Merge pull request share#244 from share/null-milestone-db

Add a `NoOpMilestoneDB` implementation

Author: ericyhwang

README.md

@@ -420,3 +420,5 @@ The `41xx` and `51xx` codes are reserved for use by ShareDB DB adapters, and the
 * 5016 - _unsubscribe PubSub method unimplemented
 * 5017 - _publish PubSub method unimplemented
 * 5018 - Required QueryEmitter listener not assigned
+* 5019 - getMilestoneSnapshot MilestoneDB method unimplemented
+* 5020 - saveMilestoneSnapshot MilestoneDB method unimplemented

lib/backend.js

@@ -3,7 +3,7 @@ var Agent = require('./agent');
 var Connection = require('./client/connection');
 var emitter = require('./emitter');
 var MemoryDB = require('./db/memory');
-var MilestoneDB = require('./milestone-db');
+var NoOpMilestoneDB = require('./milestone-db/no-op');
 var MemoryPubSub = require('./pubsub/memory');
 var ot = require('./ot');
 var projections = require('./projections');
@@ -25,7 +25,7 @@ function Backend(options) {
   this.pubsub = options.pubsub || new MemoryPubSub();
   // This contains any extra databases that can be queried
   this.extraDbs = options.extraDbs || {};
-  this.milestoneDb = options.milestoneDb || new MilestoneDB();
+  this.milestoneDb = options.milestoneDb || new NoOpMilestoneDB();
 
   // Map from projected collection -> {type, fields}
   this.projections = {};

lib/client/snapshot-request.js

@@ -11,7 +11,7 @@ function SnapshotRequest(connection, requestId, collection, id, version, callbac
     throw new Error('Callback is required for SnapshotRequest');
   }
 
-  if (!this.isValidVersion(version)) {
+  if (!util.isValidVersion(version)) {
     throw new Error('Snapshot version must be a positive integer or null');
   }
 
@@ -26,18 +26,6 @@ function SnapshotRequest(connection, requestId, collection, id, version, callbac
 }
 emitter.mixin(SnapshotRequest);
 
-SnapshotRequest.prototype.isValidVersion = function (version) {
-  if (version === null) {
-    return true;
-  }
-
-  if (!util.isInteger(version)) {
-    return false;
-  }
-
-  return version >= 0;
-}
-
 SnapshotRequest.prototype.send = function () {
   if (!this.connection.canSend) {
     return;

lib/milestone-db/index.js

@@ -1,4 +1,6 @@
 var emitter = require('../emitter');
+var ShareDBError = require('../error');
+var util = require('../util');
 
 module.exports = MilestoneDB;
 function MilestoneDB(options) {
@@ -23,17 +25,23 @@ MilestoneDB.prototype.close = function(callback) {
  *   the signature (error, snapshot) => void;
  */
 MilestoneDB.prototype.getMilestoneSnapshot = function (collection, id, version, callback) {
-  process.nextTick(callback, null, undefined);
+  var error = new ShareDBError(5019, 'getMilestoneSnapshot MilestoneDB method unimplemented');
+  if (callback) return process.nextTick(callback, error);
+  this.emit('error', error);
 };
 
 /**
  * @param {string} collection - name of the snapshot's collection
  * @param {Snapshot} snapshot - the milestone snapshot to save
  * @param {Function} callback (optional) - a callback to invoke after the snapshot has been saved.
- *   Should have the signature (error, wasSaved) => void;
+ *   Should have the signature (error) => void;
  */
 MilestoneDB.prototype.saveMilestoneSnapshot = function (collection, snapshot, callback) {
-  var saved = false;
-  if (callback) return process.nextTick(callback, null, saved);
-  this.emit('save', saved, collection, snapshot);
+  var error = new ShareDBError(5020, 'saveMilestoneSnapshot MilestoneDB method unimplemented');
+  if (callback) return process.nextTick(callback, error);
+  this.emit('error', error);
+};
+
+MilestoneDB.prototype._isValidVersion = function (version) {
+  return util.isValidVersion(version);
 };

lib/milestone-db/memory.js

@@ -1,4 +1,5 @@
 var MilestoneDB = require('./index');
+var ShareDBError = require('../error');
 
 /**
  * In-memory ShareDB milestone database
@@ -22,6 +23,11 @@ function MemoryMilestoneDB(options) {
 MemoryMilestoneDB.prototype = Object.create(MilestoneDB.prototype);
 
 MemoryMilestoneDB.prototype.getMilestoneSnapshot = function (collection, id, version, callback) {
+  if (!callback) callback = function () {};
+  if (!collection) return process.nextTick(callback, new ShareDBError(4001, 'Missing collection'));
+  if (!id) return process.nextTick(callback, new ShareDBError(4001, 'Missing ID'));
+  if (!this._isValidVersion(version)) return process.nextTick(callback, new ShareDBError(4001, 'Invalid version'));
+
   var milestoneSnapshots = this._getMilestoneSnapshotsSync(collection, id);
 
   var milestoneSnapshot;
@@ -38,21 +44,21 @@ MemoryMilestoneDB.prototype.getMilestoneSnapshot = function (collection, id, ver
 };
 
 MemoryMilestoneDB.prototype.saveMilestoneSnapshot = function (collection, snapshot, callback) {
-  var saved = false;
-  if (!snapshot) {
-    if (callback) return process.nextTick(callback, null, saved);
-    this.emit('save', saved, collection, snapshot);
-  }
+  callback = callback || function (error) {
+    if (error) return this.emit('error', error);
+    this.emit('save', collection, snapshot);
+  }.bind(this);
+
+  if (!collection) return callback(new ShareDBError(4001, 'Missing collection'));
+  if (!snapshot) return callback(new ShareDBError(4001, 'Missing snapshot'));
 
   var milestoneSnapshots = this._getMilestoneSnapshotsSync(collection, snapshot.id);
   milestoneSnapshots.push(snapshot);
   milestoneSnapshots.sort(function (a, b) {
     return a.v - b.v;
   });
 
-  saved = true;
-  if (callback) return process.nextTick(callback, null, saved);
-  this.emit('save', saved, collection, snapshot);
+  process.nextTick(callback, null);
 };
 
 MemoryMilestoneDB.prototype._getMilestoneSnapshotsSync = function (collection, id) {

lib/milestone-db/no-op.js

@@ -0,0 +1,24 @@
+var MilestoneDB = require('./index');
+
+/**
+ * A no-op implementation of the MilestoneDB class.
+ *
+ * This class exists as a simple, silent default drop-in for ShareDB, which allows the backend to call its methods with
+ * no effect.
+ */
+module.exports = NoOpMilestoneDB;
+function NoOpMilestoneDB(options) {
+  MilestoneDB.call(this, options);
+}
+
+NoOpMilestoneDB.prototype = Object.create(MilestoneDB.prototype);
+
+NoOpMilestoneDB.prototype.getMilestoneSnapshot = function (collection, id, version, callback) {
+  var snapshot = undefined;
+  process.nextTick(callback, null, snapshot);
+};
+
+NoOpMilestoneDB.prototype.saveMilestoneSnapshot = function (collection, snapshot, callback) {
+  if (callback) return process.nextTick(callback, null);
+  this.emit('save', collection, snapshot);
+};

lib/util.js

@@ -13,3 +13,8 @@ exports.isInteger = Number.isInteger || function (value) {
     isFinite(value) &&
     Math.floor(value) === value;
 };
+
+exports.isValidVersion = function (version) {
+  if (version === null) return true;
+  return exports.isInteger(version) && version >= 0;
+};