a470317b2c
Clarify that it's public API intended for use by third-party previewers. It shouldn't be removed without deprecation even though it isn't used by the built-in previewers.
63 lines
1.9 KiB
Ruby
63 lines
1.9 KiB
Ruby
# frozen_string_literal: true
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require "active_storage/downloading"
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module ActiveStorage
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# This is an abstract base class for previewers, which generate images from blobs. See
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# ActiveStorage::Previewer::PDFPreviewer and ActiveStorage::Previewer::VideoPreviewer for examples of
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# concrete subclasses.
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class Previewer
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include Downloading
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attr_reader :blob
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# Implement this method in a concrete subclass. Have it return true when given a blob from which
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# the previewer can generate an image.
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def self.accept?(blob)
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false
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end
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def initialize(blob)
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@blob = blob
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end
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# Override this method in a concrete subclass. Have it yield an attachable preview image (i.e.
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# anything accepted by ActiveStorage::Attached::One#attach).
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def preview
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raise NotImplementedError
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end
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private
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# Executes a system command, capturing its binary output in a tempfile. Yields the tempfile.
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#
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# Use this method to shell out to a system library (e.g. mupdf or ffmpeg) for preview image
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# generation. The resulting tempfile can be used as the +:io+ value in an attachable Hash:
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#
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# def preview
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# download_blob_to_tempfile do |input|
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# draw "my-drawing-command", input.path, "--format", "png", "-" do |output|
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# yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
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# end
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# end
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# end
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#
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# The output tempfile is opened in the directory returned by ActiveStorage::Downloading#tempdir.
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def draw(*argv) #:doc:
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Tempfile.open("ActiveStorage", tempdir) do |file|
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capture(*argv, to: file)
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yield file
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end
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end
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def capture(*argv, to:)
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to.binmode
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IO.popen(argv, err: File::NULL) { |out| IO.copy_stream(out, to) }
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to.rewind
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end
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def logger #:doc:
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ActiveStorage.logger
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end
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end
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end
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