
/***************************************************************************
 * TargetGroup.cc -- The "TargetGroup" class holds a group of IP           *
 * addresses, such as those from a '/16' or '10.*.*.*' specification.  It  *
 * also has a trivial HostGroupState class which handles a bunch of        *
 * expressions that go into TargetGroup classes.                           *
 *                                                                         *
 ***********************IMPORTANT NMAP LICENSE TERMS************************
 *
 * The Nmap Security Scanner is (C) 1996-2026 Nmap Software LLC ("The Nmap
 * Project"). Nmap is also a registered trademark of the Nmap Project.
 *
 * This program is distributed under the terms of the Nmap Public Source
 * License (NPSL). The exact license text applying to a particular Nmap
 * release or source code control revision is contained in the LICENSE
 * file distributed with that version of Nmap or source code control
 * revision. More Nmap copyright/legal information is available from
 * https://nmap.org/book/man-legal.html, and further information on the
 * NPSL license itself can be found at https://nmap.org/npsl/ . This
 * header summarizes some key points from the Nmap license, but is no
 * substitute for the actual license text.
 *
 * Nmap is generally free for end users to download and use themselves,
 * including commercial use. It is available from https://nmap.org.
 *
 * The Nmap license generally prohibits companies from using and
 * redistributing Nmap in commercial products, but we sell a special Nmap
 * OEM Edition with a more permissive license and special features for
 * this purpose. See https://nmap.org/oem/
 *
 * If you have received a written Nmap license agreement or contract
 * stating terms other than these (such as an Nmap OEM license), you may
 * choose to use and redistribute Nmap under those terms instead.
 *
 * The official Nmap Windows builds include the Npcap software
 * (https://npcap.com) for packet capture and transmission. It is under
 * separate license terms which forbid redistribution without special
 * permission. So the official Nmap Windows builds may not be redistributed
 * without special permission (such as an Nmap OEM license).
 *
 * 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 submit your changes as a
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 * is understood that you are offering us very broad rights to use your
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 * Agreement. This is important because we fund the project by selling licenses
 * with various terms, and also because the inability to relicense code has
 * caused devastating problems for other Free Software projects (such as KDE
 * and NASM).
 *
 * The free version of Nmap 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. Warranties,
 * indemnification and commercial support are all available through the
 * Npcap OEM program--see https://nmap.org/oem/
 *
 ***************************************************************************/

/* $Id: TargetGroup.cc 39343 2026-02-16 22:33:40Z dmiller $ */

#include "tcpip.h"
#include "TargetGroup.h"
#include "targets.h"
#include "NmapOps.h"
#include "nmap_error.h"
#include "nmap_dns.h"
#include "nmap.h"
#include "libnetutil/netutil.h"

#include <string>
#include <sstream>
#include <vector>
#include <algorithm>
#include <typeinfo>
#include <errno.h>
#include <limits.h> // CHAR_BIT

/* We use bit vectors to represent what values are allowed in an IPv4 octet.
   Each vector is built up of an array of bitvector_t (any convenient integer
   type). */
typedef unsigned long bitvector_t;
/* A 256-element bit vector, representing legal values for one octet. */
typedef bitvector_t octet_bitvector[(256 - 1) / (sizeof(unsigned long) * CHAR_BIT) + 1];

#define BITVECTOR_BITS (sizeof(bitvector_t) * CHAR_BIT)
#define BIT_SET(v, n) ((v)[(n) / BITVECTOR_BITS] |= 1UL << ((n) % BITVECTOR_BITS))
#define BIT_IS_SET(v, n) (((v)[(n) / BITVECTOR_BITS] & 1UL << ((n) % BITVECTOR_BITS)) != 0)

extern NmapOps o;

class NetBlock {
public:
  virtual ~NetBlock() {}
  NetBlock() {
    current_addr = resolvedaddrs.begin();
    }
  std::string hostname;
  std::list<struct sockaddr_storage> resolvedaddrs;
  std::list<struct sockaddr_storage> unscanned_addrs;
  std::list<struct sockaddr_storage>::const_iterator current_addr;

