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113 lines
5.1 KiB
Markdown
113 lines
5.1 KiB
Markdown
# file-entry-cache
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> Super simple cache for file metadata, useful for process that work o a given series of files
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> and that only need to repeat the job on the changed ones since the previous run of the process — Edit
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[](https://npmjs.org/package/file-entry-cache)
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[](https://travis-ci.org/royriojas/file-entry-cache)
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## install
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```bash
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npm i --save file-entry-cache
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```
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## Usage
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The module exposes two functions `create` and `createFromFile`.
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## `create(cacheName, [directory, useCheckSum])`
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- **cacheName**: the name of the cache to be created
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- **directory**: Optional the directory to load the cache from
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- **usecheckSum**: Whether to use md5 checksum to verify if file changed. If false the default will be to use the mtime and size of the file.
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## `createFromFile(pathToCache, [useCheckSum])`
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- **pathToCache**: the path to the cache file (this combines the cache name and directory)
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- **useCheckSum**: Whether to use md5 checksum to verify if file changed. If false the default will be to use the mtime and size of the file.
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```js
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// loads the cache, if one does not exists for the given
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// Id a new one will be prepared to be created
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var fileEntryCache = require('file-entry-cache');
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var cache = fileEntryCache.create('testCache');
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var files = expand('../fixtures/*.txt');
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// the first time this method is called, will return all the files
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var oFiles = cache.getUpdatedFiles(files);
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// this will persist this to disk checking each file stats and
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// updating the meta attributes `size` and `mtime`.
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// custom fields could also be added to the meta object and will be persisted
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// in order to retrieve them later
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cache.reconcile();
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// use this if you want the non visited file entries to be kept in the cache
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// for more than one execution
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//
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// cache.reconcile( true /* noPrune */)
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// on a second run
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var cache2 = fileEntryCache.create('testCache');
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// will return now only the files that were modified or none
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// if no files were modified previous to the execution of this function
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var oFiles = cache.getUpdatedFiles(files);
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// if you want to prevent a file from being considered non modified
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// something useful if a file failed some sort of validation
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// you can then remove the entry from the cache doing
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cache.removeEntry('path/to/file'); // path to file should be the same path of the file received on `getUpdatedFiles`
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// that will effectively make the file to appear again as modified until the validation is passed. In that
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// case you should not remove it from the cache
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// if you need all the files, so you can determine what to do with the changed ones
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// you can call
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var oFiles = cache.normalizeEntries(files);
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// oFiles will be an array of objects like the following
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entry = {
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key: 'some/name/file', the path to the file
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changed: true, // if the file was changed since previous run
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meta: {
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size: 3242, // the size of the file
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mtime: 231231231, // the modification time of the file
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data: {} // some extra field stored for this file (useful to save the result of a transformation on the file
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}
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}
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```
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## Motivation for this module
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I needed a super simple and dumb **in-memory cache** with optional disk persistence (write-back cache) in order to make
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a script that will beautify files with `esformatter` to execute only on the files that were changed since the last run.
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In doing so the process of beautifying files was reduced from several seconds to a small fraction of a second.
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This module uses [flat-cache](https://www.npmjs.com/package/flat-cache) a super simple `key/value` cache storage with
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optional file persistance.
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The main idea is to read the files when the task begins, apply the transforms required, and if the process succeed,
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then store the new state of the files. The next time this module request for `getChangedFiles` will return only
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the files that were modified. Making the process to end faster.
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This module could also be used by processes that modify the files applying a transform, in that case the result of the
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transform could be stored in the `meta` field, of the entries. Anything added to the meta field will be persisted.
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Those processes won't need to call `getChangedFiles` they will instead call `normalizeEntries` that will return the
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entries with a `changed` field that can be used to determine if the file was changed or not. If it was not changed
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the transformed stored data could be used instead of actually applying the transformation, saving time in case of only
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a few files changed.
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In the worst case scenario all the files will be processed. In the best case scenario only a few of them will be processed.
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## Important notes
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- The values set on the meta attribute of the entries should be `stringify-able` ones if possible, flat-cache uses `circular-json` to try to persist circular structures, but this should be considered experimental. The best results are always obtained with non circular values
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- All the changes to the cache state are done to memory first and only persisted after reconcile.
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## License
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MIT
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