General restructure for performance improvements (bug 441907, r=thunder)

services/sync/modules/engines.js

@@ -130,13 +130,6 @@ Engine.prototype = {
   },
 
   // _core, _store and _tracker need to be overridden in subclasses
-  __core: null,
-  get _core() {
-    if (!this.__core)
-      this.__core = new SyncCore();
-    return this.__core;
-  },
-
   __store: null,
   get _store() {
     if (!this.__store)
@@ -144,6 +137,13 @@ Engine.prototype = {
     return this.__store;
   },
 
+  __core: null,
+  get _core() {
+    if (!this.__core)
+      this.__core = new SyncCore(this._store);
+    return this.__core;
+  },
+
   __tracker: null,
   get _tracker() {
     if (!this.__tracker)
@@ -264,6 +264,7 @@ Engine.prototype = {
       yield this._remote.keys.getKeyAndIV(self.cb, this.engineId);
 
     // 1) Fetch server deltas
+    
     let server = {};
     let serverSnap = yield this._remote.wrap(self.cb, this._snapshot);
     server.snapshot = serverSnap.data;

services/sync/modules/engines/bookmarks.js

@@ -628,13 +628,6 @@ BookmarksEngine.prototype = {
   get logName() { return "BmkEngine"; },
   get serverPrefix() { return "user-data/bookmarks/"; },
 
-  __core: null,
-  get _core() {
-    if (!this.__core)
-      this.__core = new BookmarksSyncCore();
-    return this.__core;
-  },
-
   __store: null,
   get _store() {
     if (!this.__store)
@@ -642,6 +635,13 @@ BookmarksEngine.prototype = {
     return this.__store;
   },
 
+  __core: null,
+  get _core() {
+    if (!this.__core)
+      this.__core = new BookmarksSyncCore(this._store);
+    return this.__core;
+  },
+
   __tracker: null,
   get _tracker() {
     if (!this.__tracker)
@@ -685,23 +685,13 @@ BookmarksEngine.prototype = {
 };
 BookmarksEngine.prototype.__proto__ = new Engine();
 
-function BookmarksSyncCore() {
+function BookmarksSyncCore(store) {
+  this._store = store;
   this._init();
 }
 BookmarksSyncCore.prototype = {
   _logName: "BMSync",
-
+  _store: null,
-  __bms: null,
-  get _bms() {
-    if (!this.__bms)
-      this.__bms = Cc["@mozilla.org/browser/nav-bookmarks-service;1"].
-                   getService(Ci.nsINavBookmarksService);
-    return this.__bms;
-  },
-
-  _itemExists: function BSC__itemExists(GUID) {
-    return this._bms.getItemIdForGUID(GUID) >= 0;
-  },
 
   _getEdits: function BSC__getEdits(a, b) {
     // NOTE: we do not increment ret.numProps, as that would cause
@@ -788,6 +778,7 @@ function BookmarksStore() {
 }
 BookmarksStore.prototype = {
   _logName: "BStore",
+  _lookup: null,
 
   __bms: null,
   get _bms() {
@@ -1252,6 +1243,7 @@ BookmarksStore.prototype = {
     this._wrap(this._getNode(this._bms.bookmarksMenuFolder), items, "menu");
     this._wrap(this._getNode(this._bms.toolbarFolder), items, "toolbar");
     this._wrap(this._getNode(this._bms.unfiledBookmarksFolder), items, "unfiled");
+    this._lookup = items;
     return items;
   },
 

services/sync/modules/engines/cookies.js

@@ -54,13 +54,6 @@ CookieEngine.prototype = {
   get logName() { return "CookieEngine"; },
   get serverPrefix() { return "user-data/cookies/"; },
 
-  __core: null,
-  get _core() {
-    if (!this.__core)
-      this.__core = new CookieSyncCore();
-    return this.__core;
-  },
-
   __store: null,
   get _store() {
     if (!this.__store)
@@ -68,6 +61,13 @@ CookieEngine.prototype = {
     return this.__store;
   },
 
+  __core: null,
+  get _core() {
+    if (!this.__core)
+      this.__core = new CookieSyncCore(this._store);
+    return this.__core;
+  },
+
   __tracker: null,
   get _tracker() {
     if (!this.__tracker)
@@ -77,61 +77,13 @@ CookieEngine.prototype = {
 };
 CookieEngine.prototype.__proto__ = new Engine();
 
