etharp.c

一个基于ucos－ii和lwip的简单telent服务器

      LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: no available entry found\n"));
      return NULL;
    }
    /* set IP address */
    ip_addr_set(&arp_table[i].ipaddr, ipaddr);
    /* set Ethernet hardware address */
    for (k = 0; k < netif->hwaddr_len; ++k) {
      arp_table[i].ethaddr.addr[k] = ethaddr->addr[k];
    }
    /* reset time-stamp */
    arp_table[i].ctime = 0;
    /* mark as stable */
    arp_table[i].state = ETHARP_STATE_STABLE;
    /* no queued packet */
#if ARP_QUEUEING
    arp_table[i].p = NULL;
#endif
  }
  else
  {
    LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: no matching stable entry to update\n"));
  }
  return NULL;
}

/**
 * Updates the ARP table using the given IP packet.
 *
 * Uses the incoming IP packet's source address to update the
 * ARP cache for the local network. The function does not alter
 * or free the packet. This function must be called before the
 * packet p is passed to the IP layer.
 *
 * @param netif The lwIP network interface on which the IP packet pbuf arrived.
 * @param pbuf The IP packet that arrived on netif.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
struct pbuf *
etharp_ip_input(struct netif *netif, struct pbuf *p)
{
  struct ethip_hdr *hdr;

  /* Only insert an entry if the source IP address of the
     incoming IP packet comes from a host on the local network. */
  hdr = p->payload;
  /* source is on local network? */
  if (!ip_addr_maskcmp(&(hdr->ip.src), &(netif->ip_addr), &(netif->netmask))) {
    /* do nothing */
    return NULL;
  }

  LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_ip_input: updating ETHARP table.\n"));
  /* update ARP table, ask to insert entry */
  update_arp_entry(netif, &(hdr->ip.src), &(hdr->eth.src), ARP_INSERT_FLAG);
  return NULL;
}


/**
 * Responds to ARP requests to us. Upon ARP replies to us, add entry to cache  
 * send out queued IP packets. Updates cache with snooped address pairs.
 *
 * Should be called for incoming ARP packets. The pbuf in the argument
 * is freed by this function.
 *
 * @param netif The lwIP network interface on which the ARP packet pbuf arrived.
 * @param pbuf The ARP packet that arrived on netif. Is freed by this function.
 * @param ethaddr Ethernet address of netif.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
struct pbuf *
etharp_arp_input(struct netif *netif, struct eth_addr *ethaddr, struct pbuf *p)
{
  struct etharp_hdr *hdr;
  u8_t i;
  u8_t for_us;

  /* drop short ARP packets */
  if (p->tot_len < sizeof(struct etharp_hdr)) {
    LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | 1, ("etharp_arp_input: packet dropped, too short (%d/%d)\n", p->tot_len, sizeof(struct etharp_hdr)));
    pbuf_free(p);
    return NULL;
  }

  hdr = p->payload;
 
  /* this interface is not configured? */
  if (netif->ip_addr.addr == 0) {
    for_us = 0;
  } else {
    /* ARP packet directed to us? */
    for_us = ip_addr_cmp(&(hdr->dipaddr), &(netif->ip_addr));
  }

  /* add or update entries in the ARP cache */
  if (for_us) {
    /* insert IP address in ARP cache (assume requester wants to talk to us)
     * we might even send out a queued packet to this host */
    update_arp_entry(netif, &(hdr->sipaddr), &(hdr->shwaddr), ARP_INSERT_FLAG);
  /* request was not directed to us, but snoop anyway */
  } else {
    /* update the source IP address in the cache */
    update_arp_entry(netif, &(hdr->sipaddr), &(hdr->shwaddr), 0);
  }

  switch (htons(hdr->opcode)) {
  /* ARP request? */
  case ARP_REQUEST:
    /* ARP request. If it asked for our address, we send out a
    reply. In any case, we time-stamp any existing ARP entry,
    and possiby send out an IP packet that was queued on it. */

