Add function to ping peripheral before sending request

[evanugarte]

When Quasar is running in production, we assume the printer(s)/LED sign is at a certain IP address and forward requests to it, no questions asked. This risks having a request be forwarded to a non existent device and then the SQS message deleted meaning we cannot recover the failed request.

The ping command can be used to check if a device is up at a certain IP address. To run the ping command from Node, we can use exec. An example is below:

const { exec } = require('child_process');

exec('ping <ip address>', function(error, stdout, stderr) {
  // do something with error, stdout, stderr
});

If you're unfamiliar with ping, check out this animated YouTube video.

Some things to consider

• How do we know when the device is up/down?
  • hint: observe how the three callback function params (error, stdout, stderr) change depending on device status
• ping normally "pings" an IP address until stopped. how do we specify only a limited number of packets?

Ideal workflow

• watch the youtube video
• address the above section on things to consider
• create a function in a separate file that makes use of exec to ping a device
  • The function should return a promise, resolving true/false depending if the device is up or not.
  • If you're unfamiliar with Promises, check out this simple video.
• incorporate your new function into the LED/Print handlers.

[evanugarte]

pinging the printer should happen before Quasar replies to Clark from the print request. if the printer is down, return 500 to Clark.

game plan

• [ ] learn basic fastapi
• [ ] learn how to send a icmp packet to the printer with python
• [ ] make the logic to ping the printer only happen if a value in the config file for Quasar is set to true

game plan (clark)

• [ ] if the printer was unresponsive, on Clark we should surface this error to the user. this means the error from the Quasar API needs to be returned from the Clark API to the frontend as well