sync.Pool — Reuse Allocations

package main

import (
    "bytes"
    "fmt"
    "sync"
)

var bufPool = sync.Pool{
    New: func() any { return new(bytes.Buffer) },
}

func processRequest(payload []byte) string {
    buf := bufPool.Get().(*bytes.Buffer)
    defer func() {
        buf.Reset()                          // wipe before returning
        bufPool.Put(buf)
    }()

    buf.WriteString("processed: ")
    buf.Write(payload)
    return buf.String()
}

func main() {
    var wg sync.WaitGroup
    for i := 0; i < 10; i++ {
        wg.Add(1)
        go func(i int) {
            defer wg.Done()
            fmt.Println(processRequest([]byte(fmt.Sprintf("req-%d", i))))
        }(i)
    }
    wg.Wait()
}