  /* Parses an expression such as 192.168.0.0/16, 10.1.0-5.1-254, or
     fe80::202:e3ff:fe14:1102/112 and returns a newly allocated NetBlock. The af
     parameter is AF_INET or AF_INET6. Returns NULL in case of error. */
  static NetBlock *parse_expr(const char *target_expr, int af, std::vector<DNS::Request> &requests);

  bool is_resolved_address(const struct sockaddr_storage *ss) const;

  /* For NetBlock subclasses that need to "resolve" themselves into a different
   * NetBlock subclass, override this method. Otherwise, it's safe to reassign
   * the return value to the pointer that this method was called through.
   * On error, return NULL. */
  virtual NetBlock *resolve(const DNS::Request &req) { return this; }
  virtual void reject_last_host() {}
  virtual bool next(struct sockaddr_storage *ss, size_t *sslen) = 0;
  virtual void apply_netmask(int bits) = 0;
  virtual std::string str() const = 0;
};

class NetBlockRandomIPv4 : public NetBlock {
public:
  NetBlockRandomIPv4();

  void reject_last_host() { if (!infinite) count++; }
  void set_num_random(unsigned long num) {
    if (num == 0)
      infinite = true;
    else
      count = num;
  }
  bool next(struct sockaddr_storage *ss, size_t *sslen);
  void apply_netmask(int bits) {}
  std::string str() const {return "Random IPv4 addresses";}

private:
  struct sockaddr_in base;
  unsigned long count;
  bool infinite;
};

class NetBlockIPv4Ranges : public NetBlock {
public:
  octet_bitvector octets[4];

  NetBlockIPv4Ranges();

  bool next(struct sockaddr_storage *ss, size_t *sslen);
  void apply_netmask(int bits);
  std::string str() const;
  void set_addr(const struct sockaddr_in *addr);

private:
  unsigned int counter[4];
};

class NetBlockIPv6Netmask : public NetBlock {
public:
  void set_addr(const struct sockaddr_in6 *addr);

  bool next(struct sockaddr_storage *ss, size_t *sslen);
  void apply_netmask(int bits);
  std::string str() const;

private:
  bool exhausted;
  struct sockaddr_in6 addr;
  struct in6_addr start;
  struct in6_addr cur;
  struct in6_addr end;
};

class NetBlockHostname : public NetBlock {
public:
  NetBlockHostname(const char *hostname, int af);
  int af;
  int bits;

  NetBlock *resolve(const DNS::Request &req);

  bool next(struct sockaddr_storage *ss, size_t *sslen);
  void apply_netmask(int bits);
  std::string str() const;
};

/* Return a newly allocated string containing the part of expr up to the last
   '/' (or a copy of the whole string if there is no slash). *bits will contain
   the number after the slash, or -1 if there was no slash. In case of error
   return NULL; *bits is then undefined. */
static char *split_netmask(const char *expr, int *bits) {
  const char *slash;

  slash = strrchr(expr, '/');
  if (slash != NULL) {
    long l;
    const char *tail;

    l = parse_long(slash + 1, &tail);
    if (tail == slash + 1 || *tail != '\0' || l < 0 || l > INT_MAX)
      return NULL;
    *bits = (int) l;
  } else {
    slash = expr + strlen(expr);
    *bits = -1;
  }

  return mkstr(expr, slash);
}

/* Parse an IPv4 address with optional ranges and wildcards into bit vectors.
   Each octet must match the regular expression '(\*|#?(-#?)?(,#?(-#?)?)*)',
   where '#' stands for an integer between 0 and 255. Return 0 on success, -1 on
   error. */
static int parse_ipv4_ranges(octet_bitvector octets[4], const char *spec) {
  const char *p;
  int octet_index, i;

  p = spec;
  octet_index = 0;
  while (*p != '\0' && octet_index < 4) {
    if (*p == '*') {
      for (i = 0; i < 256; i++)
        BIT_SET(octets[octet_index], i);
      p++;
    } else {
      for (;;) {
        long start, end;
        const char *tail;

        errno = 0;
        start = parse_long(p, &tail);
        /* Is this a range open on the left? */
        if (tail == p) {
          if (*p == '-')
            start = 0;
          else
            return -1;
        }
        if (errno != 0 || start < 0 || start > 255)
          return -1;
        p = tail;

