i2pd/core/NetworkDatabase.cpp

#include <string.h>
#include "util/I2PEndian.h"
#include <fstream>
#include <vector>
#include <boost/asio.hpp>
#include <cryptopp/gzip.h>
#include "util/base64.h"
#include "util/Log.h"
#include "util/Timestamp.h"
#include "I2NPProtocol.h"
#include "tunnel/Tunnel.h"
#include "transport/Transports.h"
#include "RouterContext.h"
#include "Garlic.h"
#include "NetworkDatabase.h"
#include "util/util.h"

using namespace i2p::transport;

namespace i2p
{
namespace data
{       
    const char NetDb::m_NetDbPath[] = "netDb";
    NetDb netdb;

    NetDb::NetDb (): m_IsRunning (false), m_Thread (nullptr), m_Reseeder (nullptr)
    {
    }
    
    NetDb::~NetDb ()
    {
        Stop ();    
        delete m_Reseeder;
    }   

    void NetDb::Start ()
    {   
        Load ();
        if (m_RouterInfos.size () < 25) // reseed if # of router less than 50
        {   
            // try SU3 first
            Reseed ();

            // deprecated
            if (m_Reseeder)
            {
                // if still not enough download .dat files
                int reseedRetries = 0;
                while (m_RouterInfos.size () < 25 && reseedRetries < 5)
                {
                    m_Reseeder->reseedNow();
                    reseedRetries++;
                    Load ();
                }
            }
        }   
        m_IsRunning = true;
        m_Thread = new std::thread (std::bind (&NetDb::Run, this));
    }
    
    void NetDb::Stop ()
    {
        if (m_IsRunning)
        {   
            for (auto it: m_RouterInfos)
                it.second->SaveProfile ();
            DeleteObsoleteProfiles ();
            m_RouterInfos.clear ();
            m_Floodfills.clear ();
            if (m_Thread)
            {   
                m_IsRunning = false;
                m_Queue.WakeUp ();
                m_Thread->join (); 
                delete m_Thread;
                m_Thread = 0;
            }
            m_LeaseSets.clear();
            m_Requests.Stop ();
        }   
    }   
    
    void NetDb::Run ()
    {
        uint32_t lastSave = 0, lastPublish = 0, lastExploratory = 0, lastManageRequest = 0;
        while (m_IsRunning)
        {   
            try
            {   
                auto msg = m_Queue.GetNextWithTimeout (15000); // 15 sec
                if (msg)
                {   
                    int numMsgs = 0;    
                    while (msg)
                    {
                        switch (msg->GetTypeID ()) 
                        {
                            case eI2NPDatabaseStore:    
                                LogPrint ("DatabaseStore");
                                HandleDatabaseStoreMsg (msg);
                            break;
                            case eI2NPDatabaseSearchReply:
                                LogPrint ("DatabaseSearchReply");
                                HandleDatabaseSearchReplyMsg (msg);
                            break;
                            case eI2NPDatabaseLookup:
                                LogPrint ("DatabaseLookup");
                                HandleDatabaseLookupMsg (msg);
                            break;  
                            default: // WTF?
                                LogPrint (eLogError, "NetDb: unexpected message type ", msg->GetTypeID ());
                                //i2p::HandleI2NPMessage (msg);
                        }   
                        if (numMsgs > 100) break;
                        msg = m_Queue.Get ();
                        numMsgs++;
                    }   
                }           
                if (!m_IsRunning) break;

                uint64_t ts = i2p::util::GetSecondsSinceEpoch ();
                if (ts - lastManageRequest >= 15) // manage requests every 15 seconds
                {
                    m_Requests.ManageRequests ();
                    lastManageRequest = ts;
                }   
                if (ts - lastSave >= 60) // save routers, manage leasesets and validate subscriptions every minute
                {
                    if (lastSave)
                    {
                        SaveUpdated ();
                        ManageLeaseSets ();
                    }   
                    lastSave = ts;
                }   
                if (ts - lastPublish >= 2400) // publish every 40 minutes
                {
                    Publish ();
                    lastPublish = ts;
                }   
                if (ts - lastExploratory >= 30) // exploratory every 30 seconds
                {   
                    auto numRouters = m_RouterInfos.size ();
                    if (numRouters < 2500 || ts - lastExploratory >= 90)
                    {   
                        numRouters = 800/numRouters;
                        if (numRouters < 1) numRouters = 1;
                        if (numRouters > 9) numRouters = 9; 
                        m_Requests.ManageRequests ();                   
                        Explore (numRouters);
                        lastExploratory = ts;
                    }   
                }   
            }
            catch (std::exception& ex)
            {
                LogPrint ("NetDb: ", ex.what ());
            }   
        }   
    }   
    
