How to send a function as payload of socket notification?

ngnijland

Hello,

When I receive a socket notification in my node_helper.js file I want to sent a socket notification with an object containing a function as value of one of its keys. Like this:

const NodeHelper = require('node_helper');
const someFunction = require('./someFunction');

module.exports = NodeHelper.create({
  start: function () {
    console.log('Start node helper');
  },

  socketNotificationReceived: function (notification) {
    if (notification === 'FOO') {
      this.sendSocketNotification('FOO', { bar: someFunction });
    }
  },
});

However, when I receive this notification inside my main module file the function is not present in the payload:

  socketNotificationReceived: function (notification, payload) {
    if (notification === 'FOO') {
      console.log(payload.bar); // This logs 'undefined'
    }
  },

Any other values (object, arrays, etc) I pass in the payload are received correctly.

Does somebody know why the function I pass with the payload is undefined when I receive the socket notification in my main module file?

sdetweil

@ngnijland I think u have to send the entire function in the packet. It can’t contain the address of anything on the other side

ngnijland

@sdetweil thanks for your reply!

I don’t think I completely understand you. What do you mean with “send the entire function”? Do you mean I can’t import a reference? And should write out the function in the node_helper.js file?

@ngnijland
Impossible in the current MM legacy structure.
those processes are separated and can not share function.

2 reasons;

The function itself cannot be transferred through socket (JSON doesn’t allow it)
If the function depends on some dependencies, it will lose them.

Anyway, if the function itself is somehow simple and has no dependency, there could be some trick.

var originalPayload = {
  "something": "hello, world",
  "someFunc" : (value) => {
    console.log(value)
    return value
  }
}

originalPayload.someFunc("Original Execution.")


let replacer = (key, value) => {
  if (typeof value == "function") {
    return "__FUNC__" + value.toString()
  }
  return value
}

// Encode function in payload object
var encodedPayload = JSON.stringify(originalPayload, replacer, 2)
console.log("----")
console.log(encodedPayload)
console.log("----")
// encodedPayload will have;
// {
//   "something": "hello, world",
//   "someFunc": "__FUNC__(value) => {\n console.log(value)\n return value\n  }"
// }

// Now you can transfer this string as payload of socketNotification.
// this.sendSocketNotification("SOME_EVENT", encodedPayload)
// ...

// Let's assume you got a payload through socketNotification
var receivedPayload = encodedPayload

let reviver = (key, value) => {
  if (typeof value === 'string' && value.indexOf('__FUNC__') === 0) {
    value = value.slice(8)
    let functionTemplate = `(${value})`
    return eval(functionTemplate)
  }
  return value
}

var revivedPayload = JSON.parse(receivedPayload, reviver)
revivedPayload.someFunc("Function is revived.")

CAUTION
If the function requires dependencies (node modules, injected Object, references out of scope, …) those will be lost and it will cause an error.

ngnijland

@Sean
Ah ofcourse, thanks for the explanation!

My function does not have dependencies. I’ll use good old eval to fix this!

My use case is that I need to use a different function based on the language setting of the mirror. These functions live in a separate folder and I import them in the node_helper.js file (together with some other arrays and objects I need based on language). For now I’ll use this solution, maybe in the future I build in a build step in my module so I can import the files directly into my main module file.

https://github.com/ngnijland/MMM-text-clock/pull/2