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#pragma once
#include <span>
#include <poll.h>
#include <mutex>
#include "DNSPTRResolver.h"
using ares_channel = struct ares_channeldata *;
namespace DB
{
/*
* Implements reverse DNS resolution using c-ares lib. System reverse DNS resolution via
* gethostbyaddr or getnameinfo does not work reliably because in some systems
* it returns all PTR records for a given IP and in others it returns only one.
* */
class CaresPTRResolver : public DNSPTRResolver
{
friend class DNSPTRResolverProvider;
/*
* Allow only DNSPTRProvider to instantiate this class
* */
struct provider_token {};
static constexpr auto C_ARES_POLL_EVENTS = POLLRDNORM | POLLIN;
public:
explicit CaresPTRResolver(provider_token);
/*
* Library initialization is currently done only once in the constructor. Multiple instances of CaresPTRResolver
* will be used in the lifetime of ClickHouse, thus it's problematic to have de-init here.
* In a practical view, it makes little to no sense to de-init a DNS library since DNS requests will happen
* until the end of the program. Hence, ares_library_cleanup() will not be called.
* */
~CaresPTRResolver() override = default;
std::unordered_set<std::string> resolve(const std::string & ip) override;
std::unordered_set<std::string> resolve_v6(const std::string & ip) override;
private:
bool wait_and_process(ares_channel channel);
void cancel_requests(ares_channel channel);
void resolve(const std::string & ip, std::unordered_set<std::string> & response, ares_channel channel);
void resolve_v6(const std::string & ip, std::unordered_set<std::string> & response, ares_channel channel);
std::span<pollfd> get_readable_sockets(int * sockets, pollfd * pollfd, ares_channel channel);
int64_t calculate_timeout(ares_channel channel);
void process_possible_timeout(ares_channel channel);
void process_readable_sockets(std::span<pollfd> readable_sockets, ares_channel channel);
};
}
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