feat: Allow to change how cache is stored

Author: Mordred

README.md

@@ -10,7 +10,7 @@
     <img width="200" height="200" src="https://cdn.rawgit.com/webpack/media/e7485eb2/logo/icon-square-big.svg">
   </a>
   <h1>Cache Loader</h1>
-  <p>Caches the result of following loaders on disk</p>
+  <p>Caches the result of following loaders on disk (default) or in the database</p>
 </div>
 
 <h2 align="center">Install</h2>
@@ -47,8 +47,11 @@ module.exports = {
 
 |Name|Type|Default|Description|
 |:--:|:--:|:-----:|:----------|
-|**`cacheDirectory`**|`{String}`|`path.resolve('.cache-loader')`|Provide a cache directory where cache items should be stored|
-|**`cacheIdentifier`**|`{String}`|`cache-loader:{version} {process.env.NODE_ENV}`|Provide an invalidation identifier which is used to generate the hashes. You can use it for extra dependencies of loaders.|
+|**`cacheDirectory`**|`{String}`|`path.resolve('.cache-loader')`|Provide a cache directory where cache items should be stored (used for default read/write implementation)|
+|**`cacheIdentifier`**|`{String}`|`cache-loader:{version} {process.env.NODE_ENV}`|Provide an invalidation identifier which is used to generate the hashes. You can use it for extra dependencies of loaders.  (used for default read/write implementation)|
+|**`write`**|`{Function(cacheKey, data, callback) -> {void}}`|`undefined`|Allows you to override default write cache data to file (e.g. Redis, memcached).|
+|**`read`**|`{Function(cacheKey, callback) -> {void}}`|`undefined`|Allows you to override default read cache data from file.|
+|**`makeKey`**|`{Function(options, request) -> {string}}`|`undefined`|Allows you to override default cache key generator.|
 
