# flagged-respawn [![NPM version][npm-image]][npm-url] [![Downloads][downloads-image]][npm-url] [![Travis Build Status][travis-image]][travis-url] [![AppVeyor Build Status][appveyor-image]][appveyor-url] [![Coveralls Status][coveralls-image]][coveralls-url] [![Gitter chat][gitter-image]][gitter-url] A tool for respawning node binaries when special flags are present. ## What is it? Say you wrote a command line tool that runs arbitrary javascript (e.g. task runner, test framework, etc). For the sake of discussion, let's pretend it's a testing harness you've named `testify`. Everything is going splendidly until one day you decide to test some code that relies on a feature behind a v8 flag in node (`--harmony`, for example). Without much thought, you run `testify --harmony spec tests.js`. It doesn't work. After digging around for a bit, you realize this produces a [`process.argv`](http://nodejs.org/docs/latest/api/process.html#process_process_argv) of: `['node', '/usr/local/bin/test', '--harmony', 'spec', 'tests.js']` Crap. The `--harmony` flag is in the wrong place! It should be applied to the **node** command, not our binary. What we actually wanted was this: `['node', '--harmony', '/usr/local/bin/test', 'spec', 'tests.js']` Flagged-respawn fixes this problem and handles all the edge cases respawning creates, such as: - Providing a method to determine if a respawn is needed. - Piping stderr/stdout from the child into the parent. - Making the parent process exit with the same code as the child. - If the child is killed, making the parent exit with the same signal. To see it in action, clone this repository and run `npm install` / `npm run respawn` / `npm run nospawn`. ## Sample Usage ```js #!/usr/bin/env node const flaggedRespawn = require('flagged-respawn'); // get a list of all possible v8 flags for the running version of node const v8flags = require('v8flags').fetch(); flaggedRespawn(v8flags, process.argv, function (ready, child) { if (ready) { console.log('Running!'); // your cli code here } else { console.log('Special flags found, respawning.'); } if (process.pid !== child.pid) { console.log('Respawned to PID:', child.pid); } }); ``` ## API ### flaggedRespawn(flags, argv, [ forcedFlags, ] callback) : Void Respawns the script itself when *argv* has special flag contained in *flags* and/or *forcedFlags* is not empty. Because members of *flags* and *forcedFlags* are passed to `node` command, each of them needs to be a node flag or a V8 flag. #### Forbid respawning If `--no-respawning` flag is given in *argv*, this function does not respawned even if *argv* contains members of flags or *forcedFlags* is not empty. (This flag is also used internally to prevent from respawning more than once). #### Parameter: | Parameter | Type | Description | |:--------------|:------:|:----------------------------------------------------| | *flags* | Array | An array of node flags and V8 flags which are available when present in *argv*. | | *argv* | Array | Command line arguments to respawn. | | *forcedFlags* | Array or String | An array of node flags or a string of a single flag and V8 flags for respawning forcely. | | *callback* | function | A called function when not respawning or after respawned. | * **callback(ready, proc, argv) : Void** *callback* function is called both when respawned or not, and it can be distinguished by callback's argument: *ready*. (*ready* indicates whether a process spawned its child process (false) or not (true), but it does not indicate whether a process is a spawned child process or not. *ready* for a spawned child process is true.) *argv* is an array of command line arguments which is respawned (when *ready* is false) or is passed current process except flags within *flags* and `--no-respawning` (when *ready* is true). **Parameter:** | Parameter | Type | Description | |:----------|:-------:|:--------------------------| | *ready* | boolean | True, if not respawning and is ready to execute main function. | | *proc* | object | Child process object if respawned, otherwise current process object. | | *argv* | Array | An array of command line arguments. | ## License MIT [downloads-image]: http://img.shields.io/npm/dm/flagged-respawn.svg [npm-url]: https://www.npmjs.com/package/flagged-respawn [npm-image]: http://img.shields.io/npm/v/flagged-respawn.svg [travis-url]: https://travis-ci.org/gulpjs/flagged-respawn [travis-image]: http://img.shields.io/travis/gulpjs/flagged-respawn.svg?label=travis-ci [appveyor-url]: https://ci.appveyor.com/project/gulpjs/flagged-respawn [appveyor-image]: https://img.shields.io/appveyor/ci/gulpjs/flagged-respawn.svg?label=appveyor [coveralls-url]: https://coveralls.io/r/gulpjs/flagged-respawn [coveralls-image]: http://img.shields.io/coveralls/gulpjs/flagged-respawn/master.svg [gitter-url]: https://gitter.im/gulpjs/gulp [gitter-image]: https://badges.gitter.im/gulpjs/gulp.svg