the ebook-convert fail to retrive a cover image because there is a space in the url:
so far this problem can be bypassed by modify the cover url in recipe, for example,
self.cover_url = cover['src']
from urlib import quote
self.cover_url = quote(cover['src'], safe="%/:=&?~#+!$,;'@()*")
would it be better to fix this in ebook-convert itself?