There are already tens of Node.js scripts that spider / crawl sites, and many more Python and Ruby ones. It isn't clear how many of them they work, or that they even recurse. Or if they do, is it depth-first? Breadth-first?
This project is a work in progress. I intend to document at least its philosophy, if not methodology, better than the competition.
It's ruthless (this package used to be called "ruthless") in that it does not respect
So, you're on your own if you violate some vengeful site's TOS.
I wanted a stateful queue, in case of stops or restarts. Redis was the first choice, but I had too much metadata.
So I'm using Postgres right now. Not sure if that's the best idea. The
pages table has these columns:
id, parent_id, url, tag, depth, content, plaintext, queued, fetched, failed, error
- Seed urls are accompanied by a freeform tag, and enter the database with a depth of 0.
- The pages they link to inherit that tag, have a
parent_idset to the linking page's
- The child pages have a
depth + 1if they are on the same domain (protocol and subdomain insensitive), or
depth + 100if they do not share the domain (defined by the
hostnamefield that Node.js's
- The crawl proceeds breadth-first, so the depth never needs to be updated.
Here is an sample of depths retrieved for a single seed site (a blog) that I let run for a couple of minutes:
SELECT depth, COUNT(depth) FROM pages GROUP BY depth ORDER BY depth; Depth Count 0 1 1 81 2 319 3 731 4 851 100 22 101 151 102 1071 103 1593
As it was, I hadn't gotten through the 3-deep sites yet.
If the supplied credentials have superuser privileges, the database and
pages table will be created automatically.
Otherwise, run the following at your command line to initialize (and reset) everything to the defaults:
dropdb cameo-crawler; createdb cameo-crawler && psql cameo-crawler < schema.sql
clusterto spawn multiple workers. It's currently kind of slow, because most things happen in series.
seencache can handle most locking issues; as soon as
work()fetches a new url, add the url to seen. Even if a page is fetched twice, it's not a big deal!
- Allow a threshold depth, i.e., stop after going 10 links deep into a seed url.
- Allow constraining a query to a single domain.
Copyright 2012-2015 Christopher Brown. MIT Licensed.