utils: add "download" parameter to UI view

* Adds a "download" querystring parameter to the file_download_ui view,
  which allows the file to be sent as an attachment.

invenio_records_files/utils.py

@@ -26,7 +26,7 @@
 
 from __future__ import absolute_import, print_function
 
-from flask import abort
+from flask import abort, request
 from invenio_files_rest.models import ObjectVersion
 from invenio_files_rest.views import ObjectResource
 from invenio_records.errors import MissingModelError
@@ -83,6 +83,9 @@ def file_download_ui(pid, record, _record_file_factory=None, **kwargs):
             )
         )
 
+    If ``download`` is passed as a querystring argument, the file is sent as an
+    attachment.
+
     :param pid: The :class:`invenio_pidstore.models.PersistentIdentifier`
         instance.
     :param record: The record metadata.
@@ -110,4 +113,5 @@ def file_download_ui(pid, record, _record_file_factory=None, **kwargs):
             'pid_type': pid.pid_type,
             'pid_value': pid.pid_value,
         },
+        as_attachment=('download' in request.args)
     )

tests/test_utils.py

@@ -43,8 +43,21 @@ def test_file_download_ui(app, db, location, record_with_bucket, generic_file):
         assert response.status_code == 200
         assert response.mimetype == 'text/plain'
 
+        response = file_download_ui(
+            pid, record_with_bucket, filename=generic_file
+        )
+
         with pytest.raises(NotFound):
             file_download_ui(pid, record_with_bucket)
 
         with pytest.raises(NotFound):
             file_download_ui(pid, record_with_bucket, filename='not_found')
+
+    with app.test_request_context('/?download'):
+        response = file_download_ui(
+            pid, record_with_bucket, filename=generic_file
+        )
+        assert response.status_code == 200
+        assert response.mimetype == 'text/plain'
+        assert response.headers['Content-Disposition'] == \
+            'attachment; filename={}'.format(generic_file)