misleading messages uploading PDFs: No plugins using two-step checking found (0.9.0)

[Jorge]

Looks like the pdf plugin can't handle PDF files.

1. Setup production environment:
2. Enable PDF support: ​https://mediagoblin.readthedocs.io/en/latest/siteadmin/media-types.html#pdf-and-document

sudo apt-get install -y poppler-utils
echo "mediagoblin.media_types.pdf" >> mediagoblin_local.ini
git submodule init && git submodule update
./bin/gmg dbupdate
sudo service mediagoblin-paster restart

3. try to upload attached sample PDF

2017-02-10 00:49:20,798 INFO    [mediagoblin.init.plugins] Importing plugin module: mediagoblin.media_types.pdf
2017-02-10 01:20:43,799 INFO    [mediagoblin.media_types] No plugins handled extension .pdf
2017-02-10 01:20:43,800 INFO    [mediagoblin.media_types] No plugins using two-step checking found

From mediagoblin/media_types/init.py

def sniff_media(media_file, filename):
    '''
    Iterate through the enabled media types and find those suited
    for a certain file.
    '''
    # copy the contents to a .name-enabled temporary file for further checks
    # TODO: there are cases when copying is not required
    tmp_media_file = tempfile.NamedTemporaryFile()
    shutil.copyfileobj(media_file, tmp_media_file)
    media_file.seek(0)
    tmp_media_file.seek(0)
    try:
        return type_match_handler(tmp_media_file, filename)
    except TypeNotFound as e:
        _log.info('No plugins using two-step checking found')

Log messages look similar to #5348.

[Jorge]

I tested with lazyserver.sh raising log level to DEBUG and PDF upload magically worked. Switching back to nginx it worked as well. The PDF instantly appears in the media list.

Don't know why, but the two lines are still displayed. So it's rather a confusion instead of a functionality bug.

[ayleph]

Duplicate of #5444.