    void NetDb::AddRouterInfo (const uint8_t * buf, int len)
    {
        IdentityEx identity;
        if (identity.FromBuffer (buf, len))
            AddRouterInfo (identity.GetIdentHash (), buf, len); 
    }

    void NetDb::AddRouterInfo (const IdentHash& ident, const uint8_t * buf, int len)
    {   
        auto r = FindRouter (ident);
        if (r)
        {
            auto ts = r->GetTimestamp ();
            r->Update (buf, len);
            if (r->GetTimestamp () > ts)
                LogPrint ("RouterInfo updated");
        }   
        else    
        {   
            LogPrint ("New RouterInfo added");
            r = std::make_shared<RouterInfo> (buf, len);
            {
                std::unique_lock<std::mutex> l(m_RouterInfosMutex);
                m_RouterInfos[r->GetIdentHash ()] = r;
            }
            if (r->IsFloodfill ())
            {
                std::unique_lock<std::mutex> l(m_FloodfillsMutex);
                m_Floodfills.push_back (r);
            }   
        }   
        // take care about requested destination
        m_Requests.RequestComplete (ident, r);
    }   

    void NetDb::AddLeaseSet (const IdentHash& ident, const uint8_t * buf, int len,
        std::shared_ptr<i2p::tunnel::InboundTunnel> from)
    {
        if (!from) // unsolicited LS must be received directly
        {   
            auto it = m_LeaseSets.find(ident);
            if (it != m_LeaseSets.end ())
            {
                it->second->Update (buf, len); 
                if (it->second->IsValid ())
                    LogPrint (eLogInfo, "LeaseSet updated");
                else
                {
                    LogPrint (eLogInfo, "LeaseSet update failed");
                    m_LeaseSets.erase (it);
                }   
            }
            else
            {   
                auto leaseSet = std::make_shared<LeaseSet> (buf, len);
                if (leaseSet->IsValid ())
                {
                    LogPrint (eLogInfo, "New LeaseSet added");
                    m_LeaseSets[ident] = leaseSet;
                }
                else
                    LogPrint (eLogError, "New LeaseSet validation failed");
            }   
        }   
    }   

    std::shared_ptr<RouterInfo> NetDb::FindRouter (const IdentHash& ident) const
    {
        std::unique_lock<std::mutex> l(m_RouterInfosMutex);
        auto it = m_RouterInfos.find (ident);
        if (it != m_RouterInfos.end ())
            return it->second;
        else
            return nullptr;
    }

    std::shared_ptr<LeaseSet> NetDb::FindLeaseSet (const IdentHash& destination) const
    {
        auto it = m_LeaseSets.find (destination);
        if (it != m_LeaseSets.end ())
            return it->second;
        else
            return nullptr;
    }

    void NetDb::SetUnreachable (const IdentHash& ident, bool unreachable)
    {
        auto it = m_RouterInfos.find (ident);
        if (it != m_RouterInfos.end ())
            return it->second->SetUnreachable (unreachable);
    }

    // TODO: Move to reseed and/or scheduled tasks. (In java version, scheduler fix this as well as sort RIs.)
    bool NetDb::CreateNetDb(boost::filesystem::path directory)
    {
        LogPrint (directory.string(), " doesn't exist, trying to create it.");
        if (!boost::filesystem::create_directory (directory))
        {
            LogPrint("Failed to create directory ", directory.string());
            return false;
        }

        // list of chars might appear in base64 string
        const char * chars = i2p::util::GetBase64SubstitutionTable (); // 64 bytes
        boost::filesystem::path suffix;
        for (int i = 0; i < 64; i++)
        {
#ifndef _WIN32
            suffix = std::string ("/r") + chars[i];
#else
            suffix = std::string ("\\r") + chars[i];
#endif
            if (!boost::filesystem::create_directory( boost::filesystem::path (directory / suffix) )) return false;
        }
        return true;
    }

    void NetDb::Reseed ()
    {
        if (!m_Reseeder)
        {       
            m_Reseeder = new Reseeder ();
            m_Reseeder->LoadCertificates (); // we need certificates for SU3 verification
        }
        int reseedRetries = 0;  
        while (reseedRetries < 10 && !m_Reseeder->ReseedNowSU3 ())
            reseedRetries++;
        if (reseedRetries >= 10)
            LogPrint (eLogWarning, "Failed to reseed after 10 attempts");
    }

    void NetDb::Load ()
    {
        boost::filesystem::path p(i2p::util::filesystem::GetDataDir() / m_NetDbPath);
        if (!boost::filesystem::exists (p))
        {
            // seems netDb doesn't exist yet
            if (!CreateNetDb(p)) return;
        }
        // make sure we cleanup netDb from previous attempts
        m_RouterInfos.clear (); 
        m_Floodfills.clear ();  

