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process_updates_command.cc

// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "chrome/browser/sync/engine/process_updates_command.h"

#include <vector>

#include "base/basictypes.h"
#include "chrome/browser/sync/engine/syncer.h"
#include "chrome/browser/sync/engine/syncer_proto_util.h"
#include "chrome/browser/sync/engine/syncer_util.h"
#include "chrome/browser/sync/engine/syncproto.h"
#include "chrome/browser/sync/sessions/sync_session.h"
#include "chrome/browser/sync/syncable/directory_manager.h"
#include "chrome/browser/sync/syncable/syncable.h"

using std::vector;

namespace browser_sync {

using sessions::SyncSession;
using sessions::StatusController;

ProcessUpdatesCommand::ProcessUpdatesCommand() {}
ProcessUpdatesCommand::~ProcessUpdatesCommand() {}

bool ProcessUpdatesCommand::ModelNeutralExecuteImpl(SyncSession* session) {
  const GetUpdatesResponse& updates =
      session->status_controller()->updates_response().get_updates();
  const int update_count = updates.entries_size();

  // Don't bother processing updates if there were none.
  return update_count != 0;
}

void ProcessUpdatesCommand::ModelChangingExecuteImpl(SyncSession* session) {
  syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                session->context()->account_name());
  if (!dir.good()) {
    LOG(ERROR) << "Scoped dir lookup failed!";
    return;
  }

  StatusController* status = session->status_controller();

  const sessions::UpdateProgress& progress(status->update_progress());
  vector<sessions::VerifiedUpdate>::const_iterator it;
  for (it = progress.VerifiedUpdatesBegin();
       it != progress.VerifiedUpdatesEnd();
       ++it) {
    const sync_pb::SyncEntity& update = it->second;

    if (it->first != VERIFY_SUCCESS && it->first != VERIFY_UNDELETE)
      continue;
    switch (ProcessUpdate(dir, update)) {
      case SUCCESS_PROCESSED:
      case SUCCESS_STORED:
        break;
      default:
        NOTREACHED();
        break;
    }
  }

  status->set_num_consecutive_errors(0);

  // TODO(nick): The following line makes no sense to me.
  status->set_syncing(true);
  return;
}

namespace {
// Returns true if the entry is still ok to process.
bool ReverifyEntry(syncable::WriteTransaction* trans, const SyncEntity& entry,
                   syncable::MutableEntry* same_id) {

  const bool deleted = entry.has_deleted() && entry.deleted();
  const bool is_directory = entry.IsFolder();
  const syncable::ModelType model_type = entry.GetModelType();

  return VERIFY_SUCCESS == SyncerUtil::VerifyUpdateConsistency(trans,
                                                               entry,
                                                               same_id,
                                                               deleted,
                                                               is_directory,
                                                               model_type);
}
}  // namespace

// Process a single update. Will avoid touching global state.
ServerUpdateProcessingResult ProcessUpdatesCommand::ProcessUpdate(
    const syncable::ScopedDirLookup& dir,
    const sync_pb::SyncEntity& proto_update) {

  const SyncEntity& update = *static_cast<const SyncEntity*>(&proto_update);
  using namespace syncable;
  syncable::Id server_id = update.id();
  const std::string name = SyncerProtoUtil::NameFromSyncEntity(update);

  WriteTransaction trans(dir, SYNCER, __FILE__, __LINE__);

  // Look to see if there's a local item that should recieve this update,
  // maybe due to a duplicate client tag or a lost commit response.
  syncable::Id local_id = SyncerUtil::FindLocalIdToUpdate(&trans, update);

  // FindLocalEntryToUpdate has veto power.
  if (local_id.IsNull()) {
    return SUCCESS_PROCESSED;  // The entry has become irrelevant.
  }

  SyncerUtil::CreateNewEntry(&trans, local_id);

  // We take a two step approach. First we store the entries data in the
  // server fields of a local entry and then move the data to the local fields
  MutableEntry target_entry(&trans, GET_BY_ID, local_id);

  // We need to run the Verify checks again; the world could have changed
  // since VerifyUpdatesCommand.
  if (!ReverifyEntry(&trans, update, &target_entry)) {
    return SUCCESS_PROCESSED;  // The entry has become irrelevant.
  }

  // If we're repurposing an existing local entry with a new server ID,
  // change the ID now, after we're sure that the update can succeed.
  if (local_id != server_id) {
    DCHECK(!update.deleted());
    SyncerUtil::ChangeEntryIDAndUpdateChildren(&trans, &target_entry,
        server_id);
    // When IDs change, versions become irrelevant.  Forcing BASE_VERSION
    // to zero would ensure that this update gets applied, but would indicate
    // creation or undeletion if it were committed that way.  Instead, prefer
    // forcing BASE_VERSION to entry.version() while also forcing
    // IS_UNAPPLIED_UPDATE to true.  If the item is UNSYNCED, it's committable
    // from the new state; it may commit before the conflict resolver gets
    // a crack at it.
    if (target_entry.Get(IS_UNSYNCED) || target_entry.Get(BASE_VERSION) > 0) {
      // If either of these conditions are met, then we can expect valid client
      // fields for this entry.  When BASE_VERSION is positive, consistency is
      // enforced on the client fields at update-application time.  Otherwise,
      // we leave the BASE_VERSION field alone; it'll get updated the first time
      // we successfully apply this update.
      target_entry.Put(BASE_VERSION, update.version());
    }
    // Force application of this update, no matter what.
    target_entry.Put(IS_UNAPPLIED_UPDATE, true);
  }

  SyncerUtil::UpdateServerFieldsFromUpdate(&target_entry, update, name);

  if (target_entry.Get(SERVER_VERSION) == target_entry.Get(BASE_VERSION) &&
      !target_entry.Get(IS_UNSYNCED) &&
      !target_entry.Get(IS_UNAPPLIED_UPDATE)) {
    // If these don't match, it means that we have a different view of the
    // truth from other clients.  That's a sync bug, though we may be able
    // to recover the next time this item commits.
    LOG_IF(ERROR, !SyncerUtil::ServerAndLocalEntriesMatch(&target_entry))
        << target_entry;
  }
  return SUCCESS_PROCESSED;
}

}  // namespace browser_sync

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