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service.go
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service.go
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//go:generate go-enum --sql --marshal --file $GOFILE
package img
import (
"bytes"
"context"
"errors"
"fmt"
"image"
"io"
"github.com/disintegration/imaging"
"github.com/dsoprea/go-exif/v3"
"github.com/marusama/semaphore/v2"
exifcommon "github.com/dsoprea/go-exif/v3/common"
)
// ErrUnsupportedFormat means the given image format is not supported.
var ErrUnsupportedFormat = errors.New("unsupported image format")
// Service
type Service struct {
sem semaphore.Semaphore
}
func New(workers int) *Service {
return &Service{
sem: semaphore.New(workers),
}
}
// Format is an image file format.
/*
ENUM(
jpeg
png
gif
tiff
bmp
)
*/
type Format int
func (x Format) toImaging() imaging.Format {
switch x {
case FormatJpeg:
return imaging.JPEG
case FormatPng:
return imaging.PNG
case FormatGif:
return imaging.GIF
case FormatTiff:
return imaging.TIFF
case FormatBmp:
return imaging.BMP
default:
return imaging.JPEG
}
}
/*
ENUM(
high
medium
low
)
*/
type Quality int
func (x Quality) resampleFilter() imaging.ResampleFilter {
switch x {
case QualityHigh:
return imaging.Lanczos
case QualityMedium:
return imaging.Box
case QualityLow:
return imaging.NearestNeighbor
default:
return imaging.Box
}
}
/*
ENUM(
fit
fill
)
*/
type ResizeMode int
func (s *Service) FormatFromExtension(ext string) (Format, error) {
format, err := imaging.FormatFromExtension(ext)
if err != nil {
return -1, ErrUnsupportedFormat
}
switch format {
case imaging.JPEG:
return FormatJpeg, nil
case imaging.PNG:
return FormatPng, nil
case imaging.GIF:
return FormatGif, nil
case imaging.TIFF:
return FormatTiff, nil
case imaging.BMP:
return FormatBmp, nil
}
return -1, ErrUnsupportedFormat
}
type resizeConfig struct {
format Format
resizeMode ResizeMode
quality Quality
}
type Option func(*resizeConfig)
func WithFormat(format Format) Option {
return func(config *resizeConfig) {
config.format = format
}
}
func WithMode(mode ResizeMode) Option {
return func(config *resizeConfig) {
config.resizeMode = mode
}
}
func WithQuality(quality Quality) Option {
return func(config *resizeConfig) {
config.quality = quality
}
}
func (s *Service) Resize(ctx context.Context, in io.Reader, width, height int, out io.Writer, options ...Option) error {
if err := s.sem.Acquire(ctx, 1); err != nil {
return err
}
defer s.sem.Release(1)
format, wrappedReader, err := s.detectFormat(in)
if err != nil {
return err
}
config := resizeConfig{
format: format,
resizeMode: ResizeModeFit,
quality: QualityMedium,
}
for _, option := range options {
option(&config)
}
if config.quality == QualityLow && format == FormatJpeg {
thm, newWrappedReader, errThm := getEmbeddedThumbnail(wrappedReader)
wrappedReader = newWrappedReader
if errThm == nil {
_, err = out.Write(thm)
if err == nil {
return nil
}
}
}
img, err := imaging.Decode(wrappedReader, imaging.AutoOrientation(true))
if err != nil {
return err
}
switch config.resizeMode {
case ResizeModeFill:
img = imaging.Fill(img, width, height, imaging.Center, config.quality.resampleFilter())
case ResizeModeFit:
fallthrough //nolint:gocritic
default:
img = imaging.Fit(img, width, height, config.quality.resampleFilter())
}
return imaging.Encode(out, img, config.format.toImaging())
}
func (s *Service) detectFormat(in io.Reader) (Format, io.Reader, error) {
buf := &bytes.Buffer{}
r := io.TeeReader(in, buf)
_, imgFormat, err := image.DecodeConfig(r)
if err != nil {
return 0, nil, fmt.Errorf("%s: %w", err.Error(), ErrUnsupportedFormat)
}
format, err := ParseFormat(imgFormat)
if err != nil {
return 0, nil, ErrUnsupportedFormat
}
return format, io.MultiReader(buf, in), nil
}
func getEmbeddedThumbnail(in io.Reader) ([]byte, io.Reader, error) {
buf := &bytes.Buffer{}
r := io.TeeReader(in, buf)
wrappedReader := io.MultiReader(buf, in)
offset := 0
offsets := []int{12, 30}
head := make([]byte, 0xffff) //nolint:gomnd
_, err := r.Read(head)
if err != nil {
return nil, wrappedReader, err
}
for _, offset = range offsets {
if _, err = exif.ParseExifHeader(head[offset:]); err == nil {
break
}
}
if err != nil {
return nil, wrappedReader, err
}
im, err := exifcommon.NewIfdMappingWithStandard()
if err != nil {
return nil, wrappedReader, err
}
_, index, err := exif.Collect(im, exif.NewTagIndex(), head[offset:])
if err != nil {
return nil, wrappedReader, err
}
ifd := index.RootIfd.NextIfd()
if ifd == nil {
return nil, wrappedReader, exif.ErrNoThumbnail
}
thm, err := ifd.Thumbnail()
return thm, wrappedReader, err
}