}
}

#if DNS_LOCAL_HOSTLIST
static void
dns_init_local()
{
#if DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT)
  int i;
  struct local_hostlist_entry *entry;
  /* Dynamic: copy entries from DNS_LOCAL_HOSTLIST_INIT to list */
  struct local_hostlist_entry local_hostlist_init[] = DNS_LOCAL_HOSTLIST_INIT;
  for (i = 0; i < sizeof(local_hostlist_init) / sizeof(struct local_hostlist_entry); i++) {
    entry = mem_malloc(sizeof(struct local_hostlist_entry));
    LWIP_ASSERT("mem-error in dns_init_local", entry != NULL);
    if (entry != NULL) {
      struct local_hostlist_entry *init_entry = &local_hostlist_init[i];
      entry->name = init_entry->name;
      entry->addr = init_entry->addr;
      entry->next = local_hostlist_dynamic;
      local_hostlist_dynamic = entry;
    }
  }
#endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT) */
}

/**
 * Scans the local host-list for a hostname.
 *
 * @param hostname Hostname to look for in the local host-list
 * @return The first IP address for the hostname in the local host-list or
 *         INADDR_NONE if not found.
 */
static u32_t
dns_lookup_local(const char *hostname)
{
#if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
  struct local_hostlist_entry *entry = local_hostlist_dynamic;
  while(entry != NULL) {
    if(strcmp(entry->name, hostname) == 0) {
      return entry->addr;
    }
    entry = entry->next;
  }
#else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
  int i;
  for (i = 0; i < sizeof(local_hostlist_static) / sizeof(struct local_hostlist_entry); i++) {
    if(strcmp(local_hostlist_static[i].name, hostname) == 0) {
      return local_hostlist_static[i].addr;
    }
  }
#endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
  return INADDR_NONE;
}

#if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
/** Remove all entries from the local host-list for a specific hostname
 * and/or IP addess
 *
 * @param hostname hostname for which entries shall be removed from the local
 *                 host-list
 * @param addr address for which entries shall be removed from the local host-list
 * @return the number of removed entries
 */
int
dns_local_removehost(const char *hostname, const struct ip_addr *addr)
{
  int removed = 0;
  struct local_hostlist_entry *entry = local_hostlist_dynamic;
  struct local_hostlist_entry *last_entry = NULL;
  while (entry != NULL) {
    if (((hostname == NULL) || !strcmp(entry->name, hostname)) &&
        ((addr == NULL) || (entry->addr == addr->addr))) {
      struct local_hostlist_entry *free_entry;
      if (last_entry != NULL) {
        last_entry->next = entry->next;
      } else {
        local_hostlist_dynamic = entry->next;
      }
      free_entry = entry;
      entry = entry->next;
      mem_free(free_entry);
      removed++;
    } else {
      last_entry = entry;
      entry = entry->next;
    }
  }
  return removed;
}

/**
 * Add a hostname/IP address pair to the local host-list.
 * Duplicates are not checked.
 *
 * @param hostname hostname of the new entry
 * @param addr IP address of the new entry
 * @return ERR_OK if succeeded or ERR_MEM on memory error
 */
err_t
dns_local_addhost(const char *hostname, const struct ip_addr *addr)
{
  struct local_hostlist_entry *entry;
  entry = mem_malloc(sizeof(struct local_hostlist_entry));
  if (entry == NULL) {
    return ERR_MEM;
  }
  entry->name = hostname;
  entry->addr = addr->addr;
  entry->next = local_hostlist_dynamic;
  local_hostlist_dynamic = entry;
  return ERR_OK;
}
#endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC*/
#endif /* DNS_LOCAL_HOSTLIST */

/**
 * Look up a hostname in the array of known hostnames.
 *
 * @note This function only looks in the internal array of known
 * hostnames, it does not send out a query for the hostname if none
 * was found. The function dns_enqueue() can be used to send a query
 * for a hostname.
 *
 * @param name the hostname to look up
 * @return the hostname's IP address, as u32_t (instead of struct ip_addr to
 *         better check for failure: != INADDR_NONE) or INADDR_NONE if the hostname
 *         was not found in the cached dns_table.
 */
static u32_t
dns_lookup(const char *name)
{
  u8_t i;
#if DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN)
  u32_t addr;
#endif /* DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN) */
#if DNS_LOCAL_HOSTLIST
  if ((addr = dns_lookup_local(name)) != INADDR_NONE) {
    return addr;
  }
#endif /* DNS_LOCAL_HOSTLIST */
#ifdef DNS_LOOKUP_LOCAL_EXTERN
  if((addr = DNS_LOOKUP_LOCAL_EXTERN(name)) != INADDR_NONE) {
    return addr;
  }
#endif /* DNS_LOOKUP_LOCAL_EXTERN */

