Replace the AnnotationStorage.lastModified-getter with a proper hash-method

The current `lastModified`-getter, which only contains a time-stamp, is a fairly crude way of detecting if the stored data has actually been changed. In particular, when the `getRawValue`-method is used, the `lastModified`-getter doesn't cope with data being modified from the "outside".

To fix these issues[1], and to prevent any future bugs in this code, this patch introduces a new `AnnotationStorage.hash`-getter which computes a hash of the currently stored data. To simplify things this re-uses the existing `MurmurHash3_64`-implementation, which required moving that file into the `src/shared/`-folder, since its performance should be good enough here.

---
[1] Given how the `AnnotationStorage.lastModified`-getter was used, this would have been limited to *printing* of forms.

src/core/evaluator.js

@@ -75,7 +75,7 @@ import { DecodeStream } from "./decode_stream.js";
 import { getGlyphsUnicode } from "./glyphlist.js";
 import { getLookupTableFactory } from "./core_utils.js";
 import { getMetrics } from "./metrics.js";
-import { MurmurHash3_64 } from "./murmurhash3.js";
+import { MurmurHash3_64 } from "../shared/murmurhash3.js";
 import { OperatorList } from "./operator_list.js";
 import { PDFImage } from "./image.js";
 

src/display/annotation_storage.js

@@ -13,6 +13,7 @@
  * limitations under the License.
  */
 
+import { MurmurHash3_64 } from "../shared/murmurhash3.js";
 import { objectFromMap } from "../shared/util.js";
 
 /**
@@ -21,7 +22,6 @@ import { objectFromMap } from "../shared/util.js";
 class AnnotationStorage {
   constructor() {
     this._storage = new Map();
-    this._timeStamp = Date.now();
     this._modified = false;
 
     // Callbacks to signal when the modification state is set or reset.
@@ -85,7 +85,6 @@ class AnnotationStorage {
       this._storage.set(key, value);
     }
     if (modified) {
-      this._timeStamp = Date.now();
       this._setModified();
     }
   }
@@ -131,8 +130,13 @@ class AnnotationStorage {
    * PLEASE NOTE: Only intended for usage within the API itself.
    * @ignore
    */
-  get lastModified() {
-    return this._timeStamp.toString();
+  get hash() {
+    const hash = new MurmurHash3_64();
+
+    for (const [key, value] of this._storage) {
+      hash.update(`${key}:${JSON.stringify(value)}`);
+    }
+    return hash.hexdigest();
   }
 }
 

src/display/api.js

@@ -2402,7 +2402,7 @@ class WorkerTransport {
     isOpList = false
   ) {
     let renderingIntent = RenderingIntentFlag.DISPLAY; // Default value.
-    let lastModified = "";
+    let annotationHash = "";
 
     switch (intent) {
       case "any":
@@ -2429,7 +2429,7 @@ class WorkerTransport {
       case AnnotationMode.ENABLE_STORAGE:
         renderingIntent += RenderingIntentFlag.ANNOTATIONS_STORAGE;
 
-        lastModified = this.annotationStorage.lastModified;
+        annotationHash = this.annotationStorage.hash;
         break;
       default:
         warn(`getRenderingIntent - invalid annotationMode: ${annotationMode}`);
@@ -2441,7 +2441,7 @@ class WorkerTransport {
 
     return {
       renderingIntent,
-      cacheKey: `${renderingIntent}_${lastModified}`,
+      cacheKey: `${renderingIntent}_${annotationHash}`,
     };
   }
 

src/shared/murmurhash3.js

@@ -17,7 +17,7 @@
  * Hashes roughly 100 KB per millisecond on i7 3.4 GHz.
  */
 
-import { isArrayBuffer } from "../shared/util.js";
+import { isArrayBuffer } from "./util.js";
 
 const SEED = 0xc3d2e1f0;
 // Workaround for missing math precision in JS.

test/unit/murmurhash3_spec.js

@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 
-import { MurmurHash3_64 } from "../../src/core/murmurhash3.js";
+import { MurmurHash3_64 } from "../../src/shared/murmurhash3.js";
 
 describe("MurmurHash3_64", function () {
   it("instantiates without seed", function () {