-function CookieSyncCore() {
+function CookieSyncCore(store) {
+  this._store = store;
   this._init();
 }
 CookieSyncCore.prototype = {
   _logName: "CookieSync",
-
+  _store: null,
-  __cookieManager: null,
-  get _cookieManager() {
-    if (!this.__cookieManager)
-      this.__cookieManager = Cc["@mozilla.org/cookiemanager;1"].
-                             getService(Ci.nsICookieManager2);
-    /* need the 2nd revision of the ICookieManager interface
-       because it supports add() and the 1st one doesn't. */
-    return this.__cookieManager;
-  },
-
-
-  _itemExists: function CSC__itemExists(GUID) {
-    /* true if a cookie with the given GUID exists.
-       The GUID that we are passed should correspond to the keys
-       that we define in the JSON returned by CookieStore.wrap()
-       That is, it will be a string of the form
-       "host:path:name". */
-
-    /* TODO verify that colons can't normally appear in any of
-       the fields -- if they did it then we can't rely on .split(":")
-       to parse correctly.*/
-
-    let cookieArray = GUID.split( ":" );
-    let cookieHost = cookieArray[0];
-    let cookiePath = cookieArray[1];
-    let cookieName = cookieArray[2];
-
-    /* alternate implementation would be to instantiate a cookie from
-       cookieHost, cookiePath, and cookieName, then call
-       cookieManager.cookieExists(). Maybe that would have better
-       performance?  This implementation seems pretty slow.*/
-    let enumerator = this._cookieManager.enumerator;
-    while (enumerator.hasMoreElements())
-      {
-	let aCookie = enumerator.getNext();
-	if (aCookie.host == cookieHost &&
-	    aCookie.path == cookiePath &&
-	    aCookie.name == cookieName ) {
-	  return true;
-	}
-      }
-    return false;
-    /* Note: We can't just call cookieManager.cookieExists() with a generic
-       javascript object with .host, .path, and .name attributes attatched.
-       cookieExists is implemented in C and does a hard static_cast to an
-       nsCookie object, so duck typing doesn't work (and in fact makes
-       Firefox hard-crash as the static_cast returns null and is not checked.)
-    */
-  },
 
   _commandLike: function CSC_commandLike(a, b) {
     /* Method required to be overridden.
@@ -155,7 +107,7 @@ function CookieStore( cookieManagerStub ) {
 }
 CookieStore.prototype = {
   _logName: "CookieStore",
-
+  _lookup: null,
 
   // Documentation of the nsICookie interface says:
   // name 	ACString 	The name of the cookie. Read only.
@@ -275,7 +227,6 @@ CookieStore.prototype = {
     /* Return contents of this store, as JSON.
        A dictionary of cookies where the keys are GUIDs and the
        values are sub-dictionaries containing all cookie fields. */
-
     let items = {};
     var iter = this._cookieManager.enumerator;
     while (iter.hasMoreElements()) {
@@ -308,6 +259,7 @@ CookieStore.prototype = {
 
       }
     }
+    this._lookup = items;
     return items;
   },
 

services/sync/modules/engines/forms.js

@@ -47,58 +47,6 @@ Cu.import("resource://weave/syncCores.js");
 Cu.import("resource://weave/stores.js");
 Cu.import("resource://weave/trackers.js");
 
-/*
- * Generate GUID from a name,value pair.
- * If the concatenated length is less than 40, we just Base64 the JSON.
- * Otherwise, we Base64 the JSON of the name and SHA1 of the value.
- * The first character of the key determines which method we used:
- * '0' for full Base64, '1' for SHA-1'ed val.
- */
-function _generateFormGUID(nam, val) {
-  var key;
-  var con = nam + val;
-  
-  var jso = Cc["@mozilla.org/dom/json;1"].
-            createInstance(Ci.nsIJSON);
-
-  if (con.length <= 40) {
-    key = '0' + btoa(jso.encode([nam, val]));
-  } else {
-    val = Utils.sha1(val);
-    key = '1' + btoa(jso.encode([nam, val]));
-  }
-  
-  return key;
-}
-
-/*
- * Unwrap a name,value pair from a GUID.
- * Return an array [sha1ed, name, value]
- * sha1ed is a boolean determining if the value is SHA-1'ed or not.
- */
-function _unwrapFormGUID(guid) {
-  var jso = Cc["@mozilla.org/dom/json;1"].
-            createInstance(Ci.nsIJSON);
-  
-  var ret;
-  var dec = atob(guid.slice(1));
-  var obj = jso.decode(dec);
-  
-  switch (guid[0]) {
-    case '0':
-      ret = [false, obj[0], obj[1]];
-      break;
-    case '1':
-      ret = [true, obj[0], obj[1]];
-      break;
-    default:
-      this._log.warn("Unexpected GUID header: " + guid[0] + ", aborting!");
-      return false;
-  }
-  
-  return ret;
-}
-
 function FormEngine(pbeId) {
   this._init(pbeId);
 }
@@ -107,13 +55,6 @@ FormEngine.prototype = {
   get logName() { return "FormEngine"; },
   get serverPrefix() { return "user-data/forms/"; },
 
