nmap_dns.cc

/***************************************************************************
 * nmap_dns.cc -- Handles parallel reverse DNS resolution for target IPs   *
 *                                                                         *
 ***********************IMPORTANT NMAP LICENSE TERMS************************
 *                                                                         *
 * The Nmap Security Scanner is (C) 1996-2016 Insecure.Com LLC. Nmap is    *
 * also a registered trademark of Insecure.Com LLC.  This program is free  *
 * software; you may redistribute and/or modify it under the terms of the  *
 * GNU General Public License as published by the Free Software            *
 * Foundation; Version 2 ("GPL"), BUT ONLY WITH ALL OF THE CLARIFICATIONS  *
 * AND EXCEPTIONS DESCRIBED HEREIN.  This guarantees your right to use,    *
 * modify, and redistribute this software under certain conditions.  If    *
 * you wish to embed Nmap technology into proprietary software, we sell    *
 * alternative licenses (contact sales@nmap.com).  Dozens of software      *
 * vendors already license Nmap technology such as host discovery, port    *
 * scanning, OS detection, version detection, and the Nmap Scripting       *
 * Engine.                                                                 *
 *                                                                         *
 * Note that the GPL places important restrictions on "derivative works",  *
 * yet it does not provide a detailed definition of that term.  To avoid   *
 * misunderstandings, we interpret that term as broadly as copyright law   *
 * allows.  For example, we consider an application to constitute a        *
 * derivative work for the purpose of this license if it does any of the   *
 * following with any software or content covered by this license          *
 * ("Covered Software"):                                                   *
 *                                                                         *
 * o Integrates source code from Covered Software.                         *
 *                                                                         *
 * o Reads or includes copyrighted data files, such as Nmap's nmap-os-db   *
 * or nmap-service-probes.                                                 *
 *                                                                         *
 * o Is designed specifically to execute Covered Software and parse the    *
 * results (as opposed to typical shell or execution-menu apps, which will *
 * execute anything you tell them to).                                     *
 *                                                                         *
 * o Includes Covered Software in a proprietary executable installer.  The *
 * installers produced by InstallShield are an example of this.  Including *
 * Nmap with other software in compressed or archival form does not        *
 * trigger this provision, provided appropriate open source decompression  *
 * or de-archiving software is widely available for no charge.  For the    *
 * purposes of this license, an installer is considered to include Covered *
 * Software even if it actually retrieves a copy of Covered Software from  *
 * another source during runtime (such as by downloading it from the       *
 * Internet).                                                              *
 *                                                                         *
 * o Links (statically or dynamically) to a library which does any of the  *
 * above.                                                                  *
 *                                                                         *
 * o Executes a helper program, module, or script to do any of the above.  *
 *                                                                         *
 * This list is not exclusive, but is meant to clarify our interpretation  *
 * of derived works with some common examples.  Other people may interpret *
 * the plain GPL differently, so we consider this a special exception to   *
 * the GPL that we apply to Covered Software.  Works which meet any of     *
 * these conditions must conform to all of the terms of this license,      *
 * particularly including the GPL Section 3 requirements of providing      *
 * source code and allowing free redistribution of the work as a whole.    *
 *                                                                         *
 * As another special exception to the GPL terms, Insecure.Com LLC grants  *
 * permission to link the code of this program with any version of the     *
 * OpenSSL library which is distributed under a license identical to that  *
 * listed in the included docs/licenses/OpenSSL.txt file, and distribute   *
 * linked combinations including the two.                                  *
 *                                                                         *
 * Any redistribution of Covered Software, including any derived works,    *
 * must obey and carry forward all of the terms of this license, including *
 * obeying all GPL rules and restrictions.  For example, source code of    *
 * the whole work must be provided and free redistribution must be         *
 * allowed.  All GPL references to "this License", are to be treated as    *
 * including the terms and conditions of this license text as well.        *
 *                                                                         *
 * Because this license imposes special exceptions to the GPL, Covered     *
 * Work may not be combined (even as part of a larger work) with plain GPL *
 * software.  The terms, conditions, and exceptions of this license must   *
 * be included as well.  This license is incompatible with some other open *
 * source licenses as well.  In some cases we can relicense portions of    *
 * Nmap or grant special permissions to use it in other open source        *
 * software.  Please contact fyodor@nmap.org with any such requests.       *
 * Similarly, we don't incorporate incompatible open source software into  *
 * Covered Software without special permission from the copyright holders. *
 *                                                                         *
 * If you have any questions about the licensing restrictions on using     *
 * Nmap in other works, are happy to help.  As mentioned above, we also    *
 * offer alternative license to integrate Nmap into proprietary            *
 * applications and appliances.  These contracts have been sold to dozens  *
 * of software vendors, and generally include a perpetual license as well  *
 * as providing for priority support and updates.  They also fund the      *
 * continued development of Nmap.  Please email sales@nmap.com for further *
 * information.                                                            *
 *                                                                         *
 * If you have received a written license agreement or contract for        *
 * Covered Software stating terms other than these, you may choose to use  *
 * and redistribute Covered Software under those terms instead of these.   *
 *                                                                         *
 * Source is provided to this software because we believe users have a     *
 * right to know exactly what a program is going to do before they run it. *
 * This also allows you to audit the software for security holes.          *
 *                                                                         *
 * Source code also allows you to port Nmap to new platforms, fix bugs,    *
 * and add new features.  You are highly encouraged to send your changes   *
 * to the dev@nmap.org mailing list for possible incorporation into the    *
 * main distribution.  By sending these changes to Fyodor or one of the    *
 * Insecure.Org development mailing lists, or checking them into the Nmap  *
 * source code repository, it is understood (unless you specify otherwise) *
 * that you are offering the Nmap Project (Insecure.Com LLC) the           *
 * unlimited, non-exclusive right to reuse, modify, and relicense the      *
 * code.  Nmap will always be available Open Source, but this is important *
 * because the inability to relicense code has caused devastating problems *
 * for other Free Software projects (such as KDE and NASM).  We also       *
 * occasionally relicense the code to third parties as discussed above.    *
 * If you wish to specify special license conditions of your               *
 * contributions, just say so when you send them.                          *
 *                                                                         *
 * This program is distributed in the hope that it will be useful, but     *
 * WITHOUT ANY WARRANTY; without even the implied warranty of              *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the Nmap      *
 * license file for more details (it's in a COPYING file included with     *
 * Nmap, and also available from https://svn.nmap.org/nmap/COPYING)        *
 *                                                                         *
 ***************************************************************************/

