NFD/daemon/table/cs.cpp - ndnSIM - Gitiles

 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
  * Copyright (c) 2014,  Regents of the University of California,
  *                      Arizona Board of Regents,
  *                      Colorado State University,
  *                      University Pierre & Marie Curie, Sorbonne University,
  *                      Washington University in St. Louis,
  *                      Beijing Institute of Technology,
  *                      The University of Memphis
  *
  * This file is part of NFD (Named Data Networking Forwarding Daemon).
  * See AUTHORS.md for complete list of NFD authors and contributors.
  *
  * NFD is free software: you can redistribute it and/or modify it under the terms
  * of the GNU General Public License as published by the Free Software Foundation,
  * either version 3 of the License, or (at your option) any later version.
  *
  * NFD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
  * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
  * PURPOSE.  See the GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License along with
  * NFD, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
  *
  * \author Ilya Moiseenko <http://ilyamoiseenko.com/>
  * \author Junxiao Shi <http://www.cs.arizona.edu/people/shijunxiao/>
  * \author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
  */

 #include "cs.hpp"
 #include "core/logger.hpp"
 #include "core/random.hpp"

 #include <ndn-cxx/util/crypto.hpp>
 #include <ndn-cxx/security/signature-sha256-with-rsa.hpp>

 #include <boost/random/bernoulli_distribution.hpp>
 #include <boost/concept/assert.hpp>
 #include <boost/concept_check.hpp>
 #include <type_traits>

 /// max skip list layers
 static const size_t SKIPLIST_MAX_LAYERS = 32;
 /// probability for an entry in layer N to appear also in layer N+1
 static const double SKIPLIST_PROBABILITY = 0.25;

 NFD_LOG_INIT("ContentStore");

 namespace nfd {

 // http://en.cppreference.com/w/cpp/concept/ForwardIterator
 BOOST_CONCEPT_ASSERT((boost::ForwardIterator<Cs::const_iterator>));
 // boost::ForwardIterator follows SGI standard http://www.sgi.com/tech/stl/ForwardIterator.html,
 // which doesn't require DefaultConstructible
 #ifdef HAVE_IS_DEFAULT_CONSTRUCTIBLE
 static_assert(std::is_default_constructible<Cs::const_iterator>::value,
               "Cs::const_iterator must be default-constructible");
 #else
 BOOST_CONCEPT_ASSERT((boost::DefaultConstructible<Cs::const_iterator>));
 #endif // HAVE_IS_DEFAULT_CONSTRUCTIBLE

 Cs::Cs(size_t nMaxPackets)
   : m_nMaxPackets(nMaxPackets)
   , m_nPackets(0)
 {
   SkipListLayer* zeroLayer = new SkipListLayer();
   m_skipList.push_back(zeroLayer);

   for (size_t i = 0; i < m_nMaxPackets; i++)
     m_freeCsEntries.push(new cs::skip_list::Entry());
 }

 Cs::~Cs()
 {
   // evict all items from CS
   while (evictItem())
     ;

   BOOST_ASSERT(m_freeCsEntries.size() == m_nMaxPackets);

   while (!m_freeCsEntries.empty())
     {
       delete m_freeCsEntries.front();
       m_freeCsEntries.pop();
     }
 }

 size_t
 Cs::size() const
 {
   return m_nPackets; // size of the first layer in a skip list
 }

 void
 Cs::setLimit(size_t nMaxPackets)
 {
   size_t oldNMaxPackets = m_nMaxPackets;
   m_nMaxPackets = nMaxPackets;

   while (size() > m_nMaxPackets) {
     evictItem();
   }

   if (m_nMaxPackets >= oldNMaxPackets) {
     for (size_t i = oldNMaxPackets; i < m_nMaxPackets; i++) {
       m_freeCsEntries.push(new cs::skip_list::Entry());
     }
   }
   else {
     for (size_t i = oldNMaxPackets; i > m_nMaxPackets; i--) {
       delete m_freeCsEntries.front();
       m_freeCsEntries.pop();
     }
   }
 }

 size_t
 Cs::getLimit() const
 {
   return m_nMaxPackets;
 }

 //Reference: "Skip Lists: A Probabilistic Alternative to Balanced Trees" by W.Pugh
 std::pair<cs::skip_list::Entry*, bool>
 Cs::insertToSkipList(const Data& data, bool isUnsolicited)
 {
   NFD_LOG_TRACE("insertToSkipList() " << data.getFullName() << ", "
                 << "skipList size " << size());

   BOOST_ASSERT(m_cleanupIndex.size() <= size());
   BOOST_ASSERT(m_freeCsEntries.size() > 0);

   // take entry for the memory pool
   cs::skip_list::Entry* entry = m_freeCsEntries.front();
   m_freeCsEntries.pop();
   m_nPackets++;
   entry->setData(data, isUnsolicited);

   bool insertInFront = false;
   bool isIterated = false;
   SkipList::reverse_iterator topLayer = m_skipList.rbegin();
   SkipListLayer::iterator updateTable[SKIPLIST_MAX_LAYERS];
   SkipListLayer::iterator head = (*topLayer)->begin();

   if (!(*topLayer)->empty())
     {
       //start from the upper layer towards bottom
       int layer = m_skipList.size() - 1;
       for (SkipList::reverse_iterator rit = topLayer; rit != m_skipList.rend(); ++rit)
         {
           //if we didn't do any iterations on the higher layers, start from the begin() again
           if (!isIterated)
             head = (*rit)->begin();

           updateTable[layer] = head;

           if (head != (*rit)->end())
             {
               // it can happen when begin() contains the element in front of which we need to insert
               if (!isIterated && ((*head)->getFullName() >= entry->getFullName()))
                 {
                   --updateTable[layer];
                   insertInFront = true;
                 }
               else
                 {
                   SkipListLayer::iterator it = head;

                   while ((*it)->getFullName() < entry->getFullName())
                     {
                       head = it;
                       updateTable[layer] = it;
                       isIterated = true;

