wayland-server: Add ways of adding sockets to Display.

[trissylegs]

Wayland servers can have sockets added in several ways:

• via wl_display_add_socket. Which either: uses a given display name, WAYLAND_DISPLAY or wayland-0. (In that order)
• via wl_display_add_socket_auto. Which scans through $XDG_RUNTIME_DIR for an unused wayland-$d (where $d is < 32) and binds the first available.
• via wl_display_add_socket_fd. Which accepts a file descriptor. This can be for:
  sockets created and passed in by parent for socket activation, (eg by systemd),
  or created specifically by the library user for fine grained control.

My initial thoughts:

The first method seems to be the documented behavior of create_display. But, I'm not seeing it happen. Although it may not be the best behavior. By which I mean create_display should probably only do what wl_display_create does (the get event loop is probably fine).

Perhaps adding add_socket methods to Display or EventLoop. eg:

• fn add_socket(&mut self, name: Option<&OsStr>) -> Result<()>
  just calls wl_display_add_socket
• fn add_socket_auto(&mut self) -> Result<String>
  calls wl_display_add_socket_auto. Returns the resulting string. (Which should be utf8, although an OsString might be better anyway)
• fn add_socket_rawfd(&mut self, fd: RawFd) -> Result<()>
  calls wl_display_add_socket_fd with the passed fd.
• fn add_socket_intofd<F>(&mut self, fd: F) -> Result<()> where F: IntoRawFd
  converts fd to a RawFd and calls add_socket_rawfd.
  This as a convience method for use with unix-sockets.

I might be able to do somethings about this, but I'm a bit busy over the next week or two.

[elinorbgr]

Hmm, indeed, there is a doc issue on create_display, which really just creates a display. I'm not sure what I did here.

I completely agree with you here, I was planning to add these various methods at some point, in a quite similar way as you suggested. But I'm quite busy as well, an focused my efforts on wayland-client at first.

I'll add them as soon as I have the opportunity, should not be a lot of work.