[PLUGIN DEVELOPMENT] Centralising HTTP plugins

Hi there,

As the title suggests, I am currently in the process of working on some ‘HTTP type’ plugins for homebridge. More specifically, I’ve recently done a fair bit of work on the homebridge-thermostat plugin attempting to streamline it. However, I’ve run into an issue which stretches a bit further than my JavaScipt knowledge, despite all my attempts!

Here is a snippet of example code taken from the original index.js:

  _httpRequest: function (url, body, method, callback) {
      request({
          url: url,
          body: body,
          method: this.http_method,
          timeout: this.timeout,
          rejectUnauthorized: false,
          auth: this.auth
      },
          function (error, response, body) {
              callback(error, response, body);
          });
  },
  
  getTargetTemperature: function(callback) {
    this.log("[+] getTargetTemperature from:", this.apiroute+"/status");
    var url = this.apiroute+"/status";
    this._httpRequest(url, '', 'GET', function (error, response, responseBody) {
        if (error) {
          this.log("[!] Error getting targetTemperature: %s", error.message);
  	  callback(error);
        } else {
  	  var json = JSON.parse(responseBody);
  	  this.targetTemperature = parseFloat(json.targetTemperature);
  	  this.log("[*] targetTemperature: %s", this.targetTemperature);
  	  callback(null, this.targetTemperature);
        }
    }.bind(this));
  },

  setTargetTemperature: function(value, callback) {
    this.log("[+] setTargetTemperature from %s to %s", this.targetTemperature, value);
    var url = this.apiroute+"/targetTemperature/"+value;
    this._httpRequest(url, '', 'GET', function (error, response, responseBody) {
        if (error) {
          this.log("[!] Error setting targetTemperature", error.message);
  	  callback(error);
        } else {
          this.log("[*] Sucessfully set targetTemperature to %s", value);
  	  callback();
        }
    }.bind(this));
  },

As you can see, for the sake of simplicity, I have removed numerous get and set functions but have kept two (getTargetTemperature and setTargetTemperature) for the sake of illustrating my point.

To summarise the what happens with the Thermostat: When the state is refreshed (by opening the Home app), numerous (4-6) get functions are called, all of which contact the HTTP device simultaneously and attempt to retrieve the same JSON (containing data like the target temperature, current state etc.), they then proceed to extract just 1 field each; meaning that whilst the JSON only needs to be retrieved once, it is retrieved multiple times, which is extremely wasteful and can cause Homebridge to hang while this takes place. It is also worth noting that the set functions are not an issue because they are only called individually once you update a field like the target temperature.

I have tried seeking a solution to the issue. My first thought was creating a centralised function called something like _getStatuses which would be called by each of the get functions. If it was being called for the first time in a while, it would request the JSON once, parse each of the fields and store them ready for the other incoming requests, reducing the number of requests greatly.

However, the problem is that I have tried multiple approaches to this problem and none of them have worked to a satisfactory level for a variety of reasons, including the fact that JavaScript is asynchronous and makes it hard to work step-by-step. Thus, I am hoping that someone may have an idea or solution which will solve the problem. I would be really grateful if someone could provide an idea, some sample code or a pre-existing plugin which relates to the issue.

Thank you in advance for your help,

Kind regards, Tom

[NorthernMan54]

My rant against .on(‘get’

1. Using .on(‘get’ causes the home app to behave slow on loading, as homebridge needs to get current status from the device, rather than using the cached value.

2. Using automations with .on(‘get’ will not work as the status is not updated in real time, and only update when looking at the page in the home app

3. Device status does not change in real time when viewing in the home app, a change in room is required to update the status

On Dec 10, 2019, at 9:26 AM, graanco [e-mail] wrote:

I see you had the same issue as I am having… And I see that you decide to do a interval poll instead of using .on(‘get’. The reason why I am going after on get is I don’t want to use the polling (which does work). I would rather have the system only call when the user does. I this the wrong thought? And if I do it with on get instead of polling will this cause an issue with automation services with Homekit.

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[NorthernMan54]

@ebaauw Tks for your input on this and if you want to take a look at the final result take a look at this

https://github.com/Tommrodrigues/homebridge-web-thermostat

In the final design, we went with a 1 minute polling loop, removed all .on(‘get’ and used updateValue for everything