shares: NamespacePaddingShare can take advantage of Go's memory guarantees to zero memory and use make([]byte, LEN) instead of bytes.Repeat([]byte{0}, LEN) which is less efficient

[odeke-em]

Summary of Bug

While auditing this repository I noticed these code snippets

go-square/shares/padding.go

Line 23 in 4135f35

padding := bytes.Repeat([]byte{0}, FirstSparseShareContentSize)

and

go-square/shares/utils.go

Lines 34 to 35 in 4135f35

	padByte := []byte{0}
	padding := bytes.Repeat(padByte, missingBytes)

Insights

Those code snippets try to create zero byte slices of LEN. Go guarantees that all memory shall be zeroed per https://go.dev/ref/spec#The_zero_value and even better, make is made much more efficient than bytes.Repeat and quick benchmarks can prove this

Benchmarks

diff --git a/shares/padding.go b/shares/padding.go
index e0d905c..3c8d010 100644
--- a/shares/padding.go
+++ b/shares/padding.go
@@ -1,7 +1,6 @@
 package shares
 
 import (
-	"bytes"
 	"errors"
 
 	"github.com/celestiaorg/go-square/namespace"
@@ -20,7 +19,7 @@ func NamespacePaddingShare(ns namespace.Namespace, shareVersion uint8) (Share, e
 	if err := b.WriteSequenceLen(0); err != nil {
 		return Share{}, err
 	}
-	padding := bytes.Repeat([]byte{0}, FirstSparseShareContentSize)
+	padding := make([]byte, FirstSparseShareContentSize)
 	b.AddData(padding)
 
 	share, err := b.Build()

with this benchmark

package shares

import (
	"bytes"
	"testing"

	"github.com/celestiaorg/go-square/namespace"
)

var sink any = nil

func pad(tb testing.TB) any {
	ns1 = namespace.MustNewV0(bytes.Repeat([]byte{1}, namespace.NamespaceVersionZeroIDSize))
	got, err := NamespacePaddingShare(ns1, ShareVersionZero)
	if err != nil {
		tb.Fatal(err)
	}
	return got
}

func BenchmarkPaddingVsRepeat(b *testing.B) {
	b.ReportAllocs()

	for i := 0; i < b.N; i++ {
		sink = pad(b)
	}

	if sink == nil {
		b.Fatal("benchmark did not run!")
	}
}

which shows the improvements

$ benchstat before.txt after.txt 
name               old time/op    new time/op    delta
PaddingVsRepeat-8     674ns ± 1%     538ns ± 0%  -20.22%  (p=0.000 n=9+9)

name               old alloc/op   new alloc/op   delta
PaddingVsRepeat-8    1.31kB ± 0%    0.83kB ± 0%  -36.59%  (p=0.000 n=10+10)

name               old allocs/op  new allocs/op  delta
PaddingVsRepeat-8      12.0 ± 0%      11.0 ± 0%   -8.33%  (p=0.000 n=10+10)

/cc @elias-orijtech @liamsi

Version

4135f35

Steps to Reproduce

Please see the details above

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned