Gallery.app : Truncates the file after a blob of new image is created.

ui/file_manager/gallery/js/gallery_item.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * Object representing an image item (a photo).
  *
  * @param {!FileEntry} entry Image entry.
  * @param {!EntryLocation} locationInfo Entry location information.
  * @param {!MetadataItem} metadataItem
@@ skipping 246 matching lines @@
     ImageUtil.metrics.recordEnum(ImageUtil.getMetricName('SaveResult'), 0, 2);
     if (callback)
       callback(false);
   };
 
   var doSave = function(newFile, fileEntry) {
     var metadataPromise = metadataModel.get(
         [fileEntry],
         ['mediaMimeType', 'contentMimeType', 'ifd', 'exifLittleEndian']);
     metadataPromise.then(function(metadataItems) {
+      var metadataItem = metadataItems[0];

[fukino, 2015/03/09 07:12:35]

It's preferred to defer declaring variables until it's not used, so this code
block can be put after createWriter() as before.

Additionally, this block might be able to be a part of (the first part of) the
promise chain. 

[yawano, 2015/03/09 08:40:32]

Changed to put this block in promise chain. In the promise chain, I put this
code block just after a promise which obtains metadata.

+      metadataItem.modificationTime = new Date();
+      var metadataEncoder = ImageEncoder.encodeMetadata(
+          metadataItem, canvas, /* quality for thumbnail*/ 0.8);
+      // Contrary to what one might think 1.0 is not a good default. Opening
+      // and saving an typical photo taken with consumer camera increases
+      // its file size by 50-100%. Experiments show that 0.9 is much better.
+      // It shrinks some photos a bit, keeps others about the same size, but
+      // does not visibly lower the quality.
+      var blob = ImageEncoder.getBlob(canvas, metadataEncoder, 0.9);
+
       fileEntry.createWriter(function(fileWriter) {
-        var writeContent = function() {
-          fileWriter.onwriteend = onSuccess.bind(null, fileEntry);
-          var metadataItem = metadataItems[0];
-          metadataItem.modificationTime = new Date();
-          var metadataEncoder = ImageEncoder.encodeMetadata(
-              metadataItem, canvas, /* quality for thumbnail*/ 0.8);
-          // Contrary to what one might think 1.0 is not a good default. Opening
-          // and saving an typical photo taken with consumer camera increases
-          // its file size by 50-100%. Experiments show that 0.9 is much better.
-          // It shrinks some photos a bit, keeps others about the same size, but
-          // does not visibly lower the quality.
-          fileWriter.write(ImageEncoder.getBlob(canvas, metadataEncoder, 0.9));
-        }.bind(this);
         fileWriter.onerror = function(error) {
+          throw error;

[fukino, 2015/03/09 07:12:35]

Who handles this exception?

[yawano, 2015/03/09 08:40:32]

Done. After checking behavior, this exception is not handled properly. I changed
to use reject() call of Promise.

+        };
+
+        new Promise(function(fulfill) {
+          // Truncates the file if it overwrites.
+          if (!newFile) {

[fukino, 2015/03/09 07:12:34]

optional nit: In if-else statement, inverted condition looks redundant to me
(Especially in simple cases).

[yawano, 2015/03/09 08:40:32]

This promise is a promise to truncate the file to 0 byte if it overwrites. IMHO,
putting the codes of truncating the file (the main part of this promise) first
seems to be more readable for me. WDYT?

+            fileWriter.onwriteend = fulfill;
+            fileWriter.truncate(0);
+          } else {
+            fulfill();
+          }
+        }).then(function() {
+          return new Promise(function(fulfill) {
+            // Writes the data.
+            fileWriter.onwriteend = fulfill;
+            fileWriter.write(blob);
+          });
+        }).then(onSuccess.bind(null, fileEntry))
+        .catch(function(error) {
           onError(error);
           // Disable all callbacks on the first error.
           fileWriter.onerror = null;
           fileWriter.onwriteend = null;
-        };
-        if (newFile) {
-          writeContent();
-        } else {
-          fileWriter.onwriteend = writeContent;
-          fileWriter.truncate(0);
-        }
+        });
       }.bind(this), onError);
     }.bind(this));
   }.bind(this);
 
   var getFile = function(dir, newFile) {
     dir.getFile(name, {create: newFile, exclusive: newFile},
         function(fileEntry) {
           doSave(newFile, fileEntry);
         }.bind(this), onError);
   }.bind(this);
@@ skipping 52 matching lines @@
         return Promise.reject(str('GALLERY_FILE_EXISTS'));
       }, function() {
         return new Promise(
             this.entry_.moveTo.bind(this.entry_, parentDirectory, newFileName));
       }.bind(this));
     }.bind(this));
   }.bind(this)).then(function(entry) {
     this.entry_ = entry;
   }.bind(this));
 };