-  __core: null,
-  get _core() {
-    if (!this.__core)
-      this.__core = new FormSyncCore();
-    return this.__core;
-  },
-
   __store: null,
   get _store() {
     if (!this.__store)
@@ -121,6 +62,13 @@ FormEngine.prototype = {
     return this.__store;
   },
 
+  __core: null,
+  get _core() {
+    if (!this.__core)
+      this.__core = new FormSyncCore(this._store);
+    return this.__core;
+  },
+
   __tracker: null,
   get _tracker() {
     if (!this.__tracker)
@@ -130,43 +78,13 @@ FormEngine.prototype = {
 };
 FormEngine.prototype.__proto__ = new Engine();
 
-function FormSyncCore() {
+function FormSyncCore(store) {
+  this._store = store;
   this._init();
 }
 FormSyncCore.prototype = {
   _logName: "FormSync",
-
+  _store: null,
-  __formDB: null,
-  get _formDB() {
-    if (!this.__formDB) {
-      var file = Cc["@mozilla.org/file/directory_service;1"].
-                 getService(Ci.nsIProperties).
-                 get("ProfD", Ci.nsIFile);
-      file.append("formhistory.sqlite");
-      var stor = Cc["@mozilla.org/storage/service;1"].
-                 getService(Ci.mozIStorageService);
-      this.__formDB = stor.openDatabase(file);
-    }
-    return this.__formDB;
-  },
-
-  _itemExists: function FSC__itemExists(GUID) {
-    var found = false;
-    var stmnt = this._formDB.createStatement("SELECT * FROM moz_formhistory");
-
-    /* Same performance restrictions as PasswordSyncCore apply here:
-       caching required */
-    while (stmnt.executeStep()) {
-      var nam = stmnt.getUTF8String(1);
-      var val = stmnt.getUTF8String(2);
-      var key = _generateFormGUID(nam, val);
-
-      if (key == GUID)
-        found = true;
-    }
-
-    return found;
-  },
 
   _commandLike: function FSC_commandLike(a, b) {
     /* Not required as GUIDs for similar data sets will be the same */
@@ -180,6 +98,7 @@ function FormStore() {
 }
 FormStore.prototype = {
   _logName: "FormStore",
+  _lookup: null,
   
   __formDB: null,
   get _formDB() {
@@ -203,21 +122,6 @@ FormStore.prototype = {
     return this.__formHistory;
   },
 
-  _getValueFromSHA1: function FormStore__getValueFromSHA1(name, sha) {
-    var query = "SELECT value FROM moz_formhistory WHERE fieldname = '" + name + "'";
-    var stmnt = this._formDB.createStatement(query);
-    var found = false;
-    
-    while (stmnt.executeStep()) {
-      var val = stmnt.getUTF8String(0);
-      if (Utils.sha1(val) == sha) {
-        found = val;
-        break;
-      }
-    }
-    return found;
-  },
-  
   _createCommand: function FormStore__createCommand(command) {
     this._log.info("FormStore got createCommand: " + command);
     this._formHistory.addEntry(command.data.name, command.data.value);
@@ -226,23 +130,19 @@ FormStore.prototype = {
   _removeCommand: function FormStore__removeCommand(command) {
     this._log.info("FormStore got removeCommand: " + command);
     
-    var data = _unwrapFormGUID(command.GUID);
+    var data;
-    if (!data) {
+    if (command.GUID in this._lookup) {
+      data = this._lookup[command.GUID];
+    } else {
       this._log.warn("Invalid GUID found, ignoring remove request.");
       return;
     }
     
