Migrate from idb-keyval to native IndexedDB (#81)

Up until now, we basically had only one table and it had conceptually only one column, so we didn't have to worry about atomicity guarantees; everything was automatically atomic. As we prepare to store more kinds of data, we need transactional consistency, to avoid a situation where, e.g., one tab does a read-update-write and in doing so overwrites a write made concurrently from another tab with stale data. So idb-keyval is not for us anymore.

This change prepares for that migration.

Currently, there's no support for database versioning; if the code is deployed as-is and then later the version is upgraded, stuff will break. I'm hoping to fix this later; see #80.

frame/auction.ts

@@ -7,7 +7,7 @@
 /** @fileoverview Selection of ads, and creation of tokens to display them. */
 
 import { isArray, isKeyValueObject } from "../lib/shared/types";
-import { getAllAds } from "./database";
+import { getAllAds } from "./db_schema";
 import { FetchJsonStatus, tryFetchJson } from "./fetch";
 
 /**

frame/auction_test.ts

@@ -17,7 +17,7 @@ import {
   queryParamsMatching,
 } from "../testing/url";
 import { runAdAuction } from "./auction";
-import { setInterestGroupAds } from "./database";
+import { setInterestGroupAds } from "./db_schema";
 
 describe("runAdAuction", () => {
   clearStorageBeforeAndAfter();

frame/database.ts → frame/db_schema.ts

@@ -6,11 +6,11 @@
 
 /**
  * @fileoverview CRUD operations on our data model for persistent storage in
- * idb-keyval, with runtime type checking.
+ * IndexedDB, with runtime type checking.
  */
 
-import * as idbKeyval from "idb-keyval";
 import { isArray } from "../lib/shared/types";
+import { useStore } from "./indexeddb";
 
 /** An `Ad` from the public API serialized into storage format. */
 export type Ad = [renderingUrl: string, price: number];
@@ -24,30 +24,38 @@ function isInterestGroupAd(value: unknown): value is Ad {
 }
 
 /**
- * Stores an interest group in idb-keyval. If there's already one with the same
+ * Stores an interest group in IndexedDB. If there's already one with the same
  * name, it is overwritten.
  */
 export function setInterestGroupAds(name: string, ads: Ad[]): Promise<void> {
-  return idbKeyval.set(name, ads);
+  return useStore("readwrite", (store) => {
+    store.put(ads, name);
+  });
 }
 
-/** Deletes an interest group from idb-keyval. */
+/** Deletes an interest group from IndexedDB. */
 export function deleteInterestGroup(name: string): Promise<void> {
-  return idbKeyval.del(name);
+  return useStore("readwrite", (store) => {
+    store.delete(name);
+  });
 }
 
-/** Returns all ads from all interest groups currently stored in idb-keyval. */
+/** Returns all ads from all interest groups currently stored in IndexedDB. */
 export function getAllAds(): Promise<
   Generator<Ad, /* TReturn= */ void, /* TNext= */ void>
 > {
-  return idbKeyval.entries().then(function* (entries) {
-    for (const [key, ads] of entries) {
+  let interestGroups: unknown[];
+  return useStore("readonly", (store) => {
+    const cursor = store.getAll();
+    cursor.onsuccess = () => {
+      interestGroups = cursor.result;
+    };
+  }).then(function* () {
+    for (const ads of interestGroups) {
       function check(condition: boolean): asserts condition {
         if (!condition) {
           throw new Error(
-            `Malformed entry in idb-keyval for ${JSON.stringify(
-              key
-            )}: ${JSON.stringify(ads)}`
+            `Malformed entry in IndexedDB: ${JSON.stringify(ads)}`
           );
         }
       }

frame/database_test.ts → frame/db_schema_test.ts

@@ -5,32 +5,34 @@
  */
 
 import "jasmine";
-import * as idbKeyval from "idb-keyval";
 import { clearStorageBeforeAndAfter } from "../testing/storage";
 import {
   Ad,
   deleteInterestGroup,
   getAllAds,
   setInterestGroupAds,
-} from "./database";
+} from "./db_schema";
+import { useStore } from "./indexeddb";
 
-describe("database:", () => {
+describe("db_schema:", () => {
   clearStorageBeforeAndAfter();
 
   describe("getAllAds", () => {
-    it("should read an ad from idb-keyval", async () => {
+    it("should read an ad from IndexedDB", async () => {
       const ads: Ad[] = [["about:blank", 0.02]];
       await setInterestGroupAds("interest group name", ads);
       expect([...(await getAllAds())]).toEqual(ads);
     });
 
