Measuring `io.Writer` vs. `io.ReaderFrom`

results.txt

BenchmarkNaiveWriter	10000000	       157 ns/op	425060032.69 MB/s
BenchmarkAwesomeWriter	     500	   5721802 ns/op	11728.62 MB/s
BenchmarkDiscard	     500	   5735134 ns/op	11701.36 MB/s

writer_test.go

package main

import (
	"bytes"
	"io"
	"io/ioutil"
	"testing"
)

const todo = 64 * 1024 * 1024

type naiveWriter struct {
	o io.Writer
}

func (nw naiveWriter) Write(b []byte) (int, error) {
	return nw.o.Write(b)
}

type awesomeWriter struct {
	o io.Writer
}

func (aw awesomeWriter) Write(b []byte) (int, error) {
	return aw.o.Write(b)
}

func (aw awesomeWriter) ReadFrom(r io.Reader) (int64, error) {
	if rf, ok := aw.o.(io.ReaderFrom); ok {
		return rf.ReadFrom(r)
	}
	return io.Copy(aw.o, r)
}

func bench(b *testing.B, w io.Writer) {
	b.StopTimer()

	data := make([]byte, todo)
	b.SetBytes(todo)

	b.StartTimer()

	for i := 0; i < b.N; i++ {
		n, err := io.Copy(w, bytes.NewReader(data))
		if err != nil {
			b.Fatalf("Error copying: %v", err)
		}
		if n != todo {
			b.Fatalf("Didn't copy enough byte: %v / %v", n, todo)
		}
	}
}

func BenchmarkNaiveWriter(b *testing.B) {
	bench(b, &naiveWriter{ioutil.Discard})
}

func BenchmarkAwesomeWriter(b *testing.B) {
	bench(b, &awesomeWriter{ioutil.Discard})
}

func BenchmarkDiscard(b *testing.B) {
	bench(b, ioutil.Discard)
}