arangodb/arangod/IResearch/IResearchLinkHelper.cpp

////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2018 ArangoDB GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Andrey Abramov
/// @author Vasiliy Nabatchikov
////////////////////////////////////////////////////////////////////////////////

#include "IResearchLinkHelper.h"
#include "Basics/StaticStrings.h"
#include "IResearchCommon.h"
#include "IResearchFeature.h"
#include "IResearchLink.h"
#include "IResearchLinkMeta.h"
#include "IResearchView.h"
#include "IResearchViewCoordinator.h"
#include "Logger/LogMacros.h"
#include "Logger/Logger.h"
#include "Transaction/Methods.h"
#include "Transaction/StandaloneContext.h"
#include "Utils/CollectionNameResolver.h"
#include "Utils/ExecContext.h"
#include "VelocyPackHelper.h"
#include "VocBase/LogicalCollection.h"
#include "VocBase/Methods/Indexes.h"
#include "velocypack/Iterator.h"

namespace {

////////////////////////////////////////////////////////////////////////////////
/// @brief the string representing the link type
////////////////////////////////////////////////////////////////////////////////
std::string const& LINK_TYPE = arangodb::iresearch::DATA_SOURCE_TYPE.name();

bool createLink(arangodb::LogicalCollection& collection, arangodb::LogicalView const& view,
                arangodb::velocypack::Slice definition) {
  bool isNew = false;
  auto link = collection.createIndex(definition, isNew);
  LOG_TOPIC_IF(DEBUG, arangodb::iresearch::TOPIC, link)
      << "added link '" << link->id() << "'";

  return link && isNew;
}

bool createLink(arangodb::LogicalCollection& collection,
                arangodb::iresearch::IResearchViewCoordinator const& view,
                arangodb::velocypack::Slice definition) {
  static const std::function<bool(irs::string_ref const& key)> acceptor =
      [](irs::string_ref const& key) -> bool {
    // ignored fields
    return key != arangodb::StaticStrings::IndexType &&
           key != arangodb::iresearch::StaticStrings::ViewIdField;
  };
  arangodb::velocypack::Builder builder;

  builder.openObject();
  builder.add(arangodb::StaticStrings::IndexType, arangodb::velocypack::Value(LINK_TYPE));
  builder.add(arangodb::iresearch::StaticStrings::ViewIdField,
              arangodb::velocypack::Value(view.guid()));

  if (!arangodb::iresearch::mergeSliceSkipKeys(builder, definition, acceptor)) {
    return false;
  }

  builder.close();

  arangodb::velocypack::Builder tmp;

  return arangodb::methods::Indexes::ensureIndex(&collection, builder.slice(), true, tmp)
      .ok();
}

template <typename ViewType>
bool dropLink(arangodb::LogicalCollection& collection,
              arangodb::iresearch::IResearchLink const& link) {
  // don't need to create an extra transaction inside
  // arangodb::methods::Indexes::drop(...)
  return collection.dropIndex(link.id());
}

template <>
bool dropLink<arangodb::iresearch::IResearchViewCoordinator>(
    arangodb::LogicalCollection& collection, arangodb::iresearch::IResearchLink const& link) {
  arangodb::velocypack::Builder builder;

  builder.openObject();
  builder.add(arangodb::StaticStrings::IndexId, arangodb::velocypack::Value(link.id()));
  builder.close();

  return arangodb::methods::Indexes::drop(&collection, builder.slice()).ok();
}

template <typename ViewType>
arangodb::Result modifyLinks(std::unordered_set<TRI_voc_cid_t>& modified,
                             TRI_vocbase_t& vocbase, ViewType& view,
                             arangodb::velocypack::Slice const& links,
                             std::unordered_set<TRI_voc_cid_t> const& stale = {}) {
  if (!links.isObject()) {
    return arangodb::Result(
        TRI_ERROR_BAD_PARAMETER,
        std::string(
            "error parsing link parameters from json for arangosearch view '") +
            view.name() + "'");
  }

