mirror of https://github.com/actions/setup-python
193 lines
7.7 KiB
Markdown
193 lines
7.7 KiB
Markdown
# Stealthy-Require
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[](https://travis-ci.org/analog-nico/stealthy-require)
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[](https://coveralls.io/r/analog-nico/stealthy-require)
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[](https://david-dm.org/analog-nico/stealthy-require)
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This is probably the closest you can currently get to require something in node.js with completely bypassing the require cache.
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`stealthy-require` works like this:
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1. It clears the require cache.
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2. It calls a callback in which you require your module(s) without the cache kicking in.
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3. It clears the cache again and restores its old state.
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The restrictions are:
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- [Native modules cannot be required twice.](https://github.com/nodejs/node/issues/5016) Thus this module bypasses the require cache only for non-native (e.g. JS) modules.
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- The require cache is only bypassed for all operations that happen synchronously when a module is required. If a module lazy loads another module at a later time that require call will not bypass the cache anymore.
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This means you should have a close look at all internal require calls before you decide to use this library.
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## Installation
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[](https://npmjs.org/package/stealthy-require)
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This is a module for node.js and is installed via npm:
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``` bash
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npm install stealthy-require --save
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```
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## Usage
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Let's say you want to bypass the require cache for this require call:
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``` js
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var request = require('request');
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```
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With `stealthy-require` you can do that like this:
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``` js
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var stealthyRequire = require('stealthy-require');
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var requestFresh = stealthyRequire(require.cache, function () {
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return require('request');
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});
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```
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The require cache is bypassed for the module you require (i.e. `request`) as well as all modules the module requires (i.e. `http` and many more).
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Sometimes the require cache shall not be bypassed for specific modules. E.g. `request` is required but `tough-cookie` – on which `request` depends on – shall be required using the regular cache. For that you can pass two extra arguments to `stealthyRequire(...)`:
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- A callback that requires the modules that shall be required without bypassing the cache
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- The `module` variable
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``` js
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var stealthyRequire = require('stealthy-require');
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var requestFresh = stealthyRequire(require.cache, function () {
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return require('request');
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},
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function () {
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require('tough-cookie'); // No return needed
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// You can require multiple modules here
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}, module);
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```
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## Usage with Module Bundlers
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- [Webpack](https://webpack.github.io) works out-of-the-box like described in the [Usage section](#usage) above.
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- [Browserify](http://browserify.org) does not expose `require.cache`. However, as of `browserify@13.0.1` the cache is passed as the 6th argument to CommonJS modules. Thus you can pass this argument instead:
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``` js
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// Tweak for Browserify - using arguments[5] instead of require.cache
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var requestFresh = stealthyRequire(arguments[5], function () {
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return require('request');
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});
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```
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## Preventing a Memory Leak When Repeatedly Requiring Fresh Module Instances in Node.js
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If you are using `stealthy-require` in node.js and repeatedly require fresh module instances the `module.children` array will hold all module instances which prevents unneeded instances to be garbage collected.
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Assume your code calls `doSomething()` repeatedly.
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``` js
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var stealthyRequire = require('stealthy-require');
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function doSomething() {
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var freshInstance = stealthyRequire(require.cache, function () {
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return require('some-module');
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});
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return freshInstance.calc();
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}
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```
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After `doSomething()` returns `freshInstance` is not used anymore but won’t be garbage collected because `module.children` still holds a reference. The solution is to truncate `module.children` accordingly:
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``` js
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var stealthyRequire = require('stealthy-require');
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function doSomething() {
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var initialChildren = module.children.slice(); // Creates a shallow copy of the array
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var freshInstance = stealthyRequire(require.cache, function () {
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return require('some-module');
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});
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module.children = initialChildren;
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return freshInstance.calc();
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}
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```
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The `slice` operation removes all new `module.children` entries created during the `stealthyRequire(...)` call and thus `freshInstance` gets garbage collected after `doSomething()` returns.
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## Technical Walkthrough
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``` js
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// 1. Load stealthy-require
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var stealthyRequire = require('stealthy-require');
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// This does nothing but loading the code.
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// It has no side-effects like patching the module loader or anything.
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// Any regular require works as always.
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var request1 = require('request');
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// 2. Call stealthyRequire with passing the require cache and a callback.
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var requestFresh = stealthyRequire(require.cache, function () {
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// 2a. Before this callback gets called the require cache is cleared.
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// 2b. Any require taking place here takes place on a clean require cache.
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// Since the require call is part of the user's code it also works with module bundlers.
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return require('request');
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// Anything returned here will be returned by stealthyRequire(...).
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// 2c. After this callback gets called the require cache is
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// - cleared again and
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// - restored to its old state before step 2.
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});
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// Any regular require again works as always.
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// In this case require returns the cached request module instance.
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var request2 = require('request');
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// And voilà:
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request1 === request2 // -> true
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request1 === requestFresh // -> false
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```
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## Contributing
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To set up your development environment for `stealthy-require`:
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1. Clone this repo to your desktop,
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2. in the shell `cd` to the main folder,
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3. hit `npm install`,
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4. hit `npm install gulp -g` if you haven't installed gulp globally yet, and
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5. run `gulp dev`. (Or run `node ./node_modules/.bin/gulp dev` if you don't want to install gulp globally.)
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`gulp dev` watches all source files and if you save some changes it will lint the code and execute all tests. The test coverage report can be viewed from `./coverage/lcov-report/index.html`.
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If you want to debug a test you should use `gulp test-without-coverage` to run all tests without obscuring the code by the test coverage instrumentation.
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## Change History
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- v1.1.1 (2017-05-08)
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- Fix that stops `undefined` entries from appearing in `require.cache` *(Thanks to @jasperjn from reporting this in [issue #4](https://github.com/analog-nico/stealthy-require/issues/4))*
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- v1.1.0 (2017-04-25)
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- Added ability to disable bypassing the cache for certain modules *(Thanks to @novemberborn for suggesting this in [issue #3](https://github.com/analog-nico/stealthy-require/issues/3))*
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- Added section in README about a [potential memory leak](#preventing-a-memory-leak-when-repeatedly-requiring-fresh-module-instances-in-nodejs) *(Thanks to @Flarna and @novemberborn for bringing that up in [issue #2](https://github.com/analog-nico/stealthy-require/issues/2))*
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- Performance optimizations *(Thanks to @jcready for [pull request #1](https://github.com/analog-nico/stealthy-require/pull/1))*
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- v1.0.0 (2016-07-18)
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- **Breaking Change:** API completely changed. Please read the [Usage section](#usage) again.
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- Redesigned library to support module bundlers like [Webpack](https://webpack.github.io) and [Browserify](http://browserify.org)
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- v0.1.0 (2016-05-26)
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- Initial version
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## License (ISC)
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In case you never heard about the [ISC license](http://en.wikipedia.org/wiki/ISC_license) it is functionally equivalent to the MIT license.
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See the [LICENSE file](LICENSE) for details.
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