big update: added reactions, groups, media share

server/internal/media/thumbnail.go

@@ -0,0 +1,82 @@
+package media
+
+import (
+	"bytes"
+	"context"
+	"image"
+	_ "image/gif"
+	"image/jpeg"
+	_ "image/png"
+
+	"golang.org/x/image/draw"
+	"golang.org/x/image/webp"
+)
+
+const maxUploadSize = 25 << 20 // 25 MiB
+
+// IsImage reports whether the content type is a decodable image format.
+func IsImage(contentType string) bool {
+	switch contentType {
+	case "image/jpeg", "image/png", "image/gif", "image/webp":
+		return true
+	default:
+		return false
+	}
+}
+
+// Generate returns a JPEG thumbnail of at most maxDim on its larger side.
+// It returns nil for non-images or when the source is already small enough.
+func Generate(ctx context.Context, r *bytes.Reader, contentType string, maxDim int) ([]byte, error) {
+	if !IsImage(contentType) {
+		return nil, nil
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
+	src, err := decodeImage(r, contentType)
+	if err != nil {
+		return nil, err
+	}
+	bounds := src.Bounds()
+	w, h := bounds.Dx(), bounds.Dy()
+	if w <= maxDim && h <= maxDim {
+		return nil, nil
+	}
+
+	scale := float64(maxDim) / float64(max(w, h))
+	nw, nh := int(float64(w)*scale), int(float64(h)*scale)
+	if nw < 1 {
+		nw = 1
+	}
+	if nh < 1 {
+		nh = 1
+	}
+
+	dst := image.NewRGBA(image.Rect(0, 0, nw, nh))
+	draw.BiLinear.Scale(dst, dst.Bounds(), src, bounds, draw.Over, nil)
+
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	var buf bytes.Buffer
+	if err := jpeg.Encode(&buf, dst, &jpeg.Options{Quality: 80}); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+func decodeImage(r *bytes.Reader, contentType string) (image.Image, error) {
+	if contentType == "image/webp" {
+		return webp.Decode(r)
+	}
+	img, _, err := image.Decode(r)
+	return img, err
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}