feat(nbstore): add blob sync frontend

packages/common/nbstore/src/frontend/blob.ts

@@ -0,0 +1,23 @@
+import type { BlobRecord, BlobStorage } from '../storage';
+import type { BlobSyncEngine } from '../sync/blob';
+
+export class BlobFrontend {
+  constructor(
+    readonly storage: BlobStorage,
+    readonly sync?: BlobSyncEngine
+  ) {}
+
+  get(blobId: string) {
+    return this.sync
+      ? this.sync.downloadBlob(blobId)
+      : this.storage.get(blobId);
+  }
+
+  set(blob: BlobRecord) {
+    return this.sync ? this.sync.uploadBlob(blob) : this.storage.set(blob);
+  }
+
+  addPriority(id: string, priority: number) {
+    return this.sync?.addPriority(id, priority);
+  }
+}

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

@@ -6,14 +6,14 @@ export interface BlobRecord {
   key: string;
   data: Uint8Array;
   mime: string;
-  createdAt: Date;
+  createdAt?: Date;
 }
 
 export interface ListedBlobRecord {
   key: string;
   mime: string;
   size: number;
-  createdAt: Date;
+  createdAt?: Date;
 }
 
 export abstract class BlobStorage<

packages/common/nbstore/src/sync/blob/index.ts

@@ -1,6 +1,6 @@
 import { difference } from 'lodash-es';
 
-import type { BlobStorage } from '../../storage';
+import type { BlobRecord, BlobStorage } from '../../storage';
 import { MANUALLY_STOP, throwIfAborted } from '../../utils/throw-if-aborted';
 
 export class BlobSyncEngine {
@@ -11,6 +11,29 @@ export class BlobSyncEngine {
     readonly remotes: BlobStorage[]
   ) {}
 
+  async downloadBlob(blobId: string, signal?: AbortSignal) {
+    const localBlob = await this.local.get(blobId, signal);
+    if (localBlob) {
+      return localBlob;
+    }
+
+    for (const storage of this.remotes) {
+      const data = await storage.get(blobId, signal);
+      if (data) {
+        await this.local.set(data, signal);
+        return data;
+      }
+    }
+    return null;
+  }
+
+  async uploadBlob(blob: BlobRecord, signal?: AbortSignal) {
+    await this.local.set(blob);
+    await Promise.allSettled(
+      this.remotes.map(remote => remote.set(blob, signal))
+    );
+  }
+
   private async sync(signal?: AbortSignal) {
     throwIfAborted(signal);
 
@@ -94,4 +117,9 @@ export class BlobSyncEngine {
     this.abort?.abort();
     this.abort = null;
   }
+
+  addPriority(_id: string, _priority: number): () => void {
+    // TODO: implement
+    return () => {};
+  }
 }