Simplify get_next_host and name resolution.

TargetGroup.cc

@@ -628,7 +628,7 @@ std::string NetBlockIPv6Netmask::str() const {
  return result.str();
 }
 
-NetBlock *NetBlockHostname::resolve() const {
+NetBlock *NetBlockHostname::resolve() {
  struct addrinfo *addrs, *addr;
  std::list<struct sockaddr_storage> resolvedaddrs;
  NetBlock *netblock;

TargetGroup.h

@@ -162,6 +162,11 @@ class NetBlock {
 
  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() { return this; }
  virtual bool next(struct sockaddr_storage *ss, size_t *sslen) = 0;
  virtual void apply_netmask(int bits) = 0;
  virtual std::string str() const = 0;
@@ -203,7 +208,7 @@ class NetBlockHostname : public NetBlock {
  int af;
  int bits;
 
- NetBlock *resolve() const;
+ NetBlock *resolve();
 
  bool next(struct sockaddr_storage *ss, size_t *sslen);
  void apply_netmask(int bits);

targets.cc

@@ -383,16 +383,13 @@ int TargetGroup::get_next_host(struct sockaddr_storage *ss, size_t *sslen) {
  hostname, without doing local DNS resolution (like with a proxy scan), this
  has to be made conditional (and perhaps an error if the netmask doesn't
  limit it to exactly one address). */
- NetBlockHostname *netblock_hostname;
- netblock_hostname = dynamic_cast<NetBlockHostname *>(this->netblock);
- if (netblock_hostname != NULL) {
- this->netblock = netblock_hostname->resolve();
- if (this->netblock == NULL) {
- error("Failed to resolve \"%s\".", netblock_hostname->hostname.c_str());
- delete netblock_hostname;
- return -1;
- }
- delete netblock_hostname;
+ NetBlock *netblock_resolved = this->netblock->resolve();
+ if (netblock_resolved != NULL) {
+ this->netblock = netblock_resolved;
+ }
+ else {
+ error("Failed to resolve \"%s\".", this->netblock->hostname.c_str());
+ return -1;
  }
 
  if (this->netblock->next(ss, sslen))