Struct FileElement

message/elements.go:96–108

	}

	FileElement struct {
		FileSize uint64
		FileName string
		FileMd5  []byte
		FileURL  string
		FileID   string // group
		FileUUID string // private
		FileHash string

		// send
		FileStream io.ReadSeeker
		FileSha1   []byte
	}

	ShortVideoElement struct {
		Name     string