Ring Webapp Example

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Links

• Repo: github.com/iantruslove/gentle-intro

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"Snippets" project: build a web service for sharing text snippets

(gist.github.com anyone?)

Interface:

$ curl -X POST \
    -H "content-type: text/plain" \
    -d "Hello, world!" \
    http://server/snippets/
# Should return HTTP 302 with a Location header for us to follow

$ curl -X GET http://server/snippets/1234
Hello, world!

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Snippets: Intro to Ring

• Ring is a simple (conceptual) framework for building web applications.
  • It also has some useful code.
• Request maps:

{:server-port 8080
 :server-name "localhost"
 :uri "/foo/bar/baz"
 :scheme :https
 :headers {"content-type" "text/plain"
 :body <some Java stream object>}

• Response maps:

{:status 200
 :headers ["content-type" "text/plain"]
 :body "Hello, world!"}

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Snippets: Ring Basics

• Creating and modifying responses
  • The functions in ring.util.response are useful

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Snippets: Ring Handlers

• Straightforward requirements:
  • Take a single parameter (request map)
  • Return a response map

(fn [req]
  {:status 200 :body ""})  

• Sketch out the GET and POST handlers...
  • ...in a Compojure defroutes setup

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Snippets: Storing snippets in an atom

• reset! and swap!

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Snippets: UUIDs

• We need them, Java has them.

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Snippets: Put it together

• Write the rest of the code!

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Snippets: Simple Extensions

• Web pages
• URL shortening
• Durable datastore
• Automatic content conversion (if possible)
  • e.g. JSON <--> EDN, JSON --> HTML, ...