feat: 🎸 add file/stream utils

Author: dmitriz

test/utils.test.js

@@ -1,5 +1,5 @@
 const test = require('./config')
-const { isNil, mergeArray } = require('../utils')
+const { isNil, mergeArray, err2cb } = require('../utils')
 
 test('isNil is true for null or undefined', t=>{
 	t.is(isNil(undefined), true)
@@ -38,3 +38,10 @@ test('take the 1st array when both are of equal length', t => {
 test('take the 1st array when the 2nd has smaller length', t => {
 	t.deepEqual(mergeArray([1,3], [2]), [1,3])
 })
+
+
+test('err2cb preserves cps function without errors', t=>{
+	err2cb(c=>c(2))(t.cis(2))
+})
+
+

utils.js

@@ -1,3 +1,6 @@
+const fs = require('node:fs')
+const { createInterface } = require('node:readline')
+
 // true if and only if the value is null or undefined
 exports.isNil = x => undefined === x || null === x
 
@@ -12,3 +15,37 @@ exports.inheritPrototype = (target, source) => {
     Object.getPrototypeOf(source)
   )
 }
+
+/**
+ * Send syncronous errors into nth callback of CPS function. 
+ * Defaults to n = 2.
+ * 
+ * @param {Function} cpsF - CPS function
+ * @param [{Number} n] - number of the callback
+ * @returns {Function} cpsF - CPS function receiving sync errors into its nth callback
+ */
+exports.err2cb = (cpsF, n=2) => (...cbs) => 
+  { try {return cpsF(...cbs)} catch(err) {return cbs[n-1](err)} }
+
+
+
+// ---- File/Stream utils ---- //
+
+/**
+ * Transform file path into Node stream of the file content
+ *  based on `fs.createReadStream`
+ *  https://nodejs.org/api/fs.html#fscreatereadstreampath-options
+ */
+exports.file2stream = fs.createReadStream
+
+/**
+ * Transform Readable Node stream to CPS function with 3 callbacks (onRes, onErr, onEnd):
+ *  - onRes receives content of each line from stream;
+ *  - onErr receives errors;
+ *  - onEnd receives `null` when stream ends.
+ * 
+ * @param {Stream} input - Readable Node stream
+ * @returns {Function} - CPS function
+ */
+exports.stream2lines = input => (onRes, onErr, onEnd) => 
+    {try {createInterface(input).on('line', onRes).on('close', _ => onEnd(null))} catch(err) {onErr(err)}}