Go sub slice cloning

sub_slice_clone.go

package main

import (
	"bytes"
	"fmt"
	"unsafe"
)

type Message struct {
	buffer   []byte
	headers  []byte // buffer[0:n] sub-slice
	body     []byte // buffer[n:x] sub-slice
	trailers []byte // buffer[x: ] sub-slice
}

func (m *Message) Clone() Message {
	m2 := Message{
		buffer: make([]byte, len(m.buffer), cap(m.buffer)),
	}

	copy(m2.buffer, m.buffer)

	pBuffer := (uintptr)(unsafe.Pointer(&m.buffer[0]))
	pHeaders := (uintptr)(unsafe.Pointer(&m.headers[0]))
	pBody := (uintptr)(unsafe.Pointer(&m.body[0]))
	pTrailers := (uintptr)(unsafe.Pointer(&m.trailers[0]))

	m2.headers = m2.buffer[pHeaders-pBuffer : pHeaders-pBuffer+uintptr(len(m.headers))]
	m2.body = m2.buffer[pBody-pBuffer : pBody-pBuffer+uintptr(len(m.body))]
	m2.trailers = m2.buffer[pTrailers-pBuffer : pTrailers-pBuffer+uintptr(len(m.trailers))]

	return m2
}

func (m *Message) String() string {
	pBuffer := (uintptr)(unsafe.Pointer(&m.buffer[0]))
	pHeaders := (uintptr)(unsafe.Pointer(&m.headers[0]))
	pBody := (uintptr)(unsafe.Pointer(&m.body[0]))
	pTrailers := (uintptr)(unsafe.Pointer(&m.trailers[0]))

	buf := &bytes.Buffer{}
	fmt.Fprintf(buf, "buffer:   addr = %p, (uintptr)(unsafe.Pointer(&m.buffer[0]))   = %d, len(m.buffer)   = %2.d\n", m.buffer, (uintptr)(pBuffer), len(m.buffer))
	fmt.Fprintf(buf, "headers:  addr = %p, (uintptr)(unsafe.Pointer(&m.headers[0]))  = %d, len(m.headers)  = %2.d, bufferOffset = %d\n", m.headers, pHeaders, len(m.headers), pHeaders-pBuffer)
	fmt.Fprintf(buf, "body:     addr = %p, (uintptr)(unsafe.Pointer(&m.body[0]))     = %d, len(m.body)     = %2.d, bufferOffset = %d\n", m.body, pBody, len(m.body), pBody-pBuffer)
	fmt.Fprintf(buf, "trailers: addr = %p, (uintptr)(unsafe.Pointer(&m.trailers[0])) = %d, len(m.trailers) = %2.d, bufferOffset = %d\n", m.trailers, pTrailers, len(m.trailers), pTrailers-pBuffer)
	return buf.String()
}

func main() {
	m := Message{
		buffer: []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
	}
	m.headers = m.buffer[:3]
	m.body = m.buffer[3:6]
	m.trailers = m.buffer[6:]

	fmt.Printf("m: %p -> %v\n", &m.buffer, m.buffer)
	fmt.Printf("m: %p -> %v\n", &m.headers, m.headers)
	fmt.Printf("m: %p -> %v\n", &m.body, m.body)
	fmt.Printf("m: %p -> %v\n", &m.trailers, m.trailers)
	fmt.Print(m.String())
	m2 := m.Clone()
	fmt.Printf("m2: %p -> %v\n", &m2.buffer, m2.buffer)
	fmt.Printf("m2: %p -> %v\n", &m2.headers, m2.headers)
	fmt.Printf("m2: %p -> %v\n", &m2.body, m2.body)
	fmt.Printf("m2: %p -> %v\n", &m2.trailers, m2.trailers)
	fmt.Print(m2.String())

	m.buffer[0] = 99

	fmt.Printf("m: %p -> %v\n", &m.buffer, m.buffer)
	fmt.Printf("m: %p -> %v\n", &m.headers, m.headers)
	fmt.Printf("m: %p -> %v\n", &m.body, m.body)
	fmt.Printf("m: %p -> %v\n", &m.trailers, m.trailers)
	fmt.Printf("m2: %p -> %v\n", &m2.buffer, m2.buffer)
	fmt.Printf("m2: %p -> %v\n", &m2.headers, m2.headers)
	fmt.Printf("m2: %p -> %v\n", &m2.body, m2.body)
	fmt.Printf("m2: %p -> %v\n", &m2.trailers, m2.trailers)
	fmt.Print(m2.String())
}