-    var nam = data[1];
+    var nam = data.name;
-    var val = data[2];
+    var val = data.value;
-    if (data[0]) {
-      val = this._getValueFromSHA1(nam, val);
-    }
-    
-    if (val) {
     this._formHistory.removeEntry(nam, val);
-    } else {
+    
-      this._log.warn("Form value not found from GUID, ignoring remove request.");
+    delete this._lookup[command.GUID];
-    }
   },
 
   _editCommand: function FormStore__editCommand(command) {
@@ -251,18 +151,18 @@ FormStore.prototype = {
   },
 
   wrap: function FormStore_wrap() {
-    var items = [];
+    this._lookup = {};
     var stmnt = this._formDB.createStatement("SELECT * FROM moz_formhistory");
 
     while (stmnt.executeStep()) {
       var nam = stmnt.getUTF8String(1);
       var val = stmnt.getUTF8String(2);
-      var key = _generateFormGUID(nam, val);
+      var key = Utils.sha1(nam + val);
 
-      items[key] = { name: nam, value: val };
+      this._lookup[key] = { name: nam, value: val };
     }
     
-    return items;
+    return this._lookup;
   },
 
   wipe: function FormStore_wipe() {

services/sync/modules/engines/history.js

@@ -58,13 +58,6 @@ HistoryEngine.prototype = {
   get logName() { return "HistEngine"; },
   get serverPrefix() { return "user-data/history/"; },
 
-  __core: null,
-  get _core() {
-    if (!this.__core)
-      this.__core = new HistorySyncCore();
-    return this.__core;
-  },
-
   __store: null,
   get _store() {
     if (!this.__store)
@@ -72,6 +65,13 @@ HistoryEngine.prototype = {
     return this.__store;
   },
 
+  __core: null,
+  get _core() {
+    if (!this.__core)
+      this.__core = new HistorySyncCore(this._store);
+    return this.__core;
+  },
+
   __tracker: null,
   get _tracker() {
     if (!this.__tracker)
@@ -81,16 +81,13 @@ HistoryEngine.prototype = {
 };
 HistoryEngine.prototype.__proto__ = new Engine();
 
-function HistorySyncCore() {
+function HistorySyncCore(store) {
+  this._store = store;
   this._init();
 }
 HistorySyncCore.prototype = {
   _logName: "HistSync",
-
+  _store: null,
-  _itemExists: function HSC__itemExists(GUID) {
-    // we don't care about already-existing items; just try to re-add them
-    return false;
-  },
 
   _commandLike: function HSC_commandLike(a, b) {
     // History commands never qualify for likeness.  We will always
@@ -134,6 +131,11 @@ HistoryStore.prototype = {
     return this.__hsvc;
   },
 
+  _itemExists: function HistStore__itemExists(GUID) {
+    // we don't care about already-existing items; just try to re-add them
+    return false;
+  },
+
   _createCommand: function HistStore__createCommand(command) {
     this._log.debug("  -> creating history entry: " + command.GUID);
     try {

services/sync/modules/engines/passwords.js

@@ -43,27 +43,6 @@ Cu.import("resource://weave/engines.js");
 Cu.import("resource://weave/syncCores.js");
 Cu.import("resource://weave/stores.js");
 
-/*
- * _hashLoginInfo
- *
- * nsILoginInfo objects don't have a unique GUID, so we need to generate one
- * on the fly. This is done by taking a hash of every field in the object.
- * Note that the resulting GUID could potentiually reveal passwords via
- * dictionary attacks or brute force. But GUIDs shouldn't be obtainable by
- * anyone, so this should generally be safe.
- */
-function _hashLoginInfo(aLogin) {
-  var loginKey = aLogin.hostname      + ":" +
-                 aLogin.formSubmitURL + ":" +
-                 aLogin.httpRealm     + ":" +
-                 aLogin.username      + ":" +
-                 aLogin.password      + ":" +
-                 aLogin.usernameField + ":" +
-                 aLogin.passwordField;
-
-  return Utils.sha1(loginKey);
-}
-
 function PasswordEngine() {
   this._init();
 }
@@ -72,50 +51,29 @@ PasswordEngine.prototype = {
   get logName() { return "PasswordEngine"; },
   get serverPrefix() { return "user-data/passwords/"; },
 
-  __core: null,
-  get _core() {
-    if (!this.__core)
-      this.__core = new PasswordSyncCore();
-    return this.__core;
-  },
-
   __store: null,
   get _store() {
     if (!this.__store)
       this.__store = new PasswordStore();
     return this.__store;
+  },
+  
+  __core: null,
+  get _core() {
+    if (!this.__core)
+      this.__core = new PasswordSyncCore(this._store);
+    return this.__core;
   }
 };
 PasswordEngine.prototype.__proto__ = new Engine();
 