// mass_rdns - Parallel Asynchronous Reverse DNS Resolution
//
// One of Nmap's features is to perform reverse DNS queries
// on large number of IP addresses. Nmap supports 2 different
// methods of accomplishing this:
//
// System Resolver (specified using --system-dns):
// Performs sequential getnameinfo() calls on all the IPs.
// As reliable as your system resolver, almost guaranteed
// to be portable, but intolerably slow for scans of hundreds
// or more because the result from each query needs to be
// received before the next one can be sent.
//
// Mass/Async DNS (default):
// Attempts to resolve host names in parallel using a set
// of DNS servers. DNS servers are found here:
//
//    --dns-servers <serv1[,serv2],...>   (all platforms - overrides everything else)
//
//    /etc/resolv.conf   (only on unix)
//
//    These registry keys:   (only on windows)
//
//      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\NameServer
//      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\DhcpNameServer
//      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\*\NameServer
//      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\*\DhcpNameServer
//
//
// Also, most systems maintain a file "/etc/hosts" that contains
// IP to hostname mappings. We also try to consult these files. Here
// is where we look for the files:
//
// Unix: /etc/hosts
//
// Windows:
//   for 95/98/Me: WINDOWS_DIR\hosts
//   for NT/2000/XP Pro: WINDOWS_DIR\system32\drivers\etc\hosts
//   for XP Home: WINDOWS_DIR\system32\drivers\etc\hosts
//     --see http://accs-net.com/hosts/how_to_use_hosts.html
//
//
// Created by Doug Hoyte <doug at hcsw.org> http://www.hcsw.org
// DNS Caching and aging added by Eddie Bell ejlbell@gmail.com 2007
// IPv6 and improved DNS cache by Gioacchino Mazzurco <gmazzurco89@gmail.com> 2015


// TODO:
//
// * Tune performance parameters
//
// * Figure out best way to estimate completion time
//   and display it in a ScanProgressMeter

#ifdef WIN32
#include "nmap_winconfig.h"
#endif

#include "nmap.h"
#include "NmapOps.h"
#include "nmap_dns.h"
#include "nsock.h"
#include "nmap_error.h"
#include "nmap_tty.h"
#include "timing.h"
#include "Target.h"

#include <stdlib.h>
#include <limits.h>
#include <list>
#include <vector>

extern NmapOps o;



//------------------- Performance Parameters ---------------------

// Algorithm:
//
// A batch of num_targets hosts is passed to nmap_mass_rdns():
//   void nmap_mass_rdns(Target **targets, int num_targets)
//
// mass_dns sends out CAPACITY_MIN of these hosts to the DNS
// servers detected, alternating in sequence.

// When a request is fulfilled (either a resolved domain, NXDomain,
// or confirmed ServFail) CAPACITY_UP_STEP is added to the current
// capacity of the server the request was found by.

// When a request times out and retries on the same server,
// the server's capacity is scaled by CAPACITY_MINOR_DOWN_STEP.

// When a request times out and moves to the next server in
// sequence, the server's capacity is scaled by CAPACITY_MAJOR_DOWN_STEP.

// mass_dns tries to maintain the current number of "outstanding
// queries" on each server to that of its current capacity. The
// packet is dropped if it cycles through all specified DNS
// servers.


// Since multiple DNS servers can be specified, different sequences
// of timers are maintained. These are the various retransmission
// intervals for each server before we move on to the next DNS server:

// In milliseconds
// Each row MUST be terminated with -1
static int read_timeouts[][4] = {
  { 4000, 4000, 5000, -1 }, // 1 server
  { 2500, 4000,   -1, -1 }, // 2 servers
  { 2500, 3000,   -1, -1 }, // 3+ servers
};

#define CAPACITY_MIN 10
#define CAPACITY_MAX 200
#define CAPACITY_UP_STEP 2
#define CAPACITY_MINOR_DOWN_SCALE 0.9
#define CAPACITY_MAJOR_DOWN_SCALE 0.7

// Each request will try to resolve on at most this many servers:
#define SERVERS_TO_TRY 3


//------------------- Other Parameters ---------------------

// How often to display a short debugging summary if debugging is
// specified. Lower numbers means it's displayed more often.
#define SUMMARY_DELAY 50

// Minimum debugging level to display packet trace
#define TRACE_DEBUG_LEVEL 4

// The amount of time we wait for nsock_write() to complete before
// retransmission. This should almost never happen. (in milliseconds)
#define WRITE_TIMEOUT 100


//------------------- Internal Structures ---------------------

struct dns_server;
struct request;
typedef struct sockaddr_storage sockaddr_storage;

struct dns_server {
  std::string hostname;
  sockaddr_storage addr;
  size_t addr_len;
  nsock_iod nsd;
  int connected;
  int reqs_on_wire;
  int capacity;
  int write_busy;
  std::list<request *> to_process;
  std::list<request *> in_process;
};

struct request {
  Target *targ;
  struct timeval timeout;
  int tries;
  int servers_tried;
  dns_server *first_server;
  dns_server *curr_server;
  u16 id;
};

/*keeps record of a request going through a particular DNS server
helps in attaining faster lookup based on ID */
struct info{
  dns_server *server;
  request *tpreq;
};

class HostElem
{
public:
  HostElem(const std::string & name_, const sockaddr_storage & ip) :
    name(name_), addr(ip), cache_hits(0) {}
  ~HostElem() {}

  /* Ages entries and return true with a cache hit of 0 (the least used) */
  static bool isTimeToClean(HostElem he)
  {
    if(he.cache_hits)
    {
      he.cache_hits >>= 1;
      return false;
    }

    return true;
  }

  const std::string name;
  const sockaddr_storage addr;
  u8 cache_hits;
};

class HostCacheLine : public std::list<HostElem>{};

class HostCache
{
public:
  //            TODO: avoid hardcode this constant
  HostCache() : lines_count(256), hash_mask(lines_count-1),
    hosts_storage(new HostCacheLine[lines_count]), elements_count(0)
  {}
  ~HostCache()
  {
    delete[] hosts_storage;
  }

  u32 hash(sockaddr_storage ip)
  {
    u32 ret = 0;

    switch (ip.ss_family)
    {
      case AF_INET:
      {
        u8 * ipv4 = (u8 *) &((const struct sockaddr_in *) &ip)->sin_addr;
        // Shuffle bytes a little so we avoid awful performances in commons
        // usages patterns like 10.0.1-255.1 and lines_count 256
        ret = ipv4[0] + (ipv4[1]<<3) + (ipv4[2]<<5) + (ipv4[3]<<7);
        break;
      }
      case AF_INET6:
      {
        const struct sockaddr_in6 * sa6 = (const struct sockaddr_in6 *) &ip;
        u32 * ipv6 = (u32 *) sa6->sin6_addr.s6_addr;
        ret = ipv6[0] + ipv6[1] + ipv6[2] + ipv6[3];
        break;
      }
    }

    return ret & hash_mask;
  }

  /* Add to the dns cache. If there are too many entries
   * we age and remove the least frequently used ones to
   * make more space. */
  bool add( const sockaddr_storage & ip, const std::string & hname)
  {
    std::string discard;
    if(lookup(ip, discard)) return false;

    if(elements_count >= lines_count) prune();

    HostElem he(hname, ip);
    hosts_storage[hash(ip)].push_back(he);
    ++elements_count;
    return true;
  }

  u32 prune()
  {
    u32 original_count = elements_count;
    for(u32 i = 0; i < lines_count; ++i)
    {
      std::list<HostElem>::iterator it = find_if(hosts_storage[i].begin(),
                                                 hosts_storage[i].end(),
                                                 HostElem::isTimeToClean);
      while ( it != hosts_storage[i].end() )
      {
        it = hosts_storage[i].erase(it);
        assert(elements_count > 0);
        --elements_count;
      }
    }

    return original_count - elements_count;
  }

  /* Search for a hostname in the cache and increment
   * its cache hit counter if found */
  bool lookup(const sockaddr_storage & ip, std::string & name)
  {
    std::list<HostElem>::iterator hostI;
    u32 ip_hash = hash(ip);
    for( hostI = hosts_storage[ip_hash].begin();
         hostI != hosts_storage[ip_hash].end();
         ++hostI)
    {
      if (sockaddr_storage_equal(&hostI->addr, &ip))
      {
        if(hostI->cache_hits < UCHAR_MAX)
          hostI->cache_hits++;
        name = hostI->name;
        return true;
      }
    }
    return false;
  }

protected:
  const u32 lines_count;
  const u32 hash_mask;
  HostCacheLine * const hosts_storage;
  u32 elements_count;
};

