lib/image/image.go

package image

import (
	"bytes"
	"image/gif"
	"image/jpeg"
	"image/png"
	"io"
	"io/ioutil"
	"mime/multipart"
	"os"
)

// CompressImage 壓縮圖片至指定位置
func CompressImage(input interface{}, output string) (err error) {
	var file io.Reader
	switch input.(type) {
	case string:
		if file, err = os.Open(input.(string)); err != nil {
			return err
		}
		defer file.(*os.File).Close()
		defer os.Remove(input.(string))

	case *multipart.FileHeader:
		fileHeader := input.(*multipart.FileHeader)
		file, err = fileHeader.Open()
		if err != nil {
			return err
		}
		defer file.(multipart.File).Close()
	}

	bs, err := ioutil.ReadAll(file)
	if err != nil {
		return err
	}

	var ext string
	if _, err = jpeg.Decode(bytes.NewReader(bs)); err == nil {
		ext = "jpg"
	} else if _, err = png.Decode(bytes.NewReader(bs)); err == nil {
		ext = "png"
	} else if _, err = gif.Decode(bytes.NewReader(bs)); err == nil {
		ext = "gif"
	}

	outputFile, err := os.Create(output)
	if err != nil {
		return err
	}
	defer outputFile.Close()

	switch ext {
	case "jpg":
		img, err := jpeg.Decode(bytes.NewReader(bs))
		if err != nil {
			return err
		}
		if err = jpeg.Encode(outputFile, img, &jpeg.Options{Quality: 70}); err != nil {
			return err
		}

	case "png":
		img, err := png.Decode(bytes.NewReader(bs))
		if err != nil {
			return err
		}
		encoder := png.Encoder{CompressionLevel: png.BestCompression}
		if err = encoder.Encode(outputFile, img); err != nil {
			return err
		}

	case "gif":
		img, err := gif.DecodeAll(bytes.NewReader(bs))
		if err != nil {
			return err
		}
		if err = gif.EncodeAll(outputFile, img); err != nil {
			return err
		}

	default:
		if _, err = outputFile.Write(bs); err != nil {
			return err
		}
	}

	return nil
}