nodejs: check until URL get's online - node.js

Question

I need a "forever-watchdog" for checking if an URL is reachable or not. My case is that I have to see if a media stream gets online, and if, I would need to run a shell-script. If it's not reachable (404'd), I would keep trying again in x seconds.
Could anyone please guide me into the right directions, in terms on modules, or flowing? I had problems with resolving the destination with the
isReachable = require('is-reachable');
module.
Thanks for helping!

Answer 1

Try this, should resolve you task
'use strict';
const co = require('co');
const request = require('request');
const exec = require('child_process').exec;
let getRemoteSourceStatusPromise = function(urlForCheck){
return new Promise(function (resolve, reject) {
request(urlForCheck, function(error, response){
console.log('send request...');
if(error)
return reject(error);
let result = false;
console.log('Resource response statusCode ' + response.statusCode);
if(200 === response.statusCode){
result = true;
}
return resolve(result);
});
});
};
let callShScriptPromise = function(){
let shScriptPath = './script.sh';
return new Promise(function (resolve, reject) {
console.log('Calling sh...');
exec(shScriptPath,
function (error) {
if (error)
return reject(error);
resolve(true);
});
});
};
let sleep = function (sleepInterval) {
return new Promise(function (resolve) {
setTimeout(function () {
console.log('sleep...');
resolve();
}, sleepInterval);
});
};
let loopGenerator = function* (urlForCheck, sleepInterval){
let bShScriptStarted = false;
while(true){
let bSourceStatus = yield getRemoteSourceStatusPromise(urlForCheck);
if(bSourceStatus === true){
if(!bShScriptStarted)
bShScriptStarted = yield callShScriptPromise();
}else{
bShScriptStarted = false;
}
yield sleep(sleepInterval);
}
};
//Starting loop
co(loopGenerator('http://google.com', 30000))
.catch(function (error) {
console.log(error);
})

Answer 2

const rp = require('request-promise');
const checkIfOnline = (() -> {
return new Promise((resolve, reject)=>{
rp( url ).then( response => {
// this is where you run your script
resolve();
}).catch(error=>{
setTimeout( resolve(checkIfOnline()), 5000 );
});
});
})();

Answer 3

You can send requests to the URL repeatedly. Something like this:
//I don't know how you create nodejs server, I just leave out that part.
//I use request module. sudo npm install --save request
var request = require('request');
var URL = 'https://www.google.com';
var X = 5000; //5 seconds
var sendRequest = function(){
request(URL, function(error, response, body){
if(response.statusCode === 200){//If good
runScript(); //This is the function you write to run sh
}
setTimetout(sendRequest, X);//run the function again no matter what
});
}
sendRequest();
If you want a better forever loop, I suggest you use promise.
var rp = require('request-promise');
var options = {
uri : 'https://www.google.com',
json : true
};
var X = 5000; //5 seconds, the actual time is 5 seconds plus the time to resolve
var sendRequest_promise = function(){
//return a request promise
return rp(options).then(function(response){
return response;
});
};
var sendRequest = function(){
sendRequest_promise().then(function(response){
if(response.statusCode === 200){
runScript();
}
setTimeout(sendRequest(), X);
});
};