Golang Byte Array creation: append vs bytes.Join Benchmark

bytes_arr_test.go

package main

import (
	"testing"
	"bytes"
)

func TestBytesAppendIsEquivalentToJoin(t *testing.T) {
	prefix := []byte("announce")
	sep := "/"
	peerType := []byte("s")

	type serializedPeer []byte
	pk := serializedPeer("jackandjill")

	ihRaw := []byte("helloworld0123456789")
	type InfoHash [20]byte
	infoHashFromBytes := func(b []byte) InfoHash {
		if len(b) != 20 {
			panic("infohash must be 20 bytes")
		}
		var buf [20]byte
		copy(buf[:], b)
		return InfoHash(buf)
	}
	ih := infoHashFromBytes(ihRaw)

	data:= &byteArrayParts{
		sep: []byte(sep),
		p1: prefix,
		p2: ih[:],
		p3: peerType,
		p4: pk,
	}

	k1 := generateByteArrayUsingAppend(data)
	k2 := generateByteArrayUsingJoin(data)

	if bytes.Compare(k1, k2) != 0 {
		t.Fatal("both keys are not equal")
	}
}

func BenchmarkByteAppend(b *testing.B) {
	runByteArrayBenchmark(b, generateByteArrayUsingAppend)
}

func BenchmarkByteJoin(b *testing.B) {
	runByteArrayBenchmark(b, generateByteArrayUsingJoin)
}


type byteArrayParts struct {
	sep		[]byte
	p1 		[]byte
	p2		[]byte
	p3		[]byte
	p4		[]byte
}

func generateByteArrayUsingAppend(data *byteArrayParts) []byte {
	k := make([]byte, 0, len(data.sep) * 3 + len(data.p1) + len(data.p2) + len(data.p3) + len(data.p4))
	k = append(k, data.p1...)
	k = append(k, data.sep...)
	k = append(k, data.p2...)
	k = append(k, data.sep...)
	k = append(k, data.p3...)
	k = append(k, data.sep...)
	k = append(k, data.p4...)
	return k
}

func generateByteArrayUsingJoin(data *byteArrayParts) []byte {
	k := bytes.Join([][]byte{
		data.p1,
		data.p2,
		data.p3,
		data.p4,
	}, []byte(data.sep))
	return k
}

func runByteArrayBenchmark(b *testing.B, ef func(data *byteArrayParts) []byte) {
	data := &byteArrayParts{
		sep: []byte("/"),
		p1: []byte("announce"),
		p2: []byte("helloworld0123456789"),
		p3: []byte("s"),
		p4: []byte("jackandjill"),
	}
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		ret := ef(data)
		if len(ret) == 0 {
			b.Fatal("empty byte array received")
		}
	}
	b.StopTimer()
}

goos: darwin
goarch: amd64
pkg: learning_go
20000000 61.5 ns/op #BenchmarkByteAppend
20000000 76.4 ns/op #BenchmarkByteJoin
PASS

BenchmarkByteJoin is 24% slower on my local setup.