process.stdin still fetch bytes after clossing file descriptor 0

[piranna]

• Version: v7.10.0
• Platform: Linux msi 4.10.0-20-generic Adding Governance, Contribution Policy, and CoC #22-Ubuntu SMP Thu Apr 20 09:22:42 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
• Subsystem: Ubuntu 17.04

#!/usr/bin/env node

const close = require('fs').close

process.stdin.pipe(process.stdout)

close(0, function(err)
{
  console.log('stdin clossed', err)
})

When clossing the file descriptor zero (stdin), if something is still witten to it Node.js still fetchs that info. Since new file descriptors (both by opening files and/or using the unistd module) start at position 12, seems like Node.js itself is internally duplicating fd 0 (probably in the process.stdin stream, in fact process.stdin.fd is 0 but process.stdin._handle.TTY.fd is 9), making it difficult to manipulate the file descriptors at low level, for example when developing interactive shells like nsh where background tasks should be still running (so spawnSync() is not an option).

Probably related to #5574.

[Fishrock123]

Please see https://nodejs.org/dist/latest-v7.x/docs/api/process.html#process_a_note_on_process_i_o -- I do not think you can close stdin.

e.g., in the repl:

> process.stdin.close()
TypeError: process.stdin.close is not a function
    at repl:1:15
    at sigintHandlersWrap (vm.js:22:35)
    at sigintHandlersWrap (vm.js:96:12)
    at ContextifyScript.Script.runInThisContext (vm.js:21:12)
    at REPLServer.defaultEval (repl.js:349:29)
    at bound (domain.js:280:14)
    at REPLServer.runBound [as eval] (domain.js:293:12)
    at REPLServer.<anonymous> (repl.js:548:10)
    at emitOne (events.js:101:20)
    at REPLServer.emit (events.js:188:7)

[addaleax]

I do not think you can close stdin.

This is not about process.stdin as a stream, though.

Here is why libuv dup()s the file descriptor – ironically, Node doesn’t use non-blocking TTYs anymore.

I’m not sure there’s much to do here (unless you have concrete suggestions?). If you want the tip, you can use compare the fs.fstat(Sync) outputs to check whether two FDs refer to the same file, or just use process.stdin._handle.fd directly (even though it’s a private API).

[Trott]

This issue has been inactive for sufficiently long that it seems like perhaps it should be closed. Feel free to re-open (or leave a comment requesting that it be re-opened) if you disagree. I'm just tidying up and not acting on a super-strong opinion or anything like that.