        // load routers now
        uint64_t ts = i2p::util::GetMillisecondsSinceEpoch ();  
        int numRouters = 0;
        boost::filesystem::directory_iterator end;
        for (boost::filesystem::directory_iterator it (p); it != end; ++it)
        {
            if (boost::filesystem::is_directory (it->status()))
            {
                for (boost::filesystem::directory_iterator it1 (it->path ()); it1 != end; ++it1)
                {
#if BOOST_VERSION > 10500
                    const std::string& fullPath = it1->path().string();
#else
                    const std::string& fullPath = it1->path();
#endif
                    auto r = std::make_shared<RouterInfo>(fullPath);
                    if (!r->IsUnreachable () && (!r->UsesIntroducer () || ts < r->GetTimestamp () + 3600*1000LL)) // 1 hour
                    {   
                        r->DeleteBuffer ();
                        r->ClearProperties (); // properties are not used for regular routers
                        m_RouterInfos[r->GetIdentHash ()] = r;
                        if (r->IsFloodfill ())
                            m_Floodfills.push_back (r);
                        numRouters++;
                    }   
                    else
                    {   
                        if (boost::filesystem::exists (fullPath))  
                            boost::filesystem::remove (fullPath);
                    }   
                }   
            }   
        }
        LogPrint (numRouters, " routers loaded");
        LogPrint (m_Floodfills.size (), " floodfills loaded");  
    }   

    void NetDb::SaveUpdated ()
    {   
        auto GetFilePath = [](const boost::filesystem::path& directory, const RouterInfo * routerInfo)
        {
            std::string s(routerInfo->GetIdentHashBase64());
            return directory / (std::string("r") + s[0]) / ("routerInfo-" + s + ".dat");
        };  

        boost::filesystem::path fullDirectory (i2p::util::filesystem::GetDataDir() / m_NetDbPath);
        int count = 0, deletedCount = 0;
        auto total = m_RouterInfos.size ();
        uint64_t ts = i2p::util::GetMillisecondsSinceEpoch ();
        for (auto it: m_RouterInfos)
        {   
            if (it.second->IsUpdated ())
            {
                std::string f = GetFilePath(fullDirectory, it.second.get()).string();
                it.second->SaveToFile (f);
                it.second->SetUpdated (false);
                it.second->SetUnreachable (false);
                it.second->DeleteBuffer ();
                count++;
            }
            else 
            {
                // RouterInfo expires after 1 hour if uses introducer
                if (it.second->UsesIntroducer () && ts > it.second->GetTimestamp () + 3600*1000LL) // 1 hour
                    it.second->SetUnreachable (true);
                else if (total > 75 && ts > (i2p::context.GetStartupTime () + 600)*1000LL) // routers don't expire if less than 25 or uptime is less than 10 minutes
                {
                    if (i2p::context.IsFloodfill ())
                    {
                        if (ts > it.second->GetTimestamp () + 3600*1000LL) // 1 hours
                        {   
                            it.second->SetUnreachable (true);
                            total--;
                        }   
                    }
                    else if (total > 300)
                    {
                        if (ts > it.second->GetTimestamp () + 30*3600*1000LL) // 30 hours
                        {   
                            it.second->SetUnreachable (true);
                            total--;
                        }   
                    }
                    else if (total > 120)
                    {
                        if (ts > it.second->GetTimestamp () + 72*3600*1000LL) // 72 hours
                        {   
                            it.second->SetUnreachable (true);
                            total--;
                        }   
                    }
                }
                