//------------------- Globals ---------------------

u16 DNS::Factory::progressiveId = get_random_u16();
static std::list<dns_server> servs;
static std::list<request *> new_reqs;
static std::list<request *> deferred_reqs;
static std::map<u16, info> records;
static int total_reqs;
static nsock_pool dnspool=NULL;

/* The DNS cache, not just for entries from /etc/hosts. */
static HostCache host_cache;

static int stat_actual, stat_ok, stat_nx, stat_sf, stat_trans, stat_dropped, stat_cname;
static struct timeval starttv;
static int read_timeout_index;

static int firstrun=1;
static ScanProgressMeter *SPM;


//------------------- Prototypes and macros ---------------------
static void read_evt_handler(nsock_pool, nsock_event, void *);
static void put_dns_packet_on_wire(request *req);

#define ACTION_FINISHED 0
#define ACTION_SYSTEM_RESOLVE 1
#define ACTION_TIMEOUT 2

//------------------- Misc code ---------------------

static void output_summary() {
  int tp = stat_ok + stat_nx + stat_dropped;
  struct timeval now;

  memcpy(&now, nsock_gettimeofday(), sizeof(struct timeval));

  if (o.debugging && (tp%SUMMARY_DELAY == 0))
    log_write(LOG_STDOUT, "mass_rdns: %.2fs %d/%d [#: %lu, OK: %d, NX: %d, DR: %d, SF: %d, TR: %d]\n",
                    TIMEVAL_MSEC_SUBTRACT(now, starttv) / 1000.0,
                    tp, stat_actual,
                    (unsigned long) servs.size(), stat_ok, stat_nx, stat_dropped, stat_sf, stat_trans);
}

static void check_capacities(dns_server *tpserv) {
  if (tpserv->capacity < CAPACITY_MIN) tpserv->capacity = CAPACITY_MIN;
  if (tpserv->capacity > CAPACITY_MAX) tpserv->capacity = CAPACITY_MAX;
  if (o.debugging >= TRACE_DEBUG_LEVEL) log_write(LOG_STDOUT, "CAPACITY <%s> = %d\n", tpserv->hostname.c_str(), tpserv->capacity);
}

// Closes all nsis created in connect_dns_servers()
static void close_dns_servers() {
  std::list<dns_server>::iterator serverI;

  for(serverI = servs.begin(); serverI != servs.end(); serverI++) {
    if (serverI->connected) {
      nsock_iod_delete(serverI->nsd, NSOCK_PENDING_SILENT);
      serverI->connected = 0;
      serverI->to_process.clear();
      serverI->in_process.clear();
    }
  }
}


// Puts as many packets on the line as capacity will allow
static void do_possible_writes() {
  std::list<dns_server>::iterator servI;
  request *tpreq;

  for(servI = servs.begin(); servI != servs.end(); servI++) {
    if (servI->write_busy == 0 && servI->reqs_on_wire < servI->capacity) {
      tpreq = NULL;
      if (!servI->to_process.empty()) {
        tpreq = servI->to_process.front();
        servI->to_process.pop_front();
      } else if (!new_reqs.empty()) {
        tpreq = new_reqs.front();
        assert(tpreq != NULL);
        tpreq->first_server = tpreq->curr_server = &*servI;
        new_reqs.pop_front();
      }

      if (tpreq) {
        if (o.debugging >= TRACE_DEBUG_LEVEL)
           log_write(LOG_STDOUT, "mass_rdns: TRANSMITTING for <%s> (server <%s>)\n", tpreq->targ->targetipstr() , servI->hostname.c_str());
        stat_trans++;
        put_dns_packet_on_wire(tpreq);
      }
    }
  }
}

// nsock write handler
static void write_evt_handler(nsock_pool nsp, nsock_event evt, void *req_v) {
  info record;
  request *req = (request *) req_v;

  req->curr_server->write_busy = 0;

  req->curr_server->in_process.push_front(req);
  record.tpreq = req;
  record.server = req->curr_server;
  records[req->id] = record;

  do_possible_writes();
}

// Takes a DNS request structure and actually puts it on the wire
// (calls nsock_write()). Does various other tasks like recording
// the time for the timeout.
static void put_dns_packet_on_wire(request *req) {
  const size_t maxlen = 512;
  u8 packet[maxlen];
  size_t plen=0;

  struct timeval now, timeout;

  req->id = DNS::Factory::progressiveId;
  req->curr_server->write_busy = 1;
  req->curr_server->reqs_on_wire++;

  plen = DNS::Factory::buildReverseRequest(*req->targ->TargetSockAddr(), packet, maxlen);

  memcpy(&now, nsock_gettimeofday(), sizeof(struct timeval));
  TIMEVAL_MSEC_ADD(timeout, now, read_timeouts[read_timeout_index][req->tries]);
  memcpy(&req->timeout, &timeout, sizeof(struct timeval));

  req->tries++;

  nsock_write(dnspool, req->curr_server->nsd, write_evt_handler, WRITE_TIMEOUT, req, reinterpret_cast<const char *>(packet), plen);
}

// Processes DNS packets that have timed out
// Returns time until next read timeout
static int deal_with_timedout_reads() {
  std::list<dns_server>::iterator servI;
  std::list<dns_server>::iterator servItemp;
  std::list<request *>::iterator reqI;
  std::list<request *>::iterator nextI;
  std::map<u16, info>::iterator infoI;
  request *tpreq;
  struct timeval now;
  int tp, min_timeout = INT_MAX;

  memcpy(&now, nsock_gettimeofday(), sizeof(struct timeval));

  if (keyWasPressed())
    SPM->printStats((double) (stat_ok + stat_nx + stat_dropped) / stat_actual, &now);

  for(servI = servs.begin(); servI != servs.end(); servI++) {
    nextI = servI->in_process.begin();
    if (nextI == servI->in_process.end()) continue;

    do {
      reqI = nextI++;
      tpreq = *reqI;

      tp = TIMEVAL_MSEC_SUBTRACT(tpreq->timeout, now);
      if (tp > 0 && tp < min_timeout) min_timeout = tp;

      if (tp <= 0) {
        servI->capacity = (int) (servI->capacity * CAPACITY_MINOR_DOWN_SCALE);
        check_capacities(&*servI);
        servI->in_process.erase(reqI);
        std::map<u16, info>::iterator it = records.find(tpreq->id);
        if ( it != records.end() )
          records.erase(it);
        servI->reqs_on_wire--;