                       ++it;
                       if (it == (*rit)->end())
                         break;
                     }
                 }
             }

           if (layer > 0)
             head = (*head)->getIterators().find(layer - 1)->second; // move HEAD to the lower layer

           layer--;
         }
     }
   else
     {
       updateTable[0] = (*topLayer)->begin(); //initialization
     }

   head = updateTable[0];
   ++head; // look at the next slot to check if it contains a duplicate

   bool isCsEmpty = (size() == 0);
   bool isInBoundaries = (head != (*m_skipList.begin())->end());
   bool isNameIdentical = false;
   if (!isCsEmpty && isInBoundaries)
     {
       isNameIdentical = (*head)->getFullName() == entry->getFullName();
     }

   //check if this is a duplicate packet
   if (isNameIdentical)
     {
       NFD_LOG_TRACE("Duplicate name (with digest)");

       (*head)->setData(data, isUnsolicited); //updates stale time

       // new entry not needed, returning to the pool
       entry->release();
       m_freeCsEntries.push(entry);
       m_nPackets--;

       return std::make_pair(*head, false);
     }

   NFD_LOG_TRACE("Not a duplicate");

   size_t randomLayer = pickRandomLayer();

   while (m_skipList.size() < randomLayer + 1)
     {
       SkipListLayer* newLayer = new SkipListLayer();
       m_skipList.push_back(newLayer);

       updateTable[(m_skipList.size() - 1)] = newLayer->begin();
     }

   size_t layer = 0;
   for (SkipList::iterator i = m_skipList.begin();
        i != m_skipList.end() && layer <= randomLayer; ++i)
     {
       if (updateTable[layer] == (*i)->end() && !insertInFront)
         {
           (*i)->push_back(entry);
           SkipListLayer::iterator last = (*i)->end();
           --last;
           entry->setIterator(layer, last);

           NFD_LOG_TRACE("pushback " << &(*last));
         }
       else if (updateTable[layer] == (*i)->end() && insertInFront)
         {
           (*i)->push_front(entry);
           entry->setIterator(layer, (*i)->begin());

           NFD_LOG_TRACE("pushfront ");
         }
       else
         {
           NFD_LOG_TRACE("insertafter");
           ++updateTable[layer]; // insert after
           SkipListLayer::iterator position = (*i)->insert(updateTable[layer], entry);
           entry->setIterator(layer, position); // save iterator where item was inserted
         }
       layer++;
     }

   return std::make_pair(entry, true);
 }

 bool
 Cs::insert(const Data& data, bool isUnsolicited)
 {
   NFD_LOG_TRACE("insert() " << data.getFullName());

   if (isFull())
     {
       evictItem();
     }

   //pointer and insertion status
   std::pair<cs::skip_list::Entry*, bool> entry = insertToSkipList(data, isUnsolicited);

   //new entry
   if (static_cast<bool>(entry.first) && (entry.second == true))
     {
       m_cleanupIndex.push_back(entry.first);
       return true;
     }

   return false;
 }

 size_t
 Cs::pickRandomLayer() const
 {
   static boost::random::bernoulli_distribution<> dist(SKIPLIST_PROBABILITY);
   // TODO rewrite using geometry_distribution
   size_t layer;
   for (layer = 0; layer < SKIPLIST_MAX_LAYERS; ++layer) {
     if (!dist(getGlobalRng())) {
       break;
     }
   }
   return layer;
 }

 bool
 Cs::isFull() const
 {
   if (size() >= m_nMaxPackets) //size of the first layer vs. max size
     return true;

   return false;
 }

 bool
 Cs::eraseFromSkipList(cs::skip_list::Entry* entry)
 {
   NFD_LOG_TRACE("eraseFromSkipList() "  << entry->getFullName());
   NFD_LOG_TRACE("SkipList size " << size());

   bool isErased = false;

   const std::map<int, std::list<cs::skip_list::Entry*>::iterator>& iterators = entry->getIterators();

   if (!iterators.empty())
     {
       int layer = 0;

       for (SkipList::iterator it = m_skipList.begin(); it != m_skipList.end(); )
         {
           std::map<int, std::list<cs::skip_list::Entry*>::iterator>::const_iterator i = iterators.find(layer);

           if (i != iterators.end())
             {
               (*it)->erase(i->second);
               entry->removeIterator(layer);
               isErased = true;

               //remove layers that do not contain any elements (starting from the second layer)
               if ((layer != 0) && (*it)->empty())
                 {
                   delete *it;
                   it = m_skipList.erase(it);
                 }
               else
                 ++it;

               layer++;
             }
           else
             break;
       }
     }

   //delete entry;
   if (isErased)
   {
     entry->release();
     m_freeCsEntries.push(entry);
     m_nPackets--;
   }

   return isErased;
 }

 bool
 Cs::evictItem()
 {
   NFD_LOG_TRACE("evictItem()");

   if (!m_cleanupIndex.get<unsolicited>().empty()) {
     CleanupIndex::index<unsolicited>::type::const_iterator firstSolicited =
       m_cleanupIndex.get<unsolicited>().upper_bound(false);

     if (firstSolicited != m_cleanupIndex.get<unsolicited>().begin()) {
       --firstSolicited;
       BOOST_ASSERT((*firstSolicited)->isUnsolicited());
       NFD_LOG_TRACE("Evict from unsolicited queue");

       eraseFromSkipList(*firstSolicited);
       m_cleanupIndex.get<unsolicited>().erase(firstSolicited);
       return true;
     }
     else {
       BOOST_ASSERT(!(*m_cleanupIndex.get<unsolicited>().begin())->isUnsolicited());
     }
   }

   if (!m_cleanupIndex.get<byStaleness>().empty() &&
       (*m_cleanupIndex.get<byStaleness>().begin())->getStaleTime() < time::steady_clock::now())
   {
     NFD_LOG_TRACE("Evict from staleness queue");

     eraseFromSkipList(*m_cleanupIndex.get<byStaleness>().begin());
     m_cleanupIndex.get<byStaleness>().erase(m_cleanupIndex.get<byStaleness>().begin());
     return true;
   }

   if (!m_cleanupIndex.get<byArrival>().empty())
   {
     NFD_LOG_TRACE("Evict from arrival queue");

     eraseFromSkipList(*m_cleanupIndex.get<byArrival>().begin());
     m_cleanupIndex.get<byArrival>().erase(m_cleanupIndex.get<byArrival>().begin());
     return true;
   }

   return false;
 }

 const Data*
 Cs::find(const Interest& interest) const
 {
   NFD_LOG_TRACE("find() " << interest.getName());

