Prerequisites

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🚀 Feature Proposal

The .getResponseTime() portion of the docs states Note that unless this function is called in the [onResponse hook](https://www.fastify.io/docs/latest/Reference/Hooks#onresponse) it will always return 0.. However, I've tested it with onResponse and it doesn't return 0, it returns a very small number. This behaviour is expected, but is not represented in the docs.

I'd also like to add something to say that if you'd like to record route response time metrics, this is the place to do it.

What are your thoughts?

Reference: https://www.fastify.io/docs/latest/Reference/Reply/#getresponsetime

Motivation

Improve documentation & show how easy it is to response response time reliably (much harder in other frameworks)

Example

Note: To measure the ensure request response time, the function must be called in a onResponse hook. Calling the function in other hooks will result in 0 or very low numbers that do not represent the entire request response time.

If you would like to record request response time metrics, the result of .getResponseTime() in a onResponse hook is the recommended way to do that.