        /* Look for a range. */
        if (*p == '-') {
          p++;
          errno = 0;
          end = parse_long(p, &tail);
          /* Is this range open on the right? */
          if (tail == p)
            end = 255;
          if (errno != 0 || end < 0 || end > 255 || end < start)
            return -1;
          p = tail;
        } else {
          end = start;
        }

        /* Fill in the range in the bit vector. */
        for (i = start; i <= end; i++)
          BIT_SET(octets[octet_index], i);

        if (*p != ',')
          break;
        p++;
      }
    }
    octet_index++;
    if (octet_index < 4) {
      if (*p != '.')
        return -1;
      p++;
    }
  }
  if (*p != '\0' || octet_index < 4)
    return -1;

  return 0;
}

static NetBlock *parse_expr_without_netmask(const char *hostexp, int af, std::vector<DNS::Request> &requests) {
  struct sockaddr_storage ss;
  size_t sslen;

  if (af == AF_INET) {
    NetBlockIPv4Ranges *netblock_ranges;

    /* Check if this is an IPv4 address, with optional ranges and wildcards. */
    netblock_ranges = new NetBlockIPv4Ranges();
    if (parse_ipv4_ranges(netblock_ranges->octets, hostexp) == 0)
      return netblock_ranges;
    delete netblock_ranges;
  }

  sslen = sizeof(ss);
  if (resolve_numeric(hostexp, 0, &ss, &sslen, AF_INET6) == 0) {
    if (af != AF_INET6) {
      error("%s looks like an IPv6 target specification -- you have to use the -6 option.", hostexp);
      return NULL;
    }
    NetBlockIPv6Netmask *netblock_ipv6;

    netblock_ipv6 = new NetBlockIPv6Netmask();
    netblock_ipv6->set_addr((struct sockaddr_in6 *) &ss);
    return netblock_ipv6;
  }

  NetBlockHostname *nb = new NetBlockHostname(hostexp, af);
  DNS::Request req;
  req.name = hostexp;
  req.userdata = nb;
  req.type = DNS::ANY;
  requests.push_back(req);
  return nb;
}

/* Parses an expression such as 192.168.0.0/16, 10.1.0-5.1-254, or
   fe80::202:e3ff:fe14:1102/112 and returns a newly allocated NetBlock. The af
   parameter is AF_INET or AF_INET6. Returns NULL in case of error. */
NetBlock *NetBlock::parse_expr(const char *target_expr, int af, std::vector<DNS::Request> &requests) {
  NetBlock *netblock;
  char *hostexp;
  int bits;

  hostexp = split_netmask(target_expr, &bits);
  if (hostexp == NULL) {
    error("Unable to split netmask from target expression: \"%s\"", target_expr);
    goto bail;
  }

  if (af == AF_INET && bits > 32) {
    error("Illegal netmask in \"%s\". Assuming /32 (one host)", target_expr);
    bits = -1;
  }

  netblock = parse_expr_without_netmask(hostexp, af, requests);
  if (netblock == NULL)
    goto bail;
  netblock->apply_netmask(bits);

  free(hostexp);
  return netblock;

bail:
  free(hostexp);
  return NULL;
}

bool NetBlock::is_resolved_address(const struct sockaddr_storage *ss) const {
  for (std::list<struct sockaddr_storage>::const_iterator it = this->resolvedaddrs.begin(), end = this->resolvedaddrs.end(); it != end; ++it) {
    if (sockaddr_storage_equal(&*it, ss)) {
      return true;
    }
  }
  return false;
}

