nodejs/test/parallel/test-stream-big-push.js

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

const r = new stream.Readable({
  highWaterMark: 5,
  encoding: 'utf8'
});

let reads = 0;

function _read() {
  if (reads === 0) {
    setTimeout(function() {
      r.push(str);
    }, 1);
    reads++;
  } else if (reads === 1) {
    const ret = r.push(str);
    assert.strictEqual(ret, false);
    reads++;
  } else {
    r.push(null);
  }
}

r._read = common.mustCall(_read, 3);

r.on('end', common.mustCall(function() {}));

// push some data in to start.
// we've never gotten any read event at this point.
const ret = r.push(str);
// should be false.  > hwm
assert(!ret);
let chunk = r.read();
assert.strictEqual(chunk, str);
chunk = r.read();
assert.strictEqual(chunk, null);

r.once('readable', function() {
  // this time, we'll get *all* the remaining data, because
  // it's been added synchronously, as the read WOULD take
  // us below the hwm, and so it triggered a _read() again,
  // which synchronously added more, which we then return.
  chunk = r.read();
  assert.strictEqual(chunk, str + str);

  chunk = r.read();
  assert.strictEqual(chunk, null);
});