How to coalesce multiple requests to a device?

[FrankC2000]

Hi there!

I am writing a platform to control a single phisical device with 48 individuals light bulbs (declared as distinct accessories inside the platform). I started from homebridge-samplePlatform.

Everything work as expected when I turn the lights individually by the Home app. But when I activate a scene with more than 10 lights, it hangs the Home app with "no response" statuses. The plugin sends several individual requests (one for each light) at the same time, flooding the device.

Here's part of the log:

EventedHTTPServer [::ffff:192.168.11.19] HTTP request: /characteristics +5s
  HAPServer [CC:22:3D:E3:CE:31] HAP Request: PUT /characteristics +0ms
  Accessory [Homebridge Mac] Processing characteristic set: [{"aid":10,"iid":9,"value":false},{"aid":11,"iid":9,"value":false},{"aid":3,"iid":9,"value":1},{"aid":2,"iid":9,"value":1},{"aid":12,"iid":9,"value":1},{"aid":14,"iid":9,"value":1},{"aid":13,"iid":9,"value":1},{"aid":9,"iid":9,"value":1},{"aid":8,"iid":9,"value":false},{"aid":7,"iid":9,"value":1},{"aid":4,"iid":9,"value":1},{"aid":5,"iid":9,"value":false},{"aid":6,"iid":9,"value":1},{"aid":15,"iid":9,"value":1}] +2ms

It shows that homebridge receive just one request from HAPServer but split in several individual requests to the device (not in the log).

I guess it should coalesce all these separated requests into a single request to the device but I have no idea how to do that, I mean, which events to implement. Can anybody help me? Examples will be welcome.

Thanks in advance!

[ebaauw]

I ran into, and solved, the very same problem in my homebridge-hue plugin for Philips Hue. HomeKit sends the characteristics from a scene in one message to homebridge, but homebridge cuts this up into multiple 'set' events to the plugin, one for each characteristic. When translating each event in a separate API request to the Hue bridge, it would report errors and drop requests when recalling a HomeKit scene, see ebaauw/homebridge-hue#15.

The Hue API allows me to combine multiple settings for the same light (on/off, brightness, hue, saturation) into one request, but requires a separate request for each light. So I took the following measures:

• On receiving the first event of a light, I save the new value and set a timer for 20ms. On receiving subsequent events, I save the new values as well. When the timer fires, I send the combined saved changes in one request. See: https://github.com/ebaauw/homebridge-hue/blob/master/lib/HueLight.js#L886
• I throttle the number of parallel requests to the Hue bridge, using deferred.gate, see https://github.com/ebaauw/homebridge-hue/blob/master/lib/HueBridge.js#L136.

[FrankC2000]

Thanks, it worked!

[aboulfad]

Hoi @ebaauw , I quickly reached the limits of "kludge" in my issue and I am trying to learn your solution. Not easy as I am learning many things and to simply my challenge I decided to stay with HAPnode.js not switching to Homebridge.

I'd appreciate if you can provide some guidance to a noob dev:

1. I use an _acc.js in HAPnode, can I implement an equivalent solution in that file ? or do I have to modify some files in HAPnode itself ?
2. Is your solution "portable" to HAPnode or does it depend on any functions/classes in Homebridge ?
3. I assume the core of the solution is at function ?

Dank u well, Tot ziens ;-)

[ebaauw]

1, 2: I really don't know - I've only ever used homebridge, never native HAP-NodeJS. I do think the Service and Characteristic stuff is HAP-NodeJS, though.

3: My solution consists of the following:

• On creating a light I setup callback functions, like SetOn() that are called by HAP-NodeJS when the corresponding characteristic is changed from HomeKit, https://github.com/ebaauw/homebridge-hue/blob/73ff16c2e2871cd5fceaa30af1ba3a5af6869aa9/lib/HueLight.js#L225;
• The callback function calls request() to store the new value, https://github.com/ebaauw/homebridge-hue/blob/73ff16c2e2871cd5fceaa30af1ba3a5af6869aa9/lib/HueLight.js#L883;
• request() stores/adds the new value to desiredState. When this is the first invocation of request() (since the last put()), it sets a timeout to call put(), https://github.com/ebaauw/homebridge-hue/blob/73ff16c2e2871cd5fceaa30af1ba3a5af6869aa9/lib/HueLight.js#L979;
• put() calls bridge.request() with desiredState, possibly containing multiple new values, https://github.com/ebaauw/homebridge-hue/blob/73ff16c2e2871cd5fceaa30af1ba3a5af6869aa9/lib/HueLight.js#L999;
• bridge.request() uses deferred to throttle calls to bridge._request(), https://github.com/ebaauw/homebridge-hue/blob/73ff16c2e2871cd5fceaa30af1ba3a5af6869aa9/lib/HueBridge.js#L157;
• bridge._request() uses request to send the REST API call to the Hue bridge, https://github.com/ebaauw/homebridge-hue/blob/73ff16c2e2871cd5fceaa30af1ba3a5af6869aa9/lib/HueBridge.js#L865.

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