   bool isIterated = false;
   SkipList::const_reverse_iterator topLayer = m_skipList.rbegin();
   SkipListLayer::iterator head = (*topLayer)->begin();

   if (!(*topLayer)->empty())
     {
       //start from the upper layer towards bottom
       int layer = m_skipList.size() - 1;
       for (SkipList::const_reverse_iterator rit = topLayer; rit != m_skipList.rend(); ++rit)
         {
           //if we didn't do any iterations on the higher layers, start from the begin() again
           if (!isIterated)
             head = (*rit)->begin();

           if (head != (*rit)->end())
             {
               // it happens when begin() contains the element we want to find
               if (!isIterated && (interest.getName().isPrefixOf((*head)->getFullName())))
                 {
                   if (layer > 0)
                     {
                       layer--;
                       continue; // try lower layer
                     }
                   else
                     {
                       isIterated = true;
                     }
                 }
               else
                 {
                   SkipListLayer::iterator it = head;

                   while ((*it)->getFullName() < interest.getName())
                     {
                       NFD_LOG_TRACE((*it)->getFullName() << " < " << interest.getName());
                       head = it;
                       isIterated = true;

                       ++it;
                       if (it == (*rit)->end())
                         break;
                     }
                 }
             }

           if (layer > 0)
             {
               head = (*head)->getIterators().find(layer - 1)->second; // move HEAD to the lower layer
             }
           else //if we reached the first layer
             {
               if (isIterated)
                 return selectChild(interest, head);
             }

           layer--;
         }
     }

   return 0;
 }

 const Data*
 Cs::selectChild(const Interest& interest, SkipListLayer::iterator startingPoint) const
 {
   BOOST_ASSERT(startingPoint != (*m_skipList.begin())->end());

   if (startingPoint != (*m_skipList.begin())->begin())
     {
       BOOST_ASSERT((*startingPoint)->getFullName() < interest.getName());
     }

   NFD_LOG_TRACE("selectChild() " << interest.getChildSelector() << " "
                 << (*startingPoint)->getFullName());

   bool hasLeftmostSelector = (interest.getChildSelector() <= 0);
   bool hasRightmostSelector = !hasLeftmostSelector;

   if (hasLeftmostSelector)
     {
       bool doesInterestContainDigest = recognizeInterestWithDigest(interest, *startingPoint);
       bool isInPrefix = false;

       if (doesInterestContainDigest)
         {
           isInPrefix = interest.getName().getPrefix(-1).isPrefixOf((*startingPoint)->getFullName());
         }
       else
         {
           isInPrefix = interest.getName().isPrefixOf((*startingPoint)->getFullName());
         }

       if (isInPrefix)
         {
           if (doesComplyWithSelectors(interest, *startingPoint, doesInterestContainDigest))
             {
               return &(*startingPoint)->getData();
             }
         }
     }

   //iterate to the right
   SkipListLayer::iterator rightmost = startingPoint;
   if (startingPoint != (*m_skipList.begin())->end())
     {
       SkipListLayer::iterator rightmostCandidate = startingPoint;
       Name currentChildPrefix("");

       while (true)
         {
           ++rightmostCandidate;

           bool isInBoundaries = (rightmostCandidate != (*m_skipList.begin())->end());
           bool isInPrefix = false;
           bool doesInterestContainDigest = false;
           if (isInBoundaries)
             {
               doesInterestContainDigest = recognizeInterestWithDigest(interest,
                                                                       *rightmostCandidate);

               if (doesInterestContainDigest)
                 {
                   isInPrefix = interest.getName().getPrefix(-1)
                                  .isPrefixOf((*rightmostCandidate)->getFullName());
                 }
               else
                 {
                   isInPrefix = interest.getName().isPrefixOf((*rightmostCandidate)->getFullName());
                 }
             }

           if (isInPrefix)
             {
               if (doesComplyWithSelectors(interest, *rightmostCandidate, doesInterestContainDigest))
                 {
                   if (hasLeftmostSelector)
                     {
                       return &(*rightmostCandidate)->getData();
                     }

                   if (hasRightmostSelector)
                     {
                       if (doesInterestContainDigest)
                         {
                           // get prefix which is one component longer than Interest name
                           // (without digest)
                           const Name& childPrefix = (*rightmostCandidate)->getFullName()
                                                       .getPrefix(interest.getName().size());
                           NFD_LOG_TRACE("Child prefix" << childPrefix);

                           if (currentChildPrefix.empty() || (childPrefix != currentChildPrefix))
                             {
                               currentChildPrefix = childPrefix;
                               rightmost = rightmostCandidate;
                             }
                         }
                       else
                         {
                           // get prefix which is one component longer than Interest name
                           const Name& childPrefix = (*rightmostCandidate)->getFullName()
                                                       .getPrefix(interest.getName().size() + 1);
                           NFD_LOG_TRACE("Child prefix" << childPrefix);

                           if (currentChildPrefix.empty() || (childPrefix != currentChildPrefix))
                             {
                               currentChildPrefix = childPrefix;
                               rightmost = rightmostCandidate;
                             }
                         }
                     }
                 }
             }
           else
             break;
         }
     }

   if (rightmost != startingPoint)
     {
       return &(*rightmost)->getData();
     }

   if (hasRightmostSelector) // if rightmost was not found, try starting point
     {
       bool doesInterestContainDigest = recognizeInterestWithDigest(interest, *startingPoint);
       bool isInPrefix = false;

       if (doesInterestContainDigest)
         {
           isInPrefix = interest.getName().getPrefix(-1).isPrefixOf((*startingPoint)->getFullName());
         }
       else
         {
           isInPrefix = interest.getName().isPrefixOf((*startingPoint)->getFullName());
         }

       if (isInPrefix)
         {
           if (doesComplyWithSelectors(interest, *startingPoint, doesInterestContainDigest))
             {
               return &(*startingPoint)->getData();
             }
         }
     }

   return 0;
 }

 bool
 Cs::doesComplyWithSelectors(const Interest& interest,
                             cs::skip_list::Entry* entry,
                             bool doesInterestContainDigest) const
 {
   NFD_LOG_TRACE("doesComplyWithSelectors()");

