Tracking issue for feature(unix_socket_ancillary_data) to extend UnixStream and UnixDatagram to send and receive ancillary data. For example file descriptors.

Unresolved Questions

• Review the SocketAncillary struct before stabilization to ensure it is compatible with all OSes.
• fuchsia, haiku, illumos, ios, macos and solaris does not have MSG_CMSG_CLOEXEC constant in libc
• fuchsia and uclibc(x86_64) does not have cmsghdr struct in libc
• The current version of rust libc does not have ucred struct for the target OS emscripten, but emscripten has this struct in the standard C library

Implementation history

PR #69864, #82589, #83374