UNIX sockets and passing file descriptors

[ktimothy]

UNIX sockets have a "killer feature" - they allow to pass file descriptors from one process to another. Seem nodejs currently does not support it, though it did a long time ago http://stackoverflow.com/questions/23172610/can-you-send-a-unix-domain-file-descriptor-over-another-unix-domain-socket-in-no.

Are there plans to add full support for UNIX sockets?

[bnoordhuis]

Node.js supports them but in an indirect way. If you spawn a child process with { stdio: [ ..., 'ipc', ... ] }, you can send and receive handles (sockets, pipes, etc.) Also works on Windows.

You can wrap existing file descriptors in a handle with new net.Socket({ fd: fd }) and send over the socket but with the restriction that the file descriptor should refer to something that is pollable by interfaces like epoll. A regular file won't work, for example.

[ktimothy]

In my case I need to pass tcp socket to nodejs process over UNIX domain socket. And I do not spawn child processes with nodejs, so I cannot use the built-in mechanism. Maybe there is way to extend it to not only nodejs-spawned processes?

You can wrap existing file descriptors in a handle with

If I try to create socket from fd, I get the following error:

TypeError: Unsupported fd type: UNKNOWN
    at createHandle (net.js:35:9)
    at new Socket (net.js:144:20)

I tried to investigate the issue, and it looks like under the hood libuv cannot determine type of fd, which is UNIX domain socket.

[bnoordhuis]

Is it a AF_UNIX+SOCK_DGRAM type socket? Those aren't supported. AF_UNIX+SOCK_STREAM should work though.

[ktimothy]

Yep, its Datagram. I can still read it using fs.read.

What is the reason to not to support Datagram sockets?

[bnoordhuis]

Lack of Windows support, basically.

[rektide]

Look at https://www.npmjs.com/package/usocket for an implementation of passing file descriptors over UNIX domain sockets. Thanks UNIX.

[pauldraper]

Lack of Windows support, basically.

Thanks Windows.