如何构建Express应用以在Raspberry Pi3上运行灯条

Question

I've set up a node server on a raspberry pi to display a sequence of colors on an Adafruit Dotstar light strip. The functionality works as follows: I make an HTTP request to localhost:8000/fade , and the server responds by running the fade.js file, which is an infinite loop that fades through different colors on the light strip. Unfortunately, I'd like to be able to exit this command and shut off the light strip with another request to localhost:8000/off .

I've experimented with the child_process package in order to run the "fade" code, while also listening to new requests. However, I'm unable to kill the "fade" process.

Posted below is my app.js code. Any suggestions on how to kill the child_process, or perhaps restructure the code in some other way to accomplish the same goal? I really just need to be able to run the "fade" code continuously, while also responding to new requests.

ps This is my first JS project so go easy! Any help is appreciated.

app.js:

var express     = require('express'),
    app         = express();

app.get('/', function (req, res) {
  res.send('App is responding to requests');
});

app.get('/fade', function (req, res) {
  var fork = require('child_process').fork;
  child = fork('./sequences/fade.js');
});

app.get('/off', function (req, res) {
  var fork = require('child_process').fork;
  child = fork('./sequences/off.js');
});

app.listen(8000, function () {
  console.log('Example app listening on port 8000!')
})

fade.js:

console.log("running fade.js");
var dotstar     = require('dotstar'),
    SPI         = require('pi-spi'),
    sleep       = require('sleep');

spi = SPI.initialize('/dev/spidev0.0');
const ledStripLength = 30;

const ledStrip = new dotstar.Dotstar(spi, {
  length: ledStripLength
});

while(1) {
    fade(); //where fade is a long sequence of colors
};

Answer 1

var child; // Outer scope, available in both functions.

app.get('/fade', function (req, res) {
  var fork = require('child_process').fork;
  child = fork('./sequences/fade.js');
});

app.get('/off', function (req, res) {
  // (might be a good idea to check if child exists and is running first...)
  child.kill('SIGHUP');
});

Also http://programmergamer.blogspot.com/2013/05/clarification-on-sigint-sigterm-sigkill.html

SIGHUP: ... A process has to explicitly handle this signal for it to work. ...

So SIGINT if you want to close without handling it on the fork side, or SIGKILL to just kill that mofo.