feat: Introduce internal storing mechanism

src/storage/keyvalue/JsonResourceStorage.ts

@@ -0,0 +1,64 @@
+import { BasicRepresentation } from '../../ldp/representation/BasicRepresentation';
+import type { ResourceIdentifier } from '../../ldp/representation/ResourceIdentifier';
+import { NotFoundHttpError } from '../../util/errors/NotFoundHttpError';
+import { readableToString } from '../../util/StreamUtil';
+import type { ResourceStore } from '../ResourceStore';
+import type { KeyValueStorage } from './KeyValueStorage';
+
+/**
+ * A {@link KeyValueStorage} for strings using a {@link ResourceStore} as backend.
+ *
+ * Values will be sent as data streams to the given identifiers,
+ * so how these are stored depend on the underlying store.
+ *
+ * All non-404 errors will be re-thrown.
+ */
+export class JsonResourceStorage implements KeyValueStorage<ResourceIdentifier, unknown> {
+  private readonly source: ResourceStore;
+
+  public constructor(source: ResourceStore) {
+    this.source = source;
+  }
+
+  public async get(identifier: ResourceIdentifier): Promise<unknown | undefined> {
+    try {
+      const representation = await this.source.getRepresentation(identifier, { type: { 'application/json': 1 }});
+      return JSON.parse(await readableToString(representation.data));
+    } catch (error: unknown) {
+      if (!NotFoundHttpError.isInstance(error)) {
+        throw error;
+      }
+    }
+  }
+
+  public async has(identifier: ResourceIdentifier): Promise<boolean> {
+    try {
+      const representation = await this.source.getRepresentation(identifier, { type: { 'application/json': 1 }});
+      representation.data.destroy();
+      return true;
+    } catch (error: unknown) {
+      if (!NotFoundHttpError.isInstance(error)) {
+        throw error;
+      }
+      return false;
+    }
+  }
+
+  public async set(identifier: ResourceIdentifier, value: unknown): Promise<this> {
+    const representation = new BasicRepresentation(JSON.stringify(value), identifier, 'application/json');
+    await this.source.setRepresentation(identifier, representation);
+    return this;
+  }
+
+  public async delete(identifier: ResourceIdentifier): Promise<boolean> {
+    try {
+      await this.source.deleteResource(identifier);
+      return true;
+    } catch (error: unknown) {
+      if (!NotFoundHttpError.isInstance(error)) {
+        throw error;
+      }
+      return false;
+    }
+  }
+}