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child_process: support stdio option in fork() #7811

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child_process: support stdio option in fork()
This commit allows child_process.fork() to pass stdio options
to spawn(). This allows fork() to more easily take advantage of
additional stdio channels.
cjihrig committed Jul 20, 2016
commit b55fd52d98a6795389ed067fbbcf3712767e3bca
2 changes: 2 additions & 0 deletions doc/api/child_process.md
Original file line number Diff line number Diff line change
@@ -253,6 +253,8 @@ added: v0.5.0
piped to the parent, otherwise they will be inherited from the parent, see
the `'pipe'` and `'inherit'` options for [`child_process.spawn()`][]'s
[`stdio`][] for more details (Default: `false`)
* `stdio` {Array} Supports the array version of [`child_process.spawn()`][]'s
[`stdio`][] option. When this option is provided, it overrides `silent`.
* `uid` {Number} Sets the user identity of the process. (See setuid(2).)
* `gid` {Number} Sets the group identity of the process. (See setgid(2).)
* Return: {ChildProcess}
12 changes: 8 additions & 4 deletions lib/child_process.js
Original file line number Diff line number Diff line change
@@ -49,10 +49,14 @@ exports.fork = function(modulePath /*, args, options*/) {

args = execArgv.concat([modulePath], args);

// Leave stdin open for the IPC channel. stdout and stderr should be the
// same as the parent's if silent isn't set.
options.stdio = options.silent ? ['pipe', 'pipe', 'pipe', 'ipc'] :
[0, 1, 2, 'ipc'];
if (!Array.isArray(options.stdio)) {
// Leave stdin open for the IPC channel. stdout and stderr should be the
// same as the parent's if silent isn't set.
options.stdio = options.silent ? ['pipe', 'pipe', 'pipe', 'ipc'] :
[0, 1, 2, 'ipc'];
} else if (options.stdio.indexOf('ipc') === -1) {
throw new TypeError('Forked processes must have an IPC channel');
}

options.execPath = options.execPath || process.execPath;

54 changes: 54 additions & 0 deletions test/parallel/test-child-process-fork-stdio.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,54 @@
'use strict';
const common = require('../common');
const assert = require('assert');
const cp = require('child_process');
const net = require('net');

if (process.argv[2] === 'child') {
process.stdout.write('this should be ignored');
process.stderr.write('this should not be ignored');

const pipe = new net.Socket({ fd: 4 });

process.on('disconnect', () => {
pipe.unref();
});

pipe.setEncoding('utf8');
pipe.on('data', (data) => {
process.send(data);
});
} else {
assert.throws(() => {
cp.fork(__filename, {stdio: ['pipe', 'pipe', 'pipe', 'pipe']});
}, /Forked processes must have an IPC channel/);

let ipc = '';
let stderr = '';
const buf = Buffer.from('data to send via pipe');
const child = cp.fork(__filename, ['child'], {
stdio: [0, 'ignore', 'pipe', 'ipc', 'pipe']
});

assert.strictEqual(child.stdout, null);

child.on('message', (msg) => {
ipc += msg;

if (ipc === buf.toString()) {
child.disconnect();
}
});

child.stderr.on('data', (chunk) => {
stderr += chunk;
});

child.on('exit', common.mustCall((code, signal) => {
assert.strictEqual(code, 0);
assert.strictEqual(signal, null);
assert.strictEqual(stderr, 'this should not be ignored');
}));

child.stdio[4].write(buf);
}