Start a shell process in Gulp with callback when process started

Question

I'm trying to run some tasks in Gulp, sequentially. One of those tasks is a shell script that performs a simple $ node app.js. How can I fire the callback so I can tell Gulp that the server has started?

tl;dr

---

So here's the bigger picture of what I'm trying to accomplish:

I'm using gulp run-sequence to fire up a number of tasks sequentially, which specifies a couple ways you should be writing your tasks in order for them to be run in sequence.

Each gulp.task() must either:

• return the stream or
• call a callback on the task

My setup:

• gulp.task("clean", ..); // returns the stream, all OK
• gulp.task("compile", ..); // returns the stream, all OK
• gulp.task("spin-server", ..); // calls the callback with a hack
• gulp.task("init-browser-sync", ..); // last task

Here's my spin-server task:

gulp.task("spin-server", function(cb) {
  exec("sh shell-utilities/spin-server");

  // @HACK allow time for the server to start before `runSequence`
  // runs the next task.
  setTimeout(function() {
    cb();
  }, 2500);
});

And here's the spin-server.sh shell script:

## Start Node server ##

node server/app.js

#######
# EOF #
#######

The problem

Right now I'm using a setTimeout hack to make sure my Node/Express server has fired up before proceeding to run the init-browser-sync task.

How can I eliminate that setTimeout hack and call cb() when my Express server actually fires up?

Answer 1

Use spawn instead of exec (require('child_process').spawn) like this :

var spawn = require('child_process').spawn;

gulp.task("spin-server", function(cb) {
  var srv = spawn("sh shell-utilities/spin-server");

  srv.stdout.on('data', data => {
    if(data.includes('server listening')) { // Or whatever your server outputs when it's done initializing
      console.log('Server initialization completed');
      return cb();
    }
  });
});

When the string server listening is found in the output of the spawned process, the cb() is called and the server is guaranteed to be initialized at that point.