golang embed fs example

go-embed.go

package main

import (
	"embed"
	"io/fs"
	"log"
	"net/http"
	"os"
	"strconv"
	"time"
)

//go:embed build/*
var content embed.FS

var infoLog = log.New(os.Stdout, "[INFO] ", log.LstdFlags)
var errorLog = log.New(os.Stderr, "[ERROR] ", log.LstdFlags)

func withLogging(h http.Handler) http.Handler {
	var size int
	var err error
	logger := func(w http.ResponseWriter, r *http.Request) {
		now := time.Now()
		h.ServeHTTP(w, r)
		cLength := w.Header().Get("content-length")
		if cLength == "" {
			size = 0
		} else {
			size, err = strconv.Atoi(cLength)
			if err != nil {
				errorLog.Printf("got error parsing content length for %s\n [%s]", r.RequestURI, err)
			}
		}
		duration := time.Since(now)
		infoLog.Printf("uri=%s response_size=%d duration=%dms\n", r.RequestURI, size, duration.Milliseconds())
	}
	return http.HandlerFunc(logger)
}

func main() {
	mux := http.NewServeMux()
	mux.Handle("/admin", withLogging(
		http.HandlerFunc(
			func(w http.ResponseWriter, r *http.Request) {
				w.Write([]byte("OK\n"))
			}),
	))
	root, _ := fs.Sub(content, "build")
	mux.Handle("/", withLogging(http.FileServer(http.FS(root))))

	servicePort := ":9191"
	if p, ok := os.LookupEnv("PORT"); ok {
		servicePort = ":" + p
	}
    infoLog.Println("Listening on", servicePort)
	errorLog.Println(http.ListenAndServe(servicePort, mux))
}