simplified dns (no self-made recursion); merge PingScheduler and PingRotate; make...

[pingcheck] / src / dns / dnscache.cpp

/*
 The software in this package is distributed under the GNU General
 Public License version 2 (with a special exception described below).

 A copy of GNU General Public License (GPL) is included in this distribution,
 in the file COPYING.GPL.

 As a special exception, if other files instantiate templates or use macros
 or inline functions from this file, or you compile this file and link it
 with other works to produce a work based on this file, this file
 does not by itself cause the resulting work to be covered
 by the GNU General Public License.

 However the source code for this file must still be made available
 in accordance with section (3) of the GNU General Public License.

 This exception does not invalidate any other reasons why a work based
 on this file might be covered by the GNU General Public License.

 Christian Herdtweck, Intra2net AG 2015
 */

#include "dns/dnscache.h"

#include <fstream>
#include <logfunc.hpp>
#include <filefunc.hxx>   // I2n::file_exists
#include <boost/foreach.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/asio/placeholders.hpp>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/map.hpp>
#include <boost/serialization/string.hpp>
#include <boost/serialization/vector.hpp>
#include <boost/archive/xml_oarchive.hpp>
#include <boost/archive/xml_iarchive.hpp>

#include "dns/dnsmaster.h"

using boost::bind;
using boost::posix_time::seconds;
using I2n::Logger::GlobalLogger;

namespace Config
{
    int SaveTimerSeconds = 60;
    int MaxRetrievalRecursions = 10;
}

Cname::Cname()
    : Host()
    , Ttl()
{}

Cname::Cname(const std::string &host, const uint32_t ttl)
    : Host( host )
    , Ttl( ttl )
{}

DnsCache::DnsCache(const IoServiceItem &io_serv,
                   const std::string &cache_file)
    : IpCache()
    , CnameCache()
    , SaveTimer( *io_serv )
    , CacheFile( cache_file )
    , HasChanged( false )
{
    // load cache from file
    load_from_cachefile();

    // schedule next save
    (void) SaveTimer.expires_from_now( seconds( Config::SaveTimerSeconds ) );
    SaveTimer.async_wait( bind( &DnsCache::schedule_save, this,
                                boost::asio::placeholders::error ) );
}


DnsCache::~DnsCache()
{
    GlobalLogger.info() << "Dns Cache is being destructed";

    // save one last time without re-scheduling the next save
    save_to_cachefile();

    // cancel save timer
    SaveTimer.cancel();
}


void DnsCache::schedule_save(const boost::system::error_code &error)
{
    // just in case: ensure SaveTimer is cancelled
    SaveTimer.cancel();  // (will do nothing if already expired/cancelled)

    if ( error ==  boost::asio::error::operation_aborted )   // cancelled
    {
        GlobalLogger.error() << "DnsCache: SaveTimer was cancelled "
                             << "--> no save and no re-schedule of saving!";
        return;
    }
    else if (error)
    {
        GlobalLogger.error() << "DnsCache: Received error " << error
                             << " in schedule_save "
                             << "--> no save now but re-schedule saving";
    }
    else
        save_to_cachefile();

    // schedule next save
    (void) SaveTimer.expires_from_now( seconds( Config::SaveTimerSeconds ) );
    SaveTimer.async_wait( bind( &DnsCache::schedule_save, this,
                                boost::asio::placeholders::error ) );
}

void DnsCache::save_to_cachefile()
{
    if (!HasChanged)
    {
        GlobalLogger.info() << "DnsCache: skip saving because has not changed";
        return;
    }
    else if (CacheFile.empty())
    {
        GlobalLogger.warning()
                           << "DnsCache: skip saving because file name empty!";
        return;
    }

    try
    {
        std::ofstream ofs( CacheFile.c_str() );
        boost::archive::xml_oarchive oa(ofs);
        oa << boost::serialization::make_nvp("IpCache", IpCache);
        oa << boost::serialization::make_nvp("CnameCache", CnameCache);
        GlobalLogger.info() << "DnsCache: saved to cache file " << CacheFile;

        HasChanged = false;
    }
    catch (std::exception &exc)
    {
        GlobalLogger.warning() << "Saving failed: " << exc.what();
    }
}


void DnsCache::load_from_cachefile()
{
    if (CacheFile.empty())
    {
        GlobalLogger.warning()
                  << "DnsCache: cannot load because cache file name is empty!";
        return;
    }
    else if ( !I2n::file_exists(CacheFile) )
    {
        GlobalLogger.warning() << "DnsCache: cannot load because cache file "
                               << CacheFile << " does not exist!";
        return;
    }
    try
    {
        HostAddressVec cache;

        std::ifstream ifs( CacheFile.c_str() );
        boost::archive::xml_iarchive ia(ifs);

        ia >> boost::serialization::make_nvp("IpCache", cache);
        ia >> boost::serialization::make_nvp("CnameCache", cache);
        GlobalLogger.info() << "DnsCache: loaded from file " << CacheFile;
    }
    catch (boost::archive::archive_exception &exc)
    {
        GlobalLogger.warning() << "DnsCache: archive exception loading from "
                               << CacheFile << ": " << exc.what();
    }
    catch (std::exception &exc)
    {
        GlobalLogger.warning() << "DnsCache: exception while loading from "
                               << CacheFile << ": " << exc.what();
    }
}

void DnsCache::update(const std::string &hostname,
                      const HostAddressVec &new_data)
{
    GlobalLogger.info() << "DnsCache: update IPs for " << hostname
                        << " to " << new_data.size() << "-list";
    IpCache[hostname] = new_data;
    HasChanged = true;
}