  struct State {
    std::shared_ptr<arangodb::LogicalCollection> _collection;
    size_t _collectionsToLockOffset;  // std::numeric_limits<size_t>::max() ==
                                      // removal only
    std::shared_ptr<arangodb::iresearch::IResearchLink> _link;
    size_t _linkDefinitionsOffset;
    bool _stale = false;  // request came from the stale list
    bool _valid = true;
    explicit State(size_t collectionsToLockOffset)
        : State(collectionsToLockOffset, std::numeric_limits<size_t>::max()) {}
    State(size_t collectionsToLockOffset, size_t linkDefinitionsOffset)
        : _collectionsToLockOffset(collectionsToLockOffset),
          _linkDefinitionsOffset(linkDefinitionsOffset) {}
  };
  std::vector<std::string> collectionsToLock;
  std::vector<std::pair<arangodb::velocypack::Builder, arangodb::iresearch::IResearchLinkMeta>> linkDefinitions;
  std::vector<State> linkModifications;

  for (arangodb::velocypack::ObjectIterator linksItr(links); linksItr.valid(); ++linksItr) {
    auto collection = linksItr.key();

    if (!collection.isString()) {
      return arangodb::Result(TRI_ERROR_BAD_PARAMETER,
                              std::string(
                                  "error parsing link parameters from json for "
                                  "arangosearch view '") +
                                  view.name() + "' offset '" +
                                  arangodb::basics::StringUtils::itoa(linksItr.index()) + '"');
    }

    auto link = linksItr.value();
    auto collectionName = collection.copyString();

    if (link.isNull()) {
      linkModifications.emplace_back(collectionsToLock.size());
      collectionsToLock.emplace_back(collectionName);

      continue;  // only removal requested
    }

    static const std::function<bool(irs::string_ref const& key)> acceptor =
        [](irs::string_ref const& key) -> bool {
      // ignored fields
      return key != arangodb::StaticStrings::IndexType &&
             key != arangodb::iresearch::StaticStrings::ViewIdField;
    };
    arangodb::velocypack::Builder namedJson;

    namedJson.openObject();
    namedJson.add(arangodb::StaticStrings::IndexType, arangodb::velocypack::Value(LINK_TYPE));
    namedJson.add(arangodb::iresearch::StaticStrings::ViewIdField,
                  arangodb::velocypack::Value(view.guid()));

    if (!arangodb::iresearch::mergeSliceSkipKeys(namedJson, link, acceptor)) {
      return arangodb::Result(
          TRI_ERROR_INTERNAL,
          std::string("failed to update link definition with the view name "
                      "while updating arangosearch view '") +
              view.name() + "' collection '" + collectionName + "'");
    }

    namedJson.close();

    std::string error;
    arangodb::iresearch::IResearchLinkMeta linkMeta;

    if (!linkMeta.init(namedJson.slice(), error)) {
      return arangodb::Result(TRI_ERROR_BAD_PARAMETER,
                              std::string("error parsing link parameters from "
                                          "json for arangosearch view '") +
                                  view.name() + "' collection '" +
                                  collectionName + "' error '" + error + "'");
    }

    linkModifications.emplace_back(collectionsToLock.size(), linkDefinitions.size());
    collectionsToLock.emplace_back(collectionName);
    linkDefinitions.emplace_back(std::move(namedJson), std::move(linkMeta));
  }

  auto trxCtx = arangodb::transaction::StandaloneContext::Create(vocbase);

  // add removals for any 'stale' links not found in the 'links' definition
  for (auto& id : stale) {
    if (!trxCtx->resolver().getCollection(id)) {
      LOG_TOPIC(WARN, arangodb::iresearch::TOPIC)
          << "request for removal of a stale link to a missing collection '"
          << id << "', ignoring";

      continue;  // skip adding removal requests to stale links to non-existant
                 // collections (already dropped)
    }

    linkModifications.emplace_back(collectionsToLock.size());
    linkModifications.back()._stale = true;
    collectionsToLock.emplace_back(std::to_string(id));
  }

  if (collectionsToLock.empty()) {
    return arangodb::Result();  // nothing to update
  }

  static std::vector<std::string> const EMPTY;
  arangodb::ExecContextScope scope(
      arangodb::ExecContext::superuser());  // required to remove links from
                                            // non-RW collections

