fix: Update acl authorizer to make write rights imply append rights

src/authorization/WebAclAuthorizer.ts

@@ -64,7 +64,13 @@ export class WebAclAuthorizer extends Authorizer {
    */
   private checkPermission(agent: Credentials, store: Store, mode: string): void {
     const modeString = ACL[this.capitalize(mode) as 'Write' | 'Read' | 'Append' | 'Control'];
-    const auths = store.getQuads(null, ACL.mode, modeString, null).map((quad: Quad): Term => quad.subject);
+    const auths = this.getModePermissions(store, modeString);
+
+    // Having write permissions implies having append permissions
+    if (modeString === ACL.Append) {
+      auths.push(...this.getModePermissions(store, ACL.Write));
+    }
+
     if (!auths.some((term): boolean => this.hasAccess(agent, term, store))) {
       const isLoggedIn = typeof agent.webId === 'string';
       if (isLoggedIn) {
@@ -87,6 +93,15 @@ export class WebAclAuthorizer extends Authorizer {
     return `${mode[0].toUpperCase()}${mode.slice(1).toLowerCase()}`;
   }
 
+  /**
+   * Returns the identifiers of all authorizations that grant the given mode access for a resource.
+   * @param store - The store containing the quads of the acl resource.
+   * @param aclMode - A valid acl mode (ACL.Write/Read/...)
+   */
+  private getModePermissions(store: Store, aclMode: string): Term[] {
+    return store.getQuads(null, ACL.mode, aclMode, null).map((quad: Quad): Term => quad.subject);
+  }
+
   /**
    * Checks if the given agent has access to the modes specified by the given authorization.
    * @param agent - Credentials of agent that needs access.

test/unit/authorization/WebAclAuthorizer.test.ts

@@ -155,4 +155,20 @@ describe('A WebAclAuthorizer', (): void => {
     await expect(promise).rejects.toThrow('No ACL document found for root container');
     await expect(promise).rejects.toThrow(InternalServerError);
   });
+
+  it('allows an agent to append if they have write access.', async(): Promise<void> => {
+    credentials.webId = 'http://test.com/user';
+    identifier.path = 'http://test.com/foo';
+    permissions = {
+      read: false,
+      write: false,
+      append: true,
+    };
+    store.getRepresentation = async(): Promise<Representation> => ({ data: streamifyArray([
+      quad(nn('auth'), nn(`${acl}agent`), nn(credentials.webId!)),
+      quad(nn('auth'), nn(`${acl}accessTo`), nn(identifier.path)),
+      quad(nn('auth'), nn(`${acl}mode`), nn(`${acl}Write`)),
+    ]) } as Representation);
+    await expect(authorizer.handle({ identifier, permissions, credentials })).resolves.toBeUndefined();
+  });
 });