Episode 006: All Wrapped Up in Twitter

Functional Design in Clojure

Christoph tries to get a handle on his #clojure tweet-stream habit.

• NOT tic-tac-toe
• Follow #clojure tweet stream and see it print out in the terminal
• "We like reinventing things."
• "The terminal is the best UI out there."
• Does Twitter have an API?
• Websocket? Nope! Requires a big "E" plan: "enterprise".
• PubSub? Nope! Not from Twitter.
• Alas, we must poll the /search/tweets.json endpoint
• Problem: we're going to keep getting results we've already seen
• Avoid duplicates? Let's use core cache.
• Once again, we use loop and recur for our main loop
• Time for an API wrapper, but what does the wrapper do?
• HTTP POST form-encoded parameters
• Ack! 401 Access Denied
• "An important step in any API exploration is your first 401 response."
• "OAuth?" "Oh....auth..."
• Meet OAuth, the API bouncer.
• Make an auth function to call the OAuth endpoint and get an auth token
• Have auth return a "handle" with the auth token. Other wrapper functions will need handle.
• Need to keep handle around. Put that in the app state too.
• Let the exceptions fly!
• "Exceptions are an exceptionally accepted way of handling exceptional circumstances."
• "I caught what you meant."
• Make a fetch function that does the I/O work.
• Create a search function that takes handle and query
• Look for pure logic and move it into its own function, then it's easy to test.
• Transform args to search into a "request description" and have fetch operate on that.
• "Twitch, I mean Twitter. You know, that Internet thing that starts with t-w-i-t."
• Different layers of the wrapper:
  • Top-level functions used by the application. Sole job: sequence internal functions
  • Pure transforms from args to "request description"
  • A fetch function that follows the "orders" of the "request description"
• "The point of testing this code is not to test if Aleph works or Twitter works. The logic is in the translation function, so that's why we test it."
• "Our hero, the Twitch wrapper, is poised and ready to fetch data on our behalf. What will happen next?"

Clojure in this episode:

• loop, recur
• Thread.sleep
• get
• try, catch
• ->

Related projects:

• core.cache
• Aleph and http-kit
• Manifold
• Netty