                if (it.second->IsUnreachable ())
                {   
                    total--;
                    // delete RI file
                    if (boost::filesystem::exists (GetFilePath (fullDirectory, it.second.get ())))
                    {    
                        boost::filesystem::remove (GetFilePath (fullDirectory, it.second.get ()));
                        deletedCount++;
                    }   
                    // delete from floodfills list
                    if (it.second->IsFloodfill ())
                    {
                        std::unique_lock<std::mutex> l(m_FloodfillsMutex);
                        m_Floodfills.remove (it.second);
                    }
                }
            }   
        }   
        if (count > 0)
            LogPrint (count," new/updated routers saved");
        if (deletedCount > 0)
        {
            LogPrint (deletedCount," routers deleted");
            // clean up RouterInfos table
            std::unique_lock<std::mutex> l(m_RouterInfosMutex);
            for (auto it = m_RouterInfos.begin (); it != m_RouterInfos.end ();)
            {
                if (it->second->IsUnreachable ())
                {   
                    it->second->SaveProfile ();
                    it = m_RouterInfos.erase (it);
                }   
                else
                    it++;
            }
        }
    }

    void NetDb::RequestDestination (const IdentHash& destination, RequestedDestination::RequestComplete requestComplete)
    {
        auto dest = m_Requests.CreateRequest (destination, false, requestComplete); // non-exploratory
        if (!dest)
        {
            LogPrint (eLogWarning, "Destination ", destination.ToBase64(), " is requested already"); 
            return;         
        }

        auto floodfill = GetClosestFloodfill (destination, dest->GetExcludedPeers ());
        if (floodfill)
            transports.SendMessage (floodfill->GetIdentHash (), dest->CreateRequestMessage (floodfill->GetIdentHash ()));   
        else
        {
            LogPrint (eLogError, "No floodfills found");
            m_Requests.RequestComplete (destination, nullptr);
        }   
    }   
    
    void NetDb::HandleDatabaseStoreMsg (std::shared_ptr<const I2NPMessage> m)
    {   
        const uint8_t * buf = m->GetPayload ();
        size_t len = m->GetSize ();     
        IdentHash ident (buf + DATABASE_STORE_KEY_OFFSET);
        if (ident.IsZero ())
        {
            LogPrint (eLogError, "Database store with zero ident. Dropped");
            return;
        }   
        uint32_t replyToken = bufbe32toh (buf + DATABASE_STORE_REPLY_TOKEN_OFFSET);
        size_t offset = DATABASE_STORE_HEADER_SIZE;
        if (replyToken)
        {
            auto deliveryStatus = CreateDeliveryStatusMsg (replyToken);         
            uint32_t tunnelID = bufbe32toh (buf + offset);
            offset += 4;
            if (!tunnelID) // send response directly
                transports.SendMessage (buf + offset, deliveryStatus);
            else
            {
                auto pool = i2p::tunnel::tunnels.GetExploratoryPool ();
                auto outbound = pool ? pool->GetNextOutboundTunnel () : nullptr;
                if (outbound)
                    outbound->SendTunnelDataMsg (buf + offset, tunnelID, deliveryStatus);
                else
                    LogPrint (eLogError, "No outbound tunnels for DatabaseStore reply found");
            }       
            offset += 32;

            if (context.IsFloodfill ())
            {
                // flood it
                auto floodMsg = ToSharedI2NPMessage (NewI2NPShortMessage ());
                uint8_t * payload = floodMsg->GetPayload ();        
                memcpy (payload, buf, 33); // key + type
                htobe32buf (payload + DATABASE_STORE_REPLY_TOKEN_OFFSET, 0); // zero reply token
                memcpy (payload + DATABASE_STORE_HEADER_SIZE, buf + offset, len - offset);
                floodMsg->len += DATABASE_STORE_HEADER_SIZE + len -offset;
                floodMsg->FillI2NPMessageHeader (eI2NPDatabaseStore); 
                std::set<IdentHash> excluded;
                for (int i = 0; i < 3; i++)
                {
                    auto floodfill = GetClosestFloodfill (ident, excluded);
                    if (floodfill)
                        transports.SendMessage (floodfill->GetIdentHash (), floodMsg);
                }   
            }   
        }
        
        if (buf[DATABASE_STORE_TYPE_OFFSET]) // type
        {
            LogPrint ("LeaseSet");
            AddLeaseSet (ident, buf + offset, len - offset, m->from);
        }   
        else
        {
            LogPrint ("RouterInfo");
            size_t size = bufbe16toh (buf + offset);
            offset += 2;
            if (size > 2048 || size > len - offset)
            {
                LogPrint ("Invalid RouterInfo length ", (int)size);
                return;
            }   
            try
            {   
                CryptoPP::Gunzip decompressor;
                decompressor.Put (buf + offset, size);
                decompressor.MessageEnd();
                uint8_t uncompressed[2048];
                size_t uncomressedSize = decompressor.MaxRetrievable ();
                if (uncomressedSize <= 2048)
                {
                    decompressor.Get (uncompressed, uncomressedSize);
                    AddRouterInfo (ident, uncompressed, uncomressedSize);
                }
                else
                    LogPrint ("Invalid RouterInfo uncomressed length ", (int)uncomressedSize);
            }
            catch (CryptoPP::Exception& ex)
            {
                LogPrint (eLogError, "DatabaseStore: ", ex.what ());
            }
        }   
    }   

