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Web
Applications
Clojure
BERLIN, 22 Feb 2018
JOY CLARK
❤
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Web Applications Clojure
Joy Clark
Consultant @ innoQ
[email protected]
@iamjoyclark
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Web Applications
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Web Applications Clojure
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retrieving
a page
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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forms
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
redirects
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JavaScript
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Web Applications Clojure
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Clojure
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• Lisp Variant for the JVM
• Functional Language
• Dynamically Typed
• Immutable Data Structures
• Simplicity - Separation of Data and Behavior
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Data Structures
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
“Hello World”
3 3.14 3/2
\a
:first
foo
#“Ch.*se”
(“Hello” :first)
[3 4 3]
{:name “Joy”
:company “INNOQ”} #{3 4 3}
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Functions
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
(+ 1 2 3)
> 6
(:city {:name “INNOQ”
:city “Berlin”})
> “Berlin”
(map inc [1 2 3])
> (2 3 4)
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Web Applications ❤ Clojure
„You’ve just seen it“
- Rich Hickey
Clojure Syntax:
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Web Applications + Clojure =
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Web Applications Clojure
❤
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Something that takes a
HTTP Request and returns a
HTTP Response
Web Applications ❤ Clojure
What’s a Web Application?
Joy Clark / @iamjoyclark
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https://github.com/ring-clojure/ring
• HTTP Server abstraction
• Request & Response are data
• Web App is a function
Web Applications ❤ Clojure
Ring
Joy Clark / @iamjoyclark
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{:uri “/”
:request-method :get
:headers { … }
:params {:name “Joy”}
…}
Web Applications ❤ Clojure
Ring: Request
Joy Clark / @iamjoyclark
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{:status 200
:headers { … }
:body “Hello!”}
Web Applications ❤ Clojure
Ring: Response
Joy Clark / @iamjoyclark
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(defn example-app [request]
(let [name (get-in request [:params :name])]
{:status 200
:headers {“Content-Type” “text/plain”}
:body (str “Hello, ” name “!”)})
Web Applications ❤ Clojure
Ring: Handler
Joy Clark / @iamjoyclark
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• Jetty
• Servlet
• http-kit
• Tomcat
…
Web Applications ❤ Clojure
Ring: Adapter
Joy Clark / @iamjoyclark
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(defn wrap-logging [handler]
(fn [request]
(print request)
(let [response (handler
request)]
(print response)
response)))
Web Applications ❤ Clojure
Ring: Middleware
Joy Clark / @iamjoyclark
webapp
Java HTTP Server
Ring Server Adapter
middleware
middleware
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Ring: Middleware
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• https://github.com/ring-clojure/ring-defaults
• https://github.com/ring-clojure/ring-json
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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https://github.com/weavejester/compojure
Web Applications ❤ Clojure
Compojure
Joy Clark / @iamjoyclark
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Excursion… Clojure Macros
Web Applications Clojure
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Clojure: Macros
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
“(case 3
1 “one”
2 “two”
“more”)”
Reader
Text Data Structures
(case 3
1 “one”
2 “two”
“more”)
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Clojure: Macros
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
Expand Data Structures
(case
1 “one”
2 “two”
“more”)
Data Structures
(if (= 3 1)
“one”
(if (= 3 2)
“two”
“more”))
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Back to
Compojure…
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Compojure: Macro
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(GET “/hello” [] “Hello, world!”)
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
(fn [req]
(if (and (= (:uri req) “/hello”)
(= (:request-method req) :get))
{:body “Hello, world!”}))
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Compojure: Handler
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(defroutes app-routes
(GET “/” request (list-users request))
(POST “/” {params :params :as request}
(add-user request params))
(GET “/:username” [username :as request]
(get-user request username)))
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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• https://github.com/juxt/bidi
• http://clojure-liberator.github.io/liberator/
Web Applications ❤ Clojure
Compojure: Alternatives
Joy Clark / @iamjoyclark
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Functional composition!
Web Applications ❤ Clojure
Putting it all together
Joy Clark / @iamjoyclark
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HTML Templating
Web Applications ❤ Clojure
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Hiccup
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bar
[:div {:id “foo”}
[:span “bar”]]
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
https://github.com/weavejester/hiccup
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Hiccup
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Make sure to escape HTML when using Hiccup!
(defn render-html [input]
(hiccup.util/escape-html
(hiccup.core/html input)))
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Hiccup: Alternatives
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• https://github.com/cgrand/enlive
• https://github.com/yogthos/Selmer
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Summary
Web Applications ❤ Clojure
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Summary
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• Functional language ideal for Web Apps
• Clojure is a stable language
• Libraries vs. Frameworks
• Community is healthy and welcoming
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Interesting Libraries
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• https://github.com/technomancy/leiningen
• https://github.com/boot-clj/boot
• https://github.com/weavejester/environ
• https://github.com/krisajenkins/yesql
• https://github.com/stuartsierra/component
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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“Frameworks”
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• https://github.com/weavejester/duct
• http://www.luminusweb.net
• https://github.com/metosin/compojure-api
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Live Demo!
Web Applications Clojure
https://github.com/innoq/tutorial-clj-webapp
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State in Clojure…
Web Applications Clojure
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Web Applications Clojure
INNOQ /
„No man ever steps in the same river
twice, for it’s not the same river and
he’s not the same man“
- Heraclitus
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Clojure Identity
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• The world around us is constantly changing.
• We shouldn’t make the world “stop” so that we can
change it.
• Instead…
• We can give the world a function telling it what we
want to change.
Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Web Applications ❤ Clojure
swap!
Joy Clark / @iamjoyclark
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CSRF: Cross-Site Request Forgery
Web Applications Clojure
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CSRF
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Protect Against CSRF
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• Don't use GET requests to change state!
%0A%E2%80%A2%20https://github.com/ring-clojure/ring-anti-forgery%0AWeb%20Applications%20%E2%9D%A4%20Clojure%0AJoy%20Clark%20/%20@iamjoyclark%0A)
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CSRF
Protection
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Web Applications ❤ Clojure
Joy Clark / @iamjoyclark
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Thank you!
Joy Clark | @iamjoyclark | [email protected]
https://github.com/innoq/tutorial-clj-webapp