libfaketime-env

Create environment variables that make libfaketime work

const libfaketimeEnv = require('libfaketime-env');

(async () => {
  await libfaketimeEnv();
  //=> {LD_PRELOAD: '/usr/lib/x86_64-linux-gnu/faketime/libfaketime.so.1'}
})();

libfaketime is useful for testing date-sensitive behavior of an application or a library:

libfaketime intercepts various system calls that programs use to retrieve the current date and time. It then reports modified (faked) dates and times (as specified by you, the user) to these programs. This means you can modify the system time a program sees without having to change the time system-wide.

Installation

Use npm.

npm install libfaketime-env

API

const libfaketimeEnv = require('libfaketime-env');

libfaketimeEnv()

Return: Promise<Object>

The resultant Object has a property LD_PRELOAD (on Linux, DYLD_INSERT_LIBRARIES on macOS) whose value is an absolute path where the libfaketime library is installed.

It first checks if the library is installed to /usr/local/lib/faketime/, then use dpkg-query --listfiles libfaketime command as a fallback. When it cannot locate the library, for example, because libfaketime is manually installed to a non-default path, the Object doesn't have either LD_PRELOAD or DYLD_INSERT_LIBRARIES.

On macOS, the Object also has DYLD_FORCE_FLAT_NAMESPACE property whose value is '1'.

// On macOS
(async () => {
  await libfaketimeEnv(); /*=> {
    DYLD_INSERT_LIBRARIES: '/usr/local/Cellar/libfaketime/0.9.7_1/lib/faketime/libfaketime.1.dylib',
    DYLD_FORCE_FLAT_NAMESPACE: '1'
  } */
})();

The return value can be used with child_process functions by passing it to the env option along with the FAKETIME environment variable.

const {execFile} = require('child_process');
const {promisify} = require('util');
const libfaketimeEnv = require('libfaketime-env');

(async () => {
  const {stdout} = await promisify(execFile)('node', ['-p', 'new Date().toLocaleString("UTC")'], {
    env: {
      ...process.env,
      ...await libfaketimeEnv(),
      FAKETIME: '2012-03-04 05:06:07'
    }
  });
  //=> '2012/3/4 5:06:07\n', not the current date
})();

License

ISC License © 2019 Shinnosuke Watanabe