ActiveStorage::Previewer (original) (raw)

Namespace

Methods

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Attributes

Class Public methods

Implement this method in a concrete subclass. Have it return true when given a blob from which the previewer can generate an image.

Instance Public methods

Override this method in a concrete subclass. Have it yield an attachable preview image (i.e. anything accepted by ActiveStorage::Attached::One#attach). Pass the additional options to the underlying blob that is created.

Source: show | on GitHub

def preview(**options) raise NotImplementedError end

Instance Private methods

Downloads the blob to a tempfile on disk. Yields the tempfile.

Source: show | on GitHub

def download_blob_to_tempfile(&block) blob.open tmpdir: tmpdir, &block end

Executes a system command, capturing its binary output in a tempfile. Yields the tempfile.

Use this method to shell out to a system library (e.g. muPDF or FFmpeg) for preview image generation. The resulting tempfile can be used as the :io value in an attachable Hash:

def preview
  download_blob_to_tempfile do |input|
    draw "my-drawing-command", input.path, "--format", "png", "-" do |output|
      yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
    end
  end
end

The output tempfile is opened in the directory returned by tmpdir.

Source: show | on GitHub

def draw(*argv) open_tempfile do |file| instrument :preview, key: blob.key do capture(*argv, to: file) end

yield file

end end