void DnsCache::update(const std::string &hostname,
                      const Cname &cname)
{
    GlobalLogger.info() << "DnsCache: update CNAME for " << hostname
                        << " to " << cname.Host;
    CnameCache[hostname] = cname;
    HasChanged = true;
}


void DnsCache::update(const std::string &hostname,
                          const uint32_t new_ttl)
{
    GlobalLogger.info() << "DnsCache: ensure TTL for IPs for " << hostname
                        << " is below " << new_ttl << "s";
    HostAddressVec ips = IpCache[hostname];
    TimeToLive current_ttl;
    BOOST_FOREACH( HostAddress &addr, ips )
    {
        current_ttl = addr.get_ttl();
        if (current_ttl.get_value() > new_ttl)
        {
            current_ttl.set_value(new_ttl);
            addr.set_ttl(current_ttl);
            HasChanged = true;
        }
    }
    IpCache[hostname] = ips;
}


/**
 * @returns empty list if no (up to date) ips for hostname in cache
 */
HostAddressVec DnsCache::get_ips(const std::string &hostname,
                                 const bool check_up_to_date)
{
    HostAddressVec result = IpCache[hostname];
    if (check_up_to_date)
    {
        HostAddressVec result_up_to_date;
        uint32_t threshold = static_cast<uint32_t>(
                DnsMaster::get_instance()->get_resolved_ip_ttl_threshold() );
        BOOST_FOREACH( const HostAddress &addr, result )
        {
            if (addr.get_ttl().get_updated_value() > threshold)
                result_up_to_date.push_back(addr);
        }
        GlobalLogger.debug() << "DnsCache: From cached list of size "
             << result.size() << " return " << result_up_to_date.size()
             << " since rest out of date";
        result = result_up_to_date;
    }
    GlobalLogger.info() << "DnsCache: request IPs for " << hostname
                        << " --> " << result.size() << "-list";
    return result;
}

/**
 * @returns empty cname if no (up to date cname) for hostname in cache
 */
Cname DnsCache::get_cname(const std::string &hostname,
                          const bool check_up_to_date)
{
    Cname result_obj = CnameCache[hostname];
    GlobalLogger.info() << "DnsCache: request CNAME for " << hostname
                        << " --> \"" << result_obj.Host << "\"";
    if (result_obj.Host.empty())
        return result_obj;

    else if (check_up_to_date)
    {
        if (result_obj.Ttl.get_updated_value() > DnsMaster::get_instance()
                                              ->get_resolved_ip_ttl_threshold())
            return result_obj;
        else
        {
            GlobalLogger.debug() << "DnsCache: CNAME is out of date";
            return Cname();    // same as if there was no cname for hostname
        }
    }
    else
        return result_obj;
}

// underlying assumption in this function: for a hostname, the cache has either
// a list of IPs saved or a cname saved, but never both
HostAddressVec DnsCache::get_ips_recursive(const std::string &hostname,
                                           const bool check_up_to_date)
{
    std::string current_host = hostname;
    Cname current_cname;
    HostAddressVec result = get_ips(current_host);
    int n_recursions = 0;
    uint32_t min_cname_ttl = 0xffff;   // largest possible unsigned 4-byte value
    while ( result.empty() )
    {
        current_cname = get_cname(current_host, check_up_to_date);
        current_host = current_cname.Host;
        if (current_host.empty())
            break;
        else if (++n_recursions >= Config::MaxRetrievalRecursions)
        {
            GlobalLogger.warning() << "DnsCache: reached recursion limit of "
                << n_recursions << " in recursive IP retrieval!";
            break;
        }
        else
        {
            min_cname_ttl = min(min_cname_ttl, current_cname.Ttl.get_value());
            result = get_ips(current_host, check_up_to_date);
        }
    }

    GlobalLogger.debug() << "DnsCache: recursive IP retrieval resulted in "
                         << result.size() << "-list after " << n_recursions
                         << " recursions";

    // adjust ttl to min of ttl and min_cname_ttl
    if (n_recursions > 0)
    {
        TimeToLive cname_ttl(min_cname_ttl);

        BOOST_FOREACH( HostAddress &addr, result )
        {
            if (addr.get_ttl().get_value() > min_cname_ttl)
                addr.set_ttl(cname_ttl);
        }
    }

    return result;
}

/**
 * from a list of CNAMEs find the first one that is out of date
 *
 * required in ResolverBase::get_skipper
 * 
 * Assume you have the following situation in cache with TTLs below:
 * hostname --> cname1 --> cname2 --> ... --> cnameN [--> IP]
 *               100         0                                --> return cname2
 *               100        100        100     100            --> return cnameN
 *    ( with N < Config::MaxRetrievalRecursions )
 * hostname --> IP (no cnames involved) --> return hostname
 */
std::string DnsCache::get_first_outdated_cname(const std::string &hostname,
                                               const uint32_t ttl_thresh)
{
    std::string up_to_date_host = hostname;
    Cname cname;
    int n_recursions = 0;
    while (true)
    {
        if (++n_recursions >= Config::MaxRetrievalRecursions)
        {
            GlobalLogger.warning() << "DnsCache: reached recursion limit of "
                << n_recursions << " in search of outdated CNAMEs!";
            break;
        }

        cname = get_cname(up_to_date_host);
        if (cname.Host.empty())
            // reached end of cname list
            break;
        else if (cname.Ttl.get_updated_value() > ttl_thresh)
            // cname is up to date --> continue looking
            up_to_date_host = cname.Host;
        else
            // cname is out of date --> return that
            break;
    }
    return up_to_date_host;
}

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