resources: Support output image format in image operations

The image format is defined as the image extension of the known formats,
excluding the dot.
All of 'img.Resize "600x jpeg"', 'img.Resize "600x jpg"',
and 'img.Resize "600x png"' are valid format definitions.
If the target format is defined in the operation definition string,
then the converted image will be stored in this format. Permalinks and
media type are updated correspondingly.
Unknown image extensions in the operation definition have not effect.

See #6298

6 files changed, 95 insertions, 13 deletions

diff --git a/resources/image.go b/resources/image.go
index 26b9b8710..bb9c987a5 100644
--- a/resources/image.go
+++ b/resources/image.go
@@ -43,8 +43,6 @@ import (
 	"github.com/gohugoio/hugo/resources/images"
 
 	// Blind import for image.Decode
-
-	// Blind import for image.Decode
 	_ "golang.org/x/image/webp"
 )
 
@@ -220,17 +218,13 @@ func (i *imageResource) Filter(filters ...interface{}) (resource.Image, error) {
 	}
 
 	conf.Key = internal.HashString(gfilters)
+	conf.TargetFormat = i.Format
 
 	return i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
 		return i.Proc.Filter(src, gfilters...)
 	})
 }
 
-func (i *imageResource) isJPEG() bool {
-	name := strings.ToLower(i.getResourcePaths().relTargetDirFile.file)
-	return strings.HasSuffix(name, ".jpg") || strings.HasSuffix(name, ".jpeg")
-}
-
 // Serialize image processing. The imaging library spins up its own set of Go routines,
 // so there is not much to gain from adding more load to the mix. That
 // can even have negative effect in low resource scenarios.
@@ -260,7 +254,7 @@ func (i *imageResource) doWithImageConfig(conf images.ImageConfig, f func(src im
 			return nil, nil, &os.PathError{Op: errOp, Path: errPath, Err: err}
 		}
 
-		if i.Format == images.PNG {
+		if conf.TargetFormat == images.PNG {
 			// Apply the colour palette from the source
 			if paletted, ok := src.(*image.Paletted); ok {
 				tmp := image.NewPaletted(converted.Bounds(), paletted.Palette)
@@ -271,6 +265,8 @@ func (i *imageResource) doWithImageConfig(conf images.ImageConfig, f func(src im
 
 		ci := i.clone(converted)
 		ci.setBasePath(conf)
+		ci.Format = conf.TargetFormat
+		ci.setMediaType(conf.TargetFormat.MediaType())
 
 		return ci, converted, nil
 	})
@@ -282,11 +278,14 @@ func (i *imageResource) decodeImageConfig(action, spec string) (images.ImageConf
 		return conf, err
 	}
 
-	iconf := i.Proc.Cfg
+	// default to the source format
+	if conf.TargetFormat == 0 {
+		conf.TargetFormat = i.Format
+	}
 
-	if conf.Quality <= 0 && i.isJPEG() {
+	if conf.Quality <= 0 && conf.TargetFormat.RequiresDefaultQuality() {
 		// We need a quality setting for all JPEGs
-		conf.Quality = iconf.Quality
+		conf.Quality = i.Proc.Cfg.Quality
 	}
 
 	return conf, nil
@@ -339,6 +338,9 @@ func (i *imageResource) getImageMetaCacheTargetPath() string {
 
 func (i *imageResource) relTargetPathFromConfig(conf images.ImageConfig) dirFile {
 	p1, p2 := helpers.FileAndExt(i.getResourcePaths().relTargetDirFile.file)
+	if conf.TargetFormat != i.Format {
+		p2 = conf.TargetFormat.DefaultExtension()
+	}
 
 	h, _ := i.hash()
 	idStr := fmt.Sprintf("_hu%s_%d", h, i.size())
diff --git a/resources/image_test.go b/resources/image_test.go
index 59d6b7c9a..5fa5021c9 100644
--- a/resources/image_test.go
+++ b/resources/image_test.go
@@ -133,6 +133,46 @@ func TestImageTransformBasic(t *testing.T) {
 	c.Assert(filled, eq, filledAgain)
 }
 