NetBlockRandomIPv4::NetBlockRandomIPv4() : count(0), infinite(false) {
  memset(&base, 0, sizeof(base));
  base.sin_family = AF_INET;
}

bool NetBlockRandomIPv4::next(struct sockaddr_storage *ss, size_t *sslen) {
  if (!infinite) {
    if (count > 0) {
      count--;
    }
    else {
      return false;
    }
  }
  do {
    base.sin_addr.s_addr = get_random_unique_u32();
  } while (ip_is_reserved((const struct sockaddr_storage *)&base));
  memcpy(ss, &base, sizeof(base));
  *sslen = sizeof(base);
  return true;
}

NetBlockIPv4Ranges::NetBlockIPv4Ranges() {
  unsigned int i;

  memset(this->octets, 0, sizeof(this->octets));
  for (i = 0; i < 4; i++) {
    this->counter[i] = 0;
  }
}

bool NetBlockIPv4Ranges::next(struct sockaddr_storage *ss, size_t *sslen) {
  struct sockaddr_in *sin;
  unsigned int i;

  /* This first time this is called, the current values of this->counter
     probably do not point to set bits (they point to 0.0.0.0). Find the first
     set bit in each bitvector. If any overflow occurs, it means that there is
     not bit set for one of the octets and therefore there are not addresses
     overall. */
  for (i = 0; i < 4; i++) {
    while (this->counter[i] < 256 && !BIT_IS_SET(this->octets[i], this->counter[i]))
      this->counter[i]++;
    if (this->counter[i] >= 256)
      return false;
  }

  /* Assign the returned address based on current counters. */
  memset(ss, 0, sizeof(*ss));
  sin = (struct sockaddr_in *) ss;
  sin->sin_family = AF_INET;
  sin->sin_port = 0;
#if HAVE_SOCKADDR_SA_LEN
  sin->sin_len = sizeof(*sin);
#endif
  sin->sin_addr.s_addr = htonl((this->counter[0] << 24) | (this->counter[1] << 16) | (this->counter[2] << 8) | this->counter[3]);
  *sslen = sizeof(*sin);

  for (i = 0; i < 4; i++) {
    bool carry;

    carry = false;
    do {
      this->counter[3 - i] = (this->counter[3 - i] + 1) % 256;
      if (this->counter[3 - i] == 0)
        carry = true;
    } while (!BIT_IS_SET(this->octets[3 - i], this->counter[3 - i]));
    if (!carry)
      break;
  }
  if (i >= 4) {
    if (o.resolve_all && !this->resolvedaddrs.empty() && current_addr != this->resolvedaddrs.end() && ++current_addr != this->resolvedaddrs.end()) {
      this->set_addr((struct sockaddr_in *) &*current_addr);
    }
    else {
      /* We cycled all counters. Mark them invalid for the next call. */
      this->counter[0] = 256;
      this->counter[1] = 256;
      this->counter[2] = 256;
      this->counter[3] = 256;
    }
  }

  return true;
}

/* Expand a single-octet bit vector to include any additional addresses that
   result when mask is applied. */
static void apply_ipv4_netmask_octet(octet_bitvector bits, uint8_t mask) {
  unsigned int i, j;
  uint32_t chunk_size;

  /* Process the bit vector in chunks, first of size 1, then of size 2, up to
     size 128. Check the next bit of the mask. If it is 1, do nothing.
     Otherwise, pair up the chunks (first with the second, third with the
     fourth, etc.). For each pair of chunks, set a bit in one chunk if it is
     set in the other. chunk_size also serves as an index into the mask. */
  for (chunk_size = 1; chunk_size < 256; chunk_size <<= 1) {
    if ((mask & chunk_size) != 0)
      continue;
    for (i = 0; i < 256; i += chunk_size * 2) {
      for (j = 0; j < chunk_size; j++) {
        if (BIT_IS_SET(bits, i + j))
          BIT_SET(bits, i + j + chunk_size);
        else if (BIT_IS_SET(bits, i + j + chunk_size))
          BIT_SET(bits, i + j);
      }
    }
  }
}

