Why is fs.createReadStream always emitting buffers? Read the comment and corrected sample to find the answer ;)

sample.js

var stream = require('stream');
var util = require('util');

var Writable = stream.Writable;

module.exports = CheckEncodingWritable;

util.inherits(CheckEncodingWritable, Writable);

function CheckEncodingWritable (opts) {
  if (!(this instanceof CheckEncodingWritable)) return new CheckEncodingWritable(opts);

  opts = opts || {};
  
  Writable.call(this, opts);
}

CheckEncodingWritable.prototype._write = function (chunk, encoding, cb) {
  console.log({ encoding: encoding, chunk: chunk });
  cb();
};

require('fs')
  .createReadStream(__filename, { encoding: 'utf8' })
  .pipe(new CheckEncodingWritable())

// => 
// { encoding: 'buffer',
//   chunk: <Buffer 27 75 73 65 20 73 74 72 69 63 74 27 3b 0a 0a 76 61 72 20 73 74 72 65 61 6d 20 3d 20 72 65 71 75 69 72 65 28 27 73 74 72 65 61 6d 27 29 3b 0a 76 61 72 20 ...> }

sample_corrected.js

'use strict';

var stream = require('stream');
var util = require('util');

var Writable = stream.Writable;

module.exports = CheckEncodingWritable;

util.inherits(CheckEncodingWritable, Writable);

function CheckEncodingWritable (opts) {
  if (!(this instanceof CheckEncodingWritable)) return new CheckEncodingWritable(opts);

  opts = opts || {};
  
  Writable.call(this, opts);
}

CheckEncodingWritable.prototype._write = function (chunk, encoding, cb) {
  console.log({ encoding: encoding, chunk: chunk });
  cb();
};

require('fs')
  .createReadStream(__filename, { encoding: 'utf8' })
  .pipe(new CheckEncodingWritable({ decodeStrings: false })) // <-----
  
// =>
// { encoding: 'utf8',
//   chunk: '\'use strict\';\n\nvar stream = require(\'stream\');\nvar util = require(\'util\');\n\nvar Writable = stream.Writable;\n\nmodule.exports = CheckEncodingWritable;\n\nutil.inherits(CheckEncodingWritable, Writable);\n\nfunction CheckEncodingWritable (opts) {\n  if (!(this instanceof CheckEncodingWritable)) return new CheckEncodingWritable(opts);\n\n  opts = opts || {};\n  \n  Writable.call(this, opts);\n}\n\nCheckEncodingWritable.prototype._write = function (chunk, encoding, cb) {\n  console.log({ encoding: encoding, chunk: chunk });\n  cb();\n};\n\nvar readable = require(\'fs\')\n  .createReadStream(__filename, { encoding: \'utf8\' })\n  .pipe(new CheckEncodingWritable({ decodeStrings: false }))\n' }

After reading the docs more closely, I found that this is indeed intended

chunk will always be a buffer unless the decodeStrings option is explicitly set to false