ActiveStorage attachment not ready while Broadcasting

rubyonrails-talk
#1

I’ve encountered an issue while trying to broadcast the creation of a new image in our system. The Image model is mind, and it has_one_attached :file. I broadcast its creation via:

after_create_commit do
    broadcast_append_later_to article.online_newsletter, target: ActionView::RecordIdentifier.dom_id(article, :images),
      partial: 'online_newsletters/articles/image', locals: { editable: true }
  end

The partial is approximately:

<%= link_to image.file.variant(resize_to_limit: [2880, 2880]), data: {
  fancybox: dom_id(image.article, :images), caption: image.caption, download_src: url_for(image.file) } do %>
  <%= image_tag image.file.variant(resize_to_fill: [480, 320, crop: :attention]), class: 'is-cropped' %>
<% end %>

Unfortunately, even though the record is committed, the attachment hasn’t uploaded to S3 yet so the request for the image variant becomes a 500 error:

ActiveStorage::FileNotFoundError - ActiveStorage::FileNotFoundError

Is there a way to wait until we know that the image is in S3 before broadcasting the update? I notice that if I update the page with a turbo-stream from the controller to the user that added the image then it works just fine. I’m not sure if this is just a timing coincidence or if the request waits for the image to be in S3 before rendering the view?

Also, given dom_id is so useful in both the controller and model context now, how come it’s not required into those contexts by default? :slight_smile:

#2

Hey @Spike,

It looks like you can check this by utilizing the current active storage service. Here’s an example:

ActiveStorage::Blob.service.exist?(image.file.key)

This worked fine with simple disk storage and it looks like the S3 adapter has an implementation for that method too.

Ref:

#3

Interesting @nickhammond :slight_smile: So I suppose I could wrap that check in a while loop to delay the delivery of the broadcast until the file exists? Probably would need to throttle that though! :smiley:

Bit of a shame that there’s no hook bubbled up to the model when the file has been stored.

#4

@Spike Yah, I was thinking there’d be a stored_at or uploaded_at timestamp in the attachments table but there’s not weirdly, be a great PR though. The other use case though for this method is if that file is removed from the storage service for whatever reason you can check that.

#5

Digging into this deeper, it seems that sometimes Amazon S3 will return a 404 if we ask it for a variant too quickly after the file upload has been processed even with something like this:

  after_create_commit prepend: true do
    if file.blob.service.exist?(file.key)
      broadcast_append_to article.online_newsletter, target: dom_id(article, :images),
        partial: 'online_newsletters/articles/image', locals: { editable: true }
    end
  end
#6

I’ve found that calling .processed on the variant to force it to be created at render time is the way around this issue:

<%= image_tag image.file.variant(resize_to_fill: [480, 320, crop: :attention]).processed, class: 'is-cropped' %>

Using one of the active job broadcast methods would make this less contentious :slight_smile:

I should mention that the prepend: true on after_*_commit is very important if you’re using .processed as otherwise the file won’t exist yet.