Implement custom http.ResponseWriter in golang

CustomResponseWriter.go

package main

import (
	"fmt"
	"net/http"
)

type CustomResponseWriter struct {
	body       []byte
	statusCode int
	header     http.Header
}

func NewCustomResponseWriter() *CustomResponseWriter {
	return &CustomResponseWriter{
		header: http.Header{},
	}
}

func (w *CustomResponseWriter) Header() http.Header {
	return w.header
}

func (w *CustomResponseWriter) Write(b []byte) (int, error) {
	w.body = b
	// implement it as per your requirement 
	return 0, nil
}

func (w *CustomResponseWriter) WriteHeader(statusCode int) {
	w.statusCode = statusCode
}

var okFn = func(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusOK)
}

func main() {
	r := &http.Request{
		Method: http.MethodPost,
	}
	w := NewCustomResponseWriter()
	okFn(w, r)
	fmt.Println(w.statusCode)
}