 <h2 align="center">Examples</h2>
 
@@ -95,6 +98,82 @@ module.exports = {
 }
 ```
 
+### `Example of Database Integration`
+
+**webpack.config.js**
+```js
+const redis = require('redis'); // Or different database client - memcached, mongodb, ...
+const crypto = require('crypto');
+
+// ...
+// ... connect to client
+// ...
+
+const BUILD_CACHE_TIMEOUT = 24 * 3600; // 1 day
+
+function digest(str) {
+  return crypto.createHash('md5').update(str).digest('hex');
+}
+
+/**
+ * Generate own cache key
+ */
+function makeKey(options, request) {
+  return `build:cache:${digest(request)}`;
+}
+
+/**
+ * Read data from database and parse them
+ */
+function read(cacheKey, callback) {
+  client.get(cacheKey, (err, result) => {
+    if (err) {
+      return callback(err);
+    }
+
+    if (!result) {
+      return callback(new Error(`Key ${cacheKey} not found`));
+    }
+
+    try {
+      let data = JSON.parse(result);
+      callback(null, data);
+    } catch (e) {
+      callback(e);
+    }
+  });
+}
+
+/**
+ * Write data to database under cacheKey
+ */
+function write(cacheKey, data, callback) {
+  client.set(cacheKey, JSON.stringify(data), 'EX', BUILD_CACHE_TIMEOUT, callback);
+}
+
+module.exports = {
+  module: {
+    rules: [
+      {
+        test: /\.js$/,
+        use: [
+          {
+            loader: 'cache-loader',
+            options: {
+              read,
+              write,
+              makeKey,
+            }
+          },
+          'babel-loader'
+        ],
+        include: path.resolve('src')
+      }
+    ]
+  }
+}
+```
+
 <h2 align="center">Maintainers</h2>
 
 <table>

src/index.js

@@ -9,7 +9,18 @@ const pkgVersion = require('../package.json').version;
 const defaultCacheDirectory = path.resolve('.cache-loader');
 const ENV = process.env.NODE_ENV || 'development';
 
+const defaultOptions = {
+  cacheDirectory: defaultCacheDirectory,
+  cacheIdentifier: `cache-loader:${pkgVersion} ${ENV}`,
+  read,
+  write,
+  makeKey,
+};
+
 function loader(...args) {
+  const loaderOptions = loaderUtils.getOptions(this) || {};
+  const options = Object.assign({}, defaultOptions, loaderOptions);
+  const { write: writeFn } = options;
   const callback = this.async();
   const { data } = this;
   const dependencies = this.getDependencies().concat(this.loaders.map(l => l.path));
@@ -35,62 +46,33 @@ function loader(...args) {
       return;
     }
     const [deps, contextDeps] = taskResults;
-    const writeCacheFile = () => {
-      fs.writeFile(data.cacheFile, JSON.stringify({
-        remainingRequest: data.remainingRequest,
-        cacheIdentifier: data.cacheIdentifier,
-        dependencies: deps,
-        contextDependencies: contextDeps,
-        result: args,
-      }), 'utf-8', () => {
-        // ignore errors here
-        callback(null, ...args);
-      });
-    };
-    if (data.fileExists) {
-      // for performance skip creating directory
-      writeCacheFile();
-    } else {
-      mkdirp(path.dirname(data.cacheFile), (mkdirErr) => {
-        if (mkdirErr) {
-          callback(null, ...args);
-          return;
-        }
-        writeCacheFile();
-      });
-    }
+    writeFn(data.cacheKey, {
+      remainingRequest: data.remainingRequest,
+      dependencies: deps,
+      contextDependencies: contextDeps,
+      result: args,
+    }, () => {
+      // ignore errors here
+      callback(null, ...args);
+    });
   });
 }
 
 function pitch(remainingRequest, prevRequest, dataInput) {
   const loaderOptions = loaderUtils.getOptions(this) || {};
-  const defaultOptions = {
-    cacheDirectory: defaultCacheDirectory,
-    cacheIdentifier: `cache-loader:${pkgVersion} ${ENV}`,
-  };
   const options = Object.assign({}, defaultOptions, loaderOptions);
-  const { cacheIdentifier, cacheDirectory } = options;
+  const { read: readFn, makeKey: makeKeyFn } = options;
   const data = dataInput;
   const callback = this.async();
-  const hash = digest(`${cacheIdentifier}\n${remainingRequest}`);
-  const cacheFile = path.join(cacheDirectory, `${hash}.json`);
+  const cacheKey = makeKeyFn(options, remainingRequest);
   data.remainingRequest = remainingRequest;
-  data.cacheIdentifier = cacheIdentifier;
-  data.cacheFile = cacheFile;
-  fs.readFile(cacheFile, 'utf-8', (readFileErr, content) => {
-    if (readFileErr) {
+  data.cacheKey = cacheKey;
+  readFn(cacheKey, (readErr, cacheData) => {
+    if (readErr) {
       callback();
       return;
     }
-    data.fileExists = true;
-    let cacheData;
-    try {
-      cacheData = JSON.parse(content);
-    } catch (e) {
-      callback();
-      return;
-    }
-    if (cacheData.remainingRequest !== remainingRequest || cacheData.cacheIdentifier !== cacheIdentifier) {
+    if (cacheData.remainingRequest !== remainingRequest) {
       // in case of a hash conflict
       callback();
       return;
@@ -123,4 +105,45 @@ function digest(str) {
   return crypto.createHash('md5').update(str).digest('hex');
 }
 
+const directoriesExists = {};
+function write(cacheKey, data, callback) {
+  const dirname = path.dirname(cacheKey);
+  const content = JSON.stringify(data);
+  if (directoriesExists[dirname]) {
+    // for performance skip creating directory
+    fs.writeFile(cacheKey, content, 'utf-8', callback);
+  } else {
+    mkdirp(dirname, (mkdirErr) => {
+      if (mkdirErr) {
+        callback(mkdirErr);
+        return;
+      }
+      directoriesExists[dirname] = true;
+      fs.writeFile(cacheKey, content, 'utf-8', callback);
+    });
+  }
+}
+
+function read(cacheKey, callback) {
+  fs.readFile(cacheKey, 'utf-8', (err, content) => {
+    if (err) {
+      callback(err);
+      return;
+    }
+
+    try {
+      const data = JSON.parse(content);
+      callback(null, data);
+    } catch (e) {
+      callback(e);
+    }
+  });
+}
+
+function makeKey(options, request) {
+  const { cacheIdentifier, cacheDirectory } = options;
+  const hash = digest(`${cacheIdentifier}\n${request}`);
+  return path.join(cacheDirectory, `${hash}.json`);
+}
+
 export { loader as default, pitch };