On the client:

1. Can you tell on page load whether a resume login attempt will be made?
2. Is there a hook for when the attempt returns? Can I listen for the right DDP message?

EDIT: Looks like Meteor.userId() is defined on page load when a resume login attempt will be made, which takes care of #1.

Here are a couple solutions:

Watch DDP on client

Unfortunately by the time the stream handler is called with the result of the login method, Meteor.connection._methodInvokers has been cleared – hence the search function. It would be nice if there was a different / more efficient way to know resumeMethodId. A few possibilities:

• Is it guaranteed to have id "1"?
• A hook that is called when Meteor decides to call login
• If Meteor.connection._methodInvokers were reactive, I could do an autorun that stops after the id is found.

.

resumeAttemptComplete = (success) ->
  console.log 'resumeAttemptComplete', success

resumeMethodId = null

searchForResumeMethodId = ->
  for id, invoker of Meteor.connection._methodInvokers
    sentMessage = invoker._message
    if sentMessage.method is 'login' and sentMessage.params[0].resume?
      resumeMethodId = id

if Meteor.isClient
  Meteor.connection._stream.on 'message', (messageString) ->
    unless resumeMethodId
      searchForResumeMethodId()

    message = JSON.parse messageString

    if message.id is resumeMethodId and message.msg is 'result'
      resumeAttemptComplete !message.error

_methodInvokers definition: https://github.com/meteor/meteor/blob/de74f2707ef34d1b9361784ecb4aa57803d34ae8/packages/ddp-client/livedata_connection.js#L79-L83

Server onLogin sends event to client

// server:

// map of connection ids -> publish function contexts
let onResumePublishers = {}

Meteor.publish('onResume', function () {
  onResumePublishers[this.connection.id] = this

  this.ready()

  this.onStop(() => {
    delete onResumePublishers[this.connection.id]
  })
})

let handleLoginEvent = function({connection, type}, loggedIn) {
  if (type === 'resume') {
    let publisher = onResumePublishers[connection.id]
    if (publisher)
      publisher.added('onResume', connection.id, {loggedIn}})
  }
}

Accounts.onLogin(function (loginAttempt) {
  handleLoginEvent(loginAttempt, true)
})

Accounts.onLoginFailure(function (loginAttempt) {
  handleLoginEvent(loginAttempt, false)
})

// client: 

let resumeExpires = new Date(localStorage.getItem('Meteor.loginTokenExpires'))
let resumeAttemptBeingMade = resumeExpires && resumeExpires > new Date()

let OnResume = new Mongo.Collection('onResume')

let onResumeSubscription = Meteor.subscribe('onResume')

OnResume.find(Meteor.connection.id).observeChanges(
  added(id, {loggedIn}) {
    onResumeSubscription.stop()
    onResumeAttemptCompleted(loggedIn)
  }
})

let onResumeAttemptCompleted = function(success) {
  // ...
}