    void NetDb::HandleDatabaseSearchReplyMsg (std::shared_ptr<const I2NPMessage> msg)
    {
        const uint8_t * buf = msg->GetPayload ();
        char key[48];
        int l = i2p::util::ByteStreamToBase64 (buf, 32, key, 48);
        key[l] = 0;
        int num = buf[32]; // num
        LogPrint ("DatabaseSearchReply for ", key, " num=", num);
        IdentHash ident (buf);
        auto dest = m_Requests.FindRequest (ident); 
        if (dest)
        {   
            bool deleteDest = true;
            if (num > 0)
            {   
                auto pool = i2p::tunnel::tunnels.GetExploratoryPool ();
                auto outbound = pool ? pool->GetNextOutboundTunnel () : nullptr;
                auto inbound = pool ? pool->GetNextInboundTunnel () : nullptr;
                if (!dest->IsExploratory ())
                {
                    // reply to our destination. Try other floodfills
                    if (outbound && inbound )
                    {
                        std::vector<i2p::tunnel::TunnelMessageBlock> msgs;
                        auto count = dest->GetExcludedPeers ().size ();
                        if (count < 7)
                        {   
                            auto nextFloodfill = GetClosestFloodfill (dest->GetDestination (), dest->GetExcludedPeers ());
                            if (nextFloodfill)
                            {   
                                // tell floodfill about us 
                                msgs.push_back (i2p::tunnel::TunnelMessageBlock 
                                    { 
                                        i2p::tunnel::eDeliveryTypeRouter,
                                        nextFloodfill->GetIdentHash (), 0,
                                        CreateDatabaseStoreMsg () 
                                    });  
                                
                                // request destination
                                LogPrint ("Try ", key, " at ", count, " floodfill ", nextFloodfill->GetIdentHash ().ToBase64 ()); 
                                auto msg = dest->CreateRequestMessage (nextFloodfill, inbound);
                                msgs.push_back (i2p::tunnel::TunnelMessageBlock 
                                    { 
                                        i2p::tunnel::eDeliveryTypeRouter,
                                        nextFloodfill->GetIdentHash (), 0, msg
                                    });
                                deleteDest = false;
                            }   
                        }
                        else
                            LogPrint (key, " was not found on 7 floodfills");

                        if (msgs.size () > 0)
                            outbound->SendTunnelDataMsg (msgs); 
                    }   
                }   

                if (deleteDest)
                    // no more requests for the destinationation. delete it
                    m_Requests.RequestComplete (ident, nullptr);
            }
            else
                // no more requests for detination possible. delete it
                m_Requests.RequestComplete (ident, nullptr);
        }
        else    
            LogPrint ("Requested destination for ", key, " not found");

        // try responses
        for (int i = 0; i < num; i++)
        {
            const uint8_t * router = buf + 33 + i*32;
            char peerHash[48];
            int l1 = i2p::util::ByteStreamToBase64 (router, 32, peerHash, 48);
            peerHash[l1] = 0;
            LogPrint (i,": ", peerHash);

            auto r = FindRouter (router); 
            if (!r || i2p::util::GetMillisecondsSinceEpoch () > r->GetTimestamp () + 3600*1000LL) 
            {   
                // router with ident not found or too old (1 hour)
                LogPrint ("Found new/outdated router. Requesting RouterInfo ...");
                RequestDestination (router);
            }
            else
                LogPrint ("Bayan"); 
        }   
    }   
    
