Extract thumbnails from FreeCAD files to display as previews

app/lib/file_handlers/freecad_thumbnail_extractor.rb

@@ -0,0 +1,4 @@
+class FileHandlers::FreecadThumbnailExtractor < FileHandlers::Base
+  ENVIRONMENTS = [:server].freeze
+  INPUT_TYPES = [Mime[:fcstd]].freeze
+end

app/services/freecad_thumbnail_extractor_service.rb

@@ -0,0 +1,19 @@
+class FreecadThumbnailExtractorService
+  def initialize(file:)
+    @file = file
+  end
+
+  def call
+    thumbnail = nil
+    Archive::Reader.open_filename(@file.path) do |reader|
+      reader.each_entry do |entry|
+        next unless entry.pathname == "thumbnails/Thumbnail.png"
+        Dir.mktmpdir do |dir|
+          reader.extract(entry, Archive::EXTRACT_SECURE, destination: dir)
+          thumbnail = File.read(File.join(dir, "thumbnails/Thumbnail.png"))
+        end
+      end
+    end
+    thumbnail ? StringIO.new(thumbnail) : nil
+  end
+end

app/uploaders/application_uploader.rb

@@ -133,6 +133,10 @@ class ApplicationUploader < Shrine
       Shrine.with_file(original) do
         {render: GcodeThumbnailExtractorService.new(file: it).call}.compact
       end
+    elsif SiteSettings.generate_model_renders && FileHandlers::FreecadThumbnailExtractor.can_load?(context[:record].mime_type)
+      Shrine.with_file(original) do
+        {render: FreecadThumbnailExtractorService.new(file: it).call}.compact
+      end
     elsif SiteSettings.generate_model_renders && FileHandlers::F3d.can_load?(context[:record].mime_type) && context[:record]&.is_3d_model?
       Shrine.with_file(original) do
         up = context[:record]&.up_direction