food.go

package main

import (
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"path/filepath"
)

var (
	dest = flag.String("dest", "", "file name to store the latest image")
	port = flag.Int("port", 3000, "http port to run on")
)

type httpHandler func(w http.ResponseWriter, r *http.Request)
type fallibleHandler func(w http.ResponseWriter, r *http.Request) error

func handleOrLog(handler fallibleHandler) httpHandler {
	return func(w http.ResponseWriter, r *http.Request) {
		if err := handler(w, r); err != nil {
			log.Printf("error %v, expected nil", err)
			http.Error(w, err.Error(), http.StatusInternalServerError)
		}
	}
}

func uploadImage(w http.ResponseWriter, r *http.Request) error {
	tmpfile, err := ioutil.TempFile("/tmp", "food")
	if err != nil {
		return err
	}
	defer r.Body.Close()
	if _, err := io.Copy(tmpfile, r.Body); err != nil {
		return err
	}
	if err := tmpfile.Close(); err != nil {
		return err
	}
	if err := os.Rename(filepath.Join("/tmp", tmpfile.Name()), *dest); err != nil {
		return err
	}
	w.WriteHeader(http.StatusAccepted)
	return nil
}

func showImage(w http.ResponseWriter, r *http.Request) error {
	file, err := os.Open(*dest)
	if err != nil {
		return err
	}
	defer file.Close()
	_, err = io.Copy(w, file)
	return err
}

func main() {
	flag.Parse()
	http.HandleFunc("/upload", handleOrLog(uploadImage))
	http.HandleFunc("/show", handleOrLog(showImage))
	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", *port), nil))
}

added error handling