90 lines
3.2 KiB
Markdown
Executable file
90 lines
3.2 KiB
Markdown
Executable file
# foreground-child
|
|
|
|
Run a child as if it's the foreground process. Give it stdio. Exit
|
|
when it exits.
|
|
|
|
Mostly this module is here to support some use cases around
|
|
wrapping child processes for test coverage and such. But it's
|
|
also generally useful any time you want one program to execute
|
|
another as if it's the "main" process, for example, if a program
|
|
takes a `--cmd` argument to execute in some way.
|
|
|
|
## USAGE
|
|
|
|
```js
|
|
import { foregroundChild } from 'foreground-child'
|
|
// hybrid module, this also works:
|
|
// const { foregroundChild } = require('foreground-child')
|
|
|
|
// cats out this file
|
|
const child = foregroundChild('cat', [__filename])
|
|
|
|
// At this point, it's best to just do nothing else.
|
|
// return or whatever.
|
|
// If the child gets a signal, or just exits, then this
|
|
// parent process will exit in the same way.
|
|
```
|
|
|
|
You can provide custom spawn options by passing an object after
|
|
the program and arguments:
|
|
|
|
```js
|
|
const child = foregroundChild(`cat ${__filename}`, { shell: true })
|
|
```
|
|
|
|
A callback can optionally be provided, if you want to perform an
|
|
action before your foreground-child exits:
|
|
|
|
```js
|
|
const child = foregroundChild('cat', [__filename], spawnOptions, () => {
|
|
doSomeActions()
|
|
})
|
|
```
|
|
|
|
The callback can return a Promise in order to perform
|
|
asynchronous actions. If the callback does not return a promise,
|
|
then it must complete its actions within a single JavaScript
|
|
tick.
|
|
|
|
```js
|
|
const child = foregroundChild('cat', [__filename], async () => {
|
|
await doSomeAsyncActions()
|
|
})
|
|
```
|
|
|
|
If the callback throws or rejects, then it will be unhandled, and
|
|
node will exit in error.
|
|
|
|
If the callback returns a string value, then that will be used as
|
|
the signal to exit the parent process. If it returns a number,
|
|
then that number will be used as the parent exit status code. If
|
|
it returns boolean `false`, then the parent process will not be
|
|
terminated. If it returns `undefined`, then it will exit with the
|
|
same signal/code as the child process.
|
|
|
|
## Caveats
|
|
|
|
The "normal" standard IO file descriptors (0, 1, and 2 for stdin,
|
|
stdout, and stderr respectively) are shared with the child process.
|
|
Additionally, if there is an IPC channel set up in the parent, then
|
|
messages are proxied to the child on file descriptor 3.
|
|
|
|
In Node, it's possible to also map arbitrary file descriptors
|
|
into a child process. In these cases, foreground-child will not
|
|
map the file descriptors into the child. If file descriptors 0,
|
|
1, or 2 are used for the IPC channel, then strange behavior may
|
|
happen (like printing IPC messages to stderr, for example).
|
|
|
|
Note that a SIGKILL will always kill the parent process, but
|
|
will not proxy the signal to the child process, because SIGKILL
|
|
cannot be caught. In order to address this, a special "watchdog"
|
|
child process is spawned which will send a SIGKILL to the child
|
|
process if it does not terminate within half a second after the
|
|
watchdog receives a SIGHUP due to its parent terminating.
|
|
|
|
On Windows, issuing a `process.kill(process.pid, signal)` with a
|
|
fatal termination signal may cause the process to exit with a `1`
|
|
status code rather than reporting the signal properly. This
|
|
module tries to do the right thing, but on Windows systems, you
|
|
may see that incorrect result. There is as far as I'm aware no
|
|
workaround for this.
|