Add "FileStore" cache

Reviewed By: davidaurelio

Differential Revision: D7037483

fbshipit-source-id: b7517f2b3c8df3e5653dd1a756dfbee5bb2bd656

packages/metro-cache/package.json

@@ -10,5 +10,9 @@
   "scripts": {
     "prepare-release": "test -d build && rm -rf src.real && mv src src.real && mv build src",
     "cleanup-release": "test ! -e build && mv src build && mv src.real src"
+  },
+  "dependencies": {
+    "jest-serializer": "^22.4.0",
+    "mkdirp": "^0.5.1"
   }
 }

packages/metro-cache/src/FileStore.js

@@ -0,0 +1,62 @@
+/**
+ * Copyright (c) 2018-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @flow
+ */
+
+'use strict';
+
+const fs = require('fs');
+const mkdirp = require('mkdirp');
+const path = require('path');
+const serializer = require('jest-serializer');
+
+export type Options = {|
+  root: string,
+|};
+
+class FileStore {
+  _root: string;
+
+  constructor(options: Options) {
+    const root = options.root;
+
+    for (let i = 0; i < 256; i++) {
+      mkdirp.sync(path.join(root, ('0' + i.toString(16)).slice(-2)));
+    }
+
+    this._root = root;
+  }
+
+  get(key: Buffer): mixed {
+    try {
+      return serializer.readFileSync(this._getFilePath(key));
+    } catch (err) {
+      return null;
+    }
+  }
+
+  set(key: Buffer, value: mixed): Promise<void> {
+    return new Promise((resolve, reject) => {
+      const data = serializer.serialize(value);
+
+      fs.writeFile(this._getFilePath(key), data, err => {
+        err ? reject(err) : resolve();
+      });
+    });
+  }
+
+  _getFilePath(key: Buffer): string {
+    return path.join(
+      this._root,
+      key.slice(0, 1).toString('hex'),
+      key.slice(1).toString('hex'),
+    );
+  }
+}
+
+module.exports = FileStore;

packages/metro-cache/src/index.js

@@ -11,10 +11,12 @@
 'use strict';
 
 const Cache = require('./Cache');
+const FileStore = require('./FileStore');
 
 const stableHash = require('./stableHash');
 
 export type {CacheStore} from './types.flow';
 
 module.exports.Cache = Cache;
+module.exports.FileStore = FileStore;
 module.exports.stableHash = stableHash;