   /// \todo The following detection is not correct
   ///       1. If Interest name ends with 32-octet component doesn't mean that this component is
   ///          digest
   ///       2. Only min/max selectors (both 0) can be specified, all other selectors do not
   ///          make sense for interests with digest (though not sure if we need to enforce this)

   if (doesInterestContainDigest)
     {
       if (interest.getName().get(-1) != entry->getFullName().get(-1))
         {
           NFD_LOG_TRACE("violates implicit digest");
           return false;
         }
     }

   if (!doesInterestContainDigest)
     {
       if (interest.getMinSuffixComponents() >= 0)
         {
           size_t minDataNameLength = interest.getName().size() + interest.getMinSuffixComponents();

           bool isSatisfied = (minDataNameLength <= entry->getFullName().size());
           if (!isSatisfied)
             {
               NFD_LOG_TRACE("violates minComponents");
               return false;
             }
         }

       if (interest.getMaxSuffixComponents() >= 0)
         {
           size_t maxDataNameLength = interest.getName().size() + interest.getMaxSuffixComponents();

           bool isSatisfied = (maxDataNameLength >= entry->getFullName().size());
           if (!isSatisfied)
             {
               NFD_LOG_TRACE("violates maxComponents");
               return false;
             }
         }
     }

   if (interest.getMustBeFresh() && entry->getStaleTime() < time::steady_clock::now())
     {
       NFD_LOG_TRACE("violates mustBeFresh");
       return false;
     }

   if (!interest.getPublisherPublicKeyLocator().empty())
     {
       if (entry->getData().getSignature().getType() == ndn::Signature::Sha256WithRsa)
         {
           ndn::SignatureSha256WithRsa rsaSignature(entry->getData().getSignature());
           if (rsaSignature.getKeyLocator() != interest.getPublisherPublicKeyLocator())
             {
               NFD_LOG_TRACE("violates publisher key selector");
               return false;
             }
         }
       else
         {
           NFD_LOG_TRACE("violates publisher key selector");
           return false;
         }
     }

   if (doesInterestContainDigest)
     {
       const ndn::name::Component& lastComponent = entry->getFullName().get(-1);

       if (!lastComponent.empty())
         {
           if (interest.getExclude().isExcluded(lastComponent))
             {
               NFD_LOG_TRACE("violates exclusion");
               return false;
             }
         }
     }
   else
     {
       if (entry->getFullName().size() >= interest.getName().size() + 1)
         {
           const ndn::name::Component& nextComponent = entry->getFullName()
                                                         .get(interest.getName().size());
           if (!nextComponent.empty())
             {
               if (interest.getExclude().isExcluded(nextComponent))
                 {
                   NFD_LOG_TRACE("violates exclusion");
                   return false;
                 }
             }
         }
     }

   NFD_LOG_TRACE("complies");
   return true;
 }

 bool
 Cs::recognizeInterestWithDigest(const Interest& interest, cs::skip_list::Entry* entry) const
 {
   // only when min selector is not specified or specified with value of 0
   // and Interest's name length is exactly the length of the name of CS entry
   if (interest.getMinSuffixComponents() <= 0 &&
       interest.getName().size() == (entry->getFullName().size()))
     {
       const ndn::name::Component& last = interest.getName().get(-1);
       if (last.value_size() == ndn::crypto::SHA256_DIGEST_SIZE)
         {
           NFD_LOG_TRACE("digest recognized");
           return true;
         }
     }

   return false;
 }

 void
 Cs::erase(const Name& exactName)
 {
   NFD_LOG_TRACE("insert() " << exactName << ", "
                 << "skipList size " << size());

   bool isIterated = false;
   SkipListLayer::iterator updateTable[SKIPLIST_MAX_LAYERS];
   SkipList::reverse_iterator topLayer = m_skipList.rbegin();
   SkipListLayer::iterator head = (*topLayer)->begin();

   if (!(*topLayer)->empty())
     {
       //start from the upper layer towards bottom
       int layer = m_skipList.size() - 1;
       for (SkipList::reverse_iterator rit = topLayer; rit != m_skipList.rend(); ++rit)
         {
           //if we didn't do any iterations on the higher layers, start from the begin() again
           if (!isIterated)
             head = (*rit)->begin();

           updateTable[layer] = head;

           if (head != (*rit)->end())
             {
               // it can happen when begin() contains the element we want to remove
               if (!isIterated && ((*head)->getFullName() == exactName))
                 {
                   cs::skip_list::Entry* entryToDelete = *head;
                   NFD_LOG_TRACE("Found target " << entryToDelete->getFullName());
                   eraseFromSkipList(entryToDelete);
                   // head can become invalid after eraseFromSkipList
                   m_cleanupIndex.remove(entryToDelete);
                   return;
                 }
               else
                 {
                   SkipListLayer::iterator it = head;

                   while ((*it)->getFullName() < exactName)
                     {
                       head = it;
                       updateTable[layer] = it;
                       isIterated = true;

                       ++it;
                       if (it == (*rit)->end())
                         break;
                     }
                 }
             }

           if (layer > 0)
             head = (*head)->getIterators().find(layer - 1)->second; // move HEAD to the lower layer

           layer--;
         }
     }
   else
     {
       return;
     }

   head = updateTable[0];
   ++head; // look at the next slot to check if it contains the item we want to remove

   bool isCsEmpty = (size() == 0);
   bool isInBoundaries = (head != (*m_skipList.begin())->end());
   bool isNameIdentical = false;
   if (!isCsEmpty && isInBoundaries)
     {
       NFD_LOG_TRACE("Identical? " << (*head)->getFullName());
       isNameIdentical = (*head)->getFullName() == exactName;
     }

   if (isNameIdentical)
     {
       cs::skip_list::Entry* entryToDelete = *head;
       NFD_LOG_TRACE("Found target " << entryToDelete->getFullName());
       eraseFromSkipList(entryToDelete);
       // head can become invalid after eraseFromSkipList
       m_cleanupIndex.remove(entryToDelete);
     }
 }

 void
 Cs::printSkipList() const
 {
   NFD_LOG_TRACE("print()");
   //start from the upper layer towards bottom
   int layer = m_skipList.size() - 1;
   for (SkipList::const_reverse_iterator rit = m_skipList.rbegin(); rit != m_skipList.rend(); ++rit)
     {
       for (SkipListLayer::iterator it = (*rit)->begin(); it != (*rit)->end(); ++it)
         {
           NFD_LOG_TRACE("Layer " << layer << " " << (*it)->getFullName());
         }
       layer--;
     }
 }