/* Expand IPv4 bit vectors to include any additional addresses that result when
   the given netmask is applied. The mask is in host byte order. */
static void apply_ipv4_netmask(octet_bitvector octets[4], uint32_t mask) {
  /* Apply the mask one octet at a time. It's done this way because ranges
     span exactly one octet. */
  apply_ipv4_netmask_octet(octets[0], (mask & 0xFF000000) >> 24);
  apply_ipv4_netmask_octet(octets[1], (mask & 0x00FF0000) >> 16);
  apply_ipv4_netmask_octet(octets[2], (mask & 0x0000FF00) >> 8);
  apply_ipv4_netmask_octet(octets[3], (mask & 0x000000FF));
}

/* Expand IPv4 bit vectors to include any additional addresses that result from
   the application of a CIDR-style netmask with the given number of bits. If
   bits is negative it is taken to be 32. */
void NetBlockIPv4Ranges::apply_netmask(int bits) {
  uint32_t mask;

  if (bits > 32)
    return;
  if (bits < 0)
    bits = 32;

  if (bits == 0)
    mask = 0x00000000;
  else
    mask = 0xFFFFFFFF << (32 - bits);

  apply_ipv4_netmask(this->octets, mask);
}

static std::string bitvector_to_range_string(const octet_bitvector v) {
  unsigned int i, j;
  std::ostringstream result;

  i = 0;
  while (i < 256) {
    while (i < 256 && !BIT_IS_SET(v, i))
      i++;
    if (i >= 256)
      break;
    j = i + 1;
    while (j < 256 && BIT_IS_SET(v, j))
      j++;

    if (result.tellp() > 0)
      result << ",";
    if (i == j - 1)
      result << i;
    else if (i + 1 == j - 1)
      result << i << "," << (j - 1);
    else
      result << i << "-" << (j - 1);

    i = j;
  }

  return result.str();
}

std::string NetBlockIPv4Ranges::str() const {
  std::ostringstream result;

  result << bitvector_to_range_string(this->octets[0]);
  result << ".";
  result << bitvector_to_range_string(this->octets[1]);
  result << ".";
  result << bitvector_to_range_string(this->octets[2]);
  result << ".";
  result << bitvector_to_range_string(this->octets[3]);

  return result.str();
}

void NetBlockIPv4Ranges::set_addr(const struct sockaddr_in *addr) {
  uint32_t ip;

  assert(addr->sin_family == AF_INET);
  ip = ntohl(addr->sin_addr.s_addr);
  memset(this->octets, 0, sizeof(this->octets));
  BIT_SET(this->octets[0], (ip & 0xFF000000) >> 24);
  BIT_SET(this->octets[1], (ip & 0x00FF0000) >> 16);
  BIT_SET(this->octets[2], (ip & 0x0000FF00) >> 8);
  BIT_SET(this->octets[3], (ip & 0x000000FF));
  /* Reset counter so that set_addr can be used to reset the whole NetBlock */
  for (int i = 0; i < 4; i++) {
    this->counter[i] = 0;
  }
}

void NetBlockIPv6Netmask::set_addr(const struct sockaddr_in6 *addr) {
  assert(addr->sin6_family == AF_INET6);
  this->exhausted = false;
  this->addr = *addr;
  this->start = this->addr.sin6_addr;
  this->cur = this->addr.sin6_addr;
  this->end = this->addr.sin6_addr;
}

