@travetto/exec

travetto: Exec

Install: primary

$ npm install @travetto/exec

The exec module provides the necessary foundation for calling executables at runtime. Additionally special attention is provided to running docker containers.

Simple Execution

Just like child_process, the module exposes spawn, fork, and exec. These are generally wrappers around the underlying functionality. In addition to the base functionality, each of those functions is converted to a Promise structure, that throws an error on an non-zero return status.

A simple example would be

Code: Running a directory listing via ls

async function executeListing() {
  const { result } = Exec.spawn('ls');
  await result;
}

As you can see, the call returns not only the child process information, but the Promise to wait for. Additionally, some common patterns are provided for the default construction of the child process. In addition to the standard options for running child processes, the module also supports:

• timeout as the number of milliseconds the process can run before terminating and throwing an error
• quiet which suppresses all stdout/stderr output
• stdin as a string, buffer or stream to provide input to the program you are running;
• timeoutKill allows for registering functionality to execute when a process is force killed by timeout

Docker Support

Docker provides a unified way of executing external programs with a high level of consistency and simplicity. For that reason, the framework leverages this functionality to provide a clean cross-platform experience. The docker functionality allows you to interact with containers in two ways:

• Invoke a single operation against a container
• Spin up a container and run multiple executions against it. In this format, the container, once started, will be scheduled to terminate on Shutdown of the application.

Code: Establishing mongo as a DockerContainer instance

async function runMongo() {
  const port = 10000;
  const container = new DockerContainer('mongo:latest')
    .createTempVolume('/var/workspace')
    .exposePort(port)
    .setWorkingDir('/var/workspace')
    .forceDestroyOnShutdown();

  container.run(['--storageEngine', 'ephemeralForTest', '--port', port]);
  await container.waitForPorts();

  return;
}

Command Service

While docker containers provide a high level of flexibility, performance can be an issue. CommandService is a construct that wraps execution of a specific child program. It allows for the application to decide between using docker to invoke the child program or calling the binary against the host operating system. This is especially useful in environments where installation of programs (and specific versions) is challenging.

Code: Command Service example, using pngquant

  const converter = new CommandService({
    containerImage: 'agregad/pngquant',
    localCheck: ['pngquant', ['-h']]
  });

  async function compress(img) {
    const state = await converter.exec('pngquant', '--quality', '40-80', '--speed 1', '--force', '-');
    const out = `${img}.compressed`;

    fs.createReadStream(img).pipe(state.process.stdin);
    state.process.stdout.pipe(fs.createWriteStream(out));
    
    await state.result;
  }