        // If we've tried this server enough times, move to the next one
        if (read_timeouts[read_timeout_index][tpreq->tries] == -1) {
          servI->capacity = (int) (servI->capacity * CAPACITY_MAJOR_DOWN_SCALE);
          check_capacities(&*servI);

          servItemp = servI;
          servItemp++;

          if (servItemp == servs.end()) servItemp = servs.begin();

          tpreq->curr_server = &*servItemp;
          tpreq->tries = 0;
          tpreq->servers_tried++;

          if (tpreq->curr_server == tpreq->first_server || tpreq->servers_tried == SERVERS_TO_TRY) {
            // Either give up on the IP
            // or, for maximum reliability, put the server back into processing
            // Note it's possible that this will never terminate.
            // FIXME: Find a good compromise

            // **** We've already tried all servers... give up
            if (o.debugging >= TRACE_DEBUG_LEVEL) log_write(LOG_STDOUT, "mass_rdns: *DR*OPPING <%s>\n", tpreq->targ->targetipstr());

            output_summary();
            stat_dropped++;
            total_reqs--;
            infoI = records.find(tpreq->id);
            if ( infoI != records.end() )
              records.erase(infoI);
            delete tpreq;

            // **** OR We start at the back of this server's queue
            //servItemp->to_process.push_back(tpreq);
          } else {
            servItemp->to_process.push_back(tpreq);
          }
        } else {
          servI->to_process.push_back(tpreq);
        }

    }

    } while (nextI != servI->in_process.end());

  }

  if (min_timeout > 500) return 500;
  else return min_timeout;

}

// After processing a DNS response, we search through the IPs we're
// looking for and update their results as necessary.
// Returns non-zero if this matches a query we're looking for
static int process_result(const sockaddr_storage &ip, const std::string &result, int action, u16 id)
{
  request *tpreq;
  std::map<u16, info>::iterator infoI;
  dns_server *server;

  infoI = records.find(id);

  if( infoI != records.end() ){

    tpreq = infoI->second.tpreq;
    server = infoI->second.server;

    if( !result.empty() && !sockaddr_storage_equal(&ip, tpreq->targ->TargetSockAddr()) )
      return 0;

    if (action == ACTION_SYSTEM_RESOLVE || action == ACTION_FINISHED)
    {
      server->capacity += CAPACITY_UP_STEP;
      check_capacities(&*server);

      if(!result.empty())
      {
        tpreq->targ->setHostName(result.c_str());
        host_cache.add(* tpreq->targ->TargetSockAddr(), result);
      }

      records.erase(infoI);
      server->in_process.remove(tpreq);
      server->reqs_on_wire--;

      total_reqs--;

      if (action == ACTION_SYSTEM_RESOLVE) deferred_reqs.push_back(tpreq);
      if (action == ACTION_FINISHED) delete tpreq;
    }
    else
    {
      memcpy(&tpreq->timeout, nsock_gettimeofday(), sizeof(struct timeval));
      deal_with_timedout_reads();
    }

    do_possible_writes();

    // Close DNS servers if we're all done so that we kill
    // all events and return from nsock_loop immediateley
    if (total_reqs == 0)
      close_dns_servers();
    return 1;
  }
  return 0;
}

// Nsock read handler. One nsock read for each DNS server exists at each
// time. This function uses various helper functions as defined above.
static void read_evt_handler(nsock_pool nsp, nsock_event evt, void *) {
  u8 *buf;
  int buflen;

  if (total_reqs >= 1)
    nsock_read(nsp, nse_iod(evt), read_evt_handler, -1, NULL);

  if (nse_type(evt) != NSE_TYPE_READ || nse_status(evt) != NSE_STATUS_SUCCESS) {
    if (o.debugging)
      log_write(LOG_STDOUT, "mass_dns: warning: got a %s:%s in %s()\n",
        nse_type2str(nse_type(evt)),
        nse_status2str(nse_status(evt)), __func__);
    return;
  }

  buf = (unsigned char *) nse_readbuf(evt, &buflen);

  DNS::Packet p;
  size_t readed_bytes = p.parseFromBuffer(buf, buflen);
  if(readed_bytes < DNS::DATA) return;

  // We should have 1+ queries:
  u16 &f = p.flags;
  if(p.queries.empty() || !DNS_HAS_FLAG(f, DNS::RESPONSE) ||
     !DNS_HAS_FLAG(f, DNS::OP_STANDARD_QUERY) ||
     (f & DNS::ZERO) || DNS_HAS_ERR(f, DNS::ERR_FORMAT) ||
     DNS_HAS_ERR(f, DNS::ERR_NOT_IMPLEMENTED) || DNS_HAS_ERR(f, DNS::ERR_REFUSED))
    return;

  if (DNS_HAS_ERR(f, DNS::ERR_NAME))
  {
    sockaddr_storage discard;
    if(process_result(discard, "", ACTION_FINISHED, p.id))
    {
      if (o.debugging >= TRACE_DEBUG_LEVEL)
        log_write(LOG_STDOUT, "mass_rdns: NXDOMAIN <id = %d>\n", p.id);
      output_summary();
      stat_nx++;
    }

    return;
  }

  if (DNS_HAS_ERR(f, DNS::ERR_SERVFAIL))
  {
    sockaddr_storage discard;
    if (process_result(discard, "", ACTION_TIMEOUT, p.id))
    {
      if (o.debugging >= TRACE_DEBUG_LEVEL)
        log_write(LOG_STDOUT, "mass_rdns: SERVFAIL <id = %d>\n", p.id);
      stat_sf++;
    }

    return;
  }

  bool processing_successful = false;

  sockaddr_storage ip;
  ip.ss_family = AF_UNSPEC;
  std::string alias;

  for(std::list<DNS::Answer>::const_iterator it = p.answers.begin();
      it != p.answers.end() && !processing_successful; ++it )
  {
    const DNS::Answer &a = *it;
    if(a.record_class == DNS::CLASS_IN)
    {
      switch(a.record_type)
      {
        case DNS::PTR:
        {
          DNS::PTR_Record * ptr = static_cast<DNS::PTR_Record *>(a.record);

          if(
            // If CNAME answer filled in ip with a matching alias
            (ip.ss_family != AF_UNSPEC && a.name == alias )
            // Or if we can get an IP from reversing the .arpa PTR address
            || DNS::Factory::ptrToIp(a.name, ip))
          {
            if ((processing_successful = process_result(ip, ptr->value, ACTION_FINISHED, p.id)))
            {
              if (o.debugging >= TRACE_DEBUG_LEVEL)
              {
                char ipstr[INET6_ADDRSTRLEN];
                sockaddr_storage_iptop(&ip, ipstr);
                log_write(LOG_STDOUT, "mass_rdns: OK MATCHED <%s> to <%s>\n",
                          ipstr,
                          ptr->value.c_str());
              }
              output_summary();
              stat_ok++;
            }
          }
          break;
        }
        case DNS::CNAME:
        {
          if(DNS::Factory::ptrToIp(a.name, ip))
          {
            DNS::CNAME_Record * cname = static_cast<DNS::CNAME_Record *>(a.record);
            alias = cname->value;
            if (o.debugging >= TRACE_DEBUG_LEVEL)
            {
              char ipstr[INET6_ADDRSTRLEN];
              sockaddr_storage_iptop(&ip, ipstr);
              log_write(LOG_STDOUT, "mass_rdns: CNAME found for <%s> to <%s>\n", ipstr, alias.c_str());
            }
          }
          break;
        }
        default:
          break;
      }
    }
  }

