refactor: Simplify MethodPermissionsExtractor

src/ldp/permissions/MethodPermissionsExtractor.ts

@@ -3,30 +3,24 @@ import { Operation } from '../operations/Operation';
 import { PermissionSet } from './PermissionSet';
 import { PermissionsExtractor } from './PermissionsExtractor';
 
+const READ_METHODS = new Set([ 'GET', 'HEAD' ]);
+const WRITE_METHODS = new Set([ 'POST', 'PUT', 'DELETE' ]);
+const SUPPORTED_METHODS = new Set([ ...READ_METHODS, ...WRITE_METHODS ]);
+
 /**
  * Generates permissions for the base set of methods that always require the same permissions.
  * Specifically: GET, HEAD, POST, PUT and DELETE.
  */
 export class MethodPermissionsExtractor extends PermissionsExtractor {
-  public async canHandle(input: Operation): Promise<void> {
+  public async canHandle({ method }: Operation): Promise<void> {
-    if (!/^(?:HEAD|GET|POST|PUT|DELETE)$/u.test(input.method)) {
+    if (!SUPPORTED_METHODS.has(method)) {
-      throw new UnsupportedHttpError(`Unsupported method: ${input.method}`);
+      throw new UnsupportedHttpError(`Cannot determine permissions of ${method}`);
     }
   }
 
-  public async handle(input: Operation): Promise<PermissionSet> {
+  public async handle({ method }: Operation): Promise<PermissionSet> {
-    const requiredPermissions = {
+    const read = READ_METHODS.has(method);
-      read: /^(?:HEAD|GET)$/u.test(input.method),
+    const write = WRITE_METHODS.has(method);
-      append: false,
+    return { read, write, append: write };
-      write: /^(?:POST|PUT|DELETE)$/u.test(input.method),
-    };
-
-    const read = /^(?:HEAD|GET)$/u.test(input.method);
-    const write = /^(?:POST|PUT|DELETE)$/u.test(input.method);
-
-    // Since `append` is a specific type of write, it is true if `write` is true.
-    const append = requiredPermissions.write;
-
-    return { read, append, write };
   }
 }