sync: Process 'control' data separately

sync/engine/apply_control_data_updates.cc

+// Copyright (c) 2012 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 "sync/engine/apply_control_data_updates.h"
+
+#include "base/metrics/histogram.h"
+#include "sync/engine/conflict_resolver.h"
+#include "sync/engine/nigori_util.h"
+#include "sync/engine/syncer_util.h"
+#include "sync/syncable/directory.h"
+#include "sync/syncable/mutable_entry.h"
+#include "sync/syncable/write_transaction.h"
+#include "sync/util/cryptographer.h"
+
+using syncable::GET_BY_SERVER_TAG;
+using syncable::IS_UNAPPLIED_UPDATE;
+using syncable::IS_UNSYNCED;
+using syncable::NIGORI;
+using syncable::SERVER_SPECIFICS;
+using syncable::SPECIFICS;
+using syncable::SYNCER;
+
+namespace csync {
+
+void ApplyControlDataUpdates(syncable::Directory* dir) {
+  syncable::WriteTransaction trans(FROM_HERE, SYNCER, dir);
+  ApplyNigoriUpdates(&trans, dir->GetCryptographer(&trans));
+}
+
+void ApplyNigoriUpdates(syncable::WriteTransaction* trans,
+                        Cryptographer* cryptographer) {
+  syncable::MutableEntry nigori_node(trans, GET_BY_SERVER_TAG,
+                                     ModelTypeToRootTag(NIGORI));
+
+  // Mainly for unit tests.  We should have a Nigori node by this point.
+  if (!nigori_node.good()) {
+    return;
+  }
+
+  // We always update the cryptographer with the server's nigori node,
+  // even if we have a locally modified nigori node (we manually merge nigori
+  // data in the conflict resolver in that case). This handles the case where
+  // two clients both set a different passphrase. The second client to attempt
+  // to commit will go into a state of having pending keys, unioned the set of
+  // encrypted types, and eventually re-encrypt everything with the passphrase
+  // of the first client and commit the set of merged encryption keys. Until the
+  // second client provides the pending passphrase, the cryptographer will
+  // preserve the encryption keys based on the local passphrase, while the
+  // nigori node will preserve the server encryption keys.
+  //
+  // If non-encryption changes are made to the nigori node, they will be
+  // lost as part of conflict resolution. This is intended, as we place a higher
+  // priority on preserving the server's passphrase change to preserving local
+  // non-encryption changes. Next time the non-encryption changes are made to
+  // the nigori node (e.g. on restart), they will commit without issue.
+  if (nigori_node.Get(IS_UNAPPLIED_UPDATE)) {
+    const sync_pb::NigoriSpecifics& nigori =
+        nigori_node.Get(SERVER_SPECIFICS).nigori();
+    cryptographer->Update(nigori);
+
+    // Make sure any unsynced changes are properly encrypted as necessary.
+    // We only perform this if the cryptographer is ready. If not, these are
+    // re-encrypted at SetDecryptionPassphrase time (via ReEncryptEverything).
+    // This logic covers the case where the nigori update marked new datatypes
+    // for encryption, but didn't change the passphrase.
+    if (cryptographer->is_ready()) {
+      // Note that we don't bother to encrypt any data for which IS_UNSYNCED
+      // == false here. The machine that turned on encryption should know about
+      // and re-encrypt all synced data. It's possible it could get interrupted
+      // during this process, but we currently reencrypt everything at startup
+      // as well, so as soon as a client is restarted with this datatype marked
+      // for encryption, all the data should be updated as necessary.
+
+      // If this fails, something is wrong with the cryptographer, but there's
+      // nothing we can do about it here.
+      DVLOG(1) << "Received new nigori, encrypting unsynced changes.";
+      syncable::ProcessUnsyncedChangesForEncryption(trans, cryptographer);
+    }
+
+    if (!nigori_node.Get(IS_UNSYNCED)) { // Update only.
+      SyncerUtil::UpdateLocalDataFromServerData(trans, &nigori_node);
+    } else { // Conflict.
+      // Create a new set of specifics based on the server specifics (which
+      // preserves their encryption keys).
+      sync_pb::EntitySpecifics specifics = nigori_node.Get(SERVER_SPECIFICS);
+      sync_pb::NigoriSpecifics* server_nigori = specifics.mutable_nigori();
+      // Store the merged set of encrypted types (cryptographer->Update(..) will
+      // have merged the local types already).
+      cryptographer->UpdateNigoriFromEncryptedTypes(server_nigori);
+      // The cryptographer has the both the local and remote encryption keys
+      // (added at cryptographer->Update(..) time).
+      // If the cryptographer is ready, then it already merged both sets of keys
+      // and we can store them back in. In that case, the remote key was already
+      // part of the local keybag, so we preserve the local key as the default
+      // (including whether it's an explicit key).
+      // If the cryptographer is not ready, then the user will have to provide
+      // the passphrase to decrypt the pending keys. When they do so, the
+      // SetDecryptionPassphrase code will act based on whether the server
+      // update has an explicit passphrase or not.
+      // - If the server had an explicit passphrase, that explicit passphrase
+      //   will be preserved as the default encryption key.
+      // - If the server did not have an explicit passphrase, we assume the
+      //   local passphrase is the most up to date and preserve the local
+      //   default encryption key marked as an implicit passphrase.
+      // This works fine except for the case where we had locally set an
+      // explicit passphrase. In that case the nigori node will have the default
+      // key based on the local explicit passphassphrase, but will not have it
+      // marked as explicit. To fix this we'd have to track whether we have a
+      // explicit passphrase or not separate from the nigori, which would
+      // introduce even more complexity, so we leave it up to the user to reset
+      // that passphrase as an explicit one via settings. The goal here is to
+      // ensure both sets of encryption keys are preserved.
+      if (cryptographer->is_ready()) {
+        cryptographer->GetKeys(server_nigori->mutable_encrypted());
+        server_nigori->set_using_explicit_passphrase(
+            nigori_node.Get(SPECIFICS).nigori().
+            using_explicit_passphrase());
+      }
+      // We deliberately leave the server's device information. This client will
+      // add its own device information on restart.
+      nigori_node.Put(SPECIFICS, specifics);
+      DVLOG(1) << "Resolving simple conflict, merging nigori nodes: "
+          << nigori_node;
+
+      SyncerUtil::OverwriteServerChanges(&nigori_node);
+
+      UMA_HISTOGRAM_ENUMERATION("Sync.ResolveSimpleConflict",
+                                ConflictResolver::NIGORI_MERGE,
+                                ConflictResolver::CONFLICT_RESOLUTION_SIZE);
+    }
+  }
+}
+
+}  // namespace csync