Display image uploaded to S3 with Carrierwave/Sidekiq after form submit

Question

I'm using Sidekiq with CarrierWave and CarrierWaveBackgrounder to upload my images to S3 in the background. This works fine except for one thing: after I submit my form, the image gets enqueued in Sidekiq and processed, but the page reload happens faster than the background job, resulting in a 404 on the uploaded image. After another page refresh, the image usually shows up.

I'm wondering if there's a way to either show a tmp file (I have a image_tmp column in my database which seems to store a path to the file while it's processing/uploading), or reload my image after the processing is done.

I could poll my database for 'image_processing' to change to true, but that seems a bit like a waste of requests.

Relevant parts of my User class:

mount_uploader :profile_image, ProfileImageUploader

process_in_background :profile_image
store_in_background :profile_image

ProfileImageUploader includes Backgrounder

class ProfileImageUploader < CarrierWave::Uploader::Base

  include ::CarrierWave::Backgrounder::Delay
  include CarrierWave::MiniMagick

My db has fields for profile_image_processing and profile_image_tmp, as well as, of course, a profile_image column.

Answer 1

I have solved this by polling for the image_processing attribute. My image upload partial looks like this:

.form-group{ :class => (f.error field) ? "has-feedback has-error" : nil }
  = f.label field, :class => "col-md-3 control-label"

  .col-md-9
    = f.label field do
      = image_tag('ajax-loader.gif', class: 'image-loader hidden')
      - unless resource.image.blank?
        %p= image_tag(resource.image.thumb.url, data: { poll: resource.image_processing })
      - else
        %p No image uploaded yet.

      = f.input_field field, :as => :file
    %span.help-inline
      = f.error field, :class => "help-inline"

I then hook into the data-pollattribute with the following CoffeeScript class:

$ ->

  class ImagePoller

    constructor: (@$el) ->
      @$loader      = @$el.prev('.image-loader')
      @timer        = null
      @processing   = JSON.parse @$el.attr('data-poll')

      @resourcePath = "#{window.location.href}.json"

      @startPolling() if @processing

    startPolling: =>
      if @processing
        @toggleLoader()
        @$el.hide()
        @timer = setInterval =>
          promise = $.getJSON @resourcePath
          promise.done (data) =>
            @processing = data.image_processing
            @fetchImage(data.image.thumb.url) if not @processing
        , 100

    fetchImage: (image) ->
      clearInterval @timer
      @toggleLoader()
      @$el.attr 'src', image
      @$el.show()

    toggleLoader: ->
      @$loader.toggle()

  $('[data-poll]').each ->
    new ImagePoller $(@)

Seems to work fine for my purposes.