Support Unix domain datagram sockets

[pauldraper]

What is the problem this feature will solve?

1. Notifying SystemD of service status, via$NOTIFY_SOCKET
2. Logging to Syslog, via /dev/log

Unix datagram sockets are the only way to accomplish these very basic service tasks on UNIX-like systems, without extra configuration or leaving Node.js. (See workarounds below.) Node.js could be a good runtime for modern Linux services if it had these features.

What is the feature you are proposing to solve the problem?

Support Unix datagram sockets.

Node.js supported this feature prior to 0.5. It was removed because it couldn't be sensibly supported on one operating system -- Windows (#29339). Node.js does support several features that are missing or significantly different on Windows...POSIX signals, POSIX file permissions, fs.watch() event types.

What alternatives have you considered?

1. Changing to C, C++, Java, Python, Go, Ruby, Deno, etc -- every major language/runtime supports AF_UNIX SOCK_DGRAM.
2. Add dependencies on external executables.
3. Compile a Node.js native module (e.g. unix-dgram).