16;
      trap_msg.sip_raw[2] = dst_ip.addr >> 8;
      trap_msg.sip_raw[3] = dst_ip.addr;
      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);

      /* 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);

        snmp_inc_snmpouttraps();
        snmp_inc_snmpoutpkts();

        /** connect to the TRAP destination */
        udp_connect(trap_msg.pcb, &trap_msg.dip, SNMP_TRAP_PORT);
        udp_send(trap_msg.pcb, p);
        /** disassociate remote address and port with this pcb */
        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);
}

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);
  }
}

/**
 * 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;