node/test/parallel/test-stream-unshift-empty-chunk.js

'use strict';
require('../common');
const assert = require('assert');

// This test verifies that stream.unshift(Buffer.alloc(0)) or
// stream.unshift('') does not set state.reading=false.
const Readable = require('stream').Readable;

const r = new Readable();
let nChunks = 10;
const chunk = Buffer.alloc(10, 'x');

r._read = function(n) {
  setImmediate(function() {
    r.push(--nChunks === 0 ? null : chunk);
  });
};

let readAll = false;
const seen = [];
r.on('readable', function() {
  let chunk;
  while (chunk = r.read()) {
    seen.push(chunk.toString());
    // simulate only reading a certain amount of the data,
    // and then putting the rest of the chunk back into the
    // stream, like a parser might do.  We just fill it with
    // 'y' so that it's easy to see which bits were touched,
    // and which were not.
    const putBack = Buffer.alloc(readAll ? 0 : 5, 'y');
    readAll = !readAll;
    r.unshift(putBack);
  }
});

const expect =
  [ 'xxxxxxxxxx',
    'yyyyy',
    'xxxxxxxxxx',
    'yyyyy',
    'xxxxxxxxxx',
    'yyyyy',
    'xxxxxxxxxx',
    'yyyyy',
    'xxxxxxxxxx',
    'yyyyy',
    'xxxxxxxxxx',
    'yyyyy',
    'xxxxxxxxxx',
    'yyyyy',
    'xxxxxxxxxx',
    'yyyyy',
    'xxxxxxxxxx',
    'yyyyy' ];

r.on('end', function() {
  assert.deepStrictEqual(seen, expect);
  console.log('ok');
});