feat(nbstore): add awareness storage

packages/common/nbstore/src/impls/idb/awareness.ts

@@ -0,0 +1,43 @@
+import { share } from '../../connection';
+import {
+  type AwarenessRecord,
+  AwarenessStorage,
+} from '../../storage/awareness';
+import { IDBConnection } from './db';
+
+export class IndexedDBAwarenessStorage extends AwarenessStorage {
+  override readonly storageType = 'awareness';
+  override readonly connection = share(new IDBConnection(this.options));
+
+  private readonly subscriptions = new Map<
+    string,
+    Set<(update: AwarenessRecord, origin?: string) => void>
+  >();
+
+  private readonly cached = new Map<string, AwarenessRecord>();
+
+  override update(record: AwarenessRecord, origin?: string): Promise<void> {
+    const subscribers = this.subscriptions.get(record.docId);
+    if (subscribers) {
+      subscribers.forEach(callback => callback(record, origin));
+    }
+    this.cached.set(record.docId, record);
+    return Promise.resolve();
+  }
+
+  override subscribeUpdate(
+    id: string,
+    callback: (update: AwarenessRecord, origin?: string) => void
+  ): () => void {
+    const subscribers = this.subscriptions.get(id) ?? new Set();
+    subscribers.add(callback);
+    this.subscriptions.set(id, subscribers);
+    const cached = this.cached.get(id);
+    if (cached) {
+      callback(cached);
+    }
+    return () => {
+      subscribers.delete(callback);
+    };
+  }
+}

packages/common/nbstore/src/storage/awareness.ts

@@ -0,0 +1,26 @@
+import { Storage, type StorageOptions } from './storage';
+
+export interface AwarenessStorageOptions extends StorageOptions {}
+
+export type AwarenessRecord = {
+  docId: string;
+  bin: Uint8Array;
+};
+
+export abstract class AwarenessStorage<
+  Options extends AwarenessStorageOptions = AwarenessStorageOptions,
+> extends Storage<Options> {
+  override readonly storageType = 'awareness';
+
+  /**
+   * Update the awareness record.
+   *
+   * @param origin - Internal identifier to recognize the source in the "update" event. Will not be stored or transferred.
+   */
+  abstract update(record: AwarenessRecord, origin?: string): Promise<void>;
+
+  abstract subscribeUpdate(
+    id: string,
+    callback: (update: AwarenessRecord, origin?: string) => void
+  ): () => void;
+}

packages/common/nbstore/src/storage/index.ts

@@ -1,6 +1,8 @@
 import EventEmitter2 from 'eventemitter2';
 
 import type { ConnectionStatus } from '../connection';
+import { type Storage, type StorageType } from '../storage';
+import type { AwarenessStorage } from './awareness';
 import type { BlobStorage } from './blob';
 import type { DocStorage } from './doc';
 import { type Storage, type StorageType } from './storage';

packages/common/nbstore/src/storage/storage.ts

@@ -1,7 +1,7 @@
 import type { Connection } from '../connection';
 
 export type SpaceType = 'workspace' | 'userspace';
-export type StorageType = 'blob' | 'doc' | 'sync';
+export type StorageType = 'blob' | 'doc' | 'sync' | 'awareness';
 
 export interface StorageOptions {
   peer: string;