  if (!processing_successful) {
    if (DNS_HAS_FLAG(f, DNS::TRUNCATED)) {
      // TODO: TCP fallback, or only use system resolver if user didn't specify --dns-servers
      process_result(ip, "", ACTION_SYSTEM_RESOLVE, p.id);
    }
    else if (!alias.empty()) {
      if (o.debugging >= TRACE_DEBUG_LEVEL)
      {
        char ipstr[INET6_ADDRSTRLEN];
        sockaddr_storage_iptop(&ip, ipstr);
        log_write(LOG_STDOUT, "mass_rdns: CNAME for <%s> not processed.\n", ipstr);
      }
      // TODO: Send a PTR request for alias instead. Meanwhile, we'll just fall
      // back to using system resolver. Alternative: report the canonical name
      // (alias), but that's not very useful.
      process_result(ip, "", ACTION_SYSTEM_RESOLVE, p.id);
    }
    else {
      if (o.debugging >= TRACE_DEBUG_LEVEL) {
        log_write(LOG_STDOUT, "mass_rdns: Unable to process the response\n");
      }
    }
  }
}


// nsock connect handler - Empty because it doesn't really need to do anything...
static void connect_evt_handler(nsock_pool, nsock_event, void *) {}


// Adds DNS servers to the dns_server list. They can be separated by
// commas or spaces - NOTE this doesn't actually do any connecting!
static void add_dns_server(char *ipaddrs) {
  std::list<dns_server>::iterator servI;
  char *hostname;
  struct sockaddr_storage addr;
  size_t addr_len = sizeof(addr);

  for (hostname = strtok(ipaddrs, " ,"); hostname != NULL; hostname = strtok(NULL, " ,")) {

    if (resolve(hostname, 0, (struct sockaddr_storage *) &addr, &addr_len,
      o.spoofsource ? o.af() : PF_UNSPEC) != 0)
      continue;

    for(servI = servs.begin(); servI != servs.end(); servI++) {
      // Already added!
      if (memcmp(&addr, &servI->addr, sizeof(addr)) == 0) break;
    }

    // If it hasn't already been added, add it!
    if (servI == servs.end()) {
      dns_server tpserv;

      tpserv.hostname = hostname;
      memcpy(&tpserv.addr, &addr, sizeof(addr));
      tpserv.addr_len = addr_len;

      servs.push_front(tpserv);

      if (o.debugging) log_write(LOG_STDOUT, "mass_rdns: Using DNS server %s\n", hostname);
    }

  }

}

// Creates a new nsi for each DNS server
static void connect_dns_servers() {
  std::list<dns_server>::iterator serverI;
  for(serverI = servs.begin(); serverI != servs.end(); serverI++) {
    serverI->nsd = nsock_iod_new(dnspool, NULL);
    if (o.spoofsource) {
      struct sockaddr_storage ss;
      size_t sslen;
      o.SourceSockAddr(&ss, &sslen);
      nsock_iod_set_localaddr(serverI->nsd, &ss, sslen);
    }
    if (o.ipoptionslen)
      nsock_iod_set_ipoptions(serverI->nsd, o.ipoptions, o.ipoptionslen);
    serverI->reqs_on_wire = 0;
    serverI->capacity = CAPACITY_MIN;
    serverI->write_busy = 0;

    nsock_connect_udp(dnspool, serverI->nsd, connect_evt_handler, NULL, (struct sockaddr *) &serverI->addr, serverI->addr_len, 53);
    nsock_read(dnspool, serverI->nsd, read_evt_handler, -1, NULL);
    serverI->connected = 1;
  }

}


#ifdef WIN32
static bool interface_is_known_by_guid(const char *guid) {
  struct interface_info *iflist;
  int i, n;

  iflist = getinterfaces(&n, NULL, 0);
  if (iflist == NULL)
    return false;

  for (i = 0; i < n; i++) {
    char pcap_name[1024];
    char *pcap_guid;

    if (!DnetName2PcapName(iflist[i].devname, pcap_name, sizeof(pcap_name)))
      continue;
    pcap_guid = strchr(pcap_name, '{');
    if (pcap_guid == NULL)
      continue;
    if (strcmp(guid, pcap_guid) == 0)
      return true;
  }

  return false;
}

// Reads the Windows registry and adds all the nameservers found via the
// add_dns_server() function.
void win32_read_registry() {
  HKEY hKey;
  HKEY hKey2;
  char keybasebuf[2048];
  char buf[2048], keyname[2048], *p;
  DWORD sz, i;

  Snprintf(keybasebuf, sizeof(keybasebuf), "SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters");
  if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, keybasebuf,
                    0, KEY_READ, &hKey) != ERROR_SUCCESS) {
    if (firstrun) error("mass_dns: warning: Error opening registry to read DNS servers. Try using --system-dns or specify valid servers with --dns-servers");
    return;
  }

  sz = sizeof(buf);
  if (RegQueryValueEx(hKey, "NameServer", NULL, NULL, (LPBYTE) buf, (LPDWORD) &sz) == ERROR_SUCCESS)
    add_dns_server(buf);

  sz = sizeof(buf);
  if (RegQueryValueEx(hKey, "DhcpNameServer", NULL, NULL, (LPBYTE) buf, (LPDWORD) &sz) == ERROR_SUCCESS)
    add_dns_server(buf);

  RegCloseKey(hKey);

  Snprintf(keybasebuf, sizeof(keybasebuf), "SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters\\Interfaces");
  if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, keybasebuf,
                    0, KEY_ENUMERATE_SUB_KEYS, &hKey) == ERROR_SUCCESS) {

    for (i=0; sz = sizeof(buf), RegEnumKeyEx(hKey, i, buf, &sz, NULL, NULL, NULL, NULL) != ERROR_NO_MORE_ITEMS; i++) {

      // If we don't have pcap, interface_is_known_by_guid will crash. Just use any servers we can find.
      if (o.have_pcap && !interface_is_known_by_guid(buf)) {
        if (o.debugging > 1)
          log_write(LOG_PLAIN, "Interface %s is not known; ignoring its nameservers.\n", buf);
        continue;
      }

      Snprintf(keyname, sizeof(keyname), "SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters\\Interfaces\\%s", buf);

      if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, keyname,
                        0, KEY_READ, &hKey2) == ERROR_SUCCESS) {

        sz = sizeof(buf);
        if (RegQueryValueEx(hKey2, "DhcpNameServer", NULL, NULL, (LPBYTE) buf, (LPDWORD) &sz) == ERROR_SUCCESS)
          add_dns_server(buf);

        sz = sizeof(buf);
        if (RegQueryValueEx(hKey2, "NameServer", NULL, NULL, (LPBYTE) buf, (LPDWORD) &sz) == ERROR_SUCCESS)
          add_dns_server(buf);

        RegCloseKey(hKey2);
      }
    }

    RegCloseKey(hKey);

  }

}
#endif // WIN32



// Parses /etc/resolv.conf (unix) and adds all the nameservers found via the
// add_dns_server() function.
static void parse_resolvdotconf() {
  FILE *fp;
  char buf[2048], *tp;
  char fmt[32];
  char ipaddr[INET6_ADDRSTRLEN+1];

  fp = fopen("/etc/resolv.conf", "r");
  if (fp == NULL) {
    if (firstrun) error("mass_dns: warning: Unable to open /etc/resolv.conf. Try using --system-dns or specify valid servers with --dns-servers");
    return;
  }