-    it("should read ads from multiple entries in idb-keyval", async () => {
+    it("should read ads from multiple entries in IndexedDB", async () => {
       const ad1: Ad = ["about:blank#1", 0.01];
       const ad2: Ad = ["about:blank#2", 0.02];
       const ad3: Ad = ["about:blank#3", 0.03];
-      await idbKeyval.set("interest group name 1", [ad1]);
-      await idbKeyval.set("interest group name 2", []);
-      await idbKeyval.set("interest group name 3", [ad2, ad3]);
+      await useStore("readwrite", (store) => {
+        store.add([ad1], "interest group name 1");
+        store.add([], "interest group name 2");
+        store.add([ad2, ad3], "interest group name 3");
+      });
       expect([...(await getAllAds())]).toEqual([ad1, ad2, ad3]);
     });
   });

frame/handler.ts

@@ -18,7 +18,7 @@ import {
 } from "../lib/shared/protocol";
 import { isArray } from "../lib/shared/types";
 import { runAdAuction } from "./auction";
-import { setInterestGroupAds, deleteInterestGroup } from "./database";
+import { setInterestGroupAds, deleteInterestGroup } from "./db_schema";
 
 /**
  * Handles a `MessageEvent` representing a request to the FLEDGE API, and sends

frame/handler_test.ts

@@ -15,7 +15,7 @@ import {
 import { assert, assertType, nonNullish } from "../lib/shared/types";
 import { FakeServerHandler, setFakeServerHandler } from "../testing/http";
 import { clearStorageBeforeAndAfter } from "../testing/storage";
-import { Ad, getAllAds } from "./database";
+import { Ad, getAllAds } from "./db_schema";
 import { handleRequest } from "./handler";
 
 describe("handleRequest", () => {

frame/indexeddb.ts

@@ -0,0 +1,95 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Utilities for performing IndexedDB operations, in order to
+ * persistently store and retrieve data client-side.
+ */
+
+import { assert, assertionError } from "../lib/shared/types";
+
+const DB_NAME = "fledge-shim";
+const STORE_NAME = "interest-groups";
+
+const dbPromise = new Promise<IDBDatabase>((resolve, reject) => {
+  const dbRequest = indexedDB.open(DB_NAME, /* version= */ 1);
+  dbRequest.onupgradeneeded = ({ oldVersion, newVersion }) => {
+    // This should be called iff the database is just now being created for the
+    // first time.
+    assert(oldVersion === 0);
+    assert(newVersion === 1);
+    dbRequest.result.createObjectStore(STORE_NAME);
+  };
+  dbRequest.onsuccess = () => {
+    resolve(dbRequest.result);
+  };
+  dbRequest.onerror = () => {
+    reject(dbRequest.error);
+  };
+  dbRequest.onblocked = () => {
+    // Since the version number is 1 (the lowest allowed), it shouldn't be
+    // possible for an earlier version of the same database to already be open.
+    reject(assertionError());
+  };
+});
+
+/**
+ * Runs an arbitrary operation on the IndexedDB object store. `callback` has to
+ * be synchronous, but it can create IndexedDB requests, and those requests'
+ * `onsuccess` handlers can create further requests, and so forth; the
+ * transaction will be committed and the promise resolved after such a task
+ * finishes with no further pending requests. Such requests need not register
+ * `onerror` handlers, unless they need to do fine-grained error handling; if an
+ * exception is thrown and not caught, the transaction will be aborted without
+ * committing any writes, and the promise rejected.
+ */
+export async function useStore(
+  txMode: IDBTransactionMode,
+  callback: (store: IDBObjectStore) => void
+): Promise<void> {
+  const db = await dbPromise;
+  return new Promise((resolve, reject) => {
+    // The FLEDGE API does not offer callers any guarantees about when writes
+    // will be committed; for example, `joinAdInterestGroup` has a synchronous
+    // API that triggers a background task but does not allow the caller to
+    // await that task. Therefore, strict durability is not required for
+    // correctness. So we'll improve latency and user battery life by opting
+    // into relaxed durability, which allows the browser and OS to economize on
+    // potentially expensive writes to disk.
+    const tx = db.transaction(STORE_NAME, txMode, { durability: "relaxed" });
+    tx.oncomplete = () => {
+      resolve();
+    };
+    tx.onabort = () => {
+      reject(tx.error);
+    };
+    // No need to explicitly install an onerror handler since an error aborts
+    // the transaction.
+    const store = tx.objectStore(STORE_NAME);
+    try {
+      callback(store);
+    } catch (error: unknown) {
+      tx.abort();
+      throw error;
+    }
+  });
+}
+
+declare global {
+  interface IDBDatabase {
+    /**
+     * The `options` parameter is in the IndexedDB spec and is supported by
+     * Chrome, but is absent from the default TypeScript type definitions.
+     *
+     * @see https://www.w3.org/TR/IndexedDB/#database-interface
+     */
+    transaction(
+      storeNames: string | Iterable<string>,
+      mode?: IDBTransactionMode,
+      options?: { durability?: "default" | "strict" | "relaxed" }
+    ): IDBTransaction;
+  }
+}

