Downloading empty file with enabled cache management leads to 500 error

[Mike Fedosin]

When I tried to download an empty image file from glance with enabled cache management I got 500 error:

mfedosin@wdev:~$ glance --debug image-download 0af7b2e8-8e31-427b-a99f-9117f45418ef --file empty_file
curl -g -i -X GET -H 'Accept-Encoding: gzip, deflate' -H 'Accept: */*' -H 'User-Agent: python-glanceclient' -H 'Connection: keep-alive' -H 'X-Auth-Token: {SHA1}c91066a8c438769ed454eebd759b4f8b1e488cb6' -H 'Content-Type: application/octet-stream' http://10.0.2.15:9292/v2/images/0af7b2e8-8e31-427b-a99f-9117f45418ef/file
Request returned failure status 500.
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/glanceclient/shell.py", line 605, in main
    args.func(client, args)
  File "/usr/local/lib/python2.7/dist-packages/glanceclient/v2/shell.py", line 277, in do_image_download
    body = gc.images.data(args.id)
  File "/usr/local/lib/python2.7/dist-packages/glanceclient/v2/images.py", line 194, in data
    resp, body = self.http_client.get(url)
  File "/usr/local/lib/python2.7/dist-packages/glanceclient/common/http.py", line 284, in get
    return self._request('GET', url, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/glanceclient/common/http.py", line 276, in _request
    resp, body_iter = self._handle_response(resp)
  File "/usr/local/lib/python2.7/dist-packages/glanceclient/common/http.py", line 93, in _handle_response
    raise exc.from_response(resp, resp.content)
HTTPInternalServerError: HTTPInternalServerError (HTTP 500)
HTTPInternalServerError (HTTP 500)

Without cache management everything works fine.

Steps to reproduce on devstack:

1. Set flavor to 'keystone+cachemanagement' in glance-api.conf (flavor = keystone+cachemanagement)
2. Restart glance-api server
3. Create an image with empty file (file size is 0)
4. Try to download the image file from glance.

Expected result: new empty file will be created in local folder.

Actual result: HTTPInternalServerError (HTTP 500)

Logs from glance-api: http://paste.openstack.org/show/483545/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/266891

[OpenStack Infra (hudson-openstack)]

Change abandoned by Darja Shakhray (<email address hidden>) on branch: master
Review: https://review.openstack.org/266891
Reason: This commit is not necessary

[OpenStack Infra (hudson-openstack)]

Change abandoned by Ian Cordasco (<email address hidden>) on branch: master
Review: https://review.openstack.org/269277
Reason: As discussed on the other patch, this is unnecessary