  Snprintf(fmt, sizeof(fmt), "nameserver %%%us", INET6_ADDRSTRLEN);

  while (fgets(buf, sizeof(buf), fp)) {
    tp = buf;

    // Clip off comments #, \r, \n
    while (*tp != '\r' && *tp != '\n' && *tp != '#' && *tp) tp++;
    *tp = '\0';

    tp = buf;
    // Skip any leading whitespace
    while (*tp == ' ' || *tp == '\t') tp++;

    if (sscanf(tp, fmt, ipaddr) == 1) add_dns_server(ipaddr);
  }

  fclose(fp);
}


static void parse_etchosts(const char *fname) {
  FILE *fp;
  char buf[2048], hname[256], ipaddrstr[INET6_ADDRSTRLEN+1], *tp;
  sockaddr_storage ia;

  fp = fopen(fname, "r");
  if (fp == NULL) return; // silently is OK

  while (fgets(buf, sizeof(buf), fp)) {
    tp = buf;

    // Clip off comments #, \r, \n
    while (*tp != '\r' && *tp != '\n' && *tp != '#' && *tp) tp++;
    *tp = '\0';

    tp = buf;
    // Skip any leading whitespace
    while (*tp == ' ' || *tp == '\t') tp++;

    std::stringstream pattern;
    pattern << "%" << INET6_ADDRSTRLEN << "s %255s";
    if (sscanf(tp, pattern.str().c_str(), ipaddrstr, hname) == 2)
      if (sockaddr_storage_inet_pton(ipaddrstr, &ia))
      {
        const std::string hname_ = hname;
        host_cache.add(ia, hname_);
      }
  }

  fclose(fp);
}

static void etchosts_init(void) {
  static int initialized = 0;
  if (initialized) return;
  initialized = 1;

#ifdef WIN32
  char windows_dir[1024];
  char tpbuf[2048];
  int has_backslash;

  if (!GetWindowsDirectory(windows_dir, sizeof(windows_dir)))
    fatal("Failed to determine your windows directory");

  // If it has a backslash it's C:\, otherwise something like C:\WINNT
  has_backslash = (windows_dir[strlen(windows_dir)-1] == '\\');

  // Windows 95/98/Me:
  Snprintf(tpbuf, sizeof(tpbuf), "%s%shosts", windows_dir, has_backslash ? "" : "\\");
  parse_etchosts(tpbuf);

  // Windows NT/2000/XP/2K3:
  Snprintf(tpbuf, sizeof(tpbuf), "%s%ssystem32\\drivers\\etc\\hosts", windows_dir, has_backslash ? "" : "\\");
  parse_etchosts(tpbuf);

#else
  parse_etchosts("/etc/hosts");
#endif // WIN32
}

/* Initialize the global servs list of DNS servers. If the --dns-servers option
 * was given, use the listed servers; otherwise get the list from resolv.conf or
 * the Windows registry. If o.mass_dns is false, the list of servers is empty.
 * This function caches the results from the first time it is run. */
static void init_servs(void) {
  static bool initialized = false;

  if (initialized)
    return;

  initialized = true;

  if (!o.mass_dns)
    return;

  if (o.dns_servers) {
    add_dns_server(o.dns_servers);
  } else {
#ifndef WIN32
    parse_resolvdotconf();
#else
    win32_read_registry();
#endif
  }
}

//------------------- Main loops ---------------------


// Actual main loop
static void nmap_mass_rdns_core(Target **targets, int num_targets) {

  Target **hostI;
  std::list<request *>::iterator reqI;
  request *tpreq;
  int timeout;
  const char *tpname;
  int i;
  char spmobuf[1024];

  // If necessary, set up the dns server list
  init_servs();

  if (servs.size() == 0 && firstrun) error("mass_dns: warning: Unable to "
                                           "determine any DNS servers. Reverse"
                                           " DNS is disabled. Try using "
                                           "--system-dns or specify valid "
                                           "servers with --dns-servers");


  // If necessary, read /etc/hosts and put entries into the hashtable
  etchosts_init();


  total_reqs = 0;

  // Set up the request structure
  for(hostI = targets; hostI < targets+num_targets; hostI++)
  {
    if (!((*hostI)->flags & HOST_UP) && !o.resolve_all) continue;

    // See if it's cached
    std::string res;
    if (host_cache.lookup(*(*hostI)->TargetSockAddr(), res)) {
      tpname = res.c_str();
      (*hostI)->setHostName(tpname);
      continue;
    }

    tpreq = new request;
    tpreq->targ = *hostI;
    tpreq->tries = 0;
    tpreq->servers_tried = 0;

    new_reqs.push_back(tpreq);

    stat_actual++;
    total_reqs++;
  }

  if (total_reqs == 0 || servs.size() == 0) return;

  // And finally, do it!

  if ((dnspool = nsock_pool_new(NULL)) == NULL)
    fatal("Unable to create nsock pool in %s()", __func__);

  nsock_set_log_function(nmap_nsock_stderr_logger);
  nmap_adjust_loglevel(o.packetTrace());

  nsock_pool_set_device(dnspool, o.device);

  if (o.proxy_chain)
    nsock_pool_set_proxychain(dnspool, o.proxy_chain);

  connect_dns_servers();

  deferred_reqs.clear();

  read_timeout_index = MIN(sizeof(read_timeouts)/sizeof(read_timeouts[0]), servs.size()) - 1;

  Snprintf(spmobuf, sizeof(spmobuf), "Parallel DNS resolution of %d host%s.", num_targets, num_targets-1 ? "s" : "");
  SPM = new ScanProgressMeter(spmobuf);

  while (total_reqs > 0) {
    timeout = deal_with_timedout_reads();

    do_possible_writes();

    if (total_reqs <= 0) break;

    /* Because this can change with runtime interaction */
    nmap_adjust_loglevel(o.packetTrace());

    nsock_loop(dnspool, timeout);
  }

  SPM->endTask(NULL, NULL);
  delete SPM;

  close_dns_servers();

  nsock_pool_delete(dnspool);

  if (deferred_reqs.size() && o.debugging)
    log_write(LOG_STDOUT, "Performing system-dns for %d domain names that were deferred\n", (int) deferred_reqs.size());

  if (deferred_reqs.size()) {
    Snprintf(spmobuf, sizeof(spmobuf), "System DNS resolution of %u host%s.", (unsigned) deferred_reqs.size(), deferred_reqs.size()-1 ? "s" : "");
    SPM = new ScanProgressMeter(spmobuf);

    for(i=0, reqI = deferred_reqs.begin(); reqI != deferred_reqs.end(); reqI++, i++) {
      struct sockaddr_storage ss;
      size_t sslen;
      char hostname[FQDN_LEN + 1] = "";

      if (keyWasPressed())
        SPM->printStats((double) i / deferred_reqs.size(), NULL);

      tpreq = *reqI;

      if (tpreq->targ->TargetSockAddr(&ss, &sslen) != 0)
        fatal("Failed to get target socket address.");

      if (getnameinfo((struct sockaddr *)&ss, sslen, hostname,
                      sizeof(hostname), NULL, 0, NI_NAMEREQD) == 0) {
        stat_ok++;
        stat_cname++;
        tpreq->targ->setHostName(hostname);
      }

      delete tpreq;