frame/indexeddb_test.ts

@@ -0,0 +1,101 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { assertInstance } from "../lib/shared/types";
+import { clearStorageBeforeAndAfter } from "../testing/storage";
+import { useStore } from "./indexeddb";
+
+describe("useStore", () => {
+  clearStorageBeforeAndAfter();
+
+  const value = "IndexedDB value";
+  const key = "IndexedDB key";
+
+  it("should read its own writes across multiple transactions", async () => {
+    await useStore("readwrite", (store) => {
+      store.put(value, key);
+    });
+    await useStore("readonly", (store) => {
+      const retrievalRequest = store.get(key);
+      retrievalRequest.onsuccess = () => {
+        expect(retrievalRequest.result).toBe(value);
+      };
+    });
+  });
+
+  it("should reject if the transaction is aborted", () =>
+    expectAsync(
+      useStore("readonly", (store) => {
+        store.transaction.abort();
+      })
+    ).toBeRejectedWith(null));
+
+  it("should not commit the transaction if the main callback throws", async () => {
+    const errorMessage = "oops";
+    await expectAsync(
+      useStore("readwrite", (store) => {
+        store.add(value, key);
+        throw new Error(errorMessage);
+      })
+    ).toBeRejectedWithError(errorMessage);
+    await useStore("readonly", (store) => {
+      const countRequest = store.count();
+      countRequest.onsuccess = () => {
+        expect(countRequest.result).toBe(0);
+      };
+    });
+  });
+
+  const otherValue = "other IndexedDB value";
+  const otherKey = "other IndexedDB key";
+
+  it("should not commit the transaction if an illegal operation is attempted", async () => {
+    await useStore("readwrite", (store) => {
+      store.put(value, key);
+    });
+    await expectAsync(
+      useStore("readwrite", (store) => {
+        store.add(otherValue, otherKey);
+        // add requires that the given key not already exist.
+        store.add(otherValue, key);
+      })
+    ).toBeRejectedWith(
+      jasmine.objectContaining({
+        constructor: DOMException,
+        name: "ConstraintError",
+      })
+    );
+    await useStore("readonly", (store) => {
+      const retrievalRequest = store.get(otherKey);
+      retrievalRequest.onsuccess = () => {
+        expect(retrievalRequest.result).toBeUndefined();
+      };
+    });
+  });
+
+  it("should commit the transaction if an error is recovered from", async () => {
+    await useStore("readwrite", (store) => {
+      store.put(value, key);
+    });
+    await useStore("readwrite", (store) => {
+      store.add(otherValue, otherKey);
+      // add requires that the given key not already exist.
+      const badRequest = store.add(otherValue, key);
+      badRequest.onsuccess = fail;
+      badRequest.onerror = (event) => {
+        assertInstance(badRequest.error, DOMException);
+        expect(badRequest.error.name).toBe("ConstraintError");
+        event.preventDefault();
+      };
+    });
+    await useStore("readonly", (store) => {
+      const retrievalRequest = store.get(otherKey);
+      retrievalRequest.onsuccess = () => {
+        expect(retrievalRequest.result).toBe(otherValue);
+      };
+    });
+  });
+});

lib/public_api.ts

@@ -38,7 +38,7 @@ export interface Ad {
     /**
      * The amount that the buyer is willing to pay in order to have this ad
      * selected. The ad with the highest price is selected; in case of a tie, an
-     * ad with the highest price is selected arbitrarily (based on idb-keyval
+     * ad with the highest price is selected arbitrarily (based on IndexedDB
      * implementation details).
      *
      * This is used by our temporary hardcoded auction logic and will not exist

lib/shared/types.ts

@@ -41,6 +41,16 @@ export function isArray(value: unknown): value is readonly unknown[] {
   return Array.isArray(value);
 }
 
+/**
+ * Returns an error appropriate for when an assertion fails.
+ *
+ * Due to the generic error message, this should be used only in test code or
+ * when it is believed (but not proven) impossible for the check to fail.
+ */
+export function assertionError(): TypeError {
+  return new TypeError("Assertion failure");
+}
+
 /**
  * Throws if the given condition is false.
  *
@@ -49,7 +59,7 @@ export function isArray(value: unknown): value is readonly unknown[] {
  */
 export function assert(condition: boolean): asserts condition {
   if (!condition) {
-    throw new TypeError("Assertion failure");
+    throw assertionError();
   }
 }
 

lib/shared/types_test.ts

@@ -8,6 +8,7 @@ import "jasmine";
 import {
   assert,
   assertInstance,
+  assertionError,
   assertType,
   isArray,
   isKeyValueObject,
@@ -66,6 +67,14 @@ describe("isArray", () => {
   });
 });
 
+describe("assertionError", () => {
+  it("should return a different error on each call", () => {
+    const error1 = assertionError();
+    const error2 = assertionError();
+    expect(error1.stack).not.toBe(error2.stack);
+  });
+});
+
 describe("assert", () => {
   it("should do nothing on a true condition", () => {
     assert(true);