Improve handling of non-square avatars (#7025)

* Crop avatar before resizing (#1268)

Signed-off-by: Rob Watson <rfwatson@users.noreply.github.com>

* Fix spelling error

Signed-off-by: Rob Watson <rfwatson@users.noreply.github.com>

modules/avatar/avatar.go

@@ -5,13 +5,20 @@
 package avatar
 
 import (
+	"bytes"
 	"fmt"
 	"image"
 	"image/color/palette"
+	// Enable PNG support:
+	_ "image/png"
 	"math/rand"
 	"time"
 
+	"code.gitea.io/gitea/modules/setting"
+
 	"github.com/issue9/identicon"
+	"github.com/nfnt/resize"
+	"github.com/oliamb/cutter"
 )
 
 // AvatarSize returns avatar's size
@@ -42,3 +49,46 @@ func RandomImageSize(size int, data []byte) (image.Image, error) {
 func RandomImage(data []byte) (image.Image, error) {
 	return RandomImageSize(AvatarSize, data)
 }
+
+// Prepare accepts a byte slice as input, validates it contains an image of an
+// acceptable format, and crops and resizes it appropriately.
+func Prepare(data []byte) (*image.Image, error) {
+	imgCfg, _, err := image.DecodeConfig(bytes.NewReader(data))
+	if err != nil {
+		return nil, fmt.Errorf("DecodeConfig: %v", err)
+	}
+	if imgCfg.Width > setting.AvatarMaxWidth {
+		return nil, fmt.Errorf("Image width is too large: %d > %d", imgCfg.Width, setting.AvatarMaxWidth)
+	}
+	if imgCfg.Height > setting.AvatarMaxHeight {
+		return nil, fmt.Errorf("Image height is too large: %d > %d", imgCfg.Height, setting.AvatarMaxHeight)
+	}
+
+	img, _, err := image.Decode(bytes.NewReader(data))
+	if err != nil {
+		return nil, fmt.Errorf("Decode: %v", err)
+	}
+
+	if imgCfg.Width != imgCfg.Height {
+		var newSize, ax, ay int
+		if imgCfg.Width > imgCfg.Height {
+			newSize = imgCfg.Height
+			ax = (imgCfg.Width - imgCfg.Height) / 2
+		} else {
+			newSize = imgCfg.Width
+			ay = (imgCfg.Height - imgCfg.Width) / 2
+		}
+
+		img, err = cutter.Crop(img, cutter.Config{
+			Width:  newSize,
+			Height: newSize,
+			Anchor: image.Point{ax, ay},
+		})
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	img = resize.Resize(AvatarSize, AvatarSize, img, resize.NearestNeighbor)
+	return &img, nil
+}