node/test/parallel/test-fs-readfile.js

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

// This test ensures that fs.readFile correctly returns the
// contents of varying-sized files.

const tmpdir = require('../../test/common/tmpdir');
const assert = require('assert');
const fs = require('fs');
const path = require('path');

const prefix = `.removeme-fs-readfile-${process.pid}`;

tmpdir.refresh();

const fileInfo = [
  { name: path.join(tmpdir.path, `${prefix}-1K.txt`),
    len: 1024,
  },
  { name: path.join(tmpdir.path, `${prefix}-64K.txt`),
    len: 64 * 1024,
  },
  { name: path.join(tmpdir.path, `${prefix}-64KLessOne.txt`),
    len: (64 * 1024) - 1,
  },
  { name: path.join(tmpdir.path, `${prefix}-1M.txt`),
    len: 1 * 1024 * 1024,
  },
  { name: path.join(tmpdir.path, `${prefix}-1MPlusOne.txt`),
    len: (1 * 1024 * 1024) + 1,
  },
];

// Populate each fileInfo (and file) with unique fill.
const sectorSize = 512;
for (const e of fileInfo) {
  e.contents = Buffer.allocUnsafe(e.len);

  // This accounts for anything unusual in Node's implementation of readFile.
  // Using e.g. 'aa...aa' would miss bugs like Node re-reading
  // the same section twice instead of two separate sections.
  for (let offset = 0; offset < e.len; offset += sectorSize) {
    const fillByte = 256 * Math.random();
    const nBytesToFill = Math.min(sectorSize, e.len - offset);
    e.contents.fill(fillByte, offset, offset + nBytesToFill);
  }

  fs.writeFileSync(e.name, e.contents);
}
// All files are now populated.

// Test readFile on each size.
for (const e of fileInfo) {
  fs.readFile(e.name, common.mustCall((err, buf) => {
    console.log(`Validating readFile on file ${e.name} of length ${e.len}`);
    assert.ifError(err, 'An error occurred');
    assert.deepStrictEqual(buf, e.contents, 'Incorrect file contents');
  }));
}