WasmStorageImplementation enum

The storage implementation used by the drift and sqlite3 packages to emulate a synchronous file system on the web, used by the sqlite3 C library to store databases.

As persistence APIs exposed by Browsers are usually asynchronous, faking a synchronous file system

Inheritance

• Object
• Enum
• WasmStorageImplementation

Available extensions

• EnumName

Values

opfsShared → const WasmStorageImplementation

Uses the Origin private file system APIs provided my modern browsers to persist data.

In this storage mode, drift will host a single shared worker between tabs. As the file system API is only available in dedicated workers, the shared worker will spawn an internal dedicated worker which is thus shared between tabs as well.

The OPFS API allows synchronous access to files, but only after they have been opened asynchronously. Since sqlite3 only needs access to two files for a database files, we can just open them once and keep them open while the database is in use.

This mode is a very reliable and efficient approach to access sqlite3 on the web, and the preferred mode used by drift.

While the relevant specifications allow shared workers to spawn nested workers, this is only implemented in Firefox at the time of writing. Chrome (https://crbug.com/1088481) and Safari don't support this yet.

opfsLocks → const WasmStorageImplementation

Uses the Origin private file system APIs provided my modern browsers to persist data.

Unlike opfsShared, this storage implementation does not use a shared worker (either because it is not available or because the current browser doesn't allow shared workers to spawn dedicated workers). Instead, each tab spawns two dedicated workers that use Atomics.wait and Atomics.notify to turn the asynchronous OPFS API into a synchronous file system implementation.

While being less efficient than opfsShared, this mode is also very reliable and used by the official WASM builds of the sqlite3 project as well.

It requires cross-origin isolation, which needs to be enabled by serving your app with special headers:

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

sharedIndexedDb → const WasmStorageImplementation

Emulates a file system over IndexedDB in a shared worker.

unsafeIndexedDb → const WasmStorageImplementation

Uses the asynchronous IndexedDB API outside of any worker to persist data.

Unlike opfsShared, opfsLocks or sharedIndexedDb, this storage implementation can't prevent data races if your app is opened in multiple tabs at the same time, which is why it's declared as as unsafe.

inMemory → const WasmStorageImplementation

A fallback storage implementation that doesn't store anything.

This implementation is chosen when none of the features needed for other storage implementations are supported by the current browser. In this case, WasmDatabaseResult.missingFeatures enumerates missing browser features.

Properties

hashCode → int

The hash code for this object.

no setter, inherited

index → int

A numeric identifier for the enumerated value.

no setter, inherited

name → String

Available on Enum, provided by the EnumName extension

The name of the enum value.

no setter

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited

Constants

values → const List<WasmStorageImplementation>

A constant List of the values in this enum, in order of their declaration.