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Functional Web Architecture Designing web applications with Ring and Compojure twitter: @weavejester code: github.com/weavejester

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Ring. What is it?

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An abstraction over HTTP

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What's HTTP?

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A request / response protocol

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HTTP Request Server Response

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Ring user=> (server request) response

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Ring user=> (handler request) response

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HTTP Request GET /resource HTTP/1.1 Host: www.example.com

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HTTP Request GET /resource HTTP/1.1 Host: www.example.com method URI headers

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Request Map {:request-method :get :uri "/resource" :headers {"host" "www.example.com"}}

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HTTP Response HTTP/1.1 200 OK Content-Type: text/plain Hello World

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HTTP Response HTTP/1.1 200 OK Content-Type: text/plain Hello World status body headers

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Response Map {:status 200 :headers {"Content-Type" "text/plain"} :body "Hello World"}

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Ring Map Function Map

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No other abstractions

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HTTP Request Server Response Ring Map Function Map

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HTTP Request Server Response Ring Map Function Map Adapter

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Example (defn handler [request] {:status 200 :headers {"Content-Type" "text/plain"} :body "Hello World"})

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Example (use 'ring.util.response) (defn handler [request] (-> (response "Hello World") (content-type "text/plain")))

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Example (use 'ring.util.response 'ring.adapter.jetty) (defn handler [request] (-> (response "Hello World") (content-type "text/plain"))) (run-jetty handler {:port 3000})

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Why abstract at all?

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Power

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Power to leverage Clojure

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Middleware

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Not a new abstraction Just higher order functions

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Handler Middleware Handler Map Handler Map

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Handler Request Response

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Middleware Handler Request Response

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Middleware Handler Request Response

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Identity (defn wrap-identity [handler] (fn [request] (handler request)))

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Caching (defn wrap-cache [handler] (fn [request] (or (get-cache request) (let [response (handler request)] (put-cache! request response) response))))

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Content Types (defn wrap-content-type [handler] (fn [request] (let [ext (get-ext (:uri request)) type (ext-types ext)] (-> (handler request) (content-type type)))))

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Parameters (defn wrap-params [handler] (fn [request] (let [query (:query-string request) params (parse-params query)] (handler (assoc request :params params)))))

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Ring core middleware • Query and form parameters • Multipart file uploads • Cookies • Sessions • Content-types • Static resources

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Routing Multiple resources from the same handler

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Basic Routing (use 'ring.util.response) (defn handler [request] (case (:uri request) "/hello" (response "Hello") "/world" (response "World") :else (not-found "Page not found")))

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Compojure

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Compojure (use 'compojure.core) (def hello-route (GET "/hello" request "hello"))

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Compojure ; (GET "/hello" request "hello") (def hello-route (fn [request] (if (and (= (:request-method request) :get) (= (:uri request) "/hello")) "hello" nil))))

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Compojure ; (GET "/hello" request "hello") (def hello-route (fn [request] (if (and (= (:request-method request) :get) (= (:uri request) "/hello")) "hello" nil))))

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Compojure ; (GET "/hello" request "hello") (def hello-route (fn [request] (if (and (= (:request-method request) :get) (= (:uri request) "/hello")) "hello" nil))))

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Compojure ; (GET "/hello" request "hello") (def hello-route (fn [request] (if (and (= (:request-method request) :get) (= (:uri request) "/hello")) "hello" nil))))

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Compojure ; (GET "/hello" request "hello") (def hello-route (fn [request] (if (and (= (:request-method request) :get) (= (:uri request) "/hello")) "hello" nil))))

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Compojure (use 'compojure.core) (def handler (routes (GET "/hello" _ "hello") (GET "/world" _ "world")))

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Compojure (use 'compojure.core) (defroutes handler (GET "/hello" _ "hello") (GET "/world" _ "world"))

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GET /hello GET /world Routes Request Response

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GET /hello GET /world Routes nil Request Response

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GET /hello GET /world Routes nil Request nil

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Compojure (use 'compojure.core) (require '[compojure.route :as route]) (defroutes handler (GET "/hello" _ "hello") (GET "/world" _ "world") (route/not-found "Page Not Found"))

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GET /hello route/not-found GET /world Routes nil Request Response nil

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Compojure (use 'compojure.core) (require '[compojure.route :as route]) (defroutes handler (GET "/hello" _ "hello") (GET "/world" _ "world") (route/not-found "Page Not Found"))

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Compojure (use 'compojure.core) (require '[compojure.route :as route]) (defroutes handler (GET "/:word" request (-> request :params :word)) (route/not-found "Page Not Found"))

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Compojure (use 'compojure.core) (require '[compojure.route :as route]) (defroutes handler (GET "/:word" {{word :word} :params} word) (route/not-found "Page Not Found"))

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Compojure (use 'compojure.core) (require '[compojure.route :as route]) (defroutes handler (GET "/:word" [word] word) (route/not-found "Page Not Found"))

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Compojure (use 'compojure.core) (require '[compojure.route :as route] '[clojure.string :as str]) (defroutes handler (GET "/:word" [word] word) (GET "/:word/shout" [word] (str/upper-case word)) (route/not-found "Page Not Found"))

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Compojure (use 'compojure.core) (require '[compojure.route :as route] '[clojure.string :as str]) (defroutes handler (context "/:word" [word] (GET "/" word) (GET "/shout" (str/upper-case word))) (route/not-found "Page Not Found"))

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Compojure • Create handlers (GET, POST...) • Cascade handlers (routes) • Nest handlers (context)

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Compojure (wrap-authorize (context "/user/:uid" [uid] (let [user (get-user uid)] (routes (GET "/" [] @user) (PUT "/" [& data] (put! user data)) (DELETE "/" [] (delete! user))))))

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Compojure (defn rest-routes [model] (routes (GET "/" [] @model) (PUT "/" [& data] (put! model data)) (DELETE "/" [] (delete! user))) (wrap-authorize (context "/user/:uid" [uid] (rest-routes (get-user uid))

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What's the big idea?

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Complex handlers can be a composition of smaller handlers

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Function Orientated Architecture

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What next? Content negotiation Finite State Machines REST abstractions Clojurescript integration

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Fin. Questions?