Feat: generate thumbnails for image file

pkg/thumb/image.go

@@ -0,0 +1,79 @@
+package thumb
+
+import (
+	"errors"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/nfnt/resize"
+)
+
+// Thumb 缩略图
+type Thumb struct {
+	src image.Image
+	ext string
+}
+
+// NewThumbFromFile 从文件数据获取新的Thumb对象，
+// 尝试通过文件名name解码图像
+func NewThumbFromFile(file io.ReadSeeker, name string) (*Thumb, error) {
+	ext := strings.ToLower(filepath.Ext(name))
+	// 无扩展名时
+	if len(ext) == 0 {
+		return nil, errors.New("未知的图像类型")
+	}
+
+	var err error
+	var img image.Image
+	switch ext[1:] {
+	case "jpg":
+		img, err = jpeg.Decode(file)
+	case "jpeg":
+		img, err = jpeg.Decode(file)
+	case "gif":
+		img, err = gif.Decode(file)
+	case "png":
+		img, err = png.Decode(file)
+	default:
+		return nil, errors.New("未知的图像类型")
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	return &Thumb{
+		src: img,
+		ext: ext[1:],
+	}, nil
+}
+
+// GetThumb 生成给定最大尺寸的缩略图
+func (image *Thumb) GetThumb(width, height uint) {
+	image.src = resize.Thumbnail(width, height, image.src, resize.Lanczos3)
+}
+
+// GetSize 获取图像尺寸
+func (image *Thumb) GetSize() (int, int) {
+	b := image.src.Bounds()
+	return b.Max.X, b.Max.Y
+}
+
+// Save 保存图像到给定路径
+func (image *Thumb) Save(path string) (err error) {
+	out, err := os.Create(path)
+	defer out.Close()
+
+	if err != nil {
+		return err
+	}
+
+	err = jpeg.Encode(out, image.src, nil)
+	return err
+
+}