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Learning HTTP caching in Go
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package main | |
import ( | |
"bytes" | |
"flag" | |
"image" | |
"image/color" | |
"image/draw" | |
"image/jpeg" | |
"log" | |
"net/http" | |
"strconv" | |
"strings" | |
) | |
var root = flag.String("root", ".", "file system path") | |
func main() { | |
http.HandleFunc("/black/", blackHandler) | |
http.Handle("/", http.FileServer(http.Dir(*root))) | |
log.Println("Listening on 8080") | |
err := http.ListenAndServe(":8080", nil) | |
if err != nil { | |
log.Fatal("ListenAndServe:", err) | |
} | |
} | |
func blackHandler(w http.ResponseWriter, r *http.Request) { | |
key := "black" | |
e := `"` + key + `"` | |
w.Header().Set("Etag", e) | |
w.Header().Set("Cache-Control", "max-age=2592000") // 30 days | |
if match := r.Header.Get("If-None-Match"); match != "" { | |
if strings.Contains(match, e) { | |
w.WriteHeader(http.StatusNotModified) | |
return | |
} | |
} | |
m := image.NewRGBA(image.Rect(0, 0, 240, 240)) | |
black := color.RGBA{0, 0, 0, 255} | |
draw.Draw(m, m.Bounds(), &image.Uniform{black}, image.ZP, draw.Src) | |
var img image.Image = m | |
writeImage(w, &img) | |
} | |
// writeImage encodes an image in jpeg format and writes it into ResponseWriter. | |
func writeImage(w http.ResponseWriter, img *image.Image) { | |
buffer := new(bytes.Buffer) | |
if err := jpeg.Encode(buffer, *img, nil); err != nil { | |
log.Println("unable to encode image.") | |
} | |
w.Header().Set("Content-Type", "image/jpeg") | |
w.Header().Set("Content-Length", strconv.Itoa(len(buffer.Bytes()))) | |
if _, err := w.Write(buffer.Bytes()); err != nil { | |
log.Println("unable to write image.") | |
} | |
} |
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