为承诺中的回调添加超时并拒绝

Question

I'm converting socket.io's emit function to a promise like this.

var io = require("socket.io-client")
var Promise = require("bluebird")
var _ = require("underscore")

io.emitAsync = function(event, payload){
  return new Promise(function (resolve, reject) {
    return io.emit(event, payload, function(){
      var args = _.toArray(arguments)
      if(args[0]) reject(new Error(args[0]))
      resolve.apply(null, args)
    })
  })
}

I couldn't use promiseify because the io.emit callback doesn't return a node-style callback signature. The first argument can't be an error object. So the plan is to pass a string error message, the promise above will reject if the first argument is truthy . This is all fine and dandy, here's the problem.

If you don't return a callback in your socket.on then this promise above will never resolve or reject anything. So what I need is a timeout this callback , if nothing comes back within an allotted period of time then it will reject(new Error("timeout")) . Thing is I have no clue how to do that. Ideally I can set the seconds to wait within the function above, or if know there's no callback for a given event I'd want to resolve , so ideally it's a parameter of emitAsync itself. Thoughts?

Answer 1

You could just use the Bluebird timeout method of course…

The lower-level solution would be to use setTimeout :

new Promise(function (resolve, reject) {
  io.emit(event, payload, function(err){
    if(err) reject(new Error(err))
    resolve(_.toArray(arguments).slice(1));
  })
  setTimeout(function(){
    reject(new Error("timeout"));
  }, seconds*1000);
})