    LWIP_DEBUGF (ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: incoming ARP request\n"));
    /* we are not configured? */
    if (netif->ip_addr.addr == 0) {
      LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: we are unconfigured, ARP request ignored.\n"));
      pbuf_free(p);
      return NULL;
    }
    /* ARP request for our address? */
    if (for_us) {

      LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: replying to ARP request for our IP address\n"));
      /* re-use pbuf to send ARP reply */
      hdr->opcode = htons(ARP_REPLY);

      ip_addr_set(&(hdr->dipaddr), &(hdr->sipaddr));
      ip_addr_set(&(hdr->sipaddr), &(netif->ip_addr));

      for(i = 0; i < netif->hwaddr_len; ++i) {
        hdr->dhwaddr.addr[i] = hdr->shwaddr.addr[i];
        hdr->shwaddr.addr[i] = ethaddr->addr[i];
        hdr->ethhdr.dest.addr[i] = hdr->dhwaddr.addr[i];
        hdr->ethhdr.src.addr[i] = ethaddr->addr[i];
      }

      hdr->hwtype = htons(HWTYPE_ETHERNET);
      ARPH_HWLEN_SET(hdr, netif->hwaddr_len);

      hdr->proto = htons(ETHTYPE_IP);
      ARPH_PROTOLEN_SET(hdr, sizeof(struct ip_addr));

      hdr->ethhdr.type = htons(ETHTYPE_ARP);
      /* return ARP reply */
      netif->linkoutput(netif, p);

    /* request was not directed to us */
    } else {
      LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: incoming ARP request was not for us.\n"));
    }
    break;
  case ARP_REPLY:
    /* ARP reply. We insert or update the ARP table later. */
    LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: incoming ARP reply\n"));
#if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
    /* DHCP wants to know about ARP replies to our wanna-have-address */
    if (for_us) dhcp_arp_reply(netif, &hdr->sipaddr);
#endif
    break;
  default:
    LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: ARP unknown opcode type %d\n", htons(hdr->opcode)));
    break;
  }
  /* free ARP packet */
  pbuf_free(p);
  p = NULL;
  /* nothing to send, we did it! */
  return NULL;
}

/**
 * Resolve and fill-in Ethernet address header for outgoing packet.
 *
 * If ARP has the Ethernet address in cache, the given packet is
 * returned, ready to be sent.
 *
 * If ARP does not have the Ethernet address in cache the packet is
 * queued (if enabled and space available) and a ARP request is sent.
 * This ARP request is returned as a pbuf, which should be sent by
 * the caller.
 *
 * A returned non-NULL packet should be sent by the caller.
 *
 * If ARP failed to allocate resources, NULL is returned.
 *
 * @param netif The lwIP network interface which the IP packet will be sent on.
 * @param ipaddr The IP address of the packet destination.
 * @param pbuf The pbuf(s) containing the IP packet to be sent.
 *
 * @return If non-NULL, a packet ready to be sent by caller.
 *
 */
struct pbuf *
etharp_output(struct netif *netif, struct ip_addr *ipaddr, struct pbuf *q)
{
  struct eth_addr *dest, *srcaddr, mcastaddr;
  struct eth_hdr *ethhdr;
  s8_t i;

  /* make room for Ethernet header */
  if (pbuf_header(q, sizeof(struct eth_hdr)) != 0) {
    /* The pbuf_header() call shouldn't fail, and we'll just bail
    out if it does.. */
    LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | 2, ("etharp_output: could not allocate room for header.\n"));
    LINK_STATS_INC(link.lenerr);
    return NULL;
  }

  /* assume unresolved Ethernet address */
  dest = NULL;
  /* Construct Ethernet header. Start with looking up deciding which
     MAC address to use as a destination address. Broadcasts and
     multicasts are special, all other addresses are looked up in the
     ARP table. */

