Fix a bug in calling pselect

[zhangxp1998]

Per pselect man pages, the kth bit of self.fd_set must be set if we are interested in file descriptor k. libpnet does this once in here, when the datalink receiver/sender is initialized. However, if no descriptors are available during a pselect call, the kernel will clear self.fd_set, and next time when pnet calls pselect, it will pass a fd_set with all bits 0. The kernel will interpret this as "I don't care if any of the file descriptors are available", and will happily return 0 even if there are some packets available. See screenshot, all bits in the fd_set bit mask are set to 0(this is not supposed to happen!).

This caused an issue in another rust open source project, see discussion here.

[JuxhinDB]

Apologies for the late reply from our end. Looking into this now and will update you shortly.

[zhangxp1998]

For reference, linux's implementation sets the bit mask before every pselect call:

libpnet/pnet_datalink/src/linux.rs

Line 248 in dc2203a

libc::FD_SET(self.socket.fd, &mut self.fd_set as *mut libc::fd_set);

[JuxhinDB]

This is a nice catch, thanks a lot for fixing it @zhangxp1998. I just went over the diff and have no issues with this. Will be merging shortly :-)

Do you require a version bump?

[zhangxp1998]

Do you require a version bump?

Yes please!

[JuxhinDB]

@zhangxp1998 -- version bump in progress. Bear with me if I'm a tad slow. :-)

[JuxhinDB]

@zhangxp1998 Version has been bumped to 0.25.0

[zhangxp1998]

@zhangxp1998 Version has been bumped to 0.25.0

Awesome! Thanks a lot!