How to Handle File Uploads from Clojure on Heroku (or anywhere else)

I recently wanted to deploy a Clojure web app that allowed users to upload a CSV and work with the data. Heroku is as easy as it gets for web app deployment, but I figured I'd have to jump through some extra hoops to do the file upload. It turns out there are no hoops. Thanks to Heroku's ephemeral filesystem, we can handle file uploads just as we would on any other system, so long as we either process the file immediately or send it someplace else to be stored.

Here's how to handle a file upload in a very simple ring app.

	(ring.adapter.jetty/run-jetty
	(ring.middleware.params/wrap-params
	(ring.middleware.multipart-params/wrap-multipart-params
	(fn [request]
	(if (= :get (:request-method request))
	(render-html-form-with-file-field-called "my-file")
	(let [file (get-in req [:params "my-file" :tempfile])]
	; file is a java.io.File
	(with-open [reader (clojure.java.io/reader file)]
	; reader is a--You guessed it!--java.io.Reader
	(render-result
	(clojure.data.csv/read-csv reader))))))))
	{:port 8000})

view raw app.clj hosted with ❤ by GitHub

The 'render-' fns are left to you!