 } //namespace nfd
	/* -- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -- */
	/**
	* Copyright (c) 2014, Regents of the University of California,
	* Arizona Board of Regents,
	* Colorado State University,
	* University Pierre & Marie Curie, Sorbonne University,
	* Washington University in St. Louis,
	* Beijing Institute of Technology,
	* The University of Memphis
	*
	* This file is part of NFD (Named Data Networking Forwarding Daemon).
	* See AUTHORS.md for complete list of NFD authors and contributors.
	*
	* NFD is free software: you can redistribute it and/or modify it under the terms
	* of the GNU General Public License as published by the Free Software Foundation,
	* either version 3 of the License, or (at your option) any later version.
	*
	* NFD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
	* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
	* PURPOSE. See the GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along with
	* NFD, e.g., in COPYING.md file. If not, see <http://www.gnu.org/licenses/>.
	*
	* \author Ilya Moiseenko <http://ilyamoiseenko.com/>
	* \author Junxiao Shi <http://www.cs.arizona.edu/people/shijunxiao/>
	* \author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
	*/

	#include "cs.hpp"
	#include "core/logger.hpp"
	#include "core/random.hpp"

	#include <ndn-cxx/util/crypto.hpp>
	#include <ndn-cxx/security/signature-sha256-with-rsa.hpp>

	#include <boost/random/bernoulli_distribution.hpp>
	#include <boost/concept/assert.hpp>
	#include <boost/concept_check.hpp>
	#include <type_traits>

	/// max skip list layers
	static const size_t SKIPLIST_MAX_LAYERS = 32;
	/// probability for an entry in layer N to appear also in layer N+1
	static const double SKIPLIST_PROBABILITY = 0.25;

	NFD_LOG_INIT("ContentStore");

	namespace nfd {

	// http://en.cppreference.com/w/cpp/concept/ForwardIterator
	BOOST_CONCEPT_ASSERT((boost::ForwardIterator<Cs::const_iterator>));
	// boost::ForwardIterator follows SGI standard http://www.sgi.com/tech/stl/ForwardIterator.html,
	// which doesn't require DefaultConstructible
	#ifdef HAVE_IS_DEFAULT_CONSTRUCTIBLE
	static_assert(std::is_default_constructible<Cs::const_iterator>::value,
	"Cs::const_iterator must be default-constructible");
	#else
	BOOST_CONCEPT_ASSERT((boost::DefaultConstructible<Cs::const_iterator>));
	#endif // HAVE_IS_DEFAULT_CONSTRUCTIBLE

	Cs::Cs(size_t nMaxPackets)
	: m_nMaxPackets(nMaxPackets)
	, m_nPackets(0)
	{
	SkipListLayer* zeroLayer = new SkipListLayer();
	m_skipList.push_back(zeroLayer);

	for (size_t i = 0; i < m_nMaxPackets; i++)
	m_freeCsEntries.push(new cs::skip_list::Entry());
	}

	Cs::~Cs()
	{
	// evict all items from CS
	while (evictItem())
	;

	BOOST_ASSERT(m_freeCsEntries.size() == m_nMaxPackets);

	while (!m_freeCsEntries.empty())
	{
	delete m_freeCsEntries.front();
	m_freeCsEntries.pop();
	}
	}

	size_t
	Cs::size() const
	{
	return m_nPackets; // size of the first layer in a skip list
	}

	void
	Cs::setLimit(size_t nMaxPackets)
	{
	size_t oldNMaxPackets = m_nMaxPackets;
	m_nMaxPackets = nMaxPackets;

	while (size() > m_nMaxPackets) {
	evictItem();
	}

	if (m_nMaxPackets >= oldNMaxPackets) {
	for (size_t i = oldNMaxPackets; i < m_nMaxPackets; i++) {
	m_freeCsEntries.push(new cs::skip_list::Entry());
	}
	}
	else {
	for (size_t i = oldNMaxPackets; i > m_nMaxPackets; i--) {
	delete m_freeCsEntries.front();
	m_freeCsEntries.pop();
	}
	}
	}

	size_t
	Cs::getLimit() const
	{
	return m_nMaxPackets;
	}

	//Reference: "Skip Lists: A Probabilistic Alternative to Balanced Trees" by W.Pugh
	std::pair<cs::skip_list::Entry*, bool>
	Cs::insertToSkipList(const Data& data, bool isUnsolicited)
	{
	NFD_LOG_TRACE("insertToSkipList() " << data.getFullName() << ", "
	<< "skipList size " << size());

	BOOST_ASSERT(m_cleanupIndex.size() <= size());
	BOOST_ASSERT(m_freeCsEntries.size() > 0);

	// take entry for the memory pool
	cs::skip_list::Entry* entry = m_freeCsEntries.front();
	m_freeCsEntries.pop();
	m_nPackets++;
	entry->setData(data, isUnsolicited);

	bool insertInFront = false;
	bool isIterated = false;
	SkipList::reverse_iterator topLayer = m_skipList.rbegin();
	SkipListLayer::iterator updateTable[SKIPLIST_MAX_LAYERS];
	SkipListLayer::iterator head = (*topLayer)->begin();

	if (!(*topLayer)->empty())
	{
	//start from the upper layer towards bottom
	int layer = m_skipList.size() - 1;
	for (SkipList::reverse_iterator rit = topLayer; rit != m_skipList.rend(); ++rit)
	{
	//if we didn't do any iterations on the higher layers, start from the begin() again
	if (!isIterated)
	head = (*rit)->begin();

	updateTable[layer] = head;

	if (head != (*rit)->end())
	{
	// it can happen when begin() contains the element in front of which we need to insert
	if (!isIterated && ((*head)->getFullName() >= entry->getFullName()))
	{
	--updateTable[layer];
	insertInFront = true;
	}
	else
	{
	SkipListLayer::iterator it = head;

	while ((*it)->getFullName() < entry->getFullName())
	{
	head = it;
	updateTable[layer] = it;
	isIterated = true;

