132 lines
5.6 KiB
Ruby
132 lines
5.6 KiB
Ruby
# frozen_string_literal: true
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# Image blobs can have variants that are the result of a set of transformations applied to the original.
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# These variants are used to create thumbnails, fixed-size avatars, or any other derivative image from the
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# original.
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#
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# Variants rely on {ImageProcessing}[https://github.com/janko-m/image_processing] gem for the actual transformations
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# of the file, so you must add <tt>gem "image_processing"</tt> to your Gemfile if you wish to use variants. By
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# default, images will be processed with {ImageMagick}[http://imagemagick.org] using the
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# {MiniMagick}[https://github.com/minimagick/minimagick] gem, but you can also switch to the
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# {libvips}[http://jcupitt.github.io/libvips/] processor operated by the {ruby-vips}[https://github.com/jcupitt/ruby-vips]
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# gem).
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#
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# Rails.application.config.active_storage.variant_processor
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# # => :mini_magick
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#
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# Rails.application.config.active_storage.variant_processor = :vips
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# # => :vips
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#
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# Note that to create a variant it's necessary to download the entire blob file from the service. Because of this process,
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# you also want to be considerate about when the variant is actually processed. You shouldn't be processing variants inline
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# in a template, for example. Delay the processing to an on-demand controller, like the one provided in
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# ActiveStorage::RepresentationsController.
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#
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# To refer to such a delayed on-demand variant, simply link to the variant through the resolved route provided
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# by Active Storage like so:
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#
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# <%= image_tag Current.user.avatar.variant(resize_to_fit: [100, 100]) %>
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#
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# This will create a URL for that specific blob with that specific variant, which the ActiveStorage::RepresentationsController
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# can then produce on-demand.
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#
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# When you do want to actually produce the variant needed, call +processed+. This will check that the variant
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# has already been processed and uploaded to the service, and, if so, just return that. Otherwise it will perform
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# the transformations, upload the variant to the service, and return itself again. Example:
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#
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# avatar.variant(resize_to_fit: [100, 100]).processed.service_url
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#
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# This will create and process a variant of the avatar blob that's constrained to a height and width of 100.
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# Then it'll upload said variant to the service according to a derivative key of the blob and the transformations.
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#
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# You can combine any number of ImageMagick/libvips operations into a variant, as well as any macros provided by the
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# ImageProcessing gem (such as +resize_to_fit+):
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#
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# avatar.variant(resize_to_fit: [800, 800], monochrome: true, rotate: "-90")
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#
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# Visit the following links for a list of available ImageProcessing commands and ImageMagick/libvips operations:
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#
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# * {ImageProcessing::MiniMagick}[https://github.com/janko-m/image_processing/blob/master/doc/minimagick.md#methods]
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# * {ImageMagick reference}[https://www.imagemagick.org/script/mogrify.php]
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# * {ImageProcessing::Vips}[https://github.com/janko-m/image_processing/blob/master/doc/vips.md#methods]
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# * {ruby-vips reference}[http://www.rubydoc.info/gems/ruby-vips/Vips/Image]
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class ActiveStorage::Variant
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WEB_IMAGE_CONTENT_TYPES = %w( image/png image/jpeg image/jpg image/gif )
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attr_reader :blob, :variation
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delegate :service, to: :blob
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def initialize(blob, variation_or_variation_key)
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@blob, @variation = blob, ActiveStorage::Variation.wrap(variation_or_variation_key)
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end
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# Returns the variant instance itself after it's been processed or an existing processing has been found on the service.
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def processed
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process unless processed?
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self
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end
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# Returns a combination key of the blob and the variation that together identifies a specific variant.
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def key
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"variants/#{blob.key}/#{Digest::SHA256.hexdigest(variation.key)}"
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end
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# Returns the URL of the variant on the service. This URL is intended to be short-lived for security and not used directly
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# with users. Instead, the +service_url+ should only be exposed as a redirect from a stable, possibly authenticated URL.
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# Hiding the +service_url+ behind a redirect also gives you the power to change services without updating all URLs. And
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# it allows permanent URLs that redirect to the +service_url+ to be cached in the view.
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#
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# Use <tt>url_for(variant)</tt> (or the implied form, like +link_to variant+ or +redirect_to variant+) to get the stable URL
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# for a variant that points to the ActiveStorage::RepresentationsController, which in turn will use this +service_call+ method
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# for its redirection.
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def service_url(expires_in: ActiveStorage.service_urls_expire_in, disposition: :inline)
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service.url key, expires_in: expires_in, disposition: disposition, filename: filename, content_type: content_type
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end
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# Returns the receiving variant. Allows ActiveStorage::Variant and ActiveStorage::Preview instances to be used interchangeably.
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def image
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self
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end
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private
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def processed?
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service.exist?(key)
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end
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def process
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blob.open do |image|
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transform image do |output|
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upload output
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end
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end
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end
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def filename
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if WEB_IMAGE_CONTENT_TYPES.include?(blob.content_type)
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blob.filename
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else
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ActiveStorage::Filename.new("#{blob.filename.base}.png")
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end
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end
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def content_type
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blob.content_type.presence_in(WEB_IMAGE_CONTENT_TYPES) || "image/png"
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end
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def transform(image)
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format = "png" unless WEB_IMAGE_CONTENT_TYPES.include?(blob.content_type)
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result = variation.transform(image, format: format)
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begin
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yield result
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ensure
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result.close!
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end
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end
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def upload(file)
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service.upload(key, file)
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end
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end
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