Line by line reader in cljs

cljs-line-reader.cljs

(ns cljs-line-reader.core
  (:refer-clojure :exclude [flush])
  (:require clojure.string
            [cljs.core.async :refer [>!]])
  (:require-macros [cljs.core.async.macros :refer [go]]))

(def fs (js/require "fs"))
(def stream (js/require "stream"))
(def ^:const eol (.-EOL (js/require "os"))) ;;eg "\n" or "\r\n"

(defn- transform [chunk encoding done]
  (this-as this
    (let [data (if (.-_lastLineData this)
                 (str (.-_lastLineData this) chunk)
                 (str chunk))
          lines (clojure.string/split data (js/RegExp. eol "g"))]
      (set! (.-_lastLineData this) (last lines))
      (doseq [line (butlast lines)]
        (.push this line))
      (done))))

(defn- flush [done]
  (this-as this
    (if (.-_lastLineData this)
      (.push this (.-_lastLineData this)))
    (set! (.-_lastLineData this) nil)
    (done)))

(defn read-file-cb [file-name cb]
  (let [line-reader (.Transform stream #js {:objectMode true})
        source (.createReadStream fs file-name)]
    (set! (.-_transform line-reader) transform)
    (set! (.-_flush line-reader) flush)
    (.pipe source line-reader)
    (.on line-reader "readable"
         (fn []
           (when-let [line (.read line-reader)]
             (cb (str line)) ;;callback with each line
             (recur))))
    nil))

(defn read-file-chan [file-name out-chan]
  (let [line-reader (.Transform stream #js {:objectMode true})
        source (.createReadStream fs file-name)]
    (set! (.-_transform line-reader) transform)
    (set! (.-_flush line-reader) flush)
    (.pipe source line-reader)
    (.on line-reader "readable"
         (fn []
           (go
             (loop []
               (when-let [line (.read line-reader)]
                 (>! out-chan (str line)) ;;push line to chan
                 (recur))))))
    nil))