LevelDB database adapter for Yjs

LevelDB is a fast embedded database. It is the underlying technology of IndexedDB.

Internally, y-leveldb uses level which
allows to exchange the storage medium for a different supported database.
Hence this adapter also supports rocksdb, lmdb, and many more..

* Persistent storage for the server
* Exchangeable storage medium
* Can be used in y-websocket
* A single y-leveldb instance can handle many documents.

Use it

``sh
npm install y-leveldb --save
`

`js
import * as Y from 'yjs'
import { LeveldbPersistence } from 'y-leveldb'

const persistence = new LeveldbPersistence('./storage-location')

const ydoc = new Y.Doc()
ydoc.getArray('arr').insert(0, [1, 2, 3])
ydoc.getArray('arr').toArray() // => [1, 2, 3]

// store document updates retrieved from other clients
persistence.storeUpdate('my-doc', Y.encodeStateAsUpdate(ydoc))

// when you want to sync, or store data to a database,
// retrieve the temporary Y.Doc to consume data
const ydocPersisted = await persistence.getYDoc('my-doc')
ydocPersisted.getArray('arr') // [1, 2, 3]
`

API

$3

Create a y-leveldb persistence instance.

You can use any levelup-compatible adapter.

`js
import { LeveldbPersistence } from 'y-leveldb'
import level from 'level-mem'

const persistence = new LeveldbPersistence('./storage-location', { level })
`

#### persistence.getYDoc(docName: string): Promise

Create a Y.Doc instance with the data persisted in leveldb. Use this to
temporarily create a Yjs document to sync changes or extract data.

#### persistence.storeUpdate(docName: string, update: Uint8Array): Promise

Store a single document update to the database.

#### persistence.getStateVector(docName: string): Promise

The state vector (describing the state of the persisted document - see
Yjs docs) is maintained in a separate
field and constantly updated.

This allows you to sync changes without actually creating a Yjs document.

#### persistence.getDiff(docName: string, stateVector: Uint8Array): Promise

Get the differences directly from the database. The same as
Y.encodeStateAsUpdate(ydoc, stateVector).

#### persistence.clearDocument(docName: string): Promise

Delete a document, and all associated data from the database.

#### persistence.setMeta(docName: string, metaKey: string, value: any): Promise

Persist some meta information in the database and associate it with a document.
It is up to you what you store here. You could, for example, store credentials
here.

#### persistence.getMeta(docName: string, metaKey: string): Promise

Retrieve a store meta value from the database. Returns undefined if the
metaKey doesn't exist.

#### persistence.delMeta(docName: string, metaKey: string): Promise

Delete a store meta value.

#### persistence.getAllDocNames(docName: string): Promise>

Retrieve the names of all stored documents.

#### persistence.getAllDocStateVectors(docName: string): Promise

Retrieve the state vectors of all stored documents. You can use this to sync
two y-leveldb instances.

Note: The state vectors might be outdated if the associated document is not
yet flushed. So use with caution.

#### persistence.flushDocument(docName: string): Promise` (dev only)

Internally y-leveldb stores incremental updates. You can merge all document
updates to a single entry. You probably never have to use this.

License

y-leveldb is licensed under the MIT License.