NodeJS troubleshooting help

Aaron
Aaron Member, Administrator, Moderator, Employee Posts: 636 admin
in Connectors & Integrations #1

Hi all,

I'm not very good at JavaScript coding. I spent some time on the weekend coding up a simple app that does REST polling every minute (gathering arrival times from a bus stop, via an open API), and publishing the values via MQTT onto Solace broker using MQTT.js.

Now... I've been running the program using nohup node test.js > output.txt 2>&1 & and after several hours it just terminates. No error messages or anything in the output.txt log file (I have both stdout and stderr redirecting). And I have an error hander on the client object, so I don't think it's an MQTT error. So I have no idea why it's just terminating? Is there some NodeJS debugging things I can do, to see why it terminated unexpectedly?? Thanks!!

Comments

  • amackenzie
    amackenzie Member, Employee Posts: 268 Solace Employee
    #2

    Is there a way out of your loop that doesn't create an error condition? Maybe it's just hitting that? With Javascript, it almost always is about async race conditions.

  • giri
    giri Member, Administrator, Employee Posts: 116 admin
    #3

    Node may have crashed due to unhandled rejections (a possibility!). If you can instrument your code with a handler, at least you might know why it crashed (if at all). Refer to https://blog.heroku.com/best-practices-nodejs-errors for more details.

  • Tamimi
    Tamimi Member, Administrator, Employee Posts: 538 admin
    edited May 2021 #4

    Curious to know, are you using setinterval() for your repeated REST request? You can perhaps make it simpler

    async function getArrivalTime() {
  // do your REST fetch here. You can use whatever library so for example I am using fetch from node-fetch here 
  const baseURL = `API`;
  let res = await fetch(baseURL).catch((err) => {
    throw new Error(`Error fetching content from ${baseURL}. ${err}`);
  });

  if (!res.ok) {
    throw new Error(`Response status from ${baseURL}: ${res.status}`);
  }
  // manipulate your response
  // let body = await res.text();
  // Content body from github is base64 encoded
  // return Base64.decode(JSON.parse(body).content);
}

setInterval(() => {
  let content = await getArrivalTime();
  // Console logs, write to file...etc
  // MQTT publish to broker
}, 1000);
// Note this does it every 1 second!

    and then just run your file node file.js

  • Aaron
    Aaron Member, Administrator, Moderator, Employee Posts: 636 admin
    #5

    Hi guys, thanks for the comments.

    I have added some extra try / catch blocks around various logic. There isn't much to my program, so hopefully that catches something. And added a process.on('uncaughtException') as that blog Giri suggested, so hopefully this next run turns up something.

    Thanks Tamimi. My code does a fetch(url) .then(reponse => response.json) .then(json => { some code }); And the whole thing is wrapped in a try / catch block. So no specific error handling on the fetch like yours above, no await... you have two separate error handling checks. Wondering if I should add those?

  • Tamimi
    Tamimi Member, Administrator, Employee Posts: 538 admin
    #6

    My error handling logic is thin the fetching; if the endpoint is malformed and if the return is not 200 OK. I suspect that your error is in a fetch block since its failing silently, and almost most fetch related issues raise errors. Tho you can also add that and check it out

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