Support for building libraries enabling access to sqlite3 on the web.

What does this do?

package:sqlite3 provides all the foundations necessary to access sqlite3 on the web. As the APIs exposed by that package are direct wrappers around the sqlite3 C library compiled to WebAssembly, some limitations remain. In particular, the most reliable way to access databases on the web involves workers, which are required to use the filesystem access API.

When workers are involved however, the database is no longer running in the JavaScript context for your app. To access the database in these setups, you instead have to use asynchronous communication channels between the worker and your app. The synchronous API provided by the sqlite3 package is unsuitable for this. Further, different browsers support different persistence APIs and you need to check what's available beforehand to use the best storage engine available.

And that is what this package can do for you:

1. It provides an API enabling you to write database workers in Dart.
2. It can then use these workers for an asynchronous interface to sqlite3 databases.
3. It automatically detects available storage implementations, and can pick the best one available.

Getting started

Note: While this package can be used by end applications, it is meant as a building block for database packages like sqlite3_async or drift. Using these packages helps avoid some setup work.

Workers are responsible for opening databases and exposing them through message channels. This package takes care of these channels, but you are still responsible for opening databases in your workers. To do so, extend the DatabaseController class, e.g. like this.

With a controller ready, you can define an entrypoint for a web worker like this:

import 'package:sqlite3_web/sqlite3_web.dart';

import 'controller.dart';

void main() {
  WebSqlite.workerEntrypoint(controller: ExampleController());
}

This worker is ready to be compiled with dart compile js (consider using -O4).

Additionally, you need a sqlite3.wasm file containing native sqlite3 code to load. You can

• grab a prebuilt version from our releases,
• compile it yourself, or
• compile a custom build with your own sqlite3 extensions or functions linked directly into the module.

With those ready, this package can be used to provide async access to databases that are transparently hosted in the worker:

Future<void> connectToDatabase() async {
  final sqlite = await WebSqlite.open(
    worker: Uri.parse('worker.dart.js'),
    wasmModule: Uri.parse('sqlite3.wasm'),
  );

  final features = await sqlite.runFeatureDetection();
  print('got features: $features');

  final connection = await sqlite.connectToRecommended('my_database');
  print(await connection.database.select('select sqlite_version()'));
}

Custom requests

In some cases, it may be useful to re-use the worker communication scheme created by package:sqlite3_web for functionality implemented in your library. For instance, you could use shared workers to let different tabs connect to a single instance of a database. In that case, some synchronization primitives to coordinate which tab gets to open transactions can be implemented in the worker by overriding handleCustomRequest in WorkerDatabase. You can encode requests and responses as arbitrary values exchanged as JSAny?. On the client side, requests can be issued with Database.customRequest.