Ctrlc-wrapper NPM

ctrlc-wrapper

Windows doesn't support sending signals to other processes as it is possible on POSIX platforms.

Using kill methods on Windows (like process.kill() with Node.js) means the target process is getting killed forcefully and abruptly (similar to SIGKILL).

However, in a console, processes can be terminated with the CTRL+C key combination.
Most programming languages have an implementation to capture this signal (usually as SIGINT), allowing applications to handle it and to terminate "gracefully".

The problem is that the CTRL+C key combination cannot be easily simulated for the following reasons:

In order to be able to generate a CTRL+C signal programmatically, several Console Functions needs to be called - something which can only be done in lower-level programming languages.
The process which should receive the CTRL+C signal needs to live in its own console since the CTRL+C signal is sent to all processes attached to a console. Spawning a process in a new console, again, is something which is only possible in lower-level programming languages.

This wrapper application does exactly the points described above.

The wrapper inherits the exit code from the child process. If there's an error with the wrapper itself, the exit code is -1.

Usage

npm install ctrlc-wrapper

import { spawnWithWrapper } from 'ctrlc-wrapper';

const child = spawnWithWrapper('node test/read-echo.js');

child.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);
  if (/READING/.test(data)) {
    child.sendCtrlC();
  }
});

child.stderr.on('data', (data) => {
  console.log(`stderr: ${data}`);
});

child.on('close', (code, signal) => {
  console.log(`close: ${code} ${signal}`);
});

Test

To start the child process node test/read-echo.js with the wrapper:

go run ./cmd/start node test/read-echo.js

To terminate:

Press CTRL+C
Write ^C to stdin
Exit from within the child

Build

pnpm build

Notes

Why the separate `ctrlc.exe` binary?

It would be possible to send the CTRL+C signal directly from within start.exe but this means an additional process must be spawned (e.g. cmd /c pause) to prevent losing the original (parent) console during the console switch (FreeConsole -> AttachConsole). Using a separate binary to send the CTRL+C signal is much safer.

`CREATE_NEW_CONSOLE` vs. `CREATE_NEW_PROCESS_GROUP`

Both methods seems to protect from receiving the CTRL+C signal in the current console.

However, spawning the child with CREATE_NEW_PROCESS_GROUP would mean that we need to start another "wrapper" in which the "normal processing of CTRL+C input" is enabled first (via SetConsoleCtrlHandler) before starting the actual child process.