    void NetDb::HandleDatabaseLookupMsg (std::shared_ptr<const I2NPMessage> msg)
    {
        const uint8_t * buf = msg->GetPayload ();
        IdentHash ident (buf);
        if (ident.IsZero ())
        {
            LogPrint (eLogError, "DatabaseLookup for zero ident. Ignored");
            return;
        }   
        char key[48];
        int l = i2p::util::ByteStreamToBase64 (buf, 32, key, 48);
        key[l] = 0;
        uint8_t flag = buf[64];
        LogPrint ("DatabaseLookup for ", key, " recieved flags=", (int)flag);
        uint8_t lookupType = flag & DATABASE_LOOKUP_TYPE_FLAGS_MASK;
        const uint8_t * excluded = buf + 65;        
        uint32_t replyTunnelID = 0;
        if (flag & DATABASE_LOOKUP_DELIVERY_FLAG) //reply to tunnel
        {
            replyTunnelID = bufbe32toh (buf + 64);
            excluded += 4;
        }
        uint16_t numExcluded = bufbe16toh (excluded);   
        excluded += 2;
        if (numExcluded > 512)
        {
            LogPrint ("Number of excluded peers", numExcluded, " exceeds 512");
            numExcluded = 0; // TODO:
        } 
        
        std::shared_ptr<I2NPMessage> replyMsg;
        if (lookupType == DATABASE_LOOKUP_TYPE_EXPLORATORY_LOOKUP)
        {
            LogPrint ("Exploratory close to  ", key, " ", numExcluded, " excluded");
            std::set<IdentHash> excludedRouters;
            for (int i = 0; i < numExcluded; i++)
            {
                excludedRouters.insert (excluded);
                excluded += 32;
            }   
            std::vector<IdentHash> routers;
            for (int i = 0; i < 3; i++)
            {
                auto r = GetClosestNonFloodfill (ident, excludedRouters);
                if (r)
                {   
                    routers.push_back (r->GetIdentHash ());
                    excludedRouters.insert (r->GetIdentHash ());
                }   
            }   
            replyMsg = CreateDatabaseSearchReply (ident, routers);
        }   
        else
        {   
            if (lookupType == DATABASE_LOOKUP_TYPE_ROUTERINFO_LOOKUP  ||
                lookupType == DATABASE_LOOKUP_TYPE_NORMAL_LOOKUP)
            {   
                auto router = FindRouter (ident);
                if (router)
                {
                    LogPrint ("Requested RouterInfo ", key, " found");
                    router->LoadBuffer ();
                    if (router->GetBuffer ()) 
                        replyMsg = CreateDatabaseStoreMsg (router);
                }
            }
            
            if (!replyMsg && (lookupType == DATABASE_LOOKUP_TYPE_LEASESET_LOOKUP  ||
                lookupType == DATABASE_LOOKUP_TYPE_NORMAL_LOOKUP))
            {
                auto leaseSet = FindLeaseSet (ident);
                if (leaseSet) // we don't send back our LeaseSets
                {
                    LogPrint ("Requested LeaseSet ", key, " found");
                    replyMsg = CreateDatabaseStoreMsg (leaseSet);
                }
            }
            
            if (!replyMsg)
            {
                LogPrint ("Requested ", key, " not found. ", numExcluded, " excluded");
                std::set<IdentHash> excludedRouters;    
                for (int i = 0; i < numExcluded; i++)
                {
                    excludedRouters.insert (excluded);
                    excluded += 32;
                }
                replyMsg = CreateDatabaseSearchReply (ident, GetClosestFloodfills (ident, 3, excludedRouters));
            }
        }
        
        if (replyMsg)
        {   
            if (replyTunnelID)
            {
                // encryption might be used though tunnel only
                if (flag & DATABASE_LOOKUP_ENCYPTION_FLAG) // encrypted reply requested
                {
                    const uint8_t * sessionKey = excluded;
                    uint8_t numTags = sessionKey[32];
                    if (numTags > 0) 
                    {
                        const uint8_t * sessionTag = sessionKey + 33; // take first tag
                        i2p::garlic::GarlicRoutingSession garlic (sessionKey, sessionTag);
                        replyMsg = garlic.WrapSingleMessage (replyMsg);
                    }
                }   
                auto exploratoryPool = i2p::tunnel::tunnels.GetExploratoryPool ();
                auto outbound = exploratoryPool ? exploratoryPool->GetNextOutboundTunnel () : nullptr;
                if (outbound)
                    outbound->SendTunnelDataMsg (buf+32, replyTunnelID, replyMsg);
                else
                    transports.SendMessage (buf+32, i2p::CreateTunnelGatewayMsg (replyTunnelID, replyMsg));
            }
            else
                transports.SendMessage (buf+32, replyMsg);
        }
    }   

    void NetDb::Explore (int numDestinations)
    {   
        // new requests
        auto exploratoryPool = i2p::tunnel::tunnels.GetExploratoryPool ();
        auto outbound = exploratoryPool ? exploratoryPool->GetNextOutboundTunnel () : nullptr;
        auto inbound = exploratoryPool ? exploratoryPool->GetNextInboundTunnel () : nullptr;
        bool throughTunnels = outbound && inbound;
        
        CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
        uint8_t randomHash[32];
        std::vector<i2p::tunnel::TunnelMessageBlock> msgs;
        std::set<const RouterInfo *> floodfills;
        LogPrint ("Exploring new ", numDestinations, " routers ...");
        for (int i = 0; i < numDestinations; i++)
        {   
            rnd.GenerateBlock (randomHash, 32);
            auto dest = m_Requests.CreateRequest (randomHash, true); // exploratory
            if (!dest)
            {   
                LogPrint (eLogWarning, "Exploratory destination is requested already");
                return;     
            }   
            auto floodfill = GetClosestFloodfill (randomHash, dest->GetExcludedPeers ());
            if (floodfill && !floodfills.count (floodfill.get ())) // request floodfill only once
            {   
                floodfills.insert (floodfill.get ());
                if (i2p::transport::transports.IsConnected (floodfill->GetIdentHash ()))
                    throughTunnels = false;
                if (throughTunnels)
                {   
                    msgs.push_back (i2p::tunnel::TunnelMessageBlock 
                        { 
                            i2p::tunnel::eDeliveryTypeRouter,
                            floodfill->GetIdentHash (), 0,
                            CreateDatabaseStoreMsg () // tell floodfill about us 
                        });  
                    msgs.push_back (i2p::tunnel::TunnelMessageBlock 
                        { 
                            i2p::tunnel::eDeliveryTypeRouter,
                            floodfill->GetIdentHash (), 0, 
                            dest->CreateRequestMessage (floodfill, inbound) // explore
                        }); 
                }   
                else
                    i2p::transport::transports.SendMessage (floodfill->GetIdentHash (), dest->CreateRequestMessage (floodfill->GetIdentHash ()));
            }   
            else
                m_Requests.RequestComplete (randomHash, nullptr);
        }   
        if (throughTunnels && msgs.size () > 0)
            outbound->SendTunnelDataMsg (msgs);     
    }   

    void NetDb::Publish ()
    {
        std::set<IdentHash> excluded; // TODO: fill up later
        for (int i = 0; i < 2; i++)
        {   
            auto floodfill = GetClosestFloodfill (i2p::context.GetRouterInfo ().GetIdentHash (), excluded);
            if (floodfill)
            {
                uint32_t replyToken = i2p::context.GetRandomNumberGenerator ().GenerateWord32 ();
                LogPrint ("Publishing our RouterInfo to ", floodfill->GetIdentHashAbbreviation (), ". reply token=", replyToken);
                transports.SendMessage (floodfill->GetIdentHash (), CreateDatabaseStoreMsg (i2p::context.GetSharedRouterInfo (), replyToken));  
                excluded.insert (floodfill->GetIdentHash ());
            }
        }   
    }       

    std::shared_ptr<const RouterInfo> NetDb::GetRandomRouter () const
    {
        return GetRandomRouter (
            [](std::shared_ptr<const RouterInfo> router)->bool 
            { 
                return !router->IsHidden (); 
            });
    }   
    
    std::shared_ptr<const RouterInfo> NetDb::GetRandomRouter (std::shared_ptr<const RouterInfo> compatibleWith) const
    {
        return GetRandomRouter (
            [compatibleWith](std::shared_ptr<const RouterInfo> router)->bool 
            { 
                return !router->IsHidden () && router != compatibleWith && 
                    router->IsCompatible (*compatibleWith); 
            });
    }   

    std::shared_ptr<const RouterInfo> NetDb::GetRandomPeerTestRouter () const
    {
        return GetRandomRouter (
            [](std::shared_ptr<const RouterInfo> router)->bool 
            { 
                return !router->IsHidden () && router->IsPeerTesting (); 
            });
    }

    std::shared_ptr<const RouterInfo> NetDb::GetRandomIntroducer () const
    {
        return GetRandomRouter (
            [](std::shared_ptr<const RouterInfo> router)->bool 
            { 
                return !router->IsHidden () && router->IsIntroducer (); 
            });
    }   
    
