Clojure: read an io/stream to a byte array

stream_to_bytes.clj

(require '[clojure.java.io :as io])

(def fp "/path/to/file")

(defn stream->bytes [is]
  (loop [b (.read is) accum []]
    (if (< b 0)
      accum
      (recur (.read is) (conj accum b)))))

(with-open [is (io/input-stream (io/as-file fp))]
  (stream->bytes is))

That actually returns a PersistentVector, not a byte array. And it would be really inefficient.

Better to use a library like byte-streams, or just use Java interop:

(defn stream-bytes [is]
  (let [baos (java.io.ByteArrayOutputStream.)]
    (io/copy is baos)
    (.toByteArray baos))