mess about with media a bit more

internal/media/util.go

@@ -0,0 +1,175 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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/h2non/filetype"
+	"github.com/nfnt/resize"
+	exifremove "github.com/scottleedavis/go-exif-remove"
+)
+
+// parseContentType parses the MIME content type from a file, returning it as a string in the form (eg., "image/jpeg").
+// Returns an error if the content type is not something we can process.
+func parseContentType(f io.Reader) (string, error) {
+	head := make([]byte, 261)
+	_, err := f.Read(head)
+	if err != nil {
+		return "", fmt.Errorf("could not read first magic bytes of file: %s", err)
+	}
+
+	kind, err := filetype.Match(head)
+	if err != nil {
+		return "", err
+	}
+
+	if kind == filetype.Unknown {
+		return "", errors.New("filetype unknown")
+	}
+
+	return kind.MIME.Value, nil
+}
+
+// supportedImageType checks mime type of an image against a slice of accepted types,
+// and returns True if the mime type is accepted.
+func supportedImageType(mimeType string) bool {
+	acceptedImageTypes := []string{
+		"image/jpeg",
+		"image/gif",
+		"image/png",
+	}
+	for _, accepted := range acceptedImageTypes {
+		if mimeType == accepted {
+			return true
+		}
+	}
+	return false
+}
+
+// purgeExif is a little wrapper for the action of removing exif data from an image.
+// Only pass pngs or jpegs to this function.
+func purgeExif(b []byte) ([]byte, error) {
+	return exifremove.Remove(b)
+}
+
+func deriveImage(b []byte, extension string) (*imageAndMeta, error) {
+	var i image.Image
+	var err error
+
+	switch extension {
+	case "image/jpeg":
+		i, err = jpeg.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	case "image/png":
+		i, err = png.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	case "image/gif":
+		i, err = gif.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, fmt.Errorf("extension %s not recognised", extension)
+	}
+
+	width := i.Bounds().Size().X
+	height := i.Bounds().Size().Y
+	size := width * height
+	aspect := float64(width) / float64(height)
+
+	out := &bytes.Buffer{}
+	if err := jpeg.Encode(out, i, nil); err != nil {
+		return nil, err
+	}
+	return &imageAndMeta{
+		image:  out.Bytes(),
+		width:  width,
+		height: height,
+		size:   size,
+		aspect: aspect,
+	}, nil
+}
+
+// deriveThumbnailFromImage returns a byte slice of an 80-pixel-width thumbnail
+// of a given jpeg, png, or gif, or an error if something goes wrong.
+//
+// Note that the aspect ratio of the image will be retained,
+// so it will not necessarily be a square.
+func deriveThumbnail(b []byte, extension string) (*imageAndMeta, error) {
+	var i image.Image
+	var err error
+
+	switch extension {
+	case "image/jpeg":
+		i, err = jpeg.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	case "image/png":
+		i, err = png.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	case "image/gif":
+		i, err = gif.Decode(bytes.NewReader(b))
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, fmt.Errorf("extension %s not recognised", extension)
+	}
+
+	thumb := resize.Thumbnail(80, 0, i, resize.NearestNeighbor)
+	width := thumb.Bounds().Size().X
+	height := thumb.Bounds().Size().Y
+	size := width * height
+	aspect := float64(width) / float64(height)
+
+	out := &bytes.Buffer{}
+	if err := jpeg.Encode(out, thumb, nil); err != nil {
+		return nil, err
+	}
+	return &imageAndMeta{
+		image:  out.Bytes(),
+		width:  width,
+		height: height,
+		size:   size,
+		aspect: aspect,
+	}, nil
+}
+
+type imageAndMeta struct {
+	image  []byte
+	width  int
+	height int
+	size   int
+	aspect float64
+}