Processing

Shrine uploaders can define the #process method, which will get called whenever a file is uploaded. It is given the original file, and is expected to return the processed files.

def process(io, context)
  # you can process the original file `io` and return processed file(s)
end

However, when handling files as attachments, the same file is uploaded to temporary and permanent storage. Since we only want to apply the same processing once, we need to branch based on the context.

def process(io, context)
  if context[:action] == :store # promote phase
    # ...
  end
end

The processing plugin simplifies this by allowing us to declaratively define file processing for specified actions.

plugin :processing

process(:store) do |io, context|
  # ...
end

An example of resizing an image using the image_processing library:

require "image_processing/mini_magick"

process(:store) do |io, context|
  io.download do |original|
    ImageProcessing::MiniMagick
      .source(original)
      .resize_to_limit!(800, 800)
  end
end

The declarations are additive and inheritable, so for the same action you can declare multiple blocks, and they will be performed in the same order, with output from previous block being the input to next.

Manually Run Processing

You can manually trigger the defined processing via the uploader by calling #upload or #process and setting :action to the name of your processing block:

uploader.upload(file, action: :store)  # process and upload
uploader.process(file, action: :store) # only process

If you want the result of processing to be multiple files, use the versions plugin.