  {
    std::unordered_set<TRI_voc_cid_t> collectionsToRemove;  // track removal for potential reindex
    std::unordered_set<TRI_voc_cid_t> collectionsToUpdate;  // track reindex requests

    // resolve corresponding collection and link
    for (auto itr = linkModifications.begin(); itr != linkModifications.end();) {
      auto& state = *itr;
      auto& collectionName = collectionsToLock[state._collectionsToLockOffset];

      state._collection = trxCtx->resolver().getCollection(collectionName);

      if (!state._collection) {
        // remove modification state if removal of non-existant link on
        // non-existant collection
        if (state._linkDefinitionsOffset >= linkDefinitions.size()) {  // link removal request
          itr = linkModifications.erase(itr);

          continue;
        }

        return arangodb::Result(
            TRI_ERROR_ARANGO_DATA_SOURCE_NOT_FOUND,
            std::string(
                "failed to get collection while updating arangosearch view '") +
                view.name() + "' collection '" + collectionName + "'");
      }

      state._link =
          arangodb::iresearch::IResearchLinkHelper::find(*(state._collection), view);

      // remove modification state if removal of non-existant link
      if (!state._link  // links currently does not exist
          && state._linkDefinitionsOffset >= linkDefinitions.size()) {  // link removal request

        LOG_TOPIC(TRACE, arangodb::iresearch::TOPIC)
            << "found link for collection '" << state._collection->name()
            << "' - slated for removal";

        view.unlink(state._collection->id());  // drop any stale data for the specified collection
        itr = linkModifications.erase(itr);

        continue;
      }

      if (state._link       // links currently exists
          && !state._stale  // did not originate from the stale list (remove
                            // stale links lower)
          && state._linkDefinitionsOffset >= linkDefinitions.size()) {  // link removal request
        LOG_TOPIC(TRACE, arangodb::iresearch::TOPIC)
            << "found link '" << state._link->id() << "' for collection '"
            << state._collection->name() << "' - slated for removal";
        auto cid = state._collection->id();

        // remove duplicate removal requests (e.g. by name + by CID)
        if (collectionsToRemove.find(cid) != collectionsToRemove.end()) {  // removal previously requested
          itr = linkModifications.erase(itr);

          continue;
        }

        collectionsToRemove.emplace(cid);
      }

      if (state._link  // links currently exists
          && state._linkDefinitionsOffset < linkDefinitions.size()) {  // link update request
        LOG_TOPIC(TRACE, arangodb::iresearch::TOPIC)
            << "found link '" << state._link->id() << "' for collection '"
            << state._collection->name() << "' - slated for update";
        collectionsToUpdate.emplace(state._collection->id());
      }

      LOG_TOPIC_IF(TRACE, arangodb::iresearch::TOPIC, state._link)
          << "found link '" << state._link->id() << "' for collection '"
          << state._collection->name() << "' - unsure what to do";

      LOG_TOPIC_IF(TRACE, arangodb::iresearch::TOPIC, !state._link)
          << "no link found for collection '" << state._collection->name() << "'";

      ++itr;
    }

    // remove modification state if it came from the stale list and a separate
    // removal or reindex also present
    for (auto itr = linkModifications.begin(); itr != linkModifications.end();) {
      auto& state = *itr;
      auto cid = state._collection->id();

      // remove modification if came from the stale list and a separate reindex
      // or removal request also present otherwise consider 'stale list
      // requests' as valid removal requests
      if (state._stale  // originated from the stale list
          && (collectionsToRemove.find(cid) !=
                  collectionsToRemove.end()  // also has a removal request
                                             // (duplicate removal request)
              || collectionsToUpdate.find(cid) != collectionsToUpdate.end())) {  // also has a reindex request
        itr = linkModifications.erase(itr);
        LOG_TOPIC(TRACE, arangodb::iresearch::TOPIC)
            << "modification unnecessary, came from stale list, for link '"
            << state._link->id() << "'";

        continue;
      }

      ++itr;
    }

    // remove modification state if no change on existing link and reindex not
    // requested
    for (auto itr = linkModifications.begin(); itr != linkModifications.end();) {
      auto& state = *itr;