	++it;
	if (it == (*rit)->end())
	break;
	}
	}
	}

	if (layer > 0)
	head = (*head)->getIterators().find(layer - 1)->second; // move HEAD to the lower layer

	layer--;
	}
	}
	else
	{
	updateTable[0] = (*topLayer)->begin(); //initialization
	}

	head = updateTable[0];
	++head; // look at the next slot to check if it contains a duplicate

	bool isCsEmpty = (size() == 0);
	bool isInBoundaries = (head != (*m_skipList.begin())->end());
	bool isNameIdentical = false;
	if (!isCsEmpty && isInBoundaries)
	{
	isNameIdentical = (*head)->getFullName() == entry->getFullName();
	}

	//check if this is a duplicate packet
	if (isNameIdentical)
	{
	NFD_LOG_TRACE("Duplicate name (with digest)");

	(*head)->setData(data, isUnsolicited); //updates stale time

	// new entry not needed, returning to the pool
	entry->release();
	m_freeCsEntries.push(entry);
	m_nPackets--;

	return std::make_pair(*head, false);
	}

	NFD_LOG_TRACE("Not a duplicate");

	size_t randomLayer = pickRandomLayer();

	while (m_skipList.size() < randomLayer + 1)
	{
	SkipListLayer* newLayer = new SkipListLayer();
	m_skipList.push_back(newLayer);

	updateTable[(m_skipList.size() - 1)] = newLayer->begin();
	}

	size_t layer = 0;
	for (SkipList::iterator i = m_skipList.begin();
	i != m_skipList.end() && layer <= randomLayer; ++i)
	{
	if (updateTable[layer] == (*i)->end() && !insertInFront)
	{
	(*i)->push_back(entry);
	SkipListLayer::iterator last = (*i)->end();
	--last;
	entry->setIterator(layer, last);

	NFD_LOG_TRACE("pushback " << &(*last));
	}
	else if (updateTable[layer] == (*i)->end() && insertInFront)
	{
	(*i)->push_front(entry);
	entry->setIterator(layer, (*i)->begin());

	NFD_LOG_TRACE("pushfront ");
	}
	else
	{
	NFD_LOG_TRACE("insertafter");
	++updateTable[layer]; // insert after
	SkipListLayer::iterator position = (*i)->insert(updateTable[layer], entry);
	entry->setIterator(layer, position); // save iterator where item was inserted
	}
	layer++;
	}

	return std::make_pair(entry, true);
	}

	bool
	Cs::insert(const Data& data, bool isUnsolicited)
	{
	NFD_LOG_TRACE("insert() " << data.getFullName());

	if (isFull())
	{
	evictItem();
	}

	//pointer and insertion status
	std::pair<cs::skip_list::Entry*, bool> entry = insertToSkipList(data, isUnsolicited);

	//new entry
	if (static_cast<bool>(entry.first) && (entry.second == true))
	{
	m_cleanupIndex.push_back(entry.first);
	return true;
	}

	return false;
	}

	size_t
	Cs::pickRandomLayer() const
	{
	static boost::random::bernoulli_distribution<> dist(SKIPLIST_PROBABILITY);
	// TODO rewrite using geometry_distribution
	size_t layer;
	for (layer = 0; layer < SKIPLIST_MAX_LAYERS; ++layer) {
	if (!dist(getGlobalRng())) {
	break;
	}
	}
	return layer;
	}

	bool
	Cs::isFull() const
	{
	if (size() >= m_nMaxPackets) //size of the first layer vs. max size
	return true;

	return false;
	}

	bool
	Cs::eraseFromSkipList(cs::skip_list::Entry* entry)
	{
	NFD_LOG_TRACE("eraseFromSkipList() " << entry->getFullName());
	NFD_LOG_TRACE("SkipList size " << size());

	bool isErased = false;

	const std::map<int, std::list<cs::skip_list::Entry*>::iterator>& iterators = entry->getIterators();

	if (!iterators.empty())
	{
	int layer = 0;

	for (SkipList::iterator it = m_skipList.begin(); it != m_skipList.end(); )
	{
	std::map<int, std::list<cs::skip_list::Entry*>::iterator>::const_iterator i = iterators.find(layer);

	if (i != iterators.end())
	{
	(*it)->erase(i->second);
	entry->removeIterator(layer);
	isErased = true;

	//remove layers that do not contain any elements (starting from the second layer)
	if ((layer != 0) && (*it)->empty())
	{
	delete *it;
	it = m_skipList.erase(it);
	}
	else
	++it;

	layer++;
	}
	else
	break;
	}
	}

	//delete entry;
	if (isErased)
	{
	entry->release();
	m_freeCsEntries.push(entry);
	m_nPackets--;
	}

	return isErased;
	}

	bool
	Cs::evictItem()
	{
	NFD_LOG_TRACE("evictItem()");

	if (!m_cleanupIndex.get<unsolicited>().empty()) {
	CleanupIndex::index<unsolicited>::type::const_iterator firstSolicited =
	m_cleanupIndex.get<unsolicited>().upper_bound(false);

	if (firstSolicited != m_cleanupIndex.get<unsolicited>().begin()) {
	--firstSolicited;
	BOOST_ASSERT((*firstSolicited)->isUnsolicited());
	NFD_LOG_TRACE("Evict from unsolicited queue");

	eraseFromSkipList(*firstSolicited);
	m_cleanupIndex.get<unsolicited>().erase(firstSolicited);
	return true;
	}
	else {
	BOOST_ASSERT(!(*m_cleanupIndex.get<unsolicited>().begin())->isUnsolicited());
	}
	}

	if (!m_cleanupIndex.get<byStaleness>().empty() &&
	(*m_cleanupIndex.get<byStaleness>().begin())->getStaleTime() < time::steady_clock::now())
	{
	NFD_LOG_TRACE("Evict from staleness queue");

	eraseFromSkipList(*m_cleanupIndex.get<byStaleness>().begin());
	m_cleanupIndex.get<byStaleness>().erase(m_cleanupIndex.get<byStaleness>().begin());
	return true;
	}

	if (!m_cleanupIndex.get<byArrival>().empty())
	{
	NFD_LOG_TRACE("Evict from arrival queue");

	eraseFromSkipList(*m_cleanupIndex.get<byArrival>().begin());
	m_cleanupIndex.get<byArrival>().erase(m_cleanupIndex.get<byArrival>().begin());
	return true;
	}

