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59 lines
2.4 KiB
Markdown
59 lines
2.4 KiB
Markdown
# flagged-respawn [](http://travis-ci.org/js-cli/js-flagged-respawn)
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> A tool for respawning node binaries when special flags are present.
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[](https://nodei.co/npm/flagged-respawn/)
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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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## Release History
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* 2016-03-22 - v0.3.2 - fix issue with v8 flags values being dropped
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* 2014-09-12 - v0.3.1 - use `{ stdio: 'inherit' }` for spawn to maintain colors
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* 2014-09-11 - v0.3.0 - for real this time
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* 2014-09-11 - v0.2.0 - cleanup
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* 2014-09-04 - v0.1.1 - initial release
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