      // remove modification if removal request with an update request also
      // present
      if (state._link  // links currently exists
          && state._linkDefinitionsOffset >= linkDefinitions.size()  // link removal request
          && collectionsToUpdate.find(state._collection->id()) !=
                 collectionsToUpdate.end()) {  // also has a reindex request
        itr = linkModifications.erase(itr);
        LOG_TOPIC(TRACE, arangodb::iresearch::TOPIC)
            << "modification unnecessary, remove+update, for link '"
            << state._link->id() << "'";

        continue;
      }

      // remove modification state if no change on existing link or
      if (state._link  // links currently exists
          && state._linkDefinitionsOffset < linkDefinitions.size()  // link creation request
          && collectionsToRemove.find(state._collection->id()) ==
                 collectionsToRemove.end()  // not a reindex request
          && *(state._link) == linkDefinitions[state._linkDefinitionsOffset].second) {  // link meta not modified
        itr = linkModifications.erase(itr);
        LOG_TOPIC(TRACE, arangodb::iresearch::TOPIC)
            << "modification unnecessary, no change, for link '"
            << state._link->id() << "'";

        continue;
      }

      ++itr;
    }
  }

  // execute removals
  for (auto& state : linkModifications) {
    if (state._link) {  // link removal or recreate request
      LOG_TOPIC(DEBUG, arangodb::iresearch::TOPIC)
          << "removed link '" << state._link->id() << "'";
      state._valid = dropLink<ViewType>(*(state._collection), *(state._link));
      modified.emplace(state._collection->id());
    }
  }

  // execute additions
  for (auto& state : linkModifications) {
    if (state._valid && state._linkDefinitionsOffset < linkDefinitions.size()) {
      state._valid =
          createLink(*(state._collection), view,
                     linkDefinitions[state._linkDefinitionsOffset].first.slice());
      modified.emplace(state._collection->id());
    }
  }

  std::string error;

  // validate success
  for (auto& state : linkModifications) {
    if (!state._valid) {
      error.append(error.empty() ? "" : ", ").append(collectionsToLock[state._collectionsToLockOffset]);
    }
  }

  if (error.empty()) {
    return arangodb::Result();
  }

  return arangodb::Result(
      TRI_ERROR_ARANGO_ILLEGAL_STATE,
      std::string("failed to update links while updating arangosearch view '") +
          view.name() +
          "', retry same request or examine errors for collections: " + error);
}

}  // namespace

namespace arangodb {
namespace iresearch {

/*static*/ VPackSlice const& IResearchLinkHelper::emptyIndexSlice() {
  static const struct EmptySlice {
    VPackBuilder _builder;
    VPackSlice _slice;
    EmptySlice() {
      VPackBuilder fieldsBuilder;

      fieldsBuilder.openArray();
      fieldsBuilder.close();  // empty array
      _builder.openObject();
      _builder.add(arangodb::StaticStrings::IndexFields,
                   fieldsBuilder.slice());  // empty array
      _builder.add(arangodb::StaticStrings::IndexType,
                   arangodb::velocypack::Value(LINK_TYPE));  // the index type required by Index
      _builder.close();  // object with just one field required by the Index
                         // constructor
      _slice = _builder.slice();
    }
  } emptySlice;

  return emptySlice._slice;
}

/*static*/ bool IResearchLinkHelper::equal(arangodb::velocypack::Slice const& lhs,
                                           arangodb::velocypack::Slice const& rhs) {
  if (!lhs.isObject() || !rhs.isObject()) {
    return false;
  }

  auto lhsViewSlice = lhs.get(StaticStrings::ViewIdField);
  auto rhsViewSlice = rhs.get(StaticStrings::ViewIdField);

  if (!lhsViewSlice.equals(rhsViewSlice)) {
    if (!lhsViewSlice.isString() || !rhsViewSlice.isString()) {
      return false;
    }

    auto ls = lhsViewSlice.copyString();
    auto rs = lhsViewSlice.copyString();

    if (ls.size() > rs.size()) {
      std::swap(ls, rs);
    }

    // in the cluster, we may have identifiers of the form
    // `cxxx/` and `cxxx/yyy` which should be considered equal if the
    // one is a prefix of the other up to the `/`
    if (ls.empty() || ls.back() != '/' || ls.compare(rs.substr(0, ls.size()))) {
      return false;
    }
  }

  std::string errorField;
  IResearchLinkMeta lhsMeta;
  IResearchLinkMeta rhsMeta;

  return lhsMeta.init(lhs, errorField) && rhsMeta.init(rhs, errorField) && lhsMeta == rhsMeta;
}

