seek.go

package main

import (
	"fmt"
	"image"
	"image/color"
	"image/png"
	"io/ioutil"
	"os"
)

func main() {
	rect := image.Rectangle{image.Pt(0, 0), image.Pt(1, 1)}
	img := image.NewRGBA(rect)
	img.Set(0, 0, color.Black)

	file, _ := ioutil.TempFile(os.TempDir(), "image_test")
	defer file.Close()
	png.Encode(file, img)

	fmt.Println(png.Decode(file)) // => <nil> unexpected EOF

	file.Seek(0, 0)
	fmt.Println(png.Decode(file)) // => &{[0 0 0 255] 4 (0,0)-(1,1)} <nil>
}