return more specific error message when attemting to decode UDF volume

iso9660.go

@@ -19,6 +19,7 @@ const (
 	sectorSize         uint32 = 2048
 	systemAreaSize            = sectorSize * 16
 	standardIdentifier        = "CD001"
+	udfIdentifier             = "BEA01"
 
 	volumeTypeBoot          byte = 0
 	volumeTypePrimary       byte = 1
@@ -48,6 +49,8 @@ const (
 
 var standardIdentifierBytes = [5]byte{'C', 'D', '0', '0', '1'}
 
+var ErrUDFNotSupported = errors.New("UDF volumes are not supported")
+
 // volumeDescriptorHeader represents the data in bytes 0-6
 // of a Volume Descriptor as defined in ECMA-119 8.1
 type volumeDescriptorHeader struct {
@@ -404,8 +407,12 @@ func (vd *volumeDescriptor) UnmarshalBinary(data []byte) error {
 		return err
 	}
 
-	if string(vd.Header.Identifier[:]) != standardIdentifier {
-		return fmt.Errorf("volume descriptor %q != %q", string(vd.Header.Identifier[:]), standardIdentifier)
+	id := string(vd.Header.Identifier[:])
+	if id != standardIdentifier {
+		if id == udfIdentifier {
+			return ErrUDFNotSupported
+		}
+		return fmt.Errorf("volume descriptor %q != %q", id, standardIdentifier)
 	}
 
 	switch vd.Header.Type {

iso9660_test.go

@@ -126,6 +126,14 @@ func TestIncorrectData(t *testing.T) {
 		assert.ErrorIs(tt, err, io.ErrUnexpectedEOF)
 	})
 
+	t.Run("volumeDescriptor is UDF", func(tt *testing.T) {
+		vd := &volumeDescriptor{}
+		data := make([]byte, sectorSize)
+		copy(data[1:6], []byte(udfIdentifier))
+		err := vd.UnmarshalBinary(data)
+		assert.Equal(tt, ErrUDFNotSupported, err)
+	})
+
 	t.Run("volumeDescriptor has invalid volume type", func(tt *testing.T) {
 		vd := &volumeDescriptor{}
 		data := make([]byte, sectorSize)