  /* destination IP address is an IP broadcast address? */
  if (ip_addr_isany(ipaddr) ||
    ip_addr_isbroadcast(ipaddr, &(netif->netmask))) {
    /* broadcast on Ethernet also */
    dest = (struct eth_addr *)&ethbroadcast;
  }
  /* destination IP address is an IP multicast address? */
  else if (ip_addr_ismulticast(ipaddr)) {
    /* Hash IP multicast address to MAC address. */
    mcastaddr.addr[0] = 0x01;
    mcastaddr.addr[1] = 0x00;
    mcastaddr.addr[2] = 0x5e;
    mcastaddr.addr[3] = ip4_addr2(ipaddr) & 0x7f;
    mcastaddr.addr[4] = ip4_addr3(ipaddr);
    mcastaddr.addr[5] = ip4_addr4(ipaddr);
    /* destination Ethernet address is multicast */
    dest = &mcastaddr;
  }
  /* destination IP address is an IP unicast address */
  else {
    /* destination IP network address not on local network?
     * IP layer wants us to forward to the default gateway */
    if (!ip_addr_maskcmp(ipaddr, &(netif->ip_addr), &(netif->netmask))) {
      /* interface has default gateway? */
      if (netif->gw.addr != 0)
      {
        /* route to default gateway IP address */
        ipaddr = &(netif->gw);
      }
      /* no gateway available? */
      else
      {
        /* IP destination address outside local network, but no gateway available */
        /* { packet is discarded } */
        return NULL;
      }
    }

    /* Ethernet address for IP destination address is in ARP cache? */
    for (i = 0; i < ARP_TABLE_SIZE; ++i) {
      /* match found? */
      if (arp_table[i].state == ETHARP_STATE_STABLE &&
        ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
        dest = &arp_table[i].ethaddr;
        break;
      }
    }
    /* could not find the destination Ethernet address in ARP cache? */
    if (dest == NULL) {
      /* ARP query for the IP address, submit this IP packet for queueing */
      /* TODO: How do we handle netif->ipaddr == ipaddr? */
      etharp_query(netif, ipaddr, q);
      /* { packet was queued (ERR_OK), or discarded } */
      /* return nothing */
      return NULL;
    }
    /* destination Ethernet address resolved from ARP cache */
    else
    {
      /* fallthrough */
    }
  }

  /* destination Ethernet address known */
  if (dest != NULL) {
    /* obtain source Ethernet address of the given interface */
    srcaddr = (struct eth_addr *)netif->hwaddr;

    /* A valid IP->MAC address mapping was found, fill in the
     * Ethernet header for the outgoing packet */
    ethhdr = q->payload;

    for(i = 0; i < netif->hwaddr_len; i++) {
      ethhdr->dest.addr[i] = dest->addr[i];
      ethhdr->src.addr[i] = srcaddr->addr[i];
    }

    ethhdr->type = htons(ETHTYPE_IP);
    /* return the outgoing packet */
    return q;
  }
  /* never reached; here for safety */
  return NULL;
}

