[Compojure] how to (most efficiently?) serve a static file after compojure app decides to do so

On 18 February 2012 01:13, Don Jackson wrote:
Information needed by the first page of my application is very complex to compute,  so the user has to wait seconds.  I want to do better.

Let's say I can pre-compute a reasonable version of each user's data beforehand/every night, and I could stick this info in files somewhere (one file/user).

Now when the user hits the app, the server checks to see if a suitable precomputed version is available.  If so, the server wants to return the data
to the requestor.

On Feb 17, 2012, at 6:12 PM, James Reeves wrote:

On 18 February 2012 01:13, Don Jackson
wrote:
A naive version of this is pretty straightforward:

(ns example.app
(:import org.apache.commons.codec.digest.DigestUtils)
(:require [clojure.java.io :as io]))

(defn- find-cache-file [args]
(io/file
"/path/to/file/cache"
(DigestUtils/shaHex (pr-str args))))

(defn file-cache [func]
(fn [& args]
(let [file (find-cache-file args)]
(if (.exists file)
file
(let [response (apply func args)]
(spit file response)
response)))))

(def cached-complex-function
(file-cache complex-function))

Then you can just use cached-complex-function in place of
complex-function. If the function has been called before with those
arguments, a java.io.File object is returned, which Compojure serves
up as a static file. Otherwise the response is found and saved in a
file before being returned.

Cache expiry, i.e. clearing up old files to save space, is something
that probably needs to be added to make sure you don't run out of disk
space.

- James

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