internal/png/stdlibreader.go
func Decode(r io.Reader) (image.Image, error) {
	d := &decoder{
		r:   r,
		crc: crc32.NewIEEE(),
	}
	if err := d.checkHeader(); err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		return nil, err
	}
	for d.stage != dsSeenIEND {
		if err := d.parseChunk(); err != nil {
			if err == io.EOF {
				err = io.ErrUnexpectedEOF
			}
			return nil, err
		}
	}
	return d.img, nil
}
func Decode(r io.Reader) (image.Image, error) {
	d := &decoder{
		r:   r,
		crc: crc32.NewIEEE(),
	}
	if err := d.checkHeader(); err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		return nil, err
	}
	for d.stage != dsSeenIEND {
		if err := d.parseChunk(); err != nil {
			if err == io.EOF {
				err = io.ErrUnexpectedEOF
			}
			return nil, err
		}
	}
	return d.img, nil
}
// Decode reads a PNG image from r and returns it as an image.Image.
// The type of Image returned depends on the PNG contents.