statusCallback

August 24, 2023 ยท View on GitHub

In-depth examples for the statusCallback API parameter.

options.statusCallback(error, result)

This function, if present, is invoked after every request is finished. It uses the old-style convention (error, result): the error is only present if the request fails, while the result is always present and contains info about the request.

Warning: The format for statusCallback has changed in version 7+. The third parameter latency has been removed due to performance reasons.

Warning: The format for statusCallback has changed in version 2.0.0 onwards. It used to be statusCallback(latency, result, error), it has been changed to conform to the usual Node.js standard.

result format

The result parameter has the following attributes, always present:

  • host: the host where the request was sent.
  • path: the URL path to send the request.
  • `method: HTTP method used.
  • `statusCode: HTTP status code, 200 is OK.
  • `body: content received from the server.
  • `headers: sent by the server.
  • requestElapsed: time in milliseconds it took to complete this individual request.
  • requestIndex: 0-based index of this particular request in the sequence of all requests to be made.
  • instanceIndex: the loadtest(...) instance index. This is useful if you call loadtest() more than once.

Example Result

A sample result might look like this:

{
	host: 'localhost',
	path: '/',
	method: 'GET',
	statusCode: 200,
	body: '<html><body>hi</body></html>',
	headers: [...],
	requestElapsed: 248,
	requestIndex: 8748,
	instanceIndex: 5,
}

Full example

A full example of how to use the statusCallback follows:

import {loadTest} from 'loadtest'

function statusCallback(error, result, latency) {
    console.log('Current latency %j, result %j, error %j', latency, result, error)
    console.log('----')
    console.log('Request elapsed milliseconds: ', result.requestElapsed)
    console.log('Request index: ', result.requestIndex)
    console.log('Request loadtest() instance index: ', result.instanceIndex)
}

const options = {
    url: 'http://localhost:8000',
    maxRequests: 1000,
    statusCallback: statusCallback
}

loadTest(options, function(error) {
    if (error) {
        return console.error('Got an error: %s', error)
    }
    console.log('Tests run successfully')
})

Adding Request Data

In some situations request data needs to be available in the statusCallBack. This data can be assigned to request.labels in the requestGenerator:

const options = {
	// ...
	requestGenerator: (params, options, client, callback) => {
		// ...
        const randomInputData = Math.random().toString().substr(2, 8);
        const message = JSON.stringify({ randomInputData })
		const request = client(options, callback);
        request.labels = randomInputData;
		request.write(message);
		return request;
	}
};

Then in statusCallBack the labels can be accessed through result.labels:

function statusCallback(error, result, latency) {
    console.log(result.labels);
}