add support for image resizing

transform/transform.go

@@ -0,0 +1,48 @@
+// Package transform handles image transformation such as resizing.
+package transform
+
+import (
+	"bytes"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+
+	"github.com/nfnt/resize"
+	"github.com/willnorris/go-imageproxy/data"
+)
+
+// Transform the provided image.
+func Transform(img data.Image, opt *data.Options) (*data.Image, error) {
+	if opt == nil {
+		return &img, nil
+	}
+
+	// decode image
+	m, format, err := image.Decode(bytes.NewReader(img.Bytes))
+	if err != nil {
+		return nil, err
+	}
+
+	// resize
+	if opt.Width != 0 || opt.Height != 0 {
+		m = resize.Resize(uint(opt.Width), uint(opt.Height), m, resize.Lanczos3)
+	}
+
+	// encode image
+	buf := new(bytes.Buffer)
+	switch format {
+	case "gif":
+		gif.Encode(buf, m, nil)
+		break
+	case "jpeg":
+		jpeg.Encode(buf, m, nil)
+		break
+	case "png":
+		png.Encode(buf, m)
+		break
+	}
+
+	img.Bytes = buf.Bytes()
+	return &img, nil
+}