1 files changed, 198 insertions, 0 deletions
diff --git a/internal/media/image.go b/internal/media/image.go
new file mode 100644
index 000000000..e5390cee5
--- /dev/null
+++ b/internal/media/image.go
@@ -0,0 +1,198 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package media
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"io"
+
+	"github.com/buckket/go-blurhash"
+	"github.com/nfnt/resize"
+)
+
+const (
+	thumbnailMaxWidth  = 512
+	thumbnailMaxHeight = 512
+)
+
+type imageMeta struct {
+	width    int
+	height   int
+	size     int
+	aspect   float64
+	blurhash string // defined only for calls to deriveThumbnail if createBlurhash is true
+	small    []byte // defined only for calls to deriveStaticEmoji or deriveThumbnail
+}
+
+func decodeGif(r io.Reader) (*imageMeta, error) {
+	gif, err := gif.DecodeAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	// use the first frame to get the static characteristics
+	width := gif.Config.Width
+	height := gif.Config.Height
+	size := width * height
+	aspect := float64(width) / float64(height)
+
+	return &imageMeta{
+		width:  width,
+		height: height,
+		size:   size,
+		aspect: aspect,
+	}, nil
+}
+
+func decodeImage(r io.Reader, contentType string) (*imageMeta, error) {
+	var i image.Image
+	var err error
+
+	switch contentType {
+	case mimeImageJpeg:
+		i, err = jpeg.Decode(r)
+	case mimeImagePng:
+		i, err = png.Decode(r)
+	default:
+		err = fmt.Errorf("content type %s not recognised", contentType)
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	if i == nil {
+		return nil, errors.New("processed image was nil")
+	}
+
+	width := i.Bounds().Size().X
+	height := i.Bounds().Size().Y
+	size := width * height
+	aspect := float64(width) / float64(height)
+
+	return &imageMeta{
+		width:  width,
+		height: height,
+		size:   size,
+		aspect: aspect,
+	}, nil
+}
+
+// deriveThumbnail returns a byte slice and metadata for a thumbnail
+// of a given jpeg, png, or gif, or an error if something goes wrong.
+//
+// If createBlurhash is true, then a blurhash will also be generated from a tiny
+// version of the image. This costs precious CPU cycles, so only use it if you
+// really need a blurhash and don't have one already.
+//
+// If createBlurhash is false, then the blurhash field on the returned ImageAndMeta
+// will be an empty string.
+func deriveThumbnail(r io.Reader, contentType string, createBlurhash bool) (*imageMeta, error) {
+	var i image.Image
+	var err error
+
+	switch contentType {
+	case mimeImageJpeg:
+		i, err = jpeg.Decode(r)
+	case mimeImagePng:
+		i, err = png.Decode(r)
+	case mimeImageGif:
+		i, err = gif.Decode(r)
+	default:
+		err = fmt.Errorf("content type %s can't be thumbnailed", contentType)
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	if i == nil {
+		return nil, errors.New("processed image was nil")
+	}
+
+	thumb := resize.Thumbnail(thumbnailMaxWidth, thumbnailMaxHeight, i, resize.NearestNeighbor)
+	width := thumb.Bounds().Size().X
+	height := thumb.Bounds().Size().Y
+	size := width * height
+	aspect := float64(width) / float64(height)
+
+	im := &imageMeta{
+		width:  width,
+		height: height,
+		size:   size,
+		aspect: aspect,
+	}
+
+	if createBlurhash {
+		// for generating blurhashes, it's more cost effective to lose detail rather than
+		// pass a big image into the blurhash algorithm, so make a teeny tiny version
+		tiny := resize.Thumbnail(32, 32, thumb, resize.NearestNeighbor)
+		bh, err := blurhash.Encode(4, 3, tiny)
+		if err != nil {
+			return nil, err
+		}
+		im.blurhash = bh
+	}
+
+	out := &bytes.Buffer{}
+	if err := jpeg.Encode(out, thumb, &jpeg.Options{
+		// Quality isn't extremely important for thumbnails, so 75 is "good enough"
+		Quality: 75,
+	}); err != nil {
+		return nil, err
+	}
+	im.small = out.Bytes()
+
+	return im, nil
+}
+
+// deriveStaticEmojji takes a given gif or png of an emoji, decodes it, and re-encodes it as a static png.
+func deriveStaticEmoji(r io.Reader, contentType string) (*imageMeta, error) {
+	var i image.Image
+	var err error
+
+	switch contentType {
+	case mimeImagePng:
+		i, err = png.Decode(r)
+		if err != nil {
+			return nil, err
+		}
+	case mimeImageGif:
+		i, err = gif.Decode(r)
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, fmt.Errorf("content type %s not allowed for emoji", contentType)
+	}
+
+	out := &bytes.Buffer{}
+	if err := png.Encode(out, i); err != nil {
+		return nil, err
+	}
+	return &imageMeta{
+		small: out.Bytes(),
+	}, nil
+}