CaptchaChallenge

A (hopefully) reusable utility for doing captcha challenges. Here's how it works:

Create a CaptchaChallenge value by giving information about your Redis instance.

-- defaultConnectInfo comes from the hedis package.
myCaptchaChallenge :: CaptchaChallenge
myCaptchaChallenge = captchaChallenge defaultConnectInfo

Generate a challenge, along with a key by which we can reference it.

...
(key, captcha) <- challenge myCaptchaChallenge
-- key is a base64-encoded ByteString, and captcha is a ByteString to be
-- interpreted as a PNG.
-- Maybe send the key and captcha to a client, and await a response from them
-- with the same key, and proposed solution.
...

To attempt a solution, supply the key and a proposed solution:

outcome <- solve myCaptchaChallenge (key, solution)
case outcome of
  Passed p -> ...
  -- ^ Solution matches the one we have on file. p has type ChallengePassed;
  --   you can use that type to indicate statically that your function needs
  --   a captcha challenge before it's used.
  Failed -> ...
  -- ^ Solution is no good; are you a robot?
  BadKey -> ...
  -- ^ Key not recognized; maybe it expired?
  Exception -> ...
  -- ^ Some unknown exception; perhaps the redis store is down?

See examples/CLI.hs for an example CLI utility.

This needs Manifest-Redis in order to compile. Keys are stored in a redis manifest along with the corresponding solutions. They expire after 600 seconds, at which point subsequent solution attempts will receive BadKey because the key is not found. Once an attempted solution passes, we remove the key from redis.

avieth/CaptchaChallenge

CaptchaChallenge