regression: child_process stdin pipe close event not emitted

### Summary * **Version**: v8.12.0 and newer, all v10.x and all v11.x * **Platform**: Linux and macOS amd64 * **Subsystem**: child_process Since #18701 Node.js doesn't emit a close event when a child process closes its stdin pipe. The close is only detected if the parent tries to write to the child's stdin and receives an EPIPE. The original behaviour is preferable because it allows immediate detection of the close event, rather than waiting for a failed write. ### Reproducer This works as expected in v8.11.4 and fails in all newer versions of v8.x, as well as all v10.x and all v11.x. ```js const {spawn} = require('child_process'); const cp = spawn( 'node', [ '-e', 'fs.closeSync(0); setTimeout(() => {}, 2000)' ], {stdio: ['pipe', 'inherit', 'inherit']} ) setTimeout(() => { console.log('BUGGY! stdin close event was not emitted') process.exit(1); }, 1000); cp.stdin.on('close', () => { console.log('Ok!') process.exit(0); }); ``` ### Problem detail As far as I can tell the only way the close event can be emitted is if the `Socket` constructor calls `this.read(0)`. This triggers `onStreamRead()` to be called, which does `stream.push(null)` and eventually results in the close event. This is a little weird because stdin isn't a readable stream :) In Node 8.11.4 this worked because `child_process.js:createSocket()` called the `Socket` constructor with `options.readable === undefined`. So the `Socket` constructor sees that `options.readable !== false` and runs `this.read(0)` In PR #18701 `createSocket()` was changed to call the `Socket` constructor with `options.readable === true`. This stops `this.read(0)` from being called and the close event is not emitted. ### Hacky solution ```diff --- a/lib/internal/child_process.js +++ b/lib/internal/child_process.js @@ -286,3 +286,3 @@ function flushStdio(subprocess) { function createSocket(pipe, readable) { - return net.Socket({ handle: pipe, readable, writable: !readable }); + return n…