FIX: Make sure S3 object headers are preserved on copy (#14302)

When copying an existing upload stub temporary object
on S3 to its final destination we were not copying across
its additional headers such as content-disposition and
cache-control, which led to issues like attachments not
downloading with their original filename when clicking
the download links in posts.

This is because the metadata_directive = REPLACE option
was not being passed to object.copy_from(), so only the
source object's headers were being used. Added an option
for apply_metadata_to_destination to apply this option
conditionally, because we may not always want to replace
this metadata, but we definitely do when copying a temporary
upload.

spec/components/file_store/s3_store_spec.rb

@@ -136,6 +136,49 @@ describe FileStore::S3Store do
         end
       end
     end
+
+    describe "#move_existing_stored_upload" do
+      let(:uploaded_file) { file_from_fixtures(original_filename) }
+      let(:upload_sha1) { Digest::SHA1.hexdigest(File.read(uploaded_file)) }
+      let(:original_filename) { "smallest.png" }
+      let(:s3_client) { Aws::S3::Client.new(stub_responses: true) }
+      let(:s3_helper) { S3Helper.new(SiteSetting.s3_upload_bucket, '', client: s3_client) }
+      let(:store) { FileStore::S3Store.new(s3_helper) }
+      let(:upload_opts) do
+        {
+          acl: "public-read",
+          cache_control: "max-age=31556952, public, immutable",
+          content_type: "image/png",
+          apply_metadata_to_destination: true
+        }
+      end
+      let(:external_upload_stub) { Fabricate(:image_external_upload_stub) }
+      let(:existing_external_upload_key) { external_upload_stub.key }
+
+      before do
+        SiteSetting.authorized_extensions = "pdf|png"
+      end
+
+      it "does not provide a content_disposition for images" do
+        s3_helper.expects(:copy).with(external_upload_stub.key, kind_of(String), options: upload_opts).returns(["path", "etag"])
+        s3_helper.expects(:delete_object).with(external_upload_stub.key)
+        upload = Fabricate(:upload, extension: "png", sha1: upload_sha1, original_filename: original_filename)
+        store.move_existing_stored_upload(external_upload_stub.key, upload, "image/png")
+      end
+
+      context "when the file is a PDF" do
+        let(:external_upload_stub) { Fabricate(:attachment_external_upload_stub, original_filename: original_filename) }
+        let(:original_filename) { "small.pdf" }
+        let(:uploaded_file) { file_from_fixtures("small.pdf", "pdf") }
+
+        it "adds an attachment content-disposition with the original filename" do
+          disp_opts = { content_disposition: "attachment; filename=\"#{original_filename}\"; filename*=UTF-8''#{original_filename}", content_type: "application/pdf" }
+          s3_helper.expects(:copy).with(external_upload_stub.key, kind_of(String), options: upload_opts.merge(disp_opts)).returns(["path", "etag"])
+          upload = Fabricate(:upload, extension: "png", sha1: upload_sha1, original_filename: original_filename)
+          store.move_existing_stored_upload(external_upload_stub.key, upload, "application/pdf")
+        end
+      end
+    end
   end
 
   context 'copying files in S3' do

spec/components/s3_helper_spec.rb

@@ -95,4 +95,38 @@ describe "S3Helper" do
     expect(object1.key).to eq("folder_path/original/1X/def.xyz")
     expect(object2.key).to eq("#{FileStore::BaseStore::TEMPORARY_UPLOAD_PREFIX}folder_path/uploads/default/blah/def.xyz")
   end
+
+  describe "#copy" do
+    let(:source_key) { "#{FileStore::BaseStore::TEMPORARY_UPLOAD_PREFIX}uploads/default/blah/source.jpg" }
+    let(:destination_key) { "original/1X/destination.jpg" }
+    let(:s3_helper) { S3Helper.new("test-bucket", "", client: client) }
+
+    it "can copy an object from the source to the destination" do
+      destination_stub = Aws::S3::Object.new(bucket_name: "test-bucket", key: destination_key, client: client)
+      s3_helper.send(:s3_bucket).expects(:object).with(destination_key).returns(destination_stub)
+      destination_stub.expects(:copy_from).with(copy_source: "test-bucket/#{source_key}").returns(
+        stub(copy_object_result: stub(etag: "\"etag\""))
+      )
+      response = s3_helper.copy(source_key, destination_key)
+      expect(response.first).to eq(destination_key)
+      expect(response.second).to eq("etag")
+    end
+
+    it "puts the metadata from options onto the destination if apply_metadata_to_destination" do
+      content_disposition = "attachment; filename=\"source.jpg\"; filename*=UTF-8''source.jpg"
+      destination_stub = Aws::S3::Object.new(bucket_name: "test-bucket", key: destination_key, client: client)
+      s3_helper.send(:s3_bucket).expects(:object).with(destination_key).returns(destination_stub)
+      destination_stub.expects(:copy_from).with(
+        copy_source: "test-bucket/#{source_key}", content_disposition: content_disposition, metadata_directive: "REPLACE"
+      ).returns(
+        stub(copy_object_result: stub(etag: "\"etag\""))
+      )
+      response = s3_helper.copy(
+        source_key, destination_key,
+        options: { apply_metadata_to_destination: true, content_disposition: content_disposition }
+      )
+      expect(response.first).to eq(destination_key)
+      expect(response.second).to eq("etag")
+    end
+  end
 end