+func TestImageTransformFormat(t *testing.T) {
+	c := qt.New(t)
+
+	image := fetchSunset(c)
+
+	fileCache := image.(specProvider).getSpec().FileCaches.ImageCache().Fs
+
+	assertExtWidthHeight := func(img resource.Image, ext string, w, h int) {
+		c.Helper()
+		c.Assert(img, qt.Not(qt.IsNil))
+		c.Assert(helpers.Ext(img.RelPermalink()), qt.Equals, ext)
+		c.Assert(img.Width(), qt.Equals, w)
+		c.Assert(img.Height(), qt.Equals, h)
+	}
+
+	c.Assert(image.RelPermalink(), qt.Equals, "/a/sunset.jpg")
+	c.Assert(image.ResourceType(), qt.Equals, "image")
+	assertExtWidthHeight(image, ".jpg", 900, 562)
+
+	imagePng, err := image.Resize("450x png")
+	c.Assert(err, qt.IsNil)
+	c.Assert(imagePng.RelPermalink(), qt.Equals, "/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_450x0_resize_linear.png")
+	c.Assert(imagePng.ResourceType(), qt.Equals, "image")
+	assertExtWidthHeight(imagePng, ".png", 450, 281)
+	c.Assert(imagePng.Name(), qt.Equals, "sunset.jpg")
+	c.Assert(imagePng.MediaType().String(), qt.Equals, "image/png")
+
+	assertFileCache(c, fileCache, path.Base(imagePng.RelPermalink()), 450, 281)
+
+	imageGif, err := image.Resize("225x gif")
+	c.Assert(err, qt.IsNil)
+	c.Assert(imageGif.RelPermalink(), qt.Equals, "/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_225x0_resize_linear.gif")
+	c.Assert(imageGif.ResourceType(), qt.Equals, "image")
+	assertExtWidthHeight(imageGif, ".gif", 225, 141)
+	c.Assert(imageGif.Name(), qt.Equals, "sunset.jpg")
+	c.Assert(imageGif.MediaType().String(), qt.Equals, "image/gif")
+
+	assertFileCache(c, fileCache, path.Base(imageGif.RelPermalink()), 225, 141)
+}
+
 // https://github.com/gohugoio/hugo/issues/4261
 func TestImageTransformLongFilename(t *testing.T) {
 	c := qt.New(t)
diff --git a/resources/images/config.go b/resources/images/config.go
index a290922ab..6bc701bfe 100644
--- a/resources/images/config.go
+++ b/resources/images/config.go
@@ -187,7 +187,8 @@ func DecodeImageConfig(action, config string, defaults Imaging) (ImageConfig, er
 			} else {
 				return c, errors.New("invalid image dimensions")
 			}
-
+		} else if f, ok := ImageFormatFromExt("." + part); ok {
+			c.TargetFormat = f
 		}
 	}
 
@@ -212,6 +213,9 @@ func DecodeImageConfig(action, config string, defaults Imaging) (ImageConfig, er
 
 // ImageConfig holds configuration to create a new image from an existing one, resize etc.
 type ImageConfig struct {
+	// This defines the output format of the output image. It defaults to the source format
+	TargetFormat Format
+
 	Action string
 
 	// If set, this will be used as the key in filenames etc.
diff --git a/resources/images/image.go b/resources/images/image.go
index e72d96837..bd7500c28 100644
--- a/resources/images/image.go
+++ b/resources/images/image.go
@@ -23,6 +23,7 @@ import (
 	"io"
 	"sync"
 
+	"github.com/gohugoio/hugo/media"
 	"github.com/gohugoio/hugo/resources/images/exif"
 
 	"github.com/disintegration/gift"
@@ -59,7 +60,7 @@ type Image struct {
 }
 
 func (i *Image) EncodeTo(conf ImageConfig, img image.Image, w io.Writer) error {
-	switch i.Format {
+	switch conf.TargetFormat {
 	case JPEG:
 
 		var rgba *image.RGBA
@@ -250,6 +251,35 @@ const (
 	BMP
 )
 
+// RequiresDefaultQuality returns if the default quality needs to be applied to images of this format
+func (f Format) RequiresDefaultQuality() bool {
+	return f == JPEG
+}
+
+// DefaultExtension returns the default file extension of this format, starting with a dot.
+// For example: .jpg for JPEG
+func (f Format) DefaultExtension() string {
+	return f.MediaType().FullSuffix()
+}
+
+// MediaType returns the media type of this image, e.g. image/jpeg for JPEG
+func (f Format) MediaType() media.Type {
+	switch f {
+	case JPEG:
+		return media.JPGType
+	case PNG:
+		return media.PNGType
+	case GIF:
+		return media.GIFType
+	case TIFF:
+		return media.TIFFType
+	case BMP:
+		return media.BMPType
+	default:
+		panic(fmt.Sprintf("%d is not a valid image format", f))
+	}
+}
+
 type imageConfig struct {
 	config       image.Config
 	configInit   sync.Once
diff --git a/resources/resource.go b/resources/resource.go
index 7f52a7135..acf8e37c0 100644
--- a/resources/resource.go
+++ b/resources/resource.go
@@ -220,6 +220,10 @@ func (l *genericResource) MediaType() media.Type {
 	return l.mediaType
 }
 
+func (l *genericResource) setMediaType(mediaType media.Type) {
+	l.mediaType = mediaType
+}
+
 func (l *genericResource) Name() string {
 	return l.name
 }
diff --git a/resources/resource_metadata.go b/resources/resource_metadata.go
index 79e61e1a0..ce17df022 100644
--- a/resources/resource_metadata.go
+++ b/resources/resource_metadata.go
@@ -18,6 +18,7 @@ import (
 	"strconv"
 
 	"github.com/gohugoio/hugo/hugofs/glob"
+	"github.com/gohugoio/hugo/media"
 	"github.com/gohugoio/hugo/resources/resource"
 
 	"github.com/pkg/errors"
@@ -42,6 +43,7 @@ type metaAssignerProvider interface {
 type metaAssigner interface {
 	setTitle(title string)
 	setName(name string)
+	setMediaType(mediaType media.Type)
 	updateParams(params map[string]interface{})
 }