image: detect AVIF with miaf major brand

matchers/image.go

@@ -152,21 +152,26 @@ func Exr(buf []byte) bool {
 		buf[2] == 0x31 && buf[3] == 0x01
 }
 
+func avifBrand(brand string) bool {
+	return brand == "avif" || brand == "avis"
+}
+
 func Avif(buf []byte) bool {
 	if !isobmff.IsISOBMFF(buf) {
 		return false
 	}
 
 	majorBrand, _, compatibleBrands := isobmff.GetFtyp(buf)
-	if majorBrand == "avif" {
+	if avifBrand(majorBrand) {
 		return true
 	}
 
-	if majorBrand == "mif1" || majorBrand == "msf1" {
-		for _, compatibleBrand := range compatibleBrands {
-			if compatibleBrand == "avif" {
-				return true
-			}
+	// libavif commonly writes major brand miaf/mif1/msf1 with avif
+	// in compatible_brands. Restricting the major brand to mif1/msf1
+	// missed those files.
+	for _, compatibleBrand := range compatibleBrands {
+		if avifBrand(compatibleBrand) {
+			return true
 		}
 	}
 

matchers/image_test.go

@@ -0,0 +1,54 @@
+package matchers
+
+import (
+	"encoding/binary"
+	"testing"
+)
+
+func ftypBox(major string, brands ...string) []byte {
+	n := 16 + 4*len(brands)
+	buf := make([]byte, n)
+	binary.BigEndian.PutUint32(buf[0:4], uint32(n))
+	copy(buf[4:8], "ftyp")
+	copy(buf[8:12], major)
+	for i, b := range brands {
+		copy(buf[16+4*i:], b)
+	}
+	return buf
+}
+
+func TestAvifBrands(t *testing.T) {
+	cases := []struct {
+		name string
+		buf  []byte
+		want bool
+	}{
+		{"major avif", ftypBox("avif", "avif", "mif1", "miaf"), true},
+		{"mif1 + avif", ftypBox("mif1", "mif1", "avif"), true},
+		{"msf1 + avif", ftypBox("msf1", "msf1", "avif"), true},
+		{"miaf + avif", ftypBox("miaf", "miaf", "avif", "mif1"), true},
+		{"major avis", ftypBox("avis", "avis", "avif"), true},
+		{"miaf + avis", ftypBox("miaf", "miaf", "avis"), true},
+		{"miaf without avif", ftypBox("miaf", "miaf", "mif1"), false},
+		{"heic", ftypBox("heic", "mif1", "heic"), false},
+		{"mif1 + heic", ftypBox("mif1", "mif1", "heic"), false},
+		{"not isobmff", []byte("not a media box"), false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := Avif(tc.buf); got != tc.want {
+				t.Fatalf("Avif() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestHeifNotAvif(t *testing.T) {
+	buf := ftypBox("miaf", "miaf", "avif", "mif1")
+	if !Avif(buf) {
+		t.Fatal("miaf+avif should match Avif")
+	}
+	if Heif(buf) {
+		t.Fatal("miaf+avif should not match Heif")
+	}
+}