	return false;
	}

	const Data*
	Cs::find(const Interest& interest) const
	{
	NFD_LOG_TRACE("find() " << interest.getName());

	bool isIterated = false;
	SkipList::const_reverse_iterator topLayer = m_skipList.rbegin();
	SkipListLayer::iterator head = (*topLayer)->begin();

	if (!(*topLayer)->empty())
	{
	//start from the upper layer towards bottom
	int layer = m_skipList.size() - 1;
	for (SkipList::const_reverse_iterator rit = topLayer; rit != m_skipList.rend(); ++rit)
	{
	//if we didn't do any iterations on the higher layers, start from the begin() again
	if (!isIterated)
	head = (*rit)->begin();

	if (head != (*rit)->end())
	{
	// it happens when begin() contains the element we want to find
	if (!isIterated && (interest.getName().isPrefixOf((*head)->getFullName())))
	{
	if (layer > 0)
	{
	layer--;
	continue; // try lower layer
	}
	else
	{
	isIterated = true;
	}
	}
	else
	{
	SkipListLayer::iterator it = head;

	while ((*it)->getFullName() < interest.getName())
	{
	NFD_LOG_TRACE((*it)->getFullName() << " < " << interest.getName());
	head = it;
	isIterated = true;

	++it;
	if (it == (*rit)->end())
	break;
	}
	}
	}

	if (layer > 0)
	{
	head = (*head)->getIterators().find(layer - 1)->second; // move HEAD to the lower layer
	}
	else //if we reached the first layer
	{
	if (isIterated)
	return selectChild(interest, head);
	}

	layer--;
	}
	}

	return 0;
	}

	const Data*
	Cs::selectChild(const Interest& interest, SkipListLayer::iterator startingPoint) const
	{
	BOOST_ASSERT(startingPoint != (*m_skipList.begin())->end());

	if (startingPoint != (*m_skipList.begin())->begin())
	{
	BOOST_ASSERT((*startingPoint)->getFullName() < interest.getName());
	}

	NFD_LOG_TRACE("selectChild() " << interest.getChildSelector() << " "
	<< (*startingPoint)->getFullName());

	bool hasLeftmostSelector = (interest.getChildSelector() <= 0);
	bool hasRightmostSelector = !hasLeftmostSelector;

	if (hasLeftmostSelector)
	{
	bool doesInterestContainDigest = recognizeInterestWithDigest(interest, *startingPoint);
	bool isInPrefix = false;

	if (doesInterestContainDigest)
	{
	isInPrefix = interest.getName().getPrefix(-1).isPrefixOf((*startingPoint)->getFullName());
	}
	else
	{
	isInPrefix = interest.getName().isPrefixOf((*startingPoint)->getFullName());
	}

	if (isInPrefix)
	{
	if (doesComplyWithSelectors(interest, *startingPoint, doesInterestContainDigest))
	{
	return &(*startingPoint)->getData();
	}
	}
	}

	//iterate to the right
	SkipListLayer::iterator rightmost = startingPoint;
	if (startingPoint != (*m_skipList.begin())->end())
	{
	SkipListLayer::iterator rightmostCandidate = startingPoint;
	Name currentChildPrefix("");

	while (true)
	{
	++rightmostCandidate;

	bool isInBoundaries = (rightmostCandidate != (*m_skipList.begin())->end());
	bool isInPrefix = false;
	bool doesInterestContainDigest = false;
	if (isInBoundaries)
	{
	doesInterestContainDigest = recognizeInterestWithDigest(interest,
	*rightmostCandidate);

	if (doesInterestContainDigest)
	{
	isInPrefix = interest.getName().getPrefix(-1)
	.isPrefixOf((*rightmostCandidate)->getFullName());
	}
	else
	{
	isInPrefix = interest.getName().isPrefixOf((*rightmostCandidate)->getFullName());
	}
	}

	if (isInPrefix)
	{
	if (doesComplyWithSelectors(interest, *rightmostCandidate, doesInterestContainDigest))
	{
	if (hasLeftmostSelector)
	{
	return &(*rightmostCandidate)->getData();
	}

	if (hasRightmostSelector)
	{
	if (doesInterestContainDigest)
	{
	// get prefix which is one component longer than Interest name
	// (without digest)
	const Name& childPrefix = (*rightmostCandidate)->getFullName()
	.getPrefix(interest.getName().size());
	NFD_LOG_TRACE("Child prefix" << childPrefix);

	if (currentChildPrefix.empty() \|\| (childPrefix != currentChildPrefix))
	{
	currentChildPrefix = childPrefix;
	rightmost = rightmostCandidate;
	}
	}
	else
	{
	// get prefix which is one component longer than Interest name
	const Name& childPrefix = (*rightmostCandidate)->getFullName()
	.getPrefix(interest.getName().size() + 1);
	NFD_LOG_TRACE("Child prefix" << childPrefix);

	if (currentChildPrefix.empty() \|\| (childPrefix != currentChildPrefix))
	{
	currentChildPrefix = childPrefix;
	rightmost = rightmostCandidate;
	}
	}
	}
	}
	}
	else
	break;
	}
	}

	if (rightmost != startingPoint)
	{
	return &(*rightmost)->getData();
	}

	if (hasRightmostSelector) // if rightmost was not found, try starting point
	{
	bool doesInterestContainDigest = recognizeInterestWithDigest(interest, *startingPoint);
	bool isInPrefix = false;

	if (doesInterestContainDigest)
	{
	isInPrefix = interest.getName().getPrefix(-1).isPrefixOf((*startingPoint)->getFullName());
	}
	else
	{
	isInPrefix = interest.getName().isPrefixOf((*startingPoint)->getFullName());
	}

	if (isInPrefix)
	{
	if (doesComplyWithSelectors(interest, *startingPoint, doesInterestContainDigest))
	{
	return &(*startingPoint)->getData();
	}
	}
	}

	return 0;
	}

	bool
	Cs::doesComplyWithSelectors(const Interest& interest,
	cs::skip_list::Entry* entry,
	bool doesInterestContainDigest) const
	{
	NFD_LOG_TRACE("doesComplyWithSelectors()");

