Active Storage Previewer
This is an abstract base class for previewers, which generate images from blobs. See ActiveStorage::Previewer::MuPDFPreviewer
and ActiveStorage::Previewer::VideoPreviewer
for examples of concrete subclasses.
- CLASS ActiveStorage::Previewer::MuPDFPreviewer
- CLASS ActiveStorage::Previewer::PopplerPDFPreviewer
- CLASS ActiveStorage::Previewer::VideoPreviewer
Attributes
[R] | blob |
Class Public methods
accept?(blob) Link
Implement this method in a concrete subclass. Have it return true when given a blob from which the previewer can generate an image.
new(blob) Link
Instance Public methods
preview(**options) Link
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.
Instance Private methods
download_blob_to_tempfile(&block) Link
Downloads the blob to a tempfile on disk. Yields the tempfile.
draw(*argv) Link
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
.