/*static*/ std::shared_ptr<IResearchLink> IResearchLinkHelper::find(LogicalCollection const& collection,
                                                                    TRI_idx_iid_t id) {
  auto index = collection.lookupIndex(id);

  if (!index || arangodb::Index::TRI_IDX_TYPE_IRESEARCH_LINK != index->type()) {
    return nullptr;  // not an IResearchLink
  }

  // TODO FIXME find a better way to retrieve an IResearch Link
  // cannot use static_cast/reinterpret_cast since Index is not related to
  // IResearchLink
  auto link = std::dynamic_pointer_cast<IResearchLink>(index);

  if (link && link->id() == id) {
    return link;  // found required link
  }

  return nullptr;
}

/*static*/ std::shared_ptr<IResearchLink> IResearchLinkHelper::find(
    LogicalCollection const& collection, LogicalView const& view) {
  for (auto& index : collection.getIndexes()) {
    if (!index || arangodb::Index::TRI_IDX_TYPE_IRESEARCH_LINK != index->type()) {
      continue;  // not an IResearchLink
    }

    // TODO FIXME find a better way to retrieve an iResearch Link
    // cannot use static_cast/reinterpret_cast since Index is not related to
    // IResearchLink
    auto link = std::dynamic_pointer_cast<IResearchLink>(index);

    if (link && *link == view) {
      return link;  // found required link
    }
  }

  return nullptr;
}

/*static*/ arangodb::Result IResearchLinkHelper::normalize(arangodb::velocypack::Builder& normalized,
                                                           velocypack::Slice definition,
                                                           bool  // isCreation
) {
  if (!normalized.isOpenObject()) {
    return arangodb::Result(
        TRI_ERROR_BAD_PARAMETER,
        std::string("invalid output buffer provided for arangosearch link "
                    "normalized definition generation"));
  }

  std::string error;
  IResearchLinkMeta meta;

  if (!meta.init(definition, error)) {
    return arangodb::Result(
        TRI_ERROR_BAD_PARAMETER,
        std::string("error parsing arangosearch link parameters from json: ") + error);
  }

  normalized.add(arangodb::StaticStrings::IndexType, arangodb::velocypack::Value(LINK_TYPE));

  // copy over IResearch View identifier
  if (definition.hasKey(StaticStrings::ViewIdField)) {
    normalized.add(StaticStrings::ViewIdField, definition.get(StaticStrings::ViewIdField));
  }

  return meta.json(normalized)
             ? arangodb::Result()
             : arangodb::Result(TRI_ERROR_BAD_PARAMETER,
                                std::string("error generating arangosearch "
                                            "link normalized definition"));
}

/*static*/ std::string const& IResearchLinkHelper::type() noexcept {
  return LINK_TYPE;
}

/*static*/ arangodb::Result IResearchLinkHelper::validateLinks(
    TRI_vocbase_t& vocbase, arangodb::velocypack::Slice const& links) {
  if (!links.isObject()) {
    return arangodb::Result(
        TRI_ERROR_BAD_PARAMETER,
        std::string("while validating arangosearch link definition, error: "
                    "definition is not an object"));
  }

  size_t offset = 0;
  arangodb::CollectionNameResolver resolver(vocbase);

  for (arangodb::velocypack::ObjectIterator itr(links); itr.valid(); ++itr, ++offset) {
    auto collectionName = itr.key();
    auto linkDefinition = itr.value();

    if (!collectionName.isString()) {
      return arangodb::Result(
          TRI_ERROR_BAD_PARAMETER,
          std::string("while validating arangosearch link definition, error: "
                      "collection at offset ") +
              std::to_string(offset) + " is not a string");
    }

    auto collection = resolver.getCollection(collectionName.copyString());

    if (!collection) {
      return arangodb::Result(TRI_ERROR_ARANGO_DATA_SOURCE_NOT_FOUND,
                              std::string("while validating arangosearch link "
                                          "definition, error: collection '") +
                                  collectionName.copyString() + "' not found");
    }

