存储适配器 API

存储适配器 API 分两部分：fabricjs-document-engine/storage 里的内置适配器，以及你自己的适配器要实现的 DocumentStorage 接口。

内置适配器

function createLocalStorage(options?: LocalStorageOptions): ManagedDocumentStorage

The same as createMemoryStorage, backed by localStorage. Also offers listDocuments() and deleteDocument(id).

function createMemoryStorage(): ManagedDocumentStorage

In-memory storage with revisions, listing and versions. Useful for tests and demos.

function createKeyValueStorage(store: KeyValueStore, prefix: string): ManagedDocumentStorage

The same, on any key-value store that has { read, write, remove, keys }.

Name	Type	Default	Description
prefix	string	—	Prefix for every key, so several apps can share one origin.
storage	Storage	localStorage	Another `Storage` object, such as `sessionStorage`.

内置适配器还提供 listDocuments() 和 deleteDocument(id)，并支持版本。

function verifyStorageAdapter(storage: DocumentStorage): Promise<AdapterReport>

Runs the storage contract against your adapter and returns { ok, checks }, so you know it follows the save rules.

每项检查的含义见检查适配器。

Name	Type	Default	Description
loadDocument*	(id: string): Promise<unknown>	—	Returns the stored document, or plain Fabric JSON.
saveDocument*	(document: FabricDocument, context: SaveContext): Promise<void \| SaveResult>	—	Stores the document. Throw an error with `code: 'SAVE_CONFLICT'` when the stored revision differs from `expectedRevision`. Return `{ revision }` if your backend assigns its own number.

Name	Type	Default	Description
expectedRevision*	number \| null	—	The revision this editor last saved or loaded. `null` when the user chose to overwrite.
signal*	AbortSignal	—	Aborted when another document is opened. Pass it to `fetch`.

存储适配器实现下面四个方法，就能支持版本：

Name	Type	Default	Description
saveVersion*	(version: DocumentVersion): Promise<void>	—	Stores a full copy of the document as a version.
listVersions*	(documentId: string): Promise<VersionSummary[]>	—	Version summaries for a document, newest first.
loadVersion*	(documentId: string, versionId: string): Promise<DocumentVersion>	—	Returns one version.
deleteVersion*	(documentId: string, versionId: string): Promise<void>	—	Deletes one version.

function createConflictError(documentId: string, expectedRevision: number, actualRevision: number): DocumentEngineError

A SAVE_CONFLICT error for your storage adapter to throw.

这套存储适配器 API 背后的规则，以及完整的 REST 示例，见自定义后端。