Function Transform

transform.go:41–129

Transform the provided image. img should contain the raw bytes of an encoded image in one of the supported formats (gif, jpeg, or png). The bytes of a similarly encoded image is returned.

(img []byte, opt Options)

// encoded image in one of the supported formats (gif, jpeg, or png).  The
// bytes of a similarly encoded image is returned.
func Transform(img []byte, opt Options) ([]byte, error) {
	if !opt.transform() {
		// bail if no transformation was requested
		return img, nil
	}

	// decode image metadata
	cfg, _, err := image.DecodeConfig(bytes.NewReader(img))
	if err != nil {
		return nil, err
	}

	// prevent pixel flooding attacks
	// accept no larger than a 100 megapixel image.
	const maxPixels = 100_000_000
	if cfg.Width*cfg.Height > maxPixels {
		return nil, errors.New("image too large")
	}

	// decode image
	m, format, err := image.Decode(bytes.NewReader(img))
	if err != nil {
		return nil, err
	}

	// apply EXIF orientation for jpeg and tiff source images. Read at most
	// up to maxExifSize looking for EXIF tags.
	if format == "jpeg" || format == "tiff" {
		r := io.LimitReader(bytes.NewReader(img), maxExifSize)
		if exifOpt := exifOrientation(r); exifOpt.transform() {
			m = transformImage(m, exifOpt)
		}
	}

	// encode webp and tiff as jpeg by default
	if format == "tiff" || format == "webp" {
		format = "jpeg"
	}

	if opt.Format != "" {
		format = opt.Format
	}

	// transform and encode image
	buf := new(bytes.Buffer)
	switch format {
	case "bmp":
		m = transformImage(m, opt)
		err = bmp.Encode(buf, m)
		if err != nil {
			return nil, err
		}
	case "gif":
		fn := func(img image.Image) image.Image {
			return transformImage(img, opt)
		}
		err = gifresize.Process(buf, bytes.NewReader(img), fn)
		if err != nil {