  /* Walk through name list, return entry if found. If not, return NULL. */
  for (i = 0; i < DNS_TABLE_SIZE; ++i) {
    if ((dns_table[i].state == DNS_STATE_DONE) &&
        (strcmp(name, dns_table[i].name) == 0)) {
      LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));
      ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr));
      LWIP_DEBUGF(DNS_DEBUG, ("\n"));
      return dns_table[i].ipaddr.addr;
    }
  }

  return INADDR_NONE;
}

#if DNS_DOES_NAME_CHECK
/**
 * Compare the "dotted" name "query" with the encoded name "response"
 * to make sure an answer from the DNS server matches the current dns_table
 * entry (otherwise, answers might arrive late for hostname not on the list
 * any more).
 *
 * @param query hostname (not encoded) from the dns_table
 * @param response encoded hostname in the DNS response
 * @return 0: names equal; 1: names differ
 */
static u8_t
dns_compare_name(unsigned char *query, unsigned char *response)
{
  unsigned char n;

  do {
    n = *response++;
    /** @see RFC 1035 - 4.1.4. Message compression */
    if ((n & 0xc0) == 0xc0) {
      /* Compressed name */
      break;
    } else {
      /* Not compressed name */
      while (n > 0) {
        if ((*query) != (*response)) {
          return 1;
        }
        ++response;
        ++query;
        --n;
      };
      ++query;
    }
  } while (*response != 0);

  return 0;
}
#endif /* DNS_DOES_NAME_CHECK */

/**
 * Walk through a compact encoded DNS name and return the end of the name.
 *
 * @param query encoded DNS name in the DNS server response
 * @return end of the name
 */
static unsigned char *
dns_parse_name(unsigned char *query)
{
  unsigned char n;

  do {
    n = *query++;
    /** @see RFC 1035 - 4.1.4. Message compression */
    if ((n & 0xc0) == 0xc0) {
      /* Compressed name */
      break;
    } else {
      /* Not compressed name */
      while (n > 0) {
        ++query;
        --n;
      };
    }
  } while (*query != 0);

  return query + 1;
}

/**
 * Send a DNS query packet.
 *
 * @param numdns index of the DNS server in the dns_servers table
 * @param name hostname to query
 * @param id index of the hostname in dns_table, used as transaction ID in the
 *        DNS query packet
 * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise
 */
static err_t
dns_send(u8_t numdns, const char* name, u8_t id)
{
  err_t err;
  struct dns_hdr *hdr;
  struct dns_query qry;
  struct pbuf *p;
  char *query, *nptr;
  const char *pHostname;
  u8_t n;

  LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n",
              (u16_t)(numdns), name));
  LWIP_ASSERT("dns server out of array", numdns < DNS_MAX_SERVERS);
  LWIP_ASSERT("dns server has no IP address set", dns_servers[numdns].addr != 0);

  /* if here, we have either a new query or a retry on a previous query to process */
  p = pbuf_alloc(PBUF_TRANSPORT, SIZEOF_DNS_HDR + DNS_MAX_NAME_LENGTH +
                 SIZEOF_DNS_QUERY, PBUF_RAM);
  if (p != NULL) {
    LWIP_ASSERT("pbuf must be in one piece", p->next == NULL);
    /* fill dns header */
    hdr = (struct dns_hdr*)p->payload;
    memset(hdr, 0, SIZEOF_DNS_HDR);
    hdr->id = htons(id);
    hdr->flags1 = DNS_FLAG1_RD;
    hdr->numquestions = htons(1);
    query = (char*)hdr + SIZEOF_DNS_HDR;
    pHostname = name;
    --pHostname;

    /* convert hostname into suitable query format. */
    do {
      ++pHostname;
      nptr = query;
      ++query;
      for(n = 0; *pHostname != '.' && *pHostname != 0; ++pHostname) {
        *query = *pHostname;
        ++query;
        ++n;
      }
      *nptr = n;
    } while(*pHostname != 0);
    *query++='\0';

    /* fill dns query */
    qry.type  = htons(DNS_RRTYPE_A);
    qry.class = htons(DNS_RRCLASS_IN);
    MEMCPY( query, &qry, SIZEOF_DNS_QUERY);

    /* resize pbuf to the exact dns query */
    pbuf_realloc(p, (query + SIZEOF_DNS_QUERY) - ((char*)(p->payload)));

    /* connect to the server for faster receiving */
    udp_connect(dns_pcb, &dns_servers[numdns], DNS_SERVER_PORT);
    /* send dns packet */
    err = udp_sendto(dns_pcb, p, &dns_servers[numdns], DNS_SERVER_PORT);

    /* free pbuf */
    pbuf_free(p);
  } else {
    err = ERR_MEM;
  }

  return err;
}

/**
 * dns_check_entry() - see if pEntry has not yet been queried and, if so, sends out a query.
 * Check an entry in the dns_table:
 * - send out query for new entries
 * - retry old pending entries on timeout (also with different servers)
 * - remove completed entries from the table if their TTL has expired
 *
 * @param i index of the dns_table entry to check
 */
static void
dns_check_entry(u8_t i)
{
  struct dns_table_entry *pEntry = &dns_table[i];

  LWIP_ASSERT("array index out of bounds", i < DNS_TABLE_SIZE);

  switch(pEntry->state) {

    case DNS_STATE_NEW: {
      /* initialize new entry */
      pEntry->state   = DNS_STATE_ASKING;