Getting TTFB (time to first byte) value in golang

Question

I am trying to get value TTFB and Connect value

    c := exec.Command(
        "curl", "-w",
        "Connect: %{time_connect} TTFB: %{time_starttransfer} Total time: %{time_total}",
        "-o",
        "/dev/null",
        "http://my.domain/favicon.ico")

    cID, err := c.Run()
    fmt.Printf("%s", cID)

It prints a sting like

Connect: 0.205 TTFB: 0.353 Total time: 0.354

However, I need only the value of TTFB , Connect, Total time value in golang variable.

Also, Is there any way I can get the values without specifically using curl?

Answer 1

There's builtin support for this since Go 1.7. Go 1.7 added HTTP Tracing, read blog post: Introducing HTTP Tracing

You can specify callback functions which get called at the appropriate phases / points when making an HTTP(S) request. You can specify your callback functions by creating a value of httptrace.ClientTrace, and "arm" it using httptrace.WithClientTrace().

Here's an example function which gets a URL param, and prints the timing of getting it:

func timeGet(url string) {
    req, _ := http.NewRequest("GET", url, nil)

    var start, connect, dns, tlsHandshake time.Time

    trace := &httptrace.ClientTrace{
        DNSStart: func(dsi httptrace.DNSStartInfo) { dns = time.Now() },
        DNSDone: func(ddi httptrace.DNSDoneInfo) {
            fmt.Printf("DNS Done: %v\n", time.Since(dns))
        },

        TLSHandshakeStart: func() { tlsHandshake = time.Now() },
        TLSHandshakeDone: func(cs tls.ConnectionState, err error) {
            fmt.Printf("TLS Handshake: %v\n", time.Since(tlsHandshake))
        },

        ConnectStart: func(network, addr string) { connect = time.Now() },
        ConnectDone: func(network, addr string, err error) {
            fmt.Printf("Connect time: %v\n", time.Since(connect))
        },

        GotFirstResponseByte: func() {
            fmt.Printf("Time from start to first byte: %v\n", time.Since(start))
        },
    }

    req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
    start = time.Now()
    if _, err := http.DefaultTransport.RoundTrip(req); err != nil {
        log.Fatal(err)
    }
    fmt.Printf("Total time: %v\n", time.Since(start))
}

Example calling it:

timeGet("https://google.com")

Example output:

DNS Done: 7.998465ms
Connect time: 12.677085ms
TLS Handshake: 128.65394ms
Time from start to first byte: 176.461087ms
Total time: 176.723402ms

Also be sure to check out github.com/davecheney/httpstat which gives you a CLI utility that also uses the httptracing package under the hood.