/* Get the sin6_scope_id member of a sockaddr_in6, based on a device name. This
   is used to assign scope to all addresses that otherwise lack a scope id when
   the -e option is used. */
static int get_scope_id(const char *devname) {
  struct interface_info *ii;

  if (devname == NULL || devname[0] == '\0')
    return 0;
  ii = getInterfaceByName(devname, AF_INET6);
  if (ii != NULL)
    return ii->ifindex;
  else
    return 0;
}

static bool ipv6_equal(const struct in6_addr *a, const struct in6_addr *b) {
  return memcmp(a->s6_addr, b->s6_addr, 16) == 0;
}

bool NetBlockIPv6Netmask::next(struct sockaddr_storage *ss, size_t *sslen) {
  struct sockaddr_in6 *sin6;

  if (this->exhausted){
    if (o.resolve_all && !this->resolvedaddrs.empty() && current_addr != this->resolvedaddrs.end() && ++current_addr != this->resolvedaddrs.end()) {
      this->set_addr((struct sockaddr_in6 *) &*current_addr);
    }
    else {
      return false;
    }
  }

  memset(ss, 0, sizeof(*ss));
  sin6 = (struct sockaddr_in6 *) ss;
  sin6->sin6_family = AF_INET6;
#ifdef SIN_LEN
  sin6->sin6_len = sizeof(*sin6);
#endif
  *sslen = sizeof(*sin6);

  if (this->addr.sin6_scope_id != 0)
    sin6->sin6_scope_id = this->addr.sin6_scope_id;
  else
    sin6->sin6_scope_id = get_scope_id(o.device);

  sin6->sin6_addr = this->cur;

  if (ipv6_equal(&this->cur, &this->end))
    exhausted = true;

  /* Increment current address. */
  for (int i = 15; i >= 0; i--) {
    this->cur.s6_addr[i]++;
    if (this->cur.s6_addr[i] > 0)
      break;
  }

  return true;
}

/* Fill in an in6_addr with a CIDR-style netmask with the given number of bits. */
static void make_ipv6_netmask(struct in6_addr *mask, int bits) {
  unsigned int i;

  memset(mask, 0, sizeof(*mask));

  if (bits < 0)
    bits = 0;
  else if (bits > 128)
    bits = 128;

  if (bits == 0)
    return;

  i = 0;
  /* 0 < bits <= 128, so this loop goes at most 15 times. */
  for (; bits > 8; bits -= 8)
    mask->s6_addr[i++] = 0xFF;
  mask->s6_addr[i] = 0xFF << (8 - bits);
}

/* a = (a & mask) | (b & ~mask) */
static void ipv6_or_mask(struct in6_addr *a, const struct in6_addr *mask, const struct in6_addr *b) {
  unsigned int i;

  for (i = 0; i < sizeof(a->s6_addr) / sizeof(*a->s6_addr); i++)
    a->s6_addr[i] = (a->s6_addr[i] & mask->s6_addr[i]) | (b->s6_addr[i] & ~mask->s6_addr[i]);
}

void NetBlockIPv6Netmask::apply_netmask(int bits) {
#ifdef _AIX
  const struct in6_addr zeros = { { { 0x00, 0x00, 0x00, 0x00 } } };
  const struct in6_addr ones = { { { 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff } } };
#else
  const struct in6_addr zeros = { { { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00} } };
  const struct in6_addr ones = { { { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff} } };
#endif
  struct in6_addr mask;

  if (bits > 128)
    return;
  if (bits < 0)
    bits = 128;

  this->exhausted = false;
  make_ipv6_netmask(&mask, bits);
  ipv6_or_mask(&this->start, &mask, &zeros);
  ipv6_or_mask(&this->end, &mask, &ones);
  this->cur = this->start;
}

/* a = a & ~b */
static void recover_ipv6_netmask(struct in6_addr *a, const struct in6_addr *b) {
  unsigned int i;

  for (i = 0; i < sizeof(a->s6_addr) / sizeof(*a->s6_addr); i++)
    a->s6_addr[i] = a->s6_addr[i] & ~b->s6_addr[i];
}

static unsigned int count_ipv6_bits(const struct in6_addr *a) {
  unsigned int i, n;
  unsigned char mask;

  n = 0;
  for (i = 0; i < sizeof(a->s6_addr) / sizeof(*a->s6_addr); i++) {
    for (mask = 0x80; mask != 0; mask >>= 1) {
      if ((a->s6_addr[i] & mask) != 0)
        n++;
    }
  }

