don't create thumbnails for very large images

test plan:
 1. enable new files
 2. upload a sane-sized image file (jpg/gif/png)
    with less than 100 million pixels
 3. within a minute or so, a thumbnail image should
    be generated for the image, and visible after the
    new files page refreshes
 4. upload an image with more than 100 million pixels
    (the size of the file in bytes isn't relevant;
     you can use 100mpx.png, attached to the ticket,
     which is a 12800x8000 image which compresses down
     to 13K because it's solid blackness).
    Canvas should not generate a thumbnail for it.
    A generic icon should be used (not a solid black
    square).

fixes CNVS-17995

Change-Id: Ie5ed1f57de65fa105cb3f23ceb0b895b676375fe
Reviewed-on: https://gerrit.instructure.com/48973
Tested-by: Jenkins
Reviewed-by: James Williams  <jamesw@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>

app/models/attachment.rb

@@ -223,7 +223,6 @@ class Attachment < ActiveRecord::Base
     # try an infer encoding if it would be useful to do so
     send_later(:infer_encoding) if self.encoding.nil? && self.content_type =~ /text/ && self.context_type != 'SisBatch'
     if respond_to?(:process_attachment_with_processing, true) && thumbnailable? && !attachment_options[:thumbnails].blank? && parent_id.nil?
-      temp_file = temp_path || create_temp_file
       self.class.attachment_options[:thumbnails].each { |suffix, size| send_later_if_production(:create_thumbnail_size, suffix) }
     end
   end

app/models/thumbnail.rb

@@ -30,7 +30,8 @@ class Thumbnail < ActiveRecord::Base
       :storage => (Attachment.local_storage? ? :file_system : :s3),
       :path_prefix => Attachment.file_store_config['path_prefix'],
       :s3_access => :private,
-      :keep_profile => true
+      :keep_profile => true,
+      :thumbnail_max_image_size_pixels => Setting.get('thumbnail_max_image_size_pixels', 100_000_000)
   )
 
   before_save :set_namespace

gems/attachment_fu/lib/attachment_fu.rb

@@ -281,6 +281,8 @@ module AttachmentFu # :nodoc:
         res = self.create_or_update_thumbnail(tmp, target_size.to_s, actual_size)
       rescue AWS::S3::Errors::NoSuchKey => e
         logger.warn("error when trying to make thumbnail for attachment_id: #{self.id} (the image probably doesn't exist on s3) error details: #{e.inspect}")
+      rescue ThumbnailError => e
+        logger.warn("error creating thumbnail for attachment_id #{self.id}: #{e.inspect}")
       ensure
         tmp.unlink if tmp
       end

gems/attachment_fu/lib/attachment_fu/processors/mini_magick_processor.rb

@@ -28,6 +28,8 @@ module AttachmentFu # :nodoc:
       def process_attachment_with_processing
         return unless process_attachment_without_processing
         with_image do |img|
+          max_image_size = attachment_options[:thumbnail_max_image_size_pixels]
+          raise ThumbnailError.new("source image too large") if max_image_size && img[:width] * img[:height] > max_image_size
           resize_image_or_thumbnail! img
           self.width = img[:width] if respond_to?(:width)
           self.height = img[:height] if respond_to?(:height)

spec/factories/attachment_factory.rb

@@ -81,10 +81,15 @@ def stub_png_data(filename = 'test my file? hai!&.png', data = nil)
 end
 
 def jpeg_data_frd
-  fixture_path = '/test_image.jpg'
+  fixture_path = 'test_image.jpg'
   fixture_file_upload(fixture_path, 'image/jpeg', true)
 end
 
+def one_hundred_megapixels_of_highly_compressed_png_data
+  fixture_path = '100mpx.png'
+  fixture_file_upload(fixture_path, 'image/png', true)
+end
+
 def crocodocable_attachment_model(opts={})
   attachment_model({:content_type => 'application/pdf'}.merge(opts))
 end

spec/models/attachment_spec.rb

@@ -983,6 +983,24 @@ describe Attachment do
     end
   end
 
+  describe "thumbnail source image size limitation" do
+    before(:once) do
+      local_storage! # s3 attachment data is stubbed out, so there is no image to identify the size of
+      course
+    end
+
+    it 'creates thumbnails for smaller images' do
+      att = @course.attachments.create! :uploaded_data => jpeg_data_frd, :filename => 'ok.jpg'
+      expect(att.thumbnail).not_to be_nil
+      expect(att.thumbnail.width).not_to be_nil
+    end
+
+    it 'does not create thumbnails for larger images' do
+      att = @course.attachments.create! :uploaded_data => one_hundred_megapixels_of_highly_compressed_png_data, :filename => '3vil.png'
+      expect(att.thumbnail).to be_nil
+    end
+  end
+
   context "notifications" do
     before :once do
       course_model(:workflow_state => "available")