feat: Add LRUCache for font layout caching

Author: abihf

lib/font/embedded.js

@@ -1,3 +1,4 @@
+import LRUCache from 'lru-cache';
 import PDFFont from '../font';
 
 const toHex = function(num) {
@@ -24,7 +25,9 @@ class EmbeddedFont extends PDFFont {
     this.bbox = this.font.bbox;
 
     if (document.options.fontLayoutCache !== false) {
-      this.layoutCache = Object.create(null);
+      this.layoutCache = new LRUCache({ 
+        max: document.options.fontLayoutMaxCacheSize || 1000
+      });
     }
   }
 
@@ -49,12 +52,12 @@ class EmbeddedFont extends PDFFont {
       return this.layoutRun(text);
     }
     let cached;
-    if ((cached = this.layoutCache[text])) {
+    if ((cached = this.layoutCache.get(text))) {
       return cached;
     }
 
     const run = this.layoutRun(text);
-    this.layoutCache[text] = run;
+    this.layoutCache.set(text, run);
     return run;
   }
 

package.json

@@ -52,6 +52,7 @@
     "fontkit": "^1.8.1",
     "jpeg-exif": "^1.1.4",
     "linebreak": "^1.0.2",
+    "lru-cache": "^7.0.0",
     "png-js": "^1.0.0"
   },
   "scripts": {
@@ -89,4 +90,4 @@
       "<rootDir>/tests/unit/setupTests.js"
     ]
   }
-}
+}

yarn.lock

@@ -5030,6 +5030,11 @@ lru-cache@^6.0.0:
   dependencies:
     yallist "^4.0.0"
 
+lru-cache@^7.0.0:
+  version "7.18.3"
+  resolved "https://registry.yarnpkg.com/lru-cache/-/lru-cache-7.18.3.tgz#f793896e0fd0e954a59dfdd82f0773808df6aa89"
+  integrity sha512-jumlc0BIUrS3qJGgIkWZsyfAM7NCWiBcCDhnd+3NNM5KbBmLTgHVfWBcg6W+rLUsIpzpERPsvwUP7CckAQSOoA==
+
 [email protected]:
   version "0.25.1"
   resolved "https://registry.yarnpkg.com/magic-string/-/magic-string-0.25.1.tgz#b1c248b399cd7485da0fe7385c2fc7011843266e"