IXWebSocket/ixwebsocket/IXDNSLookup.h

/*
 *  IXDNSLookup.h
 *  Author: Benjamin Sergeant
 *  Copyright (c) 2018 Machine Zone, Inc. All rights reserved.
 *
 *  Resolve a hostname+port to a struct addrinfo obtained with getaddrinfo 
 *  Does this in a background thread so that it can be cancelled, since
 *  getaddrinfo is a blocking call, and we don't want to block the main thread on Mobile.
 */

#pragma once

#include "IXCancellationRequest.h"

#include <string>
#include <thread>
#include <atomic>
#include <condition_variable>
#include <set>

struct addrinfo;

namespace ix 
{
    class DNSLookup {
    public:
        DNSLookup(const std::string& hostname,
                  int port,
                  int64_t wait = DNSLookup::kDefaultWait);
        ~DNSLookup();

        struct addrinfo* resolve(std::string& errMsg,
                                 const CancellationRequest& isCancellationRequested,
                                 bool blocking = false);

    private:
        struct addrinfo* resolveAsync(std::string& errMsg,
                                      const CancellationRequest& isCancellationRequested);
        struct addrinfo* resolveBlocking(std::string& errMsg,
                                         const CancellationRequest& isCancellationRequested);

        static struct addrinfo* getAddrInfo(const std::string& hostname, 
                                            int port,
                                            std::string& errMsg);

        void run(); // thread runner

        std::string _hostname;
        int _port;
        int64_t _wait;
        std::string _errMsg;
        struct addrinfo* _res;

        std::atomic<bool> _done;
        std::thread _thread;
        std::condition_variable _condition;
        std::mutex _conditionVariableMutex;

        std::atomic<uint64_t> _id;
        static std::atomic<uint64_t> _nextId;
        static std::set<uint64_t> _activeJobs;
        static std::mutex _activeJobsMutex;

        const static int64_t kDefaultTimeout;
        const static int64_t kDefaultWait;
    };
}