Provide a way to have async Meteor.method return values about meteor

[dsummersl]

Here is my current workaround btw: http://bit.ly/IcN69W

[ajoslin]

If the caller has a function as its last parameter, the callback will be called by the server with the return value or thrown error.

Here's an example (hope you don't mind the coffeescript). Try it out:

# Server
Meteor.methods
  stuff: (value) ->
    if value == 1
      # given as result in callback
      return "good!" 
    else
      # thrown meteor.errors are given as error in callback
      throw new Meteor.Error 404, "value should be 1, bro" 

# Client
Meteor.call 'stuff', 1, (error, result) ->
  console.log 'expected: error=undefined, result="good"'
  console.log 'actual:', error, result

Meteor.call 'stuff', 2, (error, result) ->
  console.log 'expected: error=Meteor.error, result=undefined'
  console.log 'actual:', error, result

http://docs.meteor.com/#methods_header

[dsummersl]

Hi ajoslin,

This feature request is for the server side, actually, not the client side. As you point out the client side supports both sync and async methods for the client to call a server method. But the server method is currently only sync.

This can be a bit of a problem if the server side implementation relies on some other 3rd party async libraries. In my case I wanted to use mongoose. But it could be a number of other libraries, as the asynchronous callback is extremely common in javascript/node.js. The link I provided shows one way of working around the problem using the fibers-promise library, but it would be nice if the meteor API provided a way of implementing server side method results in a sync as well as async way.

[jacobfike]

+1 for this.

Here is another use case. I have a login form. When I submit this form I use Meteor.call('login', username, password, loginCallback); On the server, the login method needs to validate against an LDAP server, which requires an async call. However, I can't get the method to wait for the callback, so my loginCallback function gets called almost immediately, before the LDAP check has even occurred, so it does no good.

[lukestanley]

I need to call http-get to download something and cache locally and so I must also use a callback to know when it returns a cached filename.
May use something like this: http://stackoverflow.com/a/10677578/122364

[avital]

If you are just firing an http request, our http package supports a synchronous API. http://docs.meteor.com/#meteor_http_call

If you need to make an async call for some reason (for example if you're firing more than one at the same time, or using an npm module), you can use Futures to wait until your async call is complete and then use a standard return statement. Something along the lines of the following answer: http://stackoverflow.com/a/11510874/1352190.

[neekey]

+1 for this feature. I want server to do something use 'child process' and do some 'shell' command for me...

[scottburch]

For anyone who needs it. I created this temp solution to the problem which works really well.

function runSync(func) {
    var fiber = Fiber.current;
    var result, error;

    var args = Array.prototype.slice.call(arguments, 1);

    func.apply(undefined, [cb].concat(args));
    Fiber.yield();
    if (error) throw new Meteor.Error(500, error.code, error.toString());
    return result;

    function cb(err, res) {
        error = err;
        result = res;
        fiber.run();
    }
}

Use it like this.

runSync(myFunction, arg1, arg2);

function myFunction(cb, arg1, arg2) {
    // do my async thing and then call cb(err, result);
}

[scottburch]

Forgot to mention. You also need to call this.unblock(); in the method call for this to work properly.

[neekey]

@scottburch tks, It works well!

[Xample]

Meteor call supporting callback http://docs.meteor.com/#/full/meteor_call
Making use of a promise would just do it…
something like

function doStuff()
{
var promise = new Promise()
{
Meteor.call("methodName", function(error, result)
{
if (error) promise.reject(error);
else promise.resolve(result);
})
}
return promise;
}

Usage:

doStuff().then(function(result){ /* Use the result */ })

PS: code not tested
My favorite package for promises is : https://github.com/meteor/promise

Alternative: the following package does this for you:
https://atmospherejs.com/okgrow/promise

Usage:

Meteor.promise('methodName')
   .then(function(result){ console.log(result)})
   .catch(function(err){ console.error(err))}))