Support transfer rates in MiB/s or KiB/s etc

[JamesDunne]

Really just need a way to format byte rates as float64 would be sufficient enough. An additional "/s" can easily be appended.

[dustin]

The implementation that comes to mind is this:

func Rate(v float64, unit string, t time.Duration) string {
	return SI(v/t.Seconds(), unit+"/s")
}

e.g.:

func TestRate(t *testing.T) {
	tests := []struct {
		v    float64
		t    time.Duration
		want string
	}{
		{100, time.Second, "100 B/s"},
		{100, 500 * time.Millisecond, "200 B/s"},
		{100, 2 * time.Second, "50 B/s"},
	}

	for _, test := range tests {
		if got := Rate(test.v, "B", test.t); got != test.want {
			t.Errorf(`Rate %v, "B", %v) = %v; want %v`, test.v, test.t, got, test.want)
		}
	}
}

Is it worth adding that function? The downside is that I'd have to manage possible additional double formatting strings, which you could do easily today with ComputeSI in a custom implementation. The exact API there is convenient if you're OK with how the doubles format, though.