  return n;
}

std::string NetBlockIPv6Netmask::str() const {
  std::ostringstream result;
  unsigned int bits;
  struct in6_addr a;

  a = this->start;
  recover_ipv6_netmask(&a, &this->end);
  bits = count_ipv6_bits(&a);

  result << inet_ntop_ez((struct sockaddr_storage *) &this->addr, sizeof(this->addr)) << "/" << bits;

  return result.str();
}

NetBlock *NetBlockHostname::resolve(const DNS::Request &req) {
  std::list<struct sockaddr_storage> resolvedaddrs;
  std::list<struct sockaddr_storage> unscanned_addrs;
  NetBlock *netblock;

  for (size_t i = 0; i < req.ssv.size(); i++) {
    const struct sockaddr_storage &ss = req.ssv[i];
    if (ss.ss_family == af && (o.resolve_all || resolvedaddrs.empty())) {
      resolvedaddrs.push_back(ss);
    }
    else {
      unscanned_addrs.push_back(ss);
    }
  }

  if (resolvedaddrs.empty()) {
    if (!unscanned_addrs.empty()) {
      switch (this->af) {
        case AF_INET:
          error("Warning: Hostname %s resolves, but not to any IPv4 address. Try scanning with -6", this->hostname.c_str());
          break;
        case AF_INET6:
          error("Warning: Hostname %s resolves, but not to any IPv6 address. Try scanning without -6", this->hostname.c_str());
          break;
        default:
          error("Warning: Unknown address family: %d", this->af);
          break;
      }
    }
    error("Failed to resolve \"%s\".", this->hostname.c_str());
    if (this->hostname == "-")
      error("Bare '-': did you put a space between '--'?");
    return NULL;
  }
  struct sockaddr_storage &ss = resolvedaddrs.front();
  size_t sslen = sizeof(ss);

  if (!unscanned_addrs.empty() && o.verbose > 1) {
    error("Warning: Hostname %s resolves to %lu IPs. Using %s.", this->hostname.c_str(),
      (unsigned long) unscanned_addrs.size() + resolvedaddrs.size(), inet_ntop_ez(&ss, sslen));
  }

  netblock = NULL;
  if (ss.ss_family == AF_INET) {
    NetBlockIPv4Ranges *netblock_ranges;

    netblock_ranges = new NetBlockIPv4Ranges();
    netblock_ranges->set_addr((struct sockaddr_in *) &ss);
    netblock = netblock_ranges;
  } else if (ss.ss_family == AF_INET6) {
    NetBlockIPv6Netmask *netblock_ipv6;

    netblock_ipv6 = new NetBlockIPv6Netmask();
    netblock_ipv6->set_addr((struct sockaddr_in6 *) &ss);
    netblock = netblock_ipv6;
  }

  if (netblock == NULL)
    return NULL;

  netblock->hostname = this->hostname;
  netblock->resolvedaddrs.swap(resolvedaddrs);
  netblock->unscanned_addrs.swap(unscanned_addrs);
  netblock->current_addr = netblock->resolvedaddrs.begin();
  netblock->apply_netmask(this->bits);

  return netblock;
}

NetBlockHostname::NetBlockHostname(const char *hostname, int af) {
  this->hostname = hostname;
  this->af = af;
  this->bits = -1;
}

bool NetBlockHostname::next(struct sockaddr_storage *ss, size_t *sslen) {
  assert(false);
  return false;
}

void NetBlockHostname::apply_netmask(int bits) {
  this->bits = bits;
}

std::string NetBlockHostname::str() const {
  std::ostringstream result;

  result << this->hostname;
  if (this->bits >= 0)
    result << "/" << this->bits;

  return result.str();
}

TargetGroup::~TargetGroup() {
  for (std::list<NetBlock *>::iterator it = netblocks.begin();
      it != netblocks.end(); it++) {
    delete *it;
  }
}

void TargetGroup::reject_last_host() {
  assert(!netblocks.empty());
  NetBlock *nb = netblocks.front();
  nb->reject_last_host();
}