-function PasswordSyncCore() {
+function PasswordSyncCore(store) {
+  this._store = store;
   this._init();
 }
 PasswordSyncCore.prototype = {
   _logName: "PasswordSync",
-
+  _store: null,
-  __loginManager : null,
-  get _loginManager() {
-    if (!this.__loginManager)
-      this.__loginManager = Utils.getLoginManager();
-    return this.__loginManager;
-  },
-
-  _itemExists: function PSC__itemExists(GUID) {
-    var found = false;
-    var logins = this._loginManager.getAllLogins({});
-
-    // XXX It would be more efficient to compute all the hashes in one shot,
-    // cache the results, and check the cache here. That would need to happen
-    // once per sync -- not sure how to invalidate cache after current sync?
-    for (var i = 0; i < logins.length && !found; i++) {
-        var hash = _hashLoginInfo(logins[i]);
-        if (hash == GUID)
-            found = true;;
-    }
-
-    return found;
-  },
 
   _commandLike: function PSC_commandLike(a, b) {
     // Not used.
@@ -129,6 +87,7 @@ function PasswordStore() {
 }
 PasswordStore.prototype = {
   _logName: "PasswordStore",
+  _lookup: null,
 
   __loginManager: null,
   get _loginManager() {
@@ -144,6 +103,27 @@ PasswordStore.prototype = {
     return this.__nsLoginInfo;
   },
   
+  /*
+   * _hashLoginInfo
+   *
+   * nsILoginInfo objects don't have a unique GUID, so we need to generate one
+   * on the fly. This is done by taking a hash of every field in the object.
+   * Note that the resulting GUID could potentiually reveal passwords via
+   * dictionary attacks or brute force. But GUIDs shouldn't be obtainable by
+   * anyone, so this should generally be safe.
+   */
+   _hashLoginInfo: function PasswordStore__hashLoginInfo(aLogin) {
+    var loginKey = aLogin.hostname      + ":" +
+                   aLogin.formSubmitURL + ":" +
+                   aLogin.httpRealm     + ":" +
+                   aLogin.username      + ":" +
+                   aLogin.password      + ":" +
+                   aLogin.usernameField + ":" +
+                   aLogin.passwordField;
+
+    return Utils.sha1(loginKey);
+  },
+
   _createCommand: function PasswordStore__createCommand(command) {
     this._log.info("PasswordStore got createCommand: " + command );
 
@@ -180,13 +160,12 @@ PasswordStore.prototype = {
   wrap: function PasswordStore_wrap() {
     /* Return contents of this store, as JSON. */
     var items = {};
-
     var logins = this._loginManager.getAllLogins({});
 
     for (var i = 0; i < logins.length; i++) {
       var login = logins[i];
 
-      var key = _hashLoginInfo(login);
+      var key = this._hashLoginInfo(login);
 
       items[key] = { hostname      : login.hostname,
                      formSubmitURL : login.formSubmitURL,
@@ -197,6 +176,7 @@ PasswordStore.prototype = {
                      passwordField : login.passwordField };
     }
 
+    this._lookup = items;
     return items;
   },
 

services/sync/modules/engines/tabs.js

@@ -62,18 +62,18 @@ TabEngine.prototype = {
   get serverPrefix() "user-data/tabs/",
   get store() this._store,
 
-  get _core() {
-    let core = new TabSyncCore(this);
-    this.__defineGetter__("_core", function() core);
-    return this._core;
-  },
-
   get _store() {
     let store = new TabStore();
     this.__defineGetter__("_store", function() store);
     return this._store;
   },
   
+  get _core() {
+    let core = new TabSyncCore(this._store);
+    this.__defineGetter__("_core", function() core);
+    return this._core;
+  },
+
   get _tracker() {
     let tracker = new TabTracker(this);
     this.__defineGetter__("_tracker", function() tracker);
@@ -82,16 +82,15 @@ TabEngine.prototype = {
 
 };
 
-function TabSyncCore(engine) {
+function TabSyncCore(store) {
-  this._engine = engine;
+  this._store = store;
   this._init();
 }
 TabSyncCore.prototype = {
   __proto__: new SyncCore(),
 