    std::shared_ptr<const RouterInfo> NetDb::GetHighBandwidthRandomRouter (std::shared_ptr<const RouterInfo> compatibleWith) const
    {
        return GetRandomRouter (
            [compatibleWith](std::shared_ptr<const RouterInfo> router)->bool 
            { 
                return !router->IsHidden () && router != compatibleWith &&
                    router->IsCompatible (*compatibleWith) && 
                    (router->GetCaps () & RouterInfo::eHighBandwidth);
            });
    }   
    
    template<typename Filter>
    std::shared_ptr<const RouterInfo> NetDb::GetRandomRouter (Filter filter) const
    {
        CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
        uint32_t ind = rnd.GenerateWord32 (0, m_RouterInfos.size () - 1);   
        for (int j = 0; j < 2; j++)
        {   
            uint32_t i = 0;
            std::unique_lock<std::mutex> l(m_RouterInfosMutex);
            for (auto it: m_RouterInfos)
            {   
                if (i >= ind)
                {   
                    if (!it.second->IsUnreachable () && filter (it.second))
                        return it.second;
                }   
                else 
                    i++;
            }
            // we couldn't find anything, try second pass
            ind = 0;
        }   
        return nullptr; // seems we have too few routers
    }   
    
    void NetDb::PostI2NPMsg (std::shared_ptr<const I2NPMessage> msg)
    {
        if (msg) m_Queue.Put (msg); 
    }   

    std::shared_ptr<const RouterInfo> NetDb::GetClosestFloodfill (const IdentHash& destination, 
        const std::set<IdentHash>& excluded) const
    {
        std::shared_ptr<const RouterInfo> r;
        XORMetric minMetric;
        IdentHash destKey = CreateRoutingKey (destination);
        minMetric.SetMax ();
        std::unique_lock<std::mutex> l(m_FloodfillsMutex);
        for (auto it: m_Floodfills)
        {   
            if (!it->IsUnreachable ())
            {   
                XORMetric m = destKey ^ it->GetIdentHash ();
                if (m < minMetric && !excluded.count (it->GetIdentHash ()))
                {
                    minMetric = m;
                    r = it;
                }
            }   
        }   
        return r;
    }   

    std::vector<IdentHash> NetDb::GetClosestFloodfills (const IdentHash& destination, size_t num,
        std::set<IdentHash>& excluded) const
    {
        struct Sorted
        {
            std::shared_ptr<const RouterInfo> r;
            XORMetric metric;
            bool operator< (const Sorted& other) const { return metric < other.metric; };
        };

        std::set<Sorted> sorted;
        IdentHash destKey = CreateRoutingKey (destination);
        {
            std::unique_lock<std::mutex> l(m_FloodfillsMutex);
            for (auto it: m_Floodfills)
            {
                if (!it->IsUnreachable ())
                {   
                    XORMetric m = destKey ^ it->GetIdentHash ();
                    if (sorted.size () < num)
                        sorted.insert ({it, m});
                    else if (m < sorted.rbegin ()->metric)
                    {
                        sorted.insert ({it, m});
                        sorted.erase (std::prev (sorted.end ()));
                    }
                }
            }
        }

        std::vector<IdentHash> res; 
        size_t i = 0;           
        for (auto it: sorted)
        {
            if (i < num)
            {
                auto& ident = it.r->GetIdentHash ();
                if (!excluded.count (ident))
                {   
                    res.push_back (ident);
                    i++;
                }
            }
            else
                break;
        }   
        return res;
    }

    std::shared_ptr<const RouterInfo> NetDb::GetClosestNonFloodfill (const IdentHash& destination, 
        const std::set<IdentHash>& excluded) const
    {
        std::shared_ptr<const RouterInfo> r;
        XORMetric minMetric;
        IdentHash destKey = CreateRoutingKey (destination);
        minMetric.SetMax ();
        // must be called from NetDb thread only
        for (auto it: m_RouterInfos)
        {   
            if (!it.second->IsFloodfill ())
            {   
                XORMetric m = destKey ^ it.first;
                if (m < minMetric && !excluded.count (it.first))
                {
                    minMetric = m;
                    r = it.second;
                }
            }   
        }   
        return r;
    }   
    
    void NetDb::ManageLeaseSets ()
    {
        for (auto it = m_LeaseSets.begin (); it != m_LeaseSets.end ();)
        {
            if (!it->second->HasNonExpiredLeases ()) // all leases expired
            {
                LogPrint ("LeaseSet ", it->second->GetIdentHash ().ToBase64 (), " expired");
                it = m_LeaseSets.erase (it);
            }   
            else 
                it++;
        }
    }
}
}