fix: Support new ETag format in notification states

src/server/notifications/ComposedNotificationHandler.ts

@@ -1,3 +1,4 @@
+import { sameResourceState } from '../../storage/Conditions';
 import type { NotificationGenerator } from './generate/NotificationGenerator';
 import type { NotificationEmitter } from './NotificationEmitter';
 import type { NotificationHandlerInput } from './NotificationHandler';
@@ -37,7 +38,7 @@ export class ComposedNotificationHandler extends NotificationHandler {
 
     const { state } = input.channel;
     // In case the state matches there is no need to send the notification
-    if (typeof state === 'string' && state === notification.state) {
+    if (typeof state === 'string' && notification.state && sameResourceState(state, notification.state)) {
       return;
     }
 

src/storage/BasicConditions.ts

@@ -1,6 +1,6 @@
 import type { RepresentationMetadata } from '../http/representation/RepresentationMetadata';
 import { DC } from '../util/Vocabularies';
-import { getETag, isCurrentETag } from './Conditions';
+import { getETag, sameResourceState } from './Conditions';
 import type { Conditions } from './Conditions';
 
 export interface BasicConditionsOptions {
@@ -39,11 +39,12 @@ export class BasicConditions implements Conditions {
       return false;
     }
 
+    const eTag = getETag(metadata);
+    if (eTag) {
       // Helper function to see if an ETag matches the provided metadata
       // eslint-disable-next-line func-style
-    let eTagMatches = (tag: string): boolean => isCurrentETag(tag, metadata);
+      let eTagMatches = (tag: string): boolean => sameResourceState(tag, eTag);
       if (strict) {
-      const eTag = getETag(metadata);
         eTagMatches = (tag: string): boolean => tag === eTag;
       }
 
@@ -53,6 +54,7 @@ export class BasicConditions implements Conditions {
       if (this.notMatchesETag?.some(eTagMatches)) {
         return false;
       }
+    }
 
     // In practice, this will only be undefined on a backend
     // that doesn't store the modified date.

src/storage/Conditions.ts

@@ -42,31 +42,21 @@ export interface Conditions {
 export function getETag(metadata: RepresentationMetadata): string | undefined {
   const modified = metadata.get(DC.terms.modified);
   const { contentType } = metadata;
-  if (modified && contentType) {
+  if (modified) {
     const date = new Date(modified.value);
-    return `"${date.getTime()}-${contentType}"`;
+    // It is possible for the content type to be undefined,
+    // such as when only the metadata returned by a `DataAccessor` is used.
+    return `"${date.getTime()}-${contentType ?? ''}"`;
   }
 }
 
 /**
- * Validates whether a given ETag corresponds to the current state of the resource,
- * independent of the representation the ETag corresponds to.
+ * Validates whether 2 ETags correspond to the same state of a resource,
+ * independent of the representation the ETags correspond to.
  * Assumes ETags are made with the {@link getETag} function.
- * Since we base the ETag on the last modified date,
- * we know the ETag still matches as long as that didn't change.
- *
- * @param eTag - ETag to validate.
- * @param metadata - Metadata of the resource.
- *
- * @returns `true` if the ETag represents the current state of the resource.
  */
-export function isCurrentETag(eTag: string, metadata: RepresentationMetadata): boolean {
-  const modified = metadata.get(DC.terms.modified);
-  if (!modified) {
-    return false;
-  }
-  const time = eTag.split('-', 1)[0];
-  const date = new Date(modified.value);
-  // `time` will still have the initial`"` of the ETag string
-  return time === `"${date.getTime()}`;
+export function sameResourceState(eTag1: string, eTag2: string): boolean {
+  // Since we base the ETag on the last modified date,
+  // we know the ETags match as long as the date part is the same.
+  return eTag1.split('-')[0] === eTag2.split('-')[0];
 }

test/unit/server/notifications/ComposedNotificationHandler.test.ts

@@ -18,7 +18,7 @@ describe('A ComposedNotificationHandler', (): void => {
     type: 'Update',
     object: 'http://example.com/foo',
     published: '123',
-    state: '123',
+    state: '"123456-text/turtle"',
   };
   let channel: NotificationChannel;
   const representation = new BasicRepresentation();
@@ -66,8 +66,8 @@ describe('A ComposedNotificationHandler', (): void => {
     expect(emitter.handleSafe).toHaveBeenLastCalledWith({ channel, representation });
   });
 
