ensure filename is sent by store_for_attachment

test plan:
 - with and without inst-fs enabled,
   - ensure both sis import upload paths work
     (both a multipart upload and a raw post)

flag=none
fixes FOO-4400

Change-Id: I2e868989ec4552cc53ed980c24b22578cada6f0c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/344058
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Xander Moffatt <xmoffatt@instructure.com>
QA-Review: Xander Moffatt <xmoffatt@instructure.com>
Product-Review: Xander Moffatt <xmoffatt@instructure.com>

app/models/attachments/storage.rb

@@ -20,16 +20,16 @@
 class Attachments::Storage
   def self.store_for_attachment(attachment, data)
     if InstFS.enabled?
+      attachment.filename ||= detect_filename(data)
       instfs_uuid = InstFS.direct_upload(
         file_object: data,
-        file_name: attachment.display_name
+        file_name: attachment.display_name.presence || attachment.filename || "attachment"
       )
       attachment.instfs_uuid = instfs_uuid
       attachment.md5 = Digest::SHA2.new(512).file(data).hexdigest if digest_file? data
 
       # populate attachment fields if they were not already set
       attachment.size ||= data.size
-      attachment.filename ||= detect_filename(data)
       attachment.content_type ||= attachment.detect_mimetype(data)
       attachment.workflow_state = "processed"
     else

app/models/sis_batch.rb

@@ -63,7 +63,7 @@ class SisBatch < ActiveRecord::Base
   # If you are going to change any settings on the batch before it's processed,
   # do it in the block passed into this method, so that the changes are saved
   # before the batch is marked created and eligible for processing.
-  def self.create_with_attachment(account, import_type, attachment, user = nil)
+  def self.create_with_attachment(account, import_type, file_obj, user = nil)
     account.shard.activate do
       batch = SisBatch.new
       batch.account = account
@@ -73,7 +73,7 @@ class SisBatch < ActiveRecord::Base
       batch.user = user
       batch.save
 
-      att = Attachment.create_data_attachment(batch, attachment)
+      att = Attachment.create_data_attachment(batch, file_obj, file_obj.original_filename)
       batch.attachment = att
 
       yield batch if block_given?

spec/models/attachments/storage_spec.rb

@@ -33,6 +33,12 @@ describe Attachments::Storage do
       expect(@attachment.instfs_uuid).to eq(@uuid)
     end
 
+    it "infers a filename for direct_upload" do
+      att = Attachment.new
+      expect(InstFS).to receive(:direct_upload).with(file_object: @file, file_name: "a.png")
+      Attachments::Storage.store_for_attachment(att, @file)
+    end
+
     it "calls attachment_fu methods if inst-fs is not enabled" do
       allow(InstFS).to receive(:enabled?).and_return(false)
       expect(@attachment).to receive(:uploaded_data=)