From 8267fd8a524b08ab1ef4e5cca918aff984a21875 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Wed, 4 May 2022 15:03:46 +0200
Subject: [PATCH] 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               |  2 +-
 src/display/annotation_storage.js   | 12 ++++++++----
 src/display/api.js                  |  6 +++---
 src/{core => shared}/murmurhash3.js |  2 +-
 test/unit/murmurhash3_spec.js       |  2 +-
 5 files changed, 14 insertions(+), 10 deletions(-)
 rename src/{core => shared}/murmurhash3.js (98%)

diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index b9b55c8e6..68dcab9aa 100644
--- a/src/core/evaluator.js
+++ b/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";
 
diff --git a/src/display/annotation_storage.js b/src/display/annotation_storage.js
index 43099079b..458dceadc 100644
--- a/src/display/annotation_storage.js
+++ b/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();
   }
 }
 
diff --git a/src/display/api.js b/src/display/api.js
index 9c4c5f0b5..89ef148a2 100644
--- a/src/display/api.js
+++ b/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}`,
     };
   }
 
diff --git a/src/core/murmurhash3.js b/src/shared/murmurhash3.js
similarity index 98%
rename from src/core/murmurhash3.js
rename to src/shared/murmurhash3.js
index fca00f0f0..f8412ad9f 100644
--- a/src/core/murmurhash3.js
+++ b/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.
diff --git a/test/unit/murmurhash3_spec.js b/test/unit/murmurhash3_spec.js
index a665b165b..ed8777b34 100644
--- a/test/unit/murmurhash3_spec.js
+++ b/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 () {