Allow Excluding or Including Specific file extensions in image uploader

[ishields]

Allow customizing supported formats for the image uploader. For example, I'd like to be able to exclude .avif.

Maglev.configure do |config|
      config.reject_image_extensions = %w[avif]
end

The reason I want to do this is I use cloudflare to resize these images downstream and avif is not a supported input.

For now I patched it like this but this seems like something that could be customized.

# Patch Maglev::Asset to reject AVIF files
# This file is loaded by config/initializers/maglev_patch.rb
class Maglev::Asset
  # Validate that content_type is not AVIF
  validate :verify_content_types, on: :create

  private

  def verify_content_types
    # Check Active Storage attachment blob first (most reliable)
    # Maglev uses Active Storage, so check if there's an attachment
    if respond_to?(:file) && file.attached?
      blob_content_type = "#{file.blob&.content_type}#{content_type}"
      if blob_content_type.present? && (blob_content_type.include?('avif'))
        errors.add(:base, 'AVIF format is not supported. Please use JPEG, PNG, GIF, or WebP.')
        return
      end
    end
  end
end

I imagine the better way is to jusdt allow customizing the front end piece

[did]

👋@ishields, right. Changing it in the "frontend" should be fine. I'm willing to accept a PR for Maglev v3 ;-)