HTTP server that serves a randomly generated-on-the-fly GIF (using https://gist.github.com/ImJasonH/7b309a4af2d4e32a2649)

gistfile1.txt

package main

import (
	"image"
	"image/color"
	"image/color/palette"
	"log"
	"math/rand"
	"net/http"
	"time"

	supergif "gist.github.com/7b309a4af2d4e32a2649.git"
)

func main() {
	http.HandleFunc("/", serveRandomGIF)
	log.Fatal(http.ListenAndServe(":8080", nil))
}

const width = 200
const height = 200

func serveRandomGIF(w http.ResponseWriter, r *http.Request) {
	f, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "ResponseWriter does not support Flush", http.StatusBadRequest)
		return
	}
	i, err := supergif.NewIncrementalEncoder(w, randomImage())
	if err != nil {
		log.Fatal(err)
	}
	log.Println("wrote first frame")

	for {
		f.Flush()
		time.Sleep(5*time.Second)
		if err := i.EncodeNext(randomImage()); err != nil {
			log.Fatal(err)
		}
		log.Println("wrote frame")
	}
}

func randomImage() *image.Paletted {
	pm := image.NewPaletted(image.Rectangle{image.Point{0,0}, image.Point{width, height}}, palette.WebSafe)
	pm.Set(rand.Intn(width), rand.Intn(height), color.White)
	return pm
}

on line 26, instead of returning an error, just wrap the ResponseWriter in a bufio.NewWriter and you'll get Flush from that.