/* Initializes (or reinitializes) the object with a new expression, such
   as 192.168.0.0/16 , 10.1.0-5.1-254 , or fe80::202:e3ff:fe14:1102 .
    */
bool TargetGroup::load_expressions(HostGroupState *hs, int af) {
  assert(netblocks.empty());
  // This is a wild guess, but we need some sort of limit.
  static const size_t EXPR_PARSE_BATCH_SZ = o.ping_group_sz;
  const char *target_expr = NULL;
  std::vector<DNS::Request> requests;
  requests.reserve(EXPR_PARSE_BATCH_SZ/4);
  while (netblocks.size() < EXPR_PARSE_BATCH_SZ
      && NULL != (target_expr = hs->next_expression())) {
    NetBlock *nb = NetBlock::parse_expr(target_expr, af, requests);
    if (nb == NULL) {
      log_bogus_target(target_expr);
    }
    else {
      netblocks.push_back(nb);
    }
  }
  if (netblocks.empty()) {
    return false;
  }
  if (requests.size() > 0) {
    nmap_mass_dns(requests.data(), requests.size());
  }
  std::list<NetBlock *>::iterator nb_it = netblocks.begin();
  for (std::vector<DNS::Request>::const_iterator rit = requests.begin();
      rit != requests.end(); rit++) {
    const DNS::Request &req = *rit;
    NetBlock *nb_old = (NetBlock *) req.userdata;
    NetBlock *nb_new = nb_old->resolve(req);
    nb_it = std::find(nb_it, netblocks.end(), nb_old);

    if (nb_new == NULL) {
      // Resolution failed; remove the NetBlock
      nb_it = netblocks.erase(nb_it);
      delete nb_old;
    }
    else {
      assert (nb_new != nb_old);
      // Resolution succeeded; replace the NetBlock
      *nb_it = nb_new;
      delete nb_old;
    }
  }
  requests.clear();
  return !netblocks.empty();
}

void TargetGroup::generate_random_ips(unsigned long num_random) {
  NetBlockRandomIPv4 *nbrand = new NetBlockRandomIPv4();
  nbrand->set_num_random(num_random);
  netblocks.push_front(nbrand);
}

/* Grab the next host from this expression (if any) and updates its internal
   state to reflect that the IP was given out.  Returns 0 and
   fills in ss if successful.  ss must point to a pre-allocated
   sockaddr_storage structure */
int TargetGroup::get_next_host(struct sockaddr_storage *ss, size_t *sslen) {
  while (!netblocks.empty()) {

    NetBlock *nb = netblocks.front();
    if (nb->next(ss, sslen)) {
      return 0;
    }
    // Ran out of hosts in that block. Remove it.
    netblocks.pop_front();
    delete nb;
  }
  // Ran out of netblocks
  return -1;
}

/* Returns true iff the given address is the one that was resolved to create
   this target group; i.e., not one of the addresses derived from it with a
   netmask. */
bool TargetGroup::is_resolved_address(const struct sockaddr_storage *ss) const {
  assert(!netblocks.empty());
  NetBlock *nb = netblocks.front();
  return nb->is_resolved_address(ss);
}

/* Return a string of the name or address that was resolved for this group. */
const char *TargetGroup::get_resolved_name(void) const {
  assert(!netblocks.empty());
  NetBlock *nb = netblocks.front();
  if (nb->hostname.empty())
    return NULL;
  else
    return nb->hostname.c_str();
}

/* Return the list of addresses that the name for this group resolved to, but
   which were not scanned, if it came from a name resolution. */
const std::list<struct sockaddr_storage> &TargetGroup::get_unscanned_addrs(void) const {
  assert(!netblocks.empty());
  NetBlock *nb = netblocks.front();
  return nb->unscanned_addrs;
}

/* is the current expression a named host */
int TargetGroup::get_namedhost() const {
  return this->get_resolved_name() != NULL;
}