-  it('does not emit the notification if its state matches the channel state.', async(): Promise<void> => {
-    channel.state = notification.state;
+  it('does not emit the notification if it has the same resource state as the channel.', async(): Promise<void> => {
+    channel.state = '"123456-application/ld+json"';
     await expect(handler.handle({ channel, topic })).resolves.toBeUndefined();
     expect(generator.handle).toHaveBeenCalledTimes(1);
     expect(generator.handle).toHaveBeenLastCalledWith({ channel, topic });

test/unit/storage/Conditions.test.ts

@@ -1,5 +1,5 @@
 import { RepresentationMetadata } from '../../../src/http/representation/RepresentationMetadata';
-import { getETag, isCurrentETag } from '../../../src/storage/Conditions';
+import { getETag, sameResourceState } from '../../../src/storage/Conditions';
 import { CONTENT_TYPE, DC } from '../../../src/util/Vocabularies';
 
 describe('Conditions', (): void => {
@@ -13,41 +13,32 @@ describe('Conditions', (): void => {
       expect(getETag(metadata)).toBe(`"${now.getTime()}-text/turtle"`);
     });
 
-    it('returns undefined if no date or content-type was found.', async(): Promise<void> => {
+    it('creates a simpler ETag if no content type was found.', async(): Promise<void> => {
       const now = new Date();
+      expect(getETag(new RepresentationMetadata({ [DC.modified]: now.toISOString() }))).toBe(`"${now.getTime()}-"`);
+    });
+
+    it('returns undefined if no date found.', async(): Promise<void> => {
       expect(getETag(new RepresentationMetadata())).toBeUndefined();
-      expect(getETag(new RepresentationMetadata({ [DC.modified]: now.toISOString() }))).toBeUndefined();
       expect(getETag(new RepresentationMetadata({ [CONTENT_TYPE]: 'text/turtle' }))).toBeUndefined();
     });
   });
 
-  describe('#isCurrentETag', (): void => {
-    const now = new Date();
+  describe('sameResourceState', (): void => {
+    const eTag = '"123456-text/turtle"';
+    const eTagJson = '"123456-application/ld+json"';
+    const eTagWrongTime = '"654321-text/turtle"';
 
-    it('compares an ETag with the current resource state.', async(): Promise<void> => {
-      const metadata = new RepresentationMetadata({
-        [DC.modified]: now.toISOString(),
-        [CONTENT_TYPE]: 'text/turtle',
-      });
-      const eTag = getETag(metadata)!;
-      expect(isCurrentETag(eTag, metadata)).toBe(true);
-      expect(isCurrentETag('"ETag"', metadata)).toBe(false);
+    it('returns true if the ETags are the same.', async(): Promise<void> => {
+      expect(sameResourceState(eTag, eTag)).toBe(true);
     });
 
-    it('ignores the content-type.', async(): Promise<void> => {
-      const metadata = new RepresentationMetadata({
-        [DC.modified]: now.toISOString(),
-        [CONTENT_TYPE]: 'text/turtle',
-      });
-      const eTag = getETag(metadata)!;
-      metadata.contentType = 'application/ld+json';
-      expect(isCurrentETag(eTag, metadata)).toBe(true);
-      expect(isCurrentETag('"ETag"', metadata)).toBe(false);
+    it('returns true if the ETags target the same timestamp.', async(): Promise<void> => {
+      expect(sameResourceState(eTag, eTagJson)).toBe(true);
     });
 
-    it('returns false if the metadata has no last modified date.', async(): Promise<void> => {
-      const metadata = new RepresentationMetadata();
-      expect(isCurrentETag('"ETag"', metadata)).toBe(false);
+    it('returns false if the timestamp differs.', async(): Promise<void> => {
+      expect(sameResourceState(eTag, eTagWrongTime)).toBe(false);
     });
   });
 });