+/**
+ * The Resolver class is a high-level abstraction for resolving DNS entries.
+ * It can do forward and reverse IPv4 lookups, and when IPv6 is supported, will
+ * also be able to do those, transparent of protocols. Module developers must
+ * extend this class via inheritence, and then insert a pointer to their derived
+ * class into the core using Server::AddResolver(). Once you have done this,
+ * the class will be able to receive callbacks. There are two callbacks which
+ * can occur by calling virtual methods, one is a success situation, and the other
+ * an error situation.
+ */
+class Resolver : public Extensible
+{
+ private:
+ /**
+ * The lowlevel DNS object used by Resolver
+ */
+ DNS Query;
+ /**
+ * The input data, either a host or an IP address
+ */
+ std::string input;
+ /**
+ * True if a forward lookup is being performed, false if otherwise
+ */
+ bool fwd;
+ /**
+ * The DNS erver being used for lookups. If this is an empty string,
+ * the value of ServerConfig::DNSServer is used instead.
+ */
+ std::string server;
+ /**
+ * The file descriptor used for the DNS lookup
+ */
+ int fd;
+ /**
+ * The output data, e.g. a hostname or an IP.
+ */
+ std::string result;
+ public:
+ /**
+ * Initiate DNS lookup. Your class should not attempt to delete or free these
+ * objects, as the core will do this for you. They must always be created upon
+ * the heap using new, as you cannot be sure at what time they will be deleted.
+ * Allocating them on the stack or attempting to delete them yourself could cause
+ * the object to go 'out of scope' and cause a segfault in the core if the result
+ * arrives at a later time.
+ * @param source The IP or hostname to resolve
+ * @param forward Set to true to perform a forward lookup (hostname to ip) or false
+ * to perform a reverse lookup (ip to hostname). Lookups on A records and PTR
+ * records are supported. CNAME and MX are not supported by this resolver.
+ * @param dnsserver This optional parameter specifies an alterate nameserver to use.
+ * If it is not specified, or is an empty string, the value of ServerConfig::DNSServer
+ * is used instead.
+ * @throw ModuleException This class may throw an instance of ModuleException, in the
+ * event there are no more file descriptors, or a similar hard error occurs such as
+ * the network being down.
+ */
+ Resolver(const std::string &source, bool forward, const std::string &dnsserver);
+ /**
+ * The default destructor does nothing.
+ */
+ virtual ~Resolver();
+ /**
+ * When your lookup completes, this method will be called.
+ * @param result The resulting DNS lookup, either an IP address or a hostname.
+ */
+ virtual void OnLookupComplete(const std::string &result);
+ /**
+ * If an error occurs (such as NXDOMAIN, no domain name found) then this method
+ * will be called.
+ * @param e A ResolverError enum containing the error type which has occured.
+ */
+ virtual void OnError(ResolverError e);
+ /**
+ * This method is called by the core when the object's file descriptor is ready
+ * for reading, and will then dispatch a call to either OnLookupComplete or
+ * OnError. You should never call this method yourself.
+ */
+ bool ProcessResult();
+ /**
+ * Returns the file descriptor of this class. This is primarily used by the core
+ * to determine where in various tables to place a pointer to your class, but it
+ * is safe to call and use this method.
+ */
+ int GetFd();
+};
+
+/**
+ * Clear the pointer table used for Resolver classes
+ */
+void init_dns();
+/**
+ * Deal with a Resolver class which has become writeable
+ */
+void dns_deal_with_classes(int fd);
+/**
+ * Add a resolver class to our active table
+ */
+bool dns_add_class(Resolver* r);
+
+void dns_close(int fd);
+
+#ifdef THREADED_DNS
+/** This is the handler function for multi-threaded DNS.
+ * It cannot be a class member as pthread will not let us
+ * create a thread whos handler function is a member of
+ * a class (ugh).
+ */
+void* dns_task(void* arg);
+#endif
+