async shotgun

asyncInvoke.js

//cmd.js
exports.invoke = function(shell, options) {
  shell.emit('async', function(resume) {
    someAsyncFn(function(result){
     shell.log(result);
      resume();
  }); 
  
  //app.js

  var rl = require('readline'),
      shell = ...
  
  var ready = true;
  //..constructors ..
  
  rl.on('line', function(userInput) {
    shell.execute(userInput);
    if (ready) {
      rl.prompt();
    }
  });
  
  shell.on('async', function(fn) {
    ready = false;
    fn(function(){
      ready = true;
      rl.prompt();
    })
  });

Nevermind. I think I'm understanding. The readline prompt resumes before the async is finished. I think I have the solution for this. I'm going to scan the invoke function signature and count the number of arguments the function is expecting. If it asks for two then I will assume they are shell and options and the function will behave synchronously. If it asks for three then the third argument will be a callback that your command can call when it's all finished.

All this callback will do is fire the "done" event from the shell. This means that you'll be able to handle the done event and do your rl.prompt() from there.

Thank you for pointing out this flaw :)

Here's what my intended solution will look like when I'm done:

exports.invoke = function (shell, options, done) {
    shell.log("Starting async task...");
    fs.readFile(pathToFile, function (err, fileData) {
        if (err) return shell.error(err);
        shell.log("File retrieved.");
        shell.log(fileData.toString());
        done();
    });
};

I will also make done accept an err argument which will cause the shell to emit an error event before the done event.

That sounds great! I assume the done event will only be fired at the end of execute if invoke is synchronous

That's correct. chevcast/shotgun#23