mongodb - How can I stream GridFS files to web clients in Clojure/Monger? -

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i have web app using clojure, clojurescript, , monger. documents uploaded , stored in mongo via gridfs. same files can requested download; @ moment accomplished writing file (the server's) disk , serving static file, awkward; how can serve file represented gridfs object directly in clojure/java? routing handled ring/compojure.

it turns out ring/compojure infrastructure used in luminus able return output-streams, allowing easy transmission of files without touching drive. 

(ns my-app.routes.updown   "file uploading , insertion database"   (:use compojure.core)   (:require [my-app.db.core :as db] ;; db functions see here wrappers monger functions you'd expect             [ring.util.response :as r]             [ring.util.io :as io]))  (defn make-file-stream   "takes input stream--such mongodbobject stream--and streams it"   [file]     (io/piped-input-stream    (fn [output-stream]        (.writeto file output-stream))))  (defn download-file-by-id "downloads requested file, if privileges allowed"   [id-string]   (let [mongo-file (db/find-file-by-id id-string)         file-map (db/map-from-mongo-obj mongo-file)         content-type (-> file-map :metadata :contenttype)         file-name (-> file-map :filename)]         (-> mongo-file             make-file-stream             r/response             (#(r/header % "content-disposition" ; right default file-name                         (str "attachment; filename=\"" file-name "\"")))         (#(r/header % "content-type" content-type))))) ; final wrapper: offer right "open with" dialogue   ;; called main routes def so: ;; (notice no wrappers needed, wrapping took place in download-file-by-id) ;; (defroutes home-routes ;;     (get "/files/:id-string" [id-string] ;;        (up/download-file-by-id id-string)))

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