   _logName: "TabSync",
-
+  _store: null,
-  _engine: null,
 
   get _sessionStore() {
     let sessionStore = Cc["@mozilla.org/browser/sessionstore;1"].
@@ -100,27 +99,6 @@ TabSyncCore.prototype = {
     return this._sessionStore;
   },
 
-  _itemExists: function TSC__itemExists(GUID) {
-    // Note: this method returns true if the tab exists in any window, not just
-    // the window from which the tab came.  In the future, if we care about
-    // windows, we might need to make this more specific, although in that case
-    // we'll have to identify tabs by something other than URL, since even
-    // window-specific tabs look the same when identified by URL.
-
-    // Get the set of all real and virtual tabs.
-    let tabs = this._engine.store.wrap();
-
-    // XXX Should we convert both to nsIURIs and then use nsIURI::equals
-    // to compare them?
-    if (GUID in tabs) {
-      this._log.trace("_itemExists: " + GUID + " exists");
-      return true;
-    }
-
-    this._log.trace("_itemExists: " + GUID + " doesn't exist");
-    return false;
-  },
-
   _commandLike: function TSC_commandLike(a, b) {
     // Not implemented.
     return false;
@@ -263,6 +241,27 @@ TabStore.prototype = {
     self.done();
   },
 
+  _itemExists: function TabStore__itemExists(GUID) {
+    // Note: this method returns true if the tab exists in any window, not just
+    // the window from which the tab came.  In the future, if we care about
+    // windows, we might need to make this more specific, although in that case
+    // we'll have to identify tabs by something other than URL, since even
+    // window-specific tabs look the same when identified by URL.
+
+    // Get the set of all real and virtual tabs.
+    let tabs = this.wrap();
+
+    // XXX Should we convert both to nsIURIs and then use nsIURI::equals
+    // to compare them?
+    if (GUID in tabs) {
+      this._log.trace("_itemExists: " + GUID + " exists");
+      return true;
+    }
+
+    this._log.trace("_itemExists: " + GUID + " doesn't exist");
+    return false;
+  },
+
   _createCommand: function TabStore__createCommand(command) {
     this._log.debug("_createCommand: " + command.GUID);
 

services/sync/modules/stores.js

@@ -62,6 +62,9 @@ Store.prototype = {
   _logName: "Store",
   _yieldDuringApply: true,
 
+  // set this property in child object's wrap()!
+  _lookup: null,
+
   __json: null,
   get _json() {
     if (!this.__json)
@@ -102,10 +105,28 @@ Store.prototype = {
     self.done();
   },
 
+  // override only if neccessary
+  _itemExists: function Store__itemExists(GUID) {
+    if (GUID in this._lookup)
+      return true;
+    else
+      return false;
+  },
+  
   // override these in derived objects
-  wrap: function Store_wrap() {},
+  
-  wipe: function Store_wipe() {},
+  // wrap MUST save the wrapped store in the _lookup property!
-  resetGUIDs: function Store_resetGUIDs() {}
+  wrap: function Store_wrap() {
+    throw "wrap needs to be subclassed";
+  },
+  
+  wipe: function Store_wipe() {
+    throw "wipe needs to be subclassed";
+  },
+  
+  resetGUIDs: function Store_resetGUIDs() {
+    throw "resetGUIDs needs to be subclassed";
+  }
 };
 
 function SnapshotStore(name) {

services/sync/modules/syncCores.js

@@ -63,6 +63,9 @@ function SyncCore() {
 SyncCore.prototype = {
   _logName: "Sync",
   
+  // Set this property in child objects!
+  _store: null,
+  
   _init: function SC__init() {
     this._log = Log4Moz.Service.getLogger("Service." + this._logName);
   },
@@ -209,11 +212,6 @@ SyncCore.prototype = {
     }
   },
 
-  _itemExists: function SC__itemExists(GUID) {
-    this._log.error("itemExists needs to be subclassed");
-    return false;
-  },
-
   _reconcile: function SC__reconcile(listA, listB) {
     let self = yield;
 
@@ -253,7 +251,7 @@ SyncCore.prototype = {
         }
 
         // watch out for create commands with GUIDs that already exist
-        if (b.action == "create" && this._itemExists(b.GUID)) {
+        if (b.action == "create" && this._store._itemExists(b.GUID)) {
           this._log.error("Remote command has GUID that already exists " +
                           "locally. Dropping command.");
           return false; // delete b