You have to run before you can crawl

This is just a small, incomplete web crawler written as a coding test. Given a starting URL, it will store link and image URLs per page in an SQLite database as (page URL, link type, link URL) triples. The link types are page, image, stylesheet, script, object, embed, iframe, media and form. For a gathered link to be valid for crawling, it must:

• be of type page or iframe
• not have been crawled already
• have the same host and port as the page it was found on
• be permitted by robots.txt

Usage:
  cosmo [options] <url>
  cosmo -h|--help
  cosmo --version

Options:
  -h --help               Show this screen.
  --version               Show version.
  -v --verbose            Output each URL on stderr as it is fetched.
  -d --database=<file>    Database file.
  -F --flush              Flush the database before crawling.
  -f --format=<format>    Select output format (see below).

Output formats:
  nice      Hierarchical by page URL and link type
  raw       Raw triples
  dot       GraphViz DOT format graph

• There's no throttling
• Pages that fail to be retrieved are not retried
• Only HTML files are parsed, but it would be useful to parse CSS files too
• It's not at all concurrent