107 lines
5.2 KiB
Markdown
107 lines
5.2 KiB
Markdown
<p align="center">
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<a href="http://gulpjs.com">
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<img height="257" width="114" src="https://raw.githubusercontent.com/gulpjs/artwork/master/gulp-2x.png">
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</a>
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</p>
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# flagged-respawn
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[![NPM version][npm-image]][npm-url] [![Downloads][downloads-image]][npm-url] [![Build Status][ci-image]][ci-url] [![Coveralls Status][coveralls-image]][coveralls-url]
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A tool for respawning node binaries when special flags are present.
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## What is it?
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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`.
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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`.
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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:
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`['node', '/usr/local/bin/test', '--harmony', 'spec', 'tests.js']`
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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:
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`['node', '--harmony', '/usr/local/bin/test', 'spec', 'tests.js']`
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Flagged-respawn fixes this problem and handles all the edge cases respawning creates, such as:
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- Providing a method to determine if a respawn is needed.
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- Piping stderr/stdout from the child into the parent.
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- Making the parent process exit with the same code as the child.
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- If the child is killed, making the parent exit with the same signal.
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To see it in action, clone this repository and run `npm install` / `npm run respawn` / `npm run nospawn`.
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## Sample Usage
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```js
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#!/usr/bin/env node
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const flaggedRespawn = require('flagged-respawn');
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// get a list of all possible v8 flags for the running version of node
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const v8flags = require('v8flags').fetch();
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flaggedRespawn(v8flags, process.argv, function (ready, child) {
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if (ready) {
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console.log('Running!');
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// your cli code here
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} else {
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console.log('Special flags found, respawning.');
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}
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if (process.pid !== child.pid) {
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console.log('Respawned to PID:', child.pid);
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}
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});
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```
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## API
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### <u>flaggedRespawn(flags, argv, [ forcedFlags, ] callback) : Void</u>
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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.
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#### Forbid respawning
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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).
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#### Parameter:
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| Parameter | Type | Description |
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| :------------ | :-------------: | :--------------------------------------------------------------------------------------- |
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| _flags_ | Array | An array of node flags and V8 flags which are available when present in _argv_. |
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| _argv_ | Array | Command line arguments to respawn. |
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| _forcedFlags_ | Array or String | An array of node flags or a string of a single flag and V8 flags for respawning forcely. |
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| _callback_ | function | A called function when not respawning or after respawned. |
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- **<u><i>callback</i>(ready, proc, argv) : Void</u>**
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_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.)
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_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).
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**Parameter:**
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| Parameter | Type | Description |
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| :-------- | :-----: | :------------------------------------------------------------------- |
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| _ready_ | boolean | True, if not respawning and is ready to execute main function. |
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| _proc_ | object | Child process object if respawned, otherwise current process object. |
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| _argv_ | Array | An array of command line arguments. |
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## License
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MIT
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<!-- prettier-ignore-start -->
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[downloads-image]: https://img.shields.io/npm/dm/flagged-respawn.svg?style=flat-square
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[npm-url]: https://www.npmjs.com/package/flagged-respawn
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[npm-image]: https://img.shields.io/npm/v/flagged-respawn.svg?style=flat-square
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[ci-url]: https://github.com/gulpjs/flagged-respawn/actions?query=workflow:dev
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[ci-image]: https://img.shields.io/github/workflow/status/gulpjs/flagged-respawn/dev?style=flat-square
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[coveralls-url]: https://coveralls.io/r/gulpjs/flagged-respawn
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[coveralls-image]: https://img.shields.io/coveralls/gulpjs/flagged-respawn/master.svg?style=flat-square
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<!-- prettier-ignore-end -->
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