HTTP Server-Timing for Go

This is a fork of github.com/mitchellh/go-server-timing and extends it with the following features:

• Updated dependencies.
• Round down all timing information to milliseconds to not be too precise (and potentially open a side channel).
• Do not set Server-Timing header on 304 Not Modified responses.
• Set header even in the case of a panic.

To add it, do:

go get github.com/tozd/go-server-timing@tozd

If you already using github.com/mitchellh/go-server-timing as a dependency, you can also do find/replace of github.com/mitchellh/go-server-timing with github.com/tozd/go-server-timing in your code.

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This is a library including middleware for using HTTP Server-Timing with Go. This header allows a server to send timing information from the backend, such as database access time, file reads, etc. The timing information can be then be inspected in the standard browser developer tools:

Features

• Middleware for injecting the server timing struct into the request Context and writing the Server-Timing header.

• Concurrency-safe structures for easily recording timings of multiple concurrency tasks.

• Parse Server-Timing headers as a client.

• Note: No browser properly supports sending the Server-Timing header as an HTTP Trailer so the Middleware only supports a normal header currently.

Browser Support

Browser support is required to view server timings easily. Because server timings are sent as an HTTP header, there is no negative impact to sending the header to unsupported browsers.

• Either Chrome 65 or higher or Firefox 71 or higher is required to properly display server timings in the devtools.

• IE, Opera, and others are unknown at this time.

Usage

Example usage is shown below. A fully runnable example is available in the example/ directory.

func main() {
	// Our handler. In a real application this might be your root router,
	// or some subset of your router. Wrapping this ensures that all routes
	// handled by this handler have access to the server timing header struct.
	var h http.Handler = http.HandlerFunc(handler)

	// Wrap our handler with the server timing middleware
	h = servertiming.Middleware(h, nil)

	// Start!
	http.ListenAndServe(":8080", h)
}

func handler(w http.ResponseWriter, r *http.Request) {
	// Get our timing header builder from the context
	timing := servertiming.FromContext(r.Context())

	// Imagine your handler performs some tasks in a goroutine, such as
	// accessing some remote service. timing is concurrency safe so we can
	// record how long that takes. Let's simulate making 5 concurrent requests
	// to various servicse.
	var wg sync.WaitGroup
	for i := 0; i < 5; i++ {
		wg.Add(1)
		name := fmt.Sprintf("service-%d", i)
		go func(name string) {
			// This creats a new metric and starts the timer. The Stop is
			// deferred so when the function exits it'll record the duration.
			defer timing.NewMetric(name).Start().Stop()
			time.Sleep(random(25, 75))
			wg.Done()
		}(name)
	}

	// Imagine this is just some blocking code in your main handler such
	// as a SQL query. Let's record that.
	m := timing.NewMetric("sql").WithDesc("SQL query").Start()
	time.Sleep(random(20, 50))
	m.Stop()

	// Wait for the goroutine to end
	wg.Wait()

	// You could continue recording more metrics, but let's just return now
	w.WriteHeader(200)
	w.Write([]byte("Done. Check your browser inspector timing details."))
}

func random(min, max int) time.Duration {
	return (time.Duration(rand.Intn(max-min) + min)) * time.Millisecond
}