Improve avatar uploading / resizing / compressing, remove Fomantic card module (#24653)

Fixes: #8972
Fixes: #24263

And I think it also (partially) fix #24263 (no need to convert) ,
because users could upload any supported image format if it isn't larger
than AVATAR_MAX_ORIGIN_SIZE


The main idea: 

* if the uploaded file size is not larger than AVATAR_MAX_ORIGIN_SIZE,
use the origin
* if the resized size is larger than the origin, use the origin

Screenshots:

JPG:

<details>


![image](https://github.com/go-gitea/gitea/assets/2114189/70e98bb0-ecb9-4c4e-a89f-4a37d4e37f8e)

</details>

APNG:

<details>


![image](https://github.com/go-gitea/gitea/assets/2114189/9055135b-5e2d-4152-bd72-596fcb7c6671)


![image](https://github.com/go-gitea/gitea/assets/2114189/50364caf-f7f6-4241-a289-e485fe4cd582)

</details>

WebP (animated)

<details>


![image](https://github.com/go-gitea/gitea/assets/2114189/f642eb85-498a-49a5-86bf-0a7b04089ae0)

</details>

The only exception: if a WebP image is larger than MaxOriginSize and it
is animated, then current `webp` package can't decode it, so only in
this case it isn't supported. IMO no need to support such case: why a
user would upload a 1MB animated webp as avatar? crazy .....

---------

Co-authored-by: silverwind <me@silverwind.io>

modules/avatar/avatar_test.go

@@ -4,6 +4,9 @@
 package avatar
 
 import (
+	"bytes"
+	"image"
+	"image/png"
 	"os"
 	"testing"
 
@@ -25,49 +28,109 @@ func Test_RandomImage(t *testing.T) {
 	assert.NoError(t, err)
 }
 
-func Test_PrepareWithPNG(t *testing.T) {
+func Test_ProcessAvatarPNG(t *testing.T) {
 	setting.Avatar.MaxWidth = 4096
 	setting.Avatar.MaxHeight = 4096
 
 	data, err := os.ReadFile("testdata/avatar.png")
 	assert.NoError(t, err)
 
-	imgPtr, err := Prepare(data)
+	_, err = processAvatarImage(data, 262144)
 	assert.NoError(t, err)
-
-	assert.Equal(t, 290, (*imgPtr).Bounds().Max.X)
-	assert.Equal(t, 290, (*imgPtr).Bounds().Max.Y)
 }
 
-func Test_PrepareWithJPEG(t *testing.T) {
+func Test_ProcessAvatarJPEG(t *testing.T) {
 	setting.Avatar.MaxWidth = 4096
 	setting.Avatar.MaxHeight = 4096
 
 	data, err := os.ReadFile("testdata/avatar.jpeg")
 	assert.NoError(t, err)
 
-	imgPtr, err := Prepare(data)
+	_, err = processAvatarImage(data, 262144)
 	assert.NoError(t, err)
-
-	assert.Equal(t, 290, (*imgPtr).Bounds().Max.X)
-	assert.Equal(t, 290, (*imgPtr).Bounds().Max.Y)
 }
 
-func Test_PrepareWithInvalidImage(t *testing.T) {
+func Test_ProcessAvatarInvalidData(t *testing.T) {
 	setting.Avatar.MaxWidth = 5
 	setting.Avatar.MaxHeight = 5
 
-	_, err := Prepare([]byte{})
-	assert.EqualError(t, err, "DecodeConfig: image: unknown format")
+	_, err := processAvatarImage([]byte{}, 12800)
+	assert.EqualError(t, err, "image.DecodeConfig: image: unknown format")
 }
 
-func Test_PrepareWithInvalidImageSize(t *testing.T) {
+func Test_ProcessAvatarInvalidImageSize(t *testing.T) {
 	setting.Avatar.MaxWidth = 5
 	setting.Avatar.MaxHeight = 5
 
 	data, err := os.ReadFile("testdata/avatar.png")
 	assert.NoError(t, err)
 
-	_, err = Prepare(data)
-	assert.EqualError(t, err, "Image width is too large: 10 > 5")
+	_, err = processAvatarImage(data, 12800)
+	assert.EqualError(t, err, "image width is too large: 10 > 5")
+}
+
+func Test_ProcessAvatarImage(t *testing.T) {
+	setting.Avatar.MaxWidth = 4096
+	setting.Avatar.MaxHeight = 4096
+	scaledSize := DefaultAvatarSize * setting.Avatar.RenderedSizeFactor
+
+	newImgData := func(size int, optHeight ...int) []byte {
+		width := size
+		height := size
+		if len(optHeight) == 1 {
+			height = optHeight[0]
+		}
+		img := image.NewRGBA(image.Rect(0, 0, width, height))
+		bs := bytes.Buffer{}
+		err := png.Encode(&bs, img)
+		assert.NoError(t, err)
+		return bs.Bytes()
+	}
+
+	// if origin image canvas is too large, crop and resize it
+	origin := newImgData(500, 600)
+	result, err := processAvatarImage(origin, 0)
+	assert.NoError(t, err)
+	assert.NotEqual(t, origin, result)
+	decoded, err := png.Decode(bytes.NewReader(result))
+	assert.NoError(t, err)
+	assert.EqualValues(t, scaledSize, decoded.Bounds().Max.X)
+	assert.EqualValues(t, scaledSize, decoded.Bounds().Max.Y)
+
+	// if origin image is smaller than the default size, use the origin image
+	origin = newImgData(1)
+	result, err = processAvatarImage(origin, 0)
+	assert.NoError(t, err)
+	assert.Equal(t, origin, result)
+
+	// use the origin image if the origin is smaller
+	origin = newImgData(scaledSize + 100)
+	result, err = processAvatarImage(origin, 0)
+	assert.NoError(t, err)
+	assert.Less(t, len(result), len(origin))
+
+	// still use the origin image if the origin doesn't exceed the max-origin-size
+	origin = newImgData(scaledSize + 100)
+	result, err = processAvatarImage(origin, 262144)
+	assert.NoError(t, err)
+	assert.Equal(t, origin, result)
+
+	// allow to use known image format (eg: webp) if it is small enough
+	origin, err = os.ReadFile("testdata/animated.webp")
+	assert.NoError(t, err)
+	result, err = processAvatarImage(origin, 262144)
+	assert.NoError(t, err)
+	assert.Equal(t, origin, result)
+
+	// do not support unknown image formats, eg: SVG may contain embedded JS
+	origin = []byte("<svg></svg>")
+	_, err = processAvatarImage(origin, 262144)
+	assert.ErrorContains(t, err, "image: unknown format")
+
+	// make sure the canvas size limit works
+	setting.Avatar.MaxWidth = 5
+	setting.Avatar.MaxHeight = 5
+	origin = newImgData(10)
+	_, err = processAvatarImage(origin, 262144)
+	assert.ErrorContains(t, err, "image width is too large: 10 > 5")
 }