resolver.hpp

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#pragma once
 
/// @file userver/clients/dns/resolver.hpp
/// @brief @copybrief clients::dns::Resolver
 
#include <userver/clients/dns/common.hpp>
#include <userver/clients/dns/config.hpp>
#include <userver/clients/dns/exception.hpp>
#include <userver/engine/deadline.hpp>
#include <userver/engine/io/sockaddr.hpp>
#include <userver/engine/task/task_processor_fwd.hpp>
#include <userver/utils/fast_pimpl.hpp>
#include <userver/utils/statistics/relaxed_counter.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace clients::dns {
 
/// @ingroup userver_clients
///
/// @brief Caching DNS resolver implementation.
///
/// Usually retrieved from clients::dns::Component.
///
/// Combines file-based (/etc/hosts) name resolution with network-based one.
class Resolver {
 public:
  struct LookupSourceCounters {
    utils::statistics::RelaxedCounter<size_t> file{0};
    utils::statistics::RelaxedCounter<size_t> cached{0};
    utils::statistics::RelaxedCounter<size_t> cached_stale{0};
    utils::statistics::RelaxedCounter<size_t> cached_failure{0};
    utils::statistics::RelaxedCounter<size_t> network{0};
    utils::statistics::RelaxedCounter<size_t> network_failure{0};
  };
 
  Resolver(engine::TaskProcessor& fs_task_processor,
           const ResolverConfig& config);
  Resolver(const Resolver&) = delete;
  Resolver(Resolver&&) = delete;
  ~Resolver();
 
  /// Performs a domain name resolution.
  ///
  /// Sources are tried in the following order:
  ///  - Cached file lookup table
  ///  - Cached network resolution results
  ///  - Network name servers
  ///
  /// @throws clients::dns::NotResolvedException if none of the sources provide
  /// a result within the specified deadline.
  AddrVector Resolve(const std::string& name, engine::Deadline deadline);
 
  /// Returns lookup source counters.
  const LookupSourceCounters& GetLookupSourceCounters() const;
 
  /// Forces the reload of lookup table file. Waits until the reload is done.
  void ReloadHosts();
 
  /// Resets the network results cache.
  void FlushNetworkCache();
 
  /// Removes the specified domain name from the network results cache.
  void FlushNetworkCache(const std::string& name);
 
 private:
  class Impl;
  constexpr static size_t kSize = 1728;
  constexpr static size_t kAlignment = 16;
  utils::FastPimpl<Impl, kSize, kAlignment> impl_;
};
 
}  // namespace clients::dns
 
USERVER_NAMESPACE_END