WriteFileError

        pub const WriteFileError = Error || error{
            /// The `Io` implementation cannot offer a more efficient
            /// file-to-socket path; the caller should fall back to read-based
            /// copying. See `Io.Writer.sendFile`.
            Unimplemented,
            /// Reached the end of the file being read.
            EndOfStream,
            /// The source `File.Reader` failed; detailed diagnostics are found
            /// on that struct.
            ReadFailed,
        }