    }

    SPM->endTask(NULL, NULL);
    delete SPM;
  }

  deferred_reqs.clear();

}

static void nmap_system_rdns_core(Target **targets, int num_targets) {
  Target **hostI;
  Target *currenths;
  struct sockaddr_storage ss;
  size_t sslen;
  char hostname[FQDN_LEN + 1] = "";
  char spmobuf[1024];
  int i;

  for(hostI = targets; hostI < targets+num_targets; hostI++) {
    currenths = *hostI;

    if (((currenths->flags & HOST_UP) || o.resolve_all) && !o.noresolve) stat_actual++;
  }

  Snprintf(spmobuf, sizeof(spmobuf), "System DNS resolution of %d host%s.", num_targets, num_targets-1 ? "s" : "");
  SPM = new ScanProgressMeter(spmobuf);

  for(i=0, hostI = targets; hostI < targets+num_targets; hostI++, i++) {
    currenths = *hostI;

    if (keyWasPressed())
      SPM->printStats((double) i / stat_actual, NULL);

    if (((currenths->flags & HOST_UP) || o.resolve_all) && !o.noresolve) {
      if (currenths->TargetSockAddr(&ss, &sslen) != 0)
        fatal("Failed to get target socket address.");
      if (getnameinfo((struct sockaddr *)&ss, sslen, hostname,
                      sizeof(hostname), NULL, 0, NI_NAMEREQD) == 0) {
        stat_ok++;
        currenths->setHostName(hostname);
      }
    }
  }

  SPM->endTask(NULL, NULL);
  delete SPM;
}


// Publicly available function. Basically just a wrapper so we
// can record time information, restart statistics, etc.
void nmap_mass_rdns(Target **targets, int num_targets) {

  struct timeval now;

  gettimeofday(&starttv, NULL);

  stat_actual = stat_ok = stat_nx = stat_sf = stat_trans = stat_dropped = stat_cname = 0;

  if (o.mass_dns)
    nmap_mass_rdns_core(targets, num_targets);
  else
    nmap_system_rdns_core(targets, num_targets);

  gettimeofday(&now, NULL);

  if (stat_actual > 0) {
    if (o.debugging || o.verbose >= 3) {
      if (o.mass_dns) {
        // #:  Number of DNS servers used
        // OK: Number of fully reverse resolved queries
        // NX: Number of confirmations of 'No such reverse domain eXists'
        // DR: Dropped IPs (no valid responses were received)
        // SF: Number of IPs that got 'Server Failure's
        // TR: Total number of transmissions necessary. The number of domains is ideal, higher is worse
        log_write(LOG_STDOUT, "DNS resolution of %d IPs took %.2fs. Mode: Async [#: %lu, OK: %d, NX: %d, DR: %d, SF: %d, TR: %d, CN: %d]\n",
                  stat_actual, TIMEVAL_MSEC_SUBTRACT(now, starttv) / 1000.0,
                  (unsigned long) servs.size(), stat_ok, stat_nx, stat_dropped, stat_sf, stat_trans, stat_cname);
      } else {
        log_write(LOG_STDOUT, "DNS resolution of %d IPs took %.2fs. Mode: System [OK: %d, ??: %d]\n",
                  stat_actual, TIMEVAL_MSEC_SUBTRACT(now, starttv) / 1000.0,
                  stat_ok, stat_actual - stat_ok);
      }
    }
  }

  firstrun=0;
}


// Returns a list of known DNS servers
std::list<std::string> get_dns_servers() {
  init_servs();

  // If the user said --system-dns (!o.mass_dns), we should never return a list
  // of servers.
  assert(o.mass_dns || servs.empty());

  std::list<dns_server>::iterator servI;
  std::list<std::string> serverList;
  for(servI = servs.begin(); servI != servs.end(); servI++) {
    serverList.push_back(inet_socktop((struct sockaddr_storage *) &servI->addr));
  }
  return serverList;
}

bool DNS::Factory::ipToPtr(const sockaddr_storage &ip, std::string &ptr)
{
  switch (ip.ss_family) {
    case AF_INET:
    {
      ptr.clear();
      char ipv4_c[INET_ADDRSTRLEN];
      if(!sockaddr_storage_iptop(&ip, ipv4_c)) return false;

      std::string ipv4 = ipv4_c;
      std::string octet;
      std::string::const_reverse_iterator crend = ipv4.rend();
      for (std::string::const_reverse_iterator c=ipv4.rbegin(); c != crend; ++c)
        if((*c)=='.')
        {
          ptr += octet + ".";
          octet.clear();
        }
        else
          octet = (*c) + octet;

      ptr += octet + IPV4_PTR_DOMAIN;

      break;
    }
    case AF_INET6:
    {
      ptr.clear();
      const struct sockaddr_in6 &s6 = (const struct sockaddr_in6 &) ip;
      const u8 * ipv6 = s6.sin6_addr.s6_addr;
      for (short i=15; i>=0; --i)
      {
        char tmp[3];
        sprintf(tmp, "%02x", ipv6[i]);
        ptr += '.';
        ptr += tmp[1];
        ptr += '.';
        ptr += tmp[0];
      }
      ptr.erase(ptr.begin());
      ptr += IPV6_PTR_DOMAIN;
      break;
    }
    default:
      return false;
  }
  return true;
}

bool DNS::Factory::ptrToIp(const std::string &ptr, sockaddr_storage &ip)
{
  std::string ip_str;

  size_t pos = ptr.rfind(IPV6_PTR_DOMAIN);
  if(pos != std::string::npos)
  {
    u8 counter = 0;
    for (std::string::const_reverse_iterator it = ptr.rend()-pos; it != ptr.rend(); ++it)
    {
      const char &c = *it;
      if(c != '.')
      {
        ip_str += c;
        if(++counter==4) counter=0, ip_str+=':';
      }
    }

    std::string::iterator it = ip_str.end()-1;
    if( *it == ':') ip_str.erase(it);
  }

  std::string mptr = '.' + ptr;
  pos = mptr.rfind(IPV4_PTR_DOMAIN);
  if(pos != std::string::npos)
  {

    std::string octet;
    std::string::const_reverse_iterator crend = mptr.rend();
    for (std::string::const_reverse_iterator it = crend-pos; it != crend; ++it)
    {
      const char &c = *it;
      if(c == '.')
      {
        std::reverse(octet.begin(), octet.end());
        ip_str += octet + '.';
        octet.clear();
      }
      else octet += c;
    }

    std::string::iterator it = ip_str.end()-1;
    if( *it == '.') ip_str.erase(it);
  }

  if(ip_str.empty())
    return false;

  return sockaddr_storage_inet_pton(ip_str.c_str(), &ip);
}

size_t DNS::Factory::buildSimpleRequest(const std::string &name, RECORD_TYPE rt, u8 *buf, size_t maxlen)
{
  size_t ret=0 , tmp=0;
  DNS_CHECK_ACCUMLATE(ret, tmp, putUnsignedShort(progressiveId++, buf, ID, maxlen)); // Postincrement inmportant here
  DNS_CHECK_ACCUMLATE(ret, tmp, putUnsignedShort(OP_STANDARD_QUERY | RECURSION_DESIRED, buf, FLAGS_OFFSET, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, putUnsignedShort(1, buf, QDCOUNT, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, putUnsignedShort(0, buf, ANCOUNT, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, putUnsignedShort(0, buf, NSCOUNT, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, putUnsignedShort(0, buf, ARCOUNT, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, putDomainName(name, buf, DATA, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, putUnsignedShort(rt, buf, ret, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, putUnsignedShort(CLASS_IN, buf, ret, maxlen));

