makeHealthcheck returns a healthcheck http.HandlerFunc

healthCheck.go

package main

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"os"

	gohm "github.com/karrick/gohm/v2"
)

func makeHealthcheck(downfilePathname string) http.HandlerFunc {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Headers are always going to be the same for this request.
		h := w.Header()
		h.Set("Cache-Control", "no-cache, no-store")
		h.Set("Content-Type", "text/plain; charset=utf-8")

		// When no down file, reply Status OK, and text GOOD.
		fi, err := os.Stat(downfilePathname)
		if err != nil {
			if _, err = w.Write([]byte("GOOD\r\n")); err != nil {
				gohm.Error(w, err.Error(), http.StatusInternalServerError)
			}
			return
		}

		// Otherwise, reply Status Service Unavailable, with text "BAD".

		if fi.Size() == 0 {
			// When empty down file, just reply.
			gohm.Error(w, fmt.Sprintf("BAD: %s\r\n", downfilePathname), http.StatusServiceUnavailable)
			return
		}

		// Otherwise, append down file contents to response.
		message, err := ioutil.ReadFile(downfilePathname)
		if err != nil {
			message = []byte(err.Error())
		}
		gohm.Error(w, fmt.Sprintf("BAD: %s\r\n%s\r\n", downfilePathname, message), http.StatusServiceUnavailable)
	})
}