Conditionally run post-attachment migrations

Introduce placeholder migrations for Backbone models so they never implicitly
run migrations whenever they are `fetch`ed. We prefer to run our migrations
explicitly upon app startup and then let Backbone models be (slightly) dumb(er)
models, without inadvertently triggering migrations.

js/background.js

@@ -83,23 +83,15 @@
   const cancelInitializationMessage = Views.Initialization.setMessage();
   console.log('Start IndexedDB migrations');
 
-  console.log('Migrate database with attachments');
+  console.log('Run migrations on database with attachment data');
   await Migrations0DatabaseWithAttachmentData.run({ Backbone });
 
-  // console.log('Migrate attachments to disk');
-  // const database = Migrations0DatabaseWithAttachmentData.getDatabase();
-  // await MessageDataMigrator.processAll({
-  //   Backbone,
-  //   databaseName: database.name,
-  //   minDatabaseVersion: database.version,
-  //   upgradeMessageSchema,
-  // });
-
-  // console.log('Migrate database without attachments');
-  // await Migrations1DatabaseWithoutAttachmentData.run({
-  //   Backbone,
-  //   database: Whisper.Database,
-  // });
+  const database = Whisper.Database;
+  const status = await Migrations1DatabaseWithoutAttachmentData.getStatus({ database });
+  console.log('Run migrations on database without attachment data:', status);
+  if (status.canRun) {
+    await Migrations1DatabaseWithoutAttachmentData.run({ Backbone, database });
+  }
 
   console.log('Storage fetch');
   storage.fetch();

js/database.js

@@ -6,7 +6,7 @@
 (function () {
   'use strict';
 
-  const { Migrations0DatabaseWithAttachmentData } = window.Signal.Migrations;
+  const { getPlaceholderMigrations } = window.Signal.Migrations;
 
   window.Whisper = window.Whisper || {};
   window.Whisper.Database = window.Whisper.Database || {};
@@ -123,5 +123,5 @@
       request.onsuccess = resolve;
     }));
 
-  Whisper.Database.migrations = Migrations0DatabaseWithAttachmentData.migrations;
+  Whisper.Database.migrations = getPlaceholderMigrations();
 }());

js/modules/migrations/get_placeholder_migrations.js

@@ -0,0 +1,23 @@
+const Migrations0DatabaseWithAttachmentData =
+  require('./migrations_0_database_with_attachment_data');
+const Migrations1DatabaseWithoutAttachmentData =
+  require('./migrations_1_database_without_attachment_data');
+
+
+exports.getPlaceholderMigrations = () => {
+  const last0MigrationVersion =
+    Migrations0DatabaseWithAttachmentData.getLatestVersion();
+  const last1MigrationVersion =
+    Migrations1DatabaseWithoutAttachmentData.getLatestVersion();
+
+  const lastMigrationVersion = last1MigrationVersion || last0MigrationVersion;
+
+  return [{
+    version: lastMigrationVersion,
+    migrate() {
+      throw new Error('Unexpected invocation of placeholder migration!' +
+        '\n\nMigrations must explicitly be run upon application startup instead' +
+        ' of implicitly via Backbone IndexedDB adapter at any time.');
+    },
+  }];
+};

js/modules/migrations/migrations_0_database_with_attachment_data.js

@@ -154,3 +154,12 @@ exports.getDatabase = () => ({
   name: database.id,
   version: last(exports.migrations).version,
 });
+
+exports.getLatestVersion = () => {
+  const lastMigration = last(migrations);
+  if (!lastMigration) {
+    return null;
+  }
+
+  return lastMigration.version;
+};

js/modules/migrations/migrations_1_database_without_attachment_data.js

@@ -1,15 +1,50 @@
+const last = require('lodash/last');
+
+const db = require('../database');
+const settings = require('../settings');
 const { runMigrations } = require('./run_migrations');
 
 
-exports.migrations = [
+// NOTE: Add new migrations that need to traverse entire database, e.g. messages
+// store, here. These will only run after attachment migration has completed in
+// the background:
+const migrations = [
   // {
-  //   version: 18,
-  //   async migrate(transaction, next) {
-  //     console.log('Migration 18');
-  //     console.log('Attachments stored on disk');
+  //   version: 0,
+  //   migrate(transaction, next) {
   //     next();
   //   },
   // },
 ];
 
-exports.run = runMigrations;
+exports.run = async ({ Backbone, database } = {}) => {
+  const { canRun } = await exports.getStatus({ database });
+  if (!canRun) {
+    throw new Error('Cannot run migrations on database without attachment data');
+  }
+
+  await runMigrations({ Backbone, database });
+};
+
+exports.getStatus = async ({ database } = {}) => {
+  const connection = await db.open(database.id, database.version);
+  const isAttachmentMigrationComplete =
+    await settings.isAttachmentMigrationComplete(connection);
+  const hasMigrations = migrations.length > 0;
+
+  const canRun = isAttachmentMigrationComplete && hasMigrations;
+  return {
+    isAttachmentMigrationComplete,
+    hasMigrations,
+    canRun,
+  };
+};
+
+exports.getLatestVersion = () => {
+  const lastMigration = last(migrations);
+  if (!lastMigration) {
+    return null;
+  }
+
+  return lastMigration.version;
+};

preload.js

@@ -119,6 +119,8 @@
   const upgradeMessageSchema = message =>
     Message.upgradeSchema(message, upgradeSchemaContext);
 
+  const { getPlaceholderMigrations } =
+    require('./js/modules/migrations/get_placeholder_migrations');
   const { IdleDetector} = require('./js/modules/idle_detector');
 
   window.Signal = {};
@@ -128,13 +130,14 @@
   window.Signal.Debug = require('./js/modules/debug');
   window.Signal.Logs = require('./js/modules/logs');
   window.Signal.Migrations = {};
-  window.Signal.Migrations.loadAttachmentData = Attachment.loadData(readAttachmentData);
   window.Signal.Migrations.deleteAttachmentData = Attachment.deleteData(deleteAttachmentData);
-  window.Signal.Migrations.upgradeMessageSchema = upgradeMessageSchema;
+  window.Signal.Migrations.getPlaceholderMigrations =getPlaceholderMigrations;
+  window.Signal.Migrations.loadAttachmentData = Attachment.loadData(readAttachmentData);
   window.Signal.Migrations.Migrations0DatabaseWithAttachmentData =
     require('./js/modules/migrations/migrations_0_database_with_attachment_data');
   window.Signal.Migrations.Migrations1DatabaseWithoutAttachmentData =
     require('./js/modules/migrations/migrations_1_database_without_attachment_data');
+  window.Signal.Migrations.upgradeMessageSchema = upgradeMessageSchema;
   window.Signal.OS = require('./js/modules/os');
   window.Signal.Settings = require('./js/modules/settings');
   window.Signal.Types = {};