A trait for writing to the underlying FUSE endpoint. The FUSE device expects the write
operation to happen in one write transaction. Since there are cases when data needs to be
generated earlier than the header, it implies the writer implementation to keep an internal
buffer. The buffer then can be flushed once header and data are both prepared.
Parses the value of the desired attribute from the FUSE request input and returns it as an
Ok(CStr). Returns Ok(None) if buf is empty or appears to be a valid request extension that
does not contain any security context information.