appendFd
Adds a file descriptor to @message.
The file descriptor is duplicated using dup(). You keep your copy of the descriptor and the copy contained in @message will be closed when @message is finalized.
A possible cause of failure is exceeding the per-process or system-wide file descriptor limit.
Return
true in case of success, else false (and @error is set)
Since
2.22
Parameters
fd
a valid open file descriptor