Trying to import a channel when Internet isn't connected fails with a 500

Summary

I believe we used to show a graceful error message (validation-style) when you tried to import content from the internet and you weren’t connected. In the latest version, it fails rather ungracefully with a 500 (and no chance to retry).

System information

• Version: latest 0.6
• Operating system: Ubuntu
• Browser: Chrome

Traceback or relevant snippet from server.log or browser console

ERROR 2017-09-21 14:33:02,344 base Internal Server Error: /api/tasks/startremoteimport/
Traceback (most recent call last):
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/django/core/handlers/base.py", line 149, in get_response
    response = self.process_exception_by_middleware(e, request)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/django/core/handlers/base.py", line 147, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/django/views/decorators/csrf.py", line 58, in wrapped_view
    return view_func(*args, **kwargs)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/rest_framework/viewsets.py", line 87, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/rest_framework/views.py", line 466, in dispatch
    response = self.handle_exception(exc)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/rest_framework/views.py", line 463, in dispatch
    response = handler(request, *args, **kwargs)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/tasks/api.py", line 102, in startremoteimport
    get_content_database_file_url(channel_id)).status_code
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/requests/api.py", line 97, in head
    return request('head', url, **kwargs)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/requests/api.py", line 57, in request
    return session.request(method=method, url=url, **kwargs)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/requests/sessions.py", line 475, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/requests/sessions.py", line 585, in send
    r = adapter.send(request, **kwargs)
  File "/home/jamalex/.pex/install/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl.25703e51e5e72ed9c2589c2d2478ae8b2725774e/kolibri-0.6.dev020170921163803_git-py2.py3-none-any.whl/kolibri/dist/requests/adapters.py", line 467, in send
    raise ConnectionError(e, request=request)
ConnectionError: HTTPSConnectionPool(host='contentworkshop.learningequality.org', port=443): Max retries exceeded with url: /content/databases/17d7606476bd52f4ac94bd76b6f3aa8c.sqlite3 (Caused by NewConnectionError('<requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7efdf40f9790>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution',))

How to reproduce

1. Go to content import page
2. Disconnect from internet
3. Try to import channel from internet

Screenshots

[benjaoming]

I just learned the hard way that having centralized download functionality (that extends into becoming a kind of download manager) was necessary in KA Lite. It has a download_file function which is now core of (hopefully) all client-side download tasks.

Being worried about this, I went straight to the Kolibri code to check out what was done here, and I found kolibri.utils.transfer and some really nice patterns in the importcontent management command. And there’s nothing left to desire from KA Lite lessons – so just wanted to say: Great work on designing this!!!

[indirectlylit]

confirmed - this works pretty well now whether the network goes down during or before a transfer is initiated