feat(decoder): add comment support (jpeg-js#71)

Author: sparticvs

lib/decoder.js

@@ -623,6 +623,7 @@ var JpegImage = (function jpegImage() {
       var quantizationTables = [], frames = [];
       var huffmanTablesAC = [], huffmanTablesDC = [];
       var fileMarker = readUint16();
+      this.comments = [];
       if (fileMarker != 0xFFD8) { // SOI (Start of Image)
         throw new Error("SOI not found");
       }
@@ -651,6 +652,11 @@ var JpegImage = (function jpegImage() {
           case 0xFFFE: // COM (Comment)
             var appData = readDataBlock();
 
+            if (fileMarker === 0xFFFE) {
+              var comment = String.fromCharCode.apply(null, appData);
+              this.comments.push(comment);
+            }
+
             if (fileMarker === 0xFFE0) {
               if (appData[0] === 0x4A && appData[1] === 0x46 && appData[2] === 0x49 &&
                 appData[3] === 0x46 && appData[4] === 0) { // 'JFIF\x00'
@@ -1096,6 +1102,9 @@ function decode(jpegData, userOpts = {}) {
         new Uint8Array(bytesNeeded) :
         new Buffer(bytesNeeded)
     };
+    if(decoder.comments.length > 0) {
+      image["comments"] = decoder.comments;
+    }
   } catch (err){
     if (err instanceof RangeError){
       throw new Error("Could not allocate enough memory for the image. " +

test/index.js

@@ -49,6 +49,7 @@ it('should be able to decode a grayscale JPEG', function () {
   var rawImageData = jpeg.decode(jpegData);
   expect(rawImageData.width).toEqual(580);
   expect(rawImageData.height).toEqual(599);
+  expect(rawImageData.comments).toEqual(['File source: http://commons.wikimedia.org/wiki/File:Apsara-mit-Sitar.jpg']);
   var expected = fixture('apsara.rgba');
   expect(rawImageData.data).toEqual(expected);
 });