File Validation

Shrine allows validating assigned files using the validation plugin. Validation code is defined inside an Attacher.validate block:

Shrine.plugin :validation

class ImageUploader < Shrine
  Attacher.validate do
    # ... perform validation ... 
  end
end

The validation block is run when a new file is assigned, and any validation errors are stored in Shrine::Attacher#errors. Persistence plugins like sequel and activerecord will automatically merge these validation errors into the #errors hash on the model instance.

photo = Photo.new
photo.image = image_file
photo.valid? #=> false 
photo.errors[:image] #=> [...]

Validation helpers

The validation_helpers plugin provides convenient validators for built-in metadata:

Shrine.plugin :validation_helpers

class ImageUploader < Shrine
  Attacher.validate do
    validate_size      1..5*1024*1024
    validate_mime_type %w[image/jpeg image/png image/webp image/tiff]
    validate_extension %w[jpg jpeg png webp tiff tif]
  end
end

Note that for secure MIME type validation it's recommended to also load determine_mime_type and restore_cached_data plugins.

See the validation_helpers plugin documentation for more details.

Custom validations

You can also do your own custom validations:

# Gemfile 
gem "streamio-ffmpeg"

require "streamio-ffmpeg"
 
class VideoUploader < Shrine
  plugin :add_metadata
 
  add_metadata :duration do |io|
    movie = Shrine.with_file(io) { |file| FFMPEG::Movie.new(file.path) }
    movie.duration
  end
 
  Attacher.validate do
    if file.duration > 5*60*60
      errors << "duration must not be longer than 5 hours"
    end
  end
end

Inheritance

Validations are inherited from superclasses, but you need to call them manually when defining more validations:

class ApplicationUploader < Shrine
  Attacher.validate { validate_max_size 5*1024*1024 }
end

class ImageUploader < ApplicationUploader
  Attacher.validate do
    super() # empty parentheses are required 
    validate_mime_type %w[image/jpeg image/png image/webp]
  end
end

Removing invalid files

By default, an invalid file will remain assigned after validation failed, but you can have it automatically removed and deleted by loading the remove_invalid plugin.

Shrine.plugin :remove_invalid # remove and delete files that failed validation