Photos Framework requestImageDataForAsset occasionally fails

Question

I'm using the photos framework on iOS8.1 and requesting the image data for the asset using requestImageDataForAsset... Most of the time it works and I get the image data and a dictionary containing what you see below. But sometimes the call completes, but the data is nil and the dictionary contains three generic looking entries.

The calls are performed sequentially and on the same thread. It is not specific to any particular image. The error will happen on images I've successfully opened in the past. Has anyone encountered this?

+ (NSData *)retrieveAssetDataPhotosFramework:(NSURL *)urlMedia resolution:(CGFloat)resolution imageOrientation:(ALAssetOrientation*)imageOrientation {

    __block NSData *iData = nil;

    PHFetchResult *result = [PHAsset fetchAssetsWithALAssetURLs:@[urlMedia] options:nil];
    PHAsset *asset = [result firstObject];

    PHImageManager *imageManager = [PHImageManager defaultManager];
    PHImageRequestOptions *options = [[PHImageRequestOptions alloc]init];
    options.synchronous = YES;
    options.version = PHImageRequestOptionsVersionCurrent;

    @autoreleasepool {
        [imageManager requestImageDataForAsset:asset options:options resultHandler:^(NSData *imageData, NSString *dataUTI, UIImageOrientation orientation, NSDictionary *info) {
            iData = [imageData copy];
            NSLog(@"requestImageDataForAsset returned info(%@)", info);
            *imageOrientation = (ALAssetOrientation)orientation;
        }];
    }

    assert(iData.length != 0);
    return iData;
}

This is the desired result where I get image data and the dictionary of meta data:

requestImageDataForAsset returned info({
    PHImageFileDataKey = <PLXPCShMemData: 0x1702214a0> bufferLength=1753088 dataLength=1749524;
    PHImageFileOrientationKey = 1;
    PHImageFileSandboxExtensionTokenKey = "6e14948c4d0019fbb4d14cc5e021199f724f0323;00000000;00000000;000000000000001a;com.apple.app-sandbox.read;00000001;01000003;000000000009da80;/private/var/mobile/Media/DCIM/107APPLE/IMG_7258.JPG";
    PHImageFileURLKey = "file:///var/mobile/Media/DCIM/107APPLE/IMG_7258.JPG";
    PHImageFileUTIKey = "public.jpeg";
    PHImageResultDeliveredImageFormatKey = 9999;
    PHImageResultIsDegradedKey = 0;
    PHImageResultIsInCloudKey = 0;
    PHImageResultIsPlaceholderKey = 0;
    PHImageResultWantedImageFormatKey = 9999;
})

Here's what I get occasionally. image data is nil. Dictionary contains not so much.

requestImageDataForAsset returned info({
    PHImageResultDeliveredImageFormatKey = 9999;
    PHImageResultIsDegradedKey = 0;
    PHImageResultWantedImageFormatKey = 9999;
})

Answer 1

I had a problem with similar symptoms where requestImageDataForAsset returned nil image data but was also accompanied by a console error message like this:

[Generic] Failed to load image data for asset <PHAsset: 0x13d041940> 87CCAFDC-A0E3-4AC9-AD1C-3F57B897A52E/L0/001 mediaType=1/0, sourceType=2, (113x124), creationDate=2015-06-29 04:56:34 +0000, location=0, hidden=0, favorite=0 with format 9999

In my case, the problem suddenly started happening on a specific device only with assets in iCloud shared albums after upgrading from iOS 10.x to 11.0.3, and since then through to 11.2.5. Thinking that maybe requestImageDataForAsset was trying to use files locally cached in /var/mobile/Media/PhotoData/PhotoCloudSharingData/ (from the info dictionary's PHImageFileURLKey key) and that the cache may be corrupt I thought about how to clear that cache.

Toggling the 'iCloud Photo Sharing' switch in iOS' Settings -> Accounts & Passwords -> iCloud -> Photos seems to have done the trick. requestImageDataForAsset is now working for those previously failing assets.

Update 9th March 2018

I can reproduce this problem now. It seems to occur after restoring a backup from iTunes:

1. Use the iOS app and retrieve photos from an iCloud shared album.
2. Backup the iOS device using iTunes.
3. Restore the backup using iTunes.
4. Using the app again to retrieve the same photos from the iCloud shared album now fails with the above console message.

Toggling the 'iCloud Photo Sharing' switch fixes it still. Presumably the restore process somehow corrupts some cache. I've reported it as Bug 38290463 to Apple.