feat: Add a cache to the AgentGroupAccessChecker

src/authorization/access-checkers/AgentGroupAccessChecker.ts

@@ -1,6 +1,8 @@
-import type { Term } from 'n3';
+import type { Store, Term } from 'n3';
+
 import type { ResourceIdentifier } from '../../ldp/representation/ResourceIdentifier';
 import type { RepresentationConverter } from '../../storage/conversion/RepresentationConverter';
+import type { ExpiringStorage } from '../../storage/keyvalue/ExpiringStorage';
 import { fetchDataset } from '../../util/FetchUtil';
 import { promiseSome } from '../../util/PromiseUtil';
 import { readableToQuads } from '../../util/StreamUtil';
@@ -11,13 +13,23 @@ import { AccessChecker } from './AccessChecker';
 /**
  * Checks if the given WebID belongs to a group that has access.
  * Implements the behaviour of groups from the WAC specification.
+ *
+ * Fetched results will be stored in an ExpiringStorage.
+ *
+ * Requires a storage that can store JS objects.
+ * `expiration` parameter is how long entries in the cache should be stored in seconds, defaults to 3600.
  */
 export class AgentGroupAccessChecker extends AccessChecker {
   private readonly converter: RepresentationConverter;
+  private readonly cache: ExpiringStorage<string, Promise<Store>>;
+  private readonly expiration: number;
 
-  public constructor(converter: RepresentationConverter) {
+  public constructor(converter: RepresentationConverter, cache: ExpiringStorage<string, Promise<Store>>,
+    expiration = 3600) {
     super();
     this.converter = converter;
+    this.cache = cache;
+    this.expiration = expiration * 1000;
   }
 
   public async handle({ acl, rule, credentials }: AccessCheckerArgs): Promise<boolean> {
@@ -42,9 +54,24 @@ export class AgentGroupAccessChecker extends AccessChecker {
     const groupDocument: ResourceIdentifier = { path: /^[^#]*/u.exec(group.value)![0] };
 
     // Fetch the required vCard group file
-    const dataset = await fetchDataset(groupDocument.path, this.converter);
-
-    const quads = await readableToQuads(dataset.data);
+    const quads = await this.fetchCachedQuads(groupDocument.path);
     return quads.countQuads(group, VCARD.terms.hasMember, webId, null) !== 0;
   }
+
+  /**
+   * Fetches quads from the given URL.
+   * Will cache the values for later re-use.
+   */
+  private async fetchCachedQuads(url: string): Promise<Store> {
+    let result = await this.cache.get(url);
+    if (!result) {
+      const prom = (async(): Promise<Store> => {
+        const representation = await fetchDataset(url, this.converter);
+        return readableToQuads(representation.data);
+      })();
+      await this.cache.set(url, prom, this.expiration);
+      result = await prom;
+    }
+    return result;
+  }
 }