/**
 * Send an ARP request for the given IP address.
 *
 * Sends an ARP request for the given IP address, unless
 * a request for this address is already pending. Optionally
 * queues an outgoing packet on the resulting ARP entry.
 *
 * @param netif The lwIP network interface where ipaddr
 * must be queried for.
 * @param ipaddr The IP address to be resolved.
 * @param q If non-NULL, a pbuf that must be queued on the
 * ARP entry for the ipaddr IP address.
 *
 * @return NULL.
 *
 * @note Might be used in the future by manual IP configuration
 * as well.
 *
 * TODO: use the ctime field to see how long ago an ARP request was sent,
 * possibly retry.
 */
err_t etharp_query(struct netif *netif, struct ip_addr *ipaddr, struct pbuf *q)
{
  struct eth_addr *srcaddr;
  struct etharp_hdr *hdr;
  err_t result = ERR_OK;
  s8_t i;
  u8_t perform_arp_request = 1;
  /* prevent 'unused argument' warning if ARP_QUEUEING == 0 */
  (void)q;
  srcaddr = (struct eth_addr *)netif->hwaddr;
  /* bail out if this IP address is pending */
  for (i = 0; i < ARP_TABLE_SIZE; ++i) {
    if (ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
      if (arp_table[i].state == ETHARP_STATE_PENDING) {
        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | DBG_STATE, ("etharp_query: requested IP already pending as entry %u\n", i));
        /* break out of for-loop, user may wish to queue a packet on a pending entry */
        /* TODO: we will issue a new ARP request, which should not occur too often */
        /* we might want to run a faster timer on ARP to limit this */
        break;
      }
      else if (arp_table[i].state == ETHARP_STATE_STABLE) {
        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | DBG_STATE, ("etharp_query: requested IP already stable as entry %u\n", i));
        /* User wishes to queue a packet on a stable entry (or does she want to send
         * out the packet immediately, we will not know), so we force an ARP request.
         * Upon response we will send out the queued packet in etharp_update().
         * 
         * Alternatively, we could accept the stable entry, and just send out the packet
         * immediately. I chose to implement the former approach.
         */
        perform_arp_request = (q?1:0);
        break;
      }
    }
  }
  /* queried address not yet in ARP table? */
  if (i == ARP_TABLE_SIZE) {
    LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: IP address not found in ARP table\n"));
    /* find an available (unused or old) entry */
    i = find_arp_entry();
    /* bail out if no ARP entries are available */
    if (i == ERR_MEM) {
      LWIP_DEBUGF(ETHARP_DEBUG | 2, ("etharp_query: no more ARP entries available. Should seldom occur.\n"));
      return ERR_MEM;
    }
    /* i is available, create ARP entry */
    arp_table[i].state = ETHARP_STATE_PENDING;
    ip_addr_set(&arp_table[i].ipaddr, ipaddr);
  }
  /* { i is now valid } */
#if ARP_QUEUEING /* queue packet (even on a stable entry, see above) */
  etharp_enqueue(i, q);
#endif
  /* ARP request? */
  if (perform_arp_request)
  {
    struct pbuf *p;
    /* allocate a pbuf for the outgoing ARP request packet */
    p = pbuf_alloc(PBUF_LINK, sizeof(struct etharp_hdr), PBUF_RAM);
    /* could allocate pbuf? */
    if (p != NULL) {
      u8_t j;
      LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: sending ARP request.\n"));
      hdr = p->payload;
      hdr->opcode = htons(ARP_REQUEST);
      for (j = 0; j < netif->hwaddr_len; ++j)
      {
        hdr->shwaddr.addr[j] = srcaddr->addr[j];
        /* the hardware address is what we ask for, in
         * a request it is a don't-care, we use 0's */
        hdr->dhwaddr.addr[j] = 0x00;
      }
      ip_addr_set(&(hdr->dipaddr), ipaddr);
      ip_addr_set(&(hdr->sipaddr), &(netif->ip_addr));

      hdr->hwtype = htons(HWTYPE_ETHERNET);
      ARPH_HWLEN_SET(hdr, netif->hwaddr_len);

      hdr->proto = htons(ETHTYPE_IP);
      ARPH_PROTOLEN_SET(hdr, sizeof(struct ip_addr));
      for (j = 0; j < netif->hwaddr_len; ++j)
      {
        hdr->ethhdr.dest.addr[j] = 0xff;
        hdr->ethhdr.src.addr[j] = srcaddr->addr[j];
      }
      hdr->ethhdr.type = htons(ETHTYPE_ARP);
      /* send ARP query */
      result = netif->linkoutput(netif, p);
      /* free ARP query packet */
      pbuf_free(p);
      p = NULL;
    } else {
      result = ERR_MEM;
      LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | 2, ("etharp_query: could not allocate pbuf for ARP request.\n"));
    }
  }
  return result;
}