	/// \todo The following detection is not correct
	/// 1. If Interest name ends with 32-octet component doesn't mean that this component is
	/// digest
	/// 2. Only min/max selectors (both 0) can be specified, all other selectors do not
	/// make sense for interests with digest (though not sure if we need to enforce this)

	if (doesInterestContainDigest)
	{
	if (interest.getName().get(-1) != entry->getFullName().get(-1))
	{
	NFD_LOG_TRACE("violates implicit digest");
	return false;
	}
	}

	if (!doesInterestContainDigest)
	{
	if (interest.getMinSuffixComponents() >= 0)
	{
	size_t minDataNameLength = interest.getName().size() + interest.getMinSuffixComponents();

	bool isSatisfied = (minDataNameLength <= entry->getFullName().size());
	if (!isSatisfied)
	{
	NFD_LOG_TRACE("violates minComponents");
	return false;
	}
	}

	if (interest.getMaxSuffixComponents() >= 0)
	{
	size_t maxDataNameLength = interest.getName().size() + interest.getMaxSuffixComponents();

	bool isSatisfied = (maxDataNameLength >= entry->getFullName().size());
	if (!isSatisfied)
	{
	NFD_LOG_TRACE("violates maxComponents");
	return false;
	}
	}
	}

	if (interest.getMustBeFresh() && entry->getStaleTime() < time::steady_clock::now())
	{
	NFD_LOG_TRACE("violates mustBeFresh");
	return false;
	}

	if (!interest.getPublisherPublicKeyLocator().empty())
	{
	if (entry->getData().getSignature().getType() == ndn::Signature::Sha256WithRsa)
	{
	ndn::SignatureSha256WithRsa rsaSignature(entry->getData().getSignature());
	if (rsaSignature.getKeyLocator() != interest.getPublisherPublicKeyLocator())
	{
	NFD_LOG_TRACE("violates publisher key selector");
	return false;
	}
	}
	else
	{
	NFD_LOG_TRACE("violates publisher key selector");
	return false;
	}
	}

	if (doesInterestContainDigest)
	{
	const ndn::name::Component& lastComponent = entry->getFullName().get(-1);

	if (!lastComponent.empty())
	{
	if (interest.getExclude().isExcluded(lastComponent))
	{
	NFD_LOG_TRACE("violates exclusion");
	return false;
	}
	}
	}
	else
	{
	if (entry->getFullName().size() >= interest.getName().size() + 1)
	{
	const ndn::name::Component& nextComponent = entry->getFullName()
	.get(interest.getName().size());
	if (!nextComponent.empty())
	{
	if (interest.getExclude().isExcluded(nextComponent))
	{
	NFD_LOG_TRACE("violates exclusion");
	return false;
	}
	}
	}
	}

	NFD_LOG_TRACE("complies");
	return true;
	}

	bool
	Cs::recognizeInterestWithDigest(const Interest& interest, cs::skip_list::Entry* entry) const
	{
	// only when min selector is not specified or specified with value of 0
	// and Interest's name length is exactly the length of the name of CS entry
	if (interest.getMinSuffixComponents() <= 0 &&
	interest.getName().size() == (entry->getFullName().size()))
	{
	const ndn::name::Component& last = interest.getName().get(-1);
	if (last.value_size() == ndn::crypto::SHA256_DIGEST_SIZE)
	{
	NFD_LOG_TRACE("digest recognized");
	return true;
	}
	}

	return false;
	}

	void
	Cs::erase(const Name& exactName)
	{
	NFD_LOG_TRACE("insert() " << exactName << ", "
	<< "skipList size " << size());

	bool isIterated = false;
	SkipListLayer::iterator updateTable[SKIPLIST_MAX_LAYERS];
	SkipList::reverse_iterator topLayer = m_skipList.rbegin();
	SkipListLayer::iterator head = (*topLayer)->begin();

	if (!(*topLayer)->empty())
	{
	//start from the upper layer towards bottom
	int layer = m_skipList.size() - 1;
	for (SkipList::reverse_iterator rit = topLayer; rit != m_skipList.rend(); ++rit)
	{
	//if we didn't do any iterations on the higher layers, start from the begin() again
	if (!isIterated)
	head = (*rit)->begin();

	updateTable[layer] = head;

	if (head != (*rit)->end())
	{
	// it can happen when begin() contains the element we want to remove
	if (!isIterated && ((*head)->getFullName() == exactName))
	{
	cs::skip_list::Entry* entryToDelete = *head;
	NFD_LOG_TRACE("Found target " << entryToDelete->getFullName());
	eraseFromSkipList(entryToDelete);
	// head can become invalid after eraseFromSkipList
	m_cleanupIndex.remove(entryToDelete);
	return;
	}
	else
	{
	SkipListLayer::iterator it = head;

	while ((*it)->getFullName() < exactName)
	{
	head = it;
	updateTable[layer] = it;
	isIterated = true;

	++it;
	if (it == (*rit)->end())
	break;
	}
	}
	}

	if (layer > 0)
	head = (*head)->getIterators().find(layer - 1)->second; // move HEAD to the lower layer

	layer--;
	}
	}
	else
	{
	return;
	}

	head = updateTable[0];
	++head; // look at the next slot to check if it contains the item we want to remove

	bool isCsEmpty = (size() == 0);
	bool isInBoundaries = (head != (*m_skipList.begin())->end());
	bool isNameIdentical = false;
	if (!isCsEmpty && isInBoundaries)
	{
	NFD_LOG_TRACE("Identical? " << (*head)->getFullName());
	isNameIdentical = (*head)->getFullName() == exactName;
	}

	if (isNameIdentical)
	{
	cs::skip_list::Entry* entryToDelete = *head;
	NFD_LOG_TRACE("Found target " << entryToDelete->getFullName());
	eraseFromSkipList(entryToDelete);
	// head can become invalid after eraseFromSkipList
	m_cleanupIndex.remove(entryToDelete);
	}
	}

	void
	Cs::printSkipList() const
	{
	NFD_LOG_TRACE("print()");
	//start from the upper layer towards bottom
	int layer = m_skipList.size() - 1;
	for (SkipList::const_reverse_iterator rit = m_skipList.rbegin(); rit != m_skipList.rend(); ++rit)
	{
	for (SkipListLayer::iterator it = (rit)->begin(); it != (rit)->end(); ++it)
	{
	NFD_LOG_TRACE("Layer " << layer << " " << (*it)->getFullName());
	}
	layer--;
	}
	}

	} //namespace nfd