You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: handler.go
    path of file: ./repos/gluetun/internal/healthcheck
    
    the code of the file until where you have to start completion: package healthcheck

import (
	"errors"
	"net/http"
	"sync"
)

type handler struct {
	healthErr   error
	healthErrMu sync.RWMutex
}

var errHealthcheckNotRunYet = errors.New("healthcheck did not run yet")

func newHandle
    
func (h *handler) ServeHTTP(responseWriter http.ResponseWriter, request *http.Request) {
	if request.Method != http.MethodGet {
		http.Error(responseWriter, "method not supported for healthcheck", http.StatusBadRequest)
		return
	}
	if err := h.getErr(); err != nil {
		http.Error(responseWriter, err.Error(), http.StatusInternalServerError)
		return
	}
	responseWriter.WriteHeader(http.StatusOK)
}