How to open exist tty using net.Socket ?

[oppai]

Hi, there

I want to open exist tty using net.Socket. But I got an error like a below.

I have two questions.
First, how can I open tty using net.Socket module ?
Second, I success to open tty using tty.ReadStream like a them. But I didn't find it in document. It is trial function? (It is not safe to use in production?)

thank you

• Node.js Version: v14.16.0
• OS: MacOS / Linux
• Scope (install, code, runtime, meta, other?): code
• Module (and version) (if relevant): net.Socket

var fs = require('fs')
var net = require('net')

const fd = fs.openSync('/dev/ttys003', 'r+');
const tty = new net.Socket({fd, readable: true})
tty.on('data', (data) => {
  console.log(data)
})

TypeError [ERR_INVALID_FD_TYPE]: Unsupported fd type: TTY
    at createHandle (net.js:147:9)
    at new Socket (net.js:328:22)
    at Object.<anonymous> (/Users/hiroaki.murayama/progate/progate_ide/v2/src/runtime/sample.js:5:13)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47 {
  code: 'ERR_INVALID_FD_TYPE'

[RaisinTen]

I don't think opening a socket to a TTY fd is supported yet.
At the bottom of https://nodejs.org/api/net.html#net_class_net_socket:

The newly created socket can be either a TCP socket or a streaming IPC endpoint, depending on what it connect() to.

[addaleax]

@RaisinTen No, it is supported. I think this might also qualify as a bug in the net module.

In any case, one can use tty.ReadStream(fd) and tty.WriteStream(fd) to create TTY streams (which should be one class but for some reason isn’t), and both of these inherit from net.Socket.

[RaisinTen]

@addaleax The passed fd type gets rejected here:

node/lib/net.js

Lines 140 to 156 in 3bba40a

	function createHandle(fd, is_server) {
	validateInt32(fd, 'fd', 0);
	const type = guessHandleType(fd);
	if (type === 'PIPE') {
	return new Pipe(
	is_server ? PipeConstants.SERVER : PipeConstants.SOCKET
	);
	}
	if (type === 'TCP') {
	return new TCP(
	is_server ? TCPConstants.SERVER : TCPConstants.SOCKET
	);
	}
	throw new ERR_INVALID_FD_TYPE(type);
	}

. So, this can be fixed by adding an option to accept TTY fds. Should we move this issue to the main repo?

[addaleax]

Yeah, although I think there might also be another issue somewhere for merging the two TTY classes? I think that would be the best solution here.

[oppai]

Thank you, @addaleax and @RaisinTen !
I understand that net.Socket is not supported for tty fd, and I should use tty module instead of net.Socket.

So, there is no document about accepting fd in tty modules.
https://nodejs.org/api/tty.html#tty_class_tty_readstream

it is missing? or experimental function?

[addaleax]

I don’t know why the constructors are not documented, but they should be, yes.