    // check link auth as per https://github.com/arangodb/backlog/issues/459
    if (arangodb::ExecContext::CURRENT &&
        !arangodb::ExecContext::CURRENT->canUseCollection(vocbase.name(),
                                                          collection->name(),
                                                          arangodb::auth::Level::RO)) {
      return arangodb::Result(TRI_ERROR_FORBIDDEN,
                              std::string("while validating arangosearch link "
                                          "definition, error: collection '") +
                                  collectionName.copyString() +
                                  "' not authorized for read access");
    }

    IResearchLinkMeta meta;
    std::string errorField;

    if (!linkDefinition.isNull() && !meta.init(linkDefinition, errorField)) {
      return arangodb::Result(
          TRI_ERROR_BAD_PARAMETER,
          errorField.empty()
              ? (std::string(
                     "while validating arangosearch link definition, error: "
                     "invalid link definition for collection '") +
                 collectionName.copyString() + "': " + linkDefinition.toString())
              : (std::string(
                     "while validating arangosearch link definition, error: "
                     "invalid link definition for collection '") +
                 collectionName.copyString() + "' error in attribute: " + errorField));
    }
  }

  return arangodb::Result();
}

/*static*/ bool IResearchLinkHelper::visit(arangodb::LogicalCollection const& collection,
                                           std::function<bool(IResearchLink& link)> const& visitor) {
  for (auto& index : collection.getIndexes()) {
    if (!index || arangodb::Index::TRI_IDX_TYPE_IRESEARCH_LINK != index->type()) {
      continue;  // not an IResearchLink
    }

    // TODO FIXME find a better way to retrieve an iResearch Link
    // cannot use static_cast/reinterpret_cast since Index is not related to
    // IResearchLink
    auto link = std::dynamic_pointer_cast<IResearchLink>(index);

    if (link && !visitor(*link)) {
      return false;  // abort requested
    }
  }

  return true;
}

/*static*/ arangodb::Result IResearchLinkHelper::updateLinks(
    std::unordered_set<TRI_voc_cid_t>& modified, TRI_vocbase_t& vocbase,
    arangodb::LogicalView& view, arangodb::velocypack::Slice const& links,
    std::unordered_set<TRI_voc_cid_t> const& stale /*= {}*/
) {
  LOG_TOPIC(TRACE, arangodb::iresearch::TOPIC)
      << "beginning IResearchLinkHelper::updateLinks";
  try {
    if (arangodb::ServerState::instance()->isCoordinator()) {
      return modifyLinks<IResearchViewCoordinator>(modified, vocbase,
                                                   LogicalView::cast<IResearchViewCoordinator>(view),
                                                   links, stale);
    }

    return modifyLinks<IResearchView>(modified, vocbase,
                                      LogicalView::cast<IResearchView>(view), links, stale);
  } catch (arangodb::basics::Exception& e) {
    LOG_TOPIC(WARN, arangodb::iresearch::TOPIC)
        << "caught exception while updating links for arangosearch view '"
        << view.name() << "': " << e.code() << " " << e.what();
    IR_LOG_EXCEPTION();

    return arangodb::Result(
        e.code(), std::string("error updating links for arangosearch view '") +
                      view.name() + "'");
  } catch (std::exception const& e) {
    LOG_TOPIC(WARN, arangodb::iresearch::TOPIC)
        << "caught exception while updating links for arangosearch view '"
        << view.name() << "': " << e.what();
    IR_LOG_EXCEPTION();

    return arangodb::Result(
        TRI_ERROR_BAD_PARAMETER,
        std::string("error updating links for arangosearch view '") +
            view.name() + "'");
  } catch (...) {
    LOG_TOPIC(WARN, arangodb::iresearch::TOPIC)
        << "caught exception while updating links for arangosearch view '"
        << view.name() << "'";
    IR_LOG_EXCEPTION();

    return arangodb::Result(
        TRI_ERROR_BAD_PARAMETER,
        std::string("error updating links for arangosearch view '") +
            view.name() + "'");
  }
}

}  // namespace iresearch
}  // namespace arangodb

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