Node: stdio: cannot write to stdin after #1233

[bnoordhuis]

Continuing from https://github.com/nodejs/node/issues/9201#issuecomment-255103708. The change from #1233 makes it impossible to write to stdin, something that works in v0.10 and v0.12.

Test case:

var spawn = require('child_process').spawn;
var args = ['-e', 'process.stdin.write("ok\\n")'];
var proc = spawn(process.execPath, args, { stdio: ['pipe'] });
proc.stdin.pipe(process.stdout);

Trace:

$ strace -s1024 -fe write out/Release/node tmp/bug9201.js
...
[pid 25306] write(2, "events.js:160\n      throw er; // Unhandled 'error' event\n      ^\n\nError: write after end\n    at writeAfterEnd (_stream_writable.js:192:12)\n    at Socket.Writable.write (_stream_writable.js:243:5)\n    at Socket.write (net.js:661:40)\n    at [eval]:1:15\n    at ContextifyScript.Script.runInThisContext (vm.js:25:33)\n    at Object.exports.runInThisContext (vm.js:77:17)\n    at Object.<anonymous> ([eval]-wrapper:6:22)\n    at Module._compile (module.js:582:32)\n    at bootstrap_node.js:345:29\n    at _combinedTickCallback (internal/process/next_tick.js:67:7)\n", 554) = 554
...

cc @indutny

[Fishrock123]

sounds like a bug

[indutny]

@bnoordhuis does it actually work on windows? IMO, writing to stdin sounds quite ridiculous... It may not even support writes at all.

[Fishrock123]

Are we actually talking about writing to fd 0, or about writing to the node stream representing it?

[bnoordhuis]

The node stream. File descriptor 0 in the example accepts writes just fine, it's a bidirectional UNIX socket.

[Fishrock123]

That's what I was thinking. I'm not sure if we care much about that odd Windows caveat then since I don't think it is possible to hit from this codepath anyways.

[indutny]

@bnoordhuis is it always such thing, though? Is it logical to allow writes to it?

[bnoordhuis]

It's not typical but it's also not unheard of in the UNIX world. The current restriction is artificial. All other things being equal, it's better to lift it.

[Trott]

@bnoordhuis Should this remain open?

[bnoordhuis]

Just tried it again, it's still unfixed. I've added 'good first contribution' and 'help wanted' labels.

[nikshepsvn]

Would love to try tackling this @bnoordhuis, this is my first open source contribution though so I would love some help with getting started. Can you give me an idea of what I should be looking at/doing to get this done?

[bnoordhuis]

@nikshepsvn It was introduced in commit 9ae1a61 but that code has since migrated to lib/internal/process/stdio.js.

If you want a real quick test, echo | ./out/Release/node -e 'process.stdin.write(".")' should not throw an error.

FWIW, I'm also fine with closing this. I since learned that python also rejects writes to sys.stdin so at least we're in good company.

[JackDanger]

I second @bnoordhuis's recommendation to close this as Ruby and Python both open STDIN in read-only mode.

[apapirovski]

I'll close this out given the lack of activity in terms of making it actually happen and the latest feedback from @bnoordhuis and @JackDanger. If anyone still wants this though feel free to reopen or create an issue/PR.