Long running boot scripts may break the sequence of mounting middleware.

[ih2502mk]

Just pointing this out here in case someone encounters similar issue.

In a server.js file, that normally gets generated by slc loopback there is a set of middleware mounted on the app like this:

app.use(loopback.favicon());
app.use(loopback.compress());

boot(app, __dirname); 

app.use(loopback.urlNotFound());
app.use(loopback.errorHandler());

app.start = function() {
  return app.listen(function() {
    app.emit('started');
    console.log('Web server listening at: %s', app.get('url'));    
  });
};

if (require.main === module) {
  app.start();
}

The problem that I've encountered happens when I have some long running asynchronous boot script in my ./boot directory. The actual reason I believe is my boot script process.nextTick()ing its callback. I'm not using process.nextTick() directly but some module that I use — does.

What happens is while boot() function is doing its thing server.js goes on further and mounts loopback.urlNotFound() and loopback.errorHandler() prior to mounting whatever else should get mounted in other boot scripts.

boot() function accepts a callback and also makes app emit 'booted' event reliably once boot scripts finish. One of the solutions is to use 'booted' event on the app object like this:

app.use(loopback.favicon());
app.use(loopback.compress());

boot(app, __dirname); 

app.once('booted', function() {

  app.use(loopback.urlNotFound());
  app.use(loopback.errorHandler());

  app.start = function() {
    return app.listen(function() {
      app.emit('started');
      console.log('Web server listening at: %s', app.get('url'));    
    });
  };

  if (require.main === module) {
    app.start();
  }
})

[raymondfeng]

If you have async boot scripts, boot(app, __dirname, function(err) {...}); should be used to wrap the rest.

@bajtos Have we updated the generator-loopback to scaffold server.js?

[superkhau]

@raymondfeng not yet, that one is on my list

[superkhau]

@ih2502mk There is an example of the async boot script @raymondfeng mentioned here: https://github.com/strongloop/loopback-example-app-logic/blob/master/examples/async-boot-script/server.js#L16-L23

[ih2502mk]

Yes, actually doing the rest in callback is apparently better because app.once('booted', ...) may execute later than the 'booted' event emits.

[bajtos]

See strongloop/loopback-workspace#170 and the related pull requests, most notably strongloop/loopback-workspace#172.

[bajtos]

Also note that the new template registers middleware via middleware.json using phases.

Another solution (workaround) is to rewrite your code to use phases too:

boot(app, __dirname); 

app.middleware('final', loopback.urlNotFound());
app.middleware('final:after', loopback.errorHandler());

[raymondfeng]

I'm closing the issue based on the solutions proposed.