node --help | head -n1 throws an error

[jcbhmr]

Version

v21.5.0

Platform

Linux codespaces-6c49bb 6.2.0-1018-azure #18~22.04.1-Ubuntu SMP Tue Nov 21 19:25:02 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

node --help | head -n1

How often does it reproduce? Is there a required condition?

always

What is the expected behavior? Why is that the expected behavior?

expected behaviour is what deno and bun do: don't error lol

What do you see instead?

@jcbhmr ➜ /workspaces/my-app (main) $ node --help | head -n1
Usage: node [options] [ script.js ] [arguments]
node:events:497
      throw er; // Unhandled 'error' event
      ^

Error: write EPIPE
    at afterWriteDispatched (node:internal/stream_base_commons:160:15)
    at writeGeneric (node:internal/stream_base_commons:151:3)
    at Socket._writeGeneric (node:net:952:11)
    at Socket._write (node:net:964:8)
    at writeOrBuffer (node:internal/streams/writable:564:12)
    at _write (node:internal/streams/writable:493:10)
    at Writable.write (node:internal/streams/writable:502:10)
    at print (node:internal/main/print_help:216:10)
    at node:internal/main/print_help:233:1
Emitted 'error' event on Socket instance at:
    at emitErrorNT (node:internal/streams/destroy:169:8)
    at emitErrorCloseNT (node:internal/streams/destroy:128:3)
    at process.processTicksAndRejections (node:internal/process/task_queues:82:21) {
  errno: -32,
  code: 'EPIPE',
  syscall: 'write'
}

Node.js v21.5.0
@jcbhmr ➜ /workspaces/my-app (main) $ echo $?
0

Additional information

No response

[kvakil]

$? after a pipe is the exit code of the last command in the pipe, which in this case is head -n1. That's why you get 0. If you're using Bash, ${PIPESTATUS[0]} will give you the exit code of node --help which in this case is indeed 1.

expected behaviour is what deno and bun do: don't error lol

Could you elaborate a little on why you need this? Is it causing issues for you or just something you noticed out of curiosity?

[jcbhmr]

Ohhhh so that's why it exited with code 0! 🤦‍♀️

Context of how I noticed this: I was trying to trim the massive --help menus of a bunch of different commands like clang, deno, bun, cargo, rustc, node, etc. and node --help | head -n20 failed. 🤷‍♀️

[jcbhmr]

This works:

node -e 'console.log("a\n".repeat(2000))' | head -n5

This works:

node -e 'process.stdout.write("a\n".repeat(2000))' | head -n5

This is what the node --help printing code looks like:

node/lib/internal/main/print_help.js

Lines 200 to 233 in c25878d

	function print(stream) {
	const { options, aliases } = require('internal/options');
	// Use 75 % of the available width, and at least 70 characters.
	const width = MathMax(70, (stream.columns || 0) * 0.75);
	const firstColumn = MathFloor(width * 0.4);
	const secondColumn = MathFloor(width * 0.57);
	options.set('-', { helpText: 'script read from stdin ' +
	'(default if no file name is provided, ' +
	'interactive mode if a tty)' });
	options.set('--', { helpText: 'indicate the end of node options' });
	stream.write(
	'Usage: node [options] [ script.js ] [arguments]\n' +
	' node inspect [options] [ script.js | host:port ] [arguments]\n\n' +
	'Options:\n');
	stream.write(indent(format({
	options, aliases, firstColumn, secondColumn,
	}), 2));
	stream.write('\nEnvironment variables:\n');
	stream.write(format({
	options: envVars, firstColumn, secondColumn,
	}));
	stream.write('\nDocumentation can be found at https://nodejs.org/\n');
	}
	prepareMainThreadExecution();
	markBootstrapComplete();
	print(process.stdout);

Specifically note the use of multiple .write() calls.

This FAILS:

node -e 'for (const i of Array(1000).keys()) process.stdout.write(`${i}\n`)' | head -n5

This works:

node -e 'for (const i of Array(1000).keys()) console.log(i)' | head -n5

What I suggest:

• use console.log() which appears to already have this swallowing error behaviour
• OR if that can't happen: change the node --help printing code to use helpText += partN and .write(helpText) with a try block with a catch (error) and if (error?.code !== 'EPIPE') throw error rethrow

This would:

1. Not interfere with the useful and expected feature of throwing on closed pipes
2. Stop the weird error from happening with node --help