Stories: add bounds check in saving, don't process an empty Story block

[mzorz]

Fixes #13678

The problem is there seem to be Posts with empty Story blocks in their content:

    <!-- wp:jetpack/story -->
    <div class="wp-block-jetpack-story wp-story"></div>
    <!-- /wp:jetpack/story -->

Therefore, when the findAllStoryBlocksInPostAndPerformOnEachMediaFilesJson iterator tries to find the mediaFiles attribute within the block, it fails to do so (the code is not really prepared to expect a non-existent mediaFiles attribute).

This PR adds a check to avoid processing mediaFiles for a block that simply doesn't contain any (that is, an empty block that hasn't been assigned any media files yet).

To test:

1. create a new Post
2. add a Story block, but don't do anything with it to it's left empty
3. add a media block (image block, video block)
4. add a media item to it
5. while it's uploading, exit the editor
6. observe it doesn't crash and finalizes uploads correctly
7. check on your site and observe the Post renders correctly

Note: I noticed once the post may be uploaded containing a local path to the media file, but I haven't been able to reproduce, and is unrelated to this particular change.

Regression Notes

1. Potential unintended areas of impact

Uploads of media when a Story block is also on the same Post.

2. What I did to test those areas of impact (or what existing automated tests I relied on)

Tried uploading media (Image block) manually.

3. What automated tests I added (or what prevented me from doing so)

Added a unit test to check that if a Story block contains no mediaFiles array (as is the case for a Story block that has been added through the Block Picker on Gutenberg mobile), then do not try to process the array.

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[mzorz]

@renanferrari requesting your review since we were able to detect this one after your logging work done on #14185 and #14191 👍

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APK here.

[renanferrari]

Hey @mzorz, thanks once again for submitting this and for keeping me in the loop on this issue!

Code looks good and I can confirm your changes prevent the app from crashing, as it was expected. However, I noticed that even though the image upload seems to complete successfully, it still doesn't show up in the post. This is what I get instead:

On this particular post, that empty media block remained there, but in another post, it was just blank:

I'm not sure if that's the unrelated error you mentioned where the post is uploaded containing a local path to the media file or if it's something else. Other than that, everything is working as expected.

[mzorz]

Thanks for testing @renanferrari ! 🙇

I'm not sure if that's the unrelated error you mentioned where the post is uploaded containing a local path to the media file or if it's something else. Other than that, everything is working as expected.

TBH I'm not sure why in one case the placeholder is shown (seems to be the block is valid though) - second image shows probably a valid block and it found the image but couldn't render it somehow, wondering are you able to select the block?

But yes in any case it's an unrelated problem 👍

[renanferrari]

wondering are you able to select the block?

Yes, I'm actually able to select the block in both cases:

But yes in any case it's an unrelated problem 👍

In this case, feel free to merge this once all the checks have been completed. Great job on fixing these issues 👍

[mzorz]

Thank you @renanferrari 🙇