text: // Copyright (c) 2018, Ryo Currency Project
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  #pragma once
  
  #include <functional>
  #include <string>
  #include <vector>
  
  namespace tools
  {
  
  // RFC defines for record types and classes for DNS, gleaned from ldns source
  const static int DNS_CLASS_IN = 1;
  const static int DNS_TYPE_A = 1;
  const static int DNS_TYPE_TXT = 16;
  const static int DNS_TYPE_AAAA = 8;
  
  struct DNSResolverData;
  
  /**
   * @brief Provides high-level access to DNS resolution
   *
   * This class is designed to provide a high-level abstraction to DNS resolution
   * functionality, including access to TXT records and such.  It will also
   * handle DNSSEC validation of the results.
   */
  class DNSResolver
  {
    private:
  	/**
     * @brief Constructs an instance of DNSResolver
     *
     * Constructs a class instance and does setup stuff for the backend resolver.
     */
  	DNSResolver();
  
    public:
  	/**
     * @brief takes care of freeing C pointers and such
     */
  	~DNSResolver();
  
  	/**
     * @brief gets ipv4 addresses from DNS query of a URL
     *
     * returns a vector of all IPv4 "A" records for given URL.
     * If no "A" records found, returns an empty vector.
     *
     * @param url A string containing a URL to query for
     *
     * @param dnssec_available 
     *
     * @return vector of strings containing ipv4 addresses
     */
  	std::vector<std::string> get_ipv4(const std::string &url, bool &dnssec_available, bool &dnssec_valid);
  
  	/**
     * @brief gets ipv6 addresses from DNS query
     *
     * returns a vector of all IPv6 "A" records for given URL.
     * If no "A" records found, returns an empty vector.
     *
     * @param url A string containing a URL to query for
     *
     * @return vector of strings containing ipv6 addresses
     */
  	std::vector<std::string> get_ipv6(const std::string &url, bool &dnssec_available, bool &dnssec_valid);
  
  	/**
     * @brief gets all TXT records from a DNS query for the supplied URL;
     * if no TXT record present returns an empty vector.
     *
     * @param url A string containing a URL to query for
     *
     * @return A vector of strings containing a TXT record; or an empty vector
     */
  	// TODO: modify this to accommodate DNSSEC
  	std::vector<std::string> get_txt_record(const std::string &url, bool &dnssec_available, bool &dnssec_valid);
  
  	/**
     * @brief Gets a DNS address from OpenAlias format
     *
     * If the address looks good, but contains one @ symbol, replace that with a .
     * e.g. donate@getmonero.org becomes donate.getmonero.org
     *
     * @param oa_addr  OpenAlias address
     *
     * @return dns_addr  DNS address
     */
  	std::string get_dns_format_from_oa_address(const std::string &oa_addr);
  
  	/**
     * @brief Gets the singleton instance of DNSResolver
     *
     * @return returns a pointer to the singleton
     */
  	static DNSResolver &instance();
  
  	/**
     * @brief Gets a new instance of DNSResolver
     *
     * @return returns a pointer to the new object
     */
  	static DNSResolver create();
  
    private:
  	/**
     * @brief gets all records of a given type from a DNS query for the supplied URL;
     * if no such record is present returns an empty vector.
     *
     * @param url A string containing a URL to query for
     * @param record_type the record type to retrieve (DNS_TYPE_A, etc)
     * @param reader a function that converts a record data to a string
     *
     * @return A vector of strings containing the requested record; or an empty vector
     */
  	// TODO: modify this to accommodate DNSSEC
  	std::vector<std::string> get_record(const std::string &url, int record_type, std::string (*reader)(const char *, size_t), bool &dnssec_available, bool &dnssec_valid);
  
  	/**
     * @brief Checks a string to see if it looks like a URL
     *
     * @param addr the string to be checked
     *
     * @return true if it looks enough like a URL, false if not
     */
  	bool check_address_syntax(const char *addr) const;
  
  	DNSResolverData *m_data;
  }; // class DNSResolver
  
  namespace dns_utils
  {
  
  std::string address_from_txt_record(const std::string &s);
  std::vector<std::string> addresses_from_url(const std::string &url, bool &dnssec_valid);
  
  std::string get_account_address_as_str_from_url(const std::string &url, bool &dnssec_valid, std::function<std::string(const std::string &, const std::vector<std::string> &, bool)> confirm_dns);
  
  bool load_txt_records_from_dns(std::vector<std::string> &records, const std::vector<std::string> &dns_urls);
  
  std::vector<std::string> parse_dns_public(const char *s);
  
  } // namespace tools::dns_utils
  
  } // namespace tools
  