free memory after image decode

README.md

@@ -57,9 +57,14 @@ const decode = require('heic-decode');
       data    // Uint8ClampedArray containing pixel data
     } = await image.decode();
   }
+
+  // when you are done, make sure to free all memory used to convert the images
+  images.dispose();
 })();
 ```
 
+> Note: when decoding a single image (i.e. using `decode`), all resources are freed automatically after the conversion. However, when decoding all images in a file (i.e. using `decode.all`), you can decode the images at any time, so there is no safe time for the library to free resources -- you need to make sure to call `dispose` once you are done.
+
 When the images are decoded, the return value is a plain object in the format of [`ImageData`](https://developer.mozilla.org/en-US/docs/Web/API/ImageData). You can use this object to integrate with other imaging libraries for processing.
 
 _Note that while the decoder returns a Promise, it does the majority of the work synchronously, so you should consider using a worker thread in order to not block the main thread in highly concurrent production environments._

lib.js

@@ -53,20 +53,37 @@ module.exports = libheif => {
     const decoder = new libheif.HeifDecoder();
     const data = decoder.decode(buffer);
 
+    const dispose = () => {
+      for (const image of data) {
+        image.free();
+      }
+
+      decoder.decoder.delete();
+    };
+
     if (!data.length) {
       throw new Error('HEIF image not found');
     }
 
     if (!all) {
-      return await decodeImage(data[0]);
+      try {
+        return await decodeImage(data[0]);
+      } finally {
+        dispose();
+      }
     }
 
-    return data.map(image => {
+    return Object.defineProperty(data.map(image => {
       return {
         width: image.get_width(),
         height: image.get_height(),
         decode: async () => await decodeImage(image)
       };
+    }), 'dispose', {
+      enumerable: false,
+      configurable: false,
+      writable: false,
+      value: dispose
     });
   };
 

package.json

@@ -25,7 +25,7 @@
   },
   "homepage": "https://github.com/catdad-experiments/heic-decode#readme",
   "dependencies": {
-    "libheif-js": "^1.17.1"
+    "libheif-js": "^1.19.8"
   },
   "devDependencies": {
     "buffer-to-uint8array": "^1.1.0",

test/index.test.js

@@ -63,6 +63,7 @@ function runTests(decode) {
     const images = await decode.all({ buffer });
 
     expect(images).to.have.lengthOf(3);
+    expect(images).to.have.property('dispose').and.to.be.a('function');
 
     const controls = await Promise.all([
       readControl('0003-0-control.png'),
@@ -86,6 +87,8 @@ function runTests(decode) {
 
       compare(control.data, image.data, control.width, control.height, `actual image at index ${i} did not match control`);
     }
+
+    images.dispose();
   });
 
   it('throws if data other than a HEIC image is passed in', async () => {