  return ret;
}

size_t DNS::Factory::buildReverseRequest(const sockaddr_storage &ip, u8 *buf, size_t maxlen)
{
  std::string name;
  if(ipToPtr(ip,name))
    return buildSimpleRequest(name, PTR, buf, maxlen);
  return 0;
}

size_t DNS::Factory::putUnsignedShort(u16 num, u8 *buf, size_t offset, size_t maxlen)
{
  size_t max_access = offset+1;
  if(buf && (maxlen > max_access))
  {
    buf[offset] = (num >> 8) & 0xFF;
    buf[max_access] = num & 0xFF;
    return 2;
  }

  return 0;
}

size_t DNS::Factory::putDomainName(const std::string &name, u8 *buf, size_t offset, size_t maxlen)
{
  size_t ret=0;
  if( !( buf && (maxlen > (offset + name.length() + 1))) ) return ret;

  std::string namew = name + ".";
  std::string accumulator;
  for (std::string::const_iterator c=namew.begin(); c != namew.end(); ++c)
  {
    if((*c)=='.')
    {
      u8 lenght = accumulator.length();
      *(buf+offset+ret) = lenght;
      ret += 1;

      memcpy(buf+offset+ret, accumulator.c_str(), lenght);
      ret += lenght;
      accumulator.clear();
    }
    else
      accumulator += (*c);
  }

  *(buf+offset+ret) = 0;
  ret += 1;

  return ret;
}

size_t DNS::Factory::parseUnsignedShort(u16 &num, const u8 *buf, size_t offset, size_t maxlen)
{
  size_t max_access = offset+1;
  if(buf && (maxlen > max_access))
  {
    const u8 * n = buf + offset;
    num = n[1] + (n[0]<<8);
    return 2;
  }

  return 0;
}

size_t DNS::Factory::parseUnsignedInt(u32 &num, const u8 *buf, size_t offset, size_t maxlen)
{
  size_t max_access = offset+3;
  if(buf && (maxlen > max_access))
  {
    const u8 * n = buf + offset;
    num = n[3] + (n[2]<<8) + (n[1]<<16) + (n[0]<<24);
    return 4;
  }

  return 0;
}

size_t DNS::Factory::parseDomainName(std::string &name, const u8 *buf, size_t offset, size_t maxlen)
{
  size_t tmp, ret = 0;

  name.clear();
  while(u8 label_length = buf[offset+ret++]) // Postincrement important here
  {
    if((label_length & COMPRESSED_NAME) == COMPRESSED_NAME)
    {
      --ret; // The byte it's part of the pointer, wasn't really consumed yet
      u16 real_offset;
      DNS_CHECK_ACCUMLATE(ret, tmp, parseUnsignedShort(real_offset, buf, offset+ret, maxlen));
      real_offset -= COMPRESSED_NAME<<8;
      if( real_offset < offset)
      {
        std::string val;
        DNS_CHECK_ACCUMLATE(tmp, tmp, parseDomainName(val, buf, real_offset, maxlen));
        name+=val;
        return ret;
      }
      else return 0;
    }

    for(u8 i=0; i<label_length; ++i)
    {
      size_t index = offset+ret++;  // Postincrement important here
      DNS_CHECK_UPPER_BOUND(index, maxlen);
      name += buf[index];
    }
    name += '.';
  }

  std::string::iterator it = name.end()-1;
  if( *it == '.') name.erase(it);

  return ret;
}

size_t DNS::A_Record::parseFromBuffer(const u8 *buf, size_t offset, size_t maxlen)
{
  size_t tmp, ret = 0;
  u32 num;
  DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedInt(num, buf, offset, maxlen));

  memset(&value, 0, sizeof(value));
  struct sockaddr_in * ip4addr = (sockaddr_in *) &value;
  ip4addr->sin_family = AF_INET;
  ip4addr->sin_addr.s_addr = htonl(num);

  return ret;
}

size_t DNS::Query::parseFromBuffer(const u8 *buf, size_t offset, size_t maxlen)
{
  size_t ret=0;

  if (buf && ((maxlen - offset) > 5))
  {
    size_t tmp=0;
    DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseDomainName(name, buf, offset+ret, maxlen));
    DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(record_type, buf, offset+ret, maxlen));
    DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(record_class, buf, offset+ret, maxlen));
  }

  return ret;
}

size_t DNS::Answer::parseFromBuffer(const u8 *buf, size_t offset, size_t maxlen)
{
  size_t ret=0;

  if (buf && ((maxlen - offset) > 7))
  {
    size_t tmp;
    DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseDomainName(name, buf, offset+ret, maxlen));
    DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(record_type, buf, offset+ret, maxlen));
    DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(record_class, buf, offset+ret, maxlen));
    DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedInt(ttl, buf, offset+ret, maxlen));
    DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(length, buf, offset+ret, maxlen));

    DNS_CHECK_UPPER_BOUND(offset+ret+length, maxlen);

    switch(record_type)
    {
    case A:
    {
      record = new A_Record();
      break;
    }
    case CNAME:
    {
      record = new CNAME_Record();
      break;
    }
    case PTR:
    {
      record = new PTR_Record();
      break;
    }
    default:
      return 0;
    }

    DNS_CHECK_ACCUMLATE(ret, tmp, record->parseFromBuffer(buf, offset+ret, maxlen));
  }

  return ret;
}

DNS::Answer& DNS::Answer::operator=(const Answer &r)
{
  name = r.name;
  record_type = r.record_type;
  record_class = r.record_class;
  ttl = r.ttl;
  length = r.length;
  record = r.record->clone();
  return *this;
}

size_t DNS::Packet::parseFromBuffer(const u8 *buf, size_t maxlen)
{
  if( !buf || maxlen < DATA) return 0;

  size_t tmp, ret = 0;
  DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(id, buf, ID, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(flags, buf, FLAGS_OFFSET, maxlen));

  u16 queries_counter, answers_counter, authorities_counter, additionals_counter;
  DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(queries_counter, buf, QDCOUNT, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(answers_counter, buf, ANCOUNT, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(authorities_counter, buf, NSCOUNT, maxlen));
  DNS_CHECK_ACCUMLATE(ret, tmp, Factory::parseUnsignedShort(additionals_counter, buf, ARCOUNT, maxlen));

  queries.clear();
  for(u16 i=0; i<queries_counter; ++i)
  {
    Query q;
    DNS_CHECK_ACCUMLATE(ret, tmp, q.parseFromBuffer(buf, ret, maxlen));
    queries.push_back(q);
  }

  answers.clear();
  for(u16 i=0; i<answers_counter; ++i)
  {
    Answer a;
    DNS_CHECK_ACCUMLATE(ret, tmp, a.parseFromBuffer(buf, ret, maxlen));
    answers.push_back(a);
  };

  return ret;
}