drain a core.async chan

drain

(defn drain
  "Takes all values available on a chan then returns the number taken to the channel drain creates. Compatible with cljs too."
  [c]
    (go
      (loop [r 0]
       (alt!
        (timeout 100) r
        c ([v] (recur (inc r)))))))
        
(defn drainf
  "Takes all values available on a chan then returns a vector of them, leaving the channel empty. Compatible with cljs too. Optionally takes a single function which accepts a single value and will process each drained value with this function, while also placing original value onto the vector."
  [c & f]
  (go
   (loop [r []]
     (alt!
      (timeout 700) r
      c ([v] 
           (when f ;;handling side-effects during draining
             ((first f) v))
           (recur (conj r v)))))))