Use a single file delimited with null characters

Reviewed By: rafeca

Differential Revision: D7232425

fbshipit-source-id: c51387b94cd990ed3ba9be5c82b14c2a7773c7e7

packages/metro-cache/src/FileStore.js

@@ -20,6 +20,9 @@ export type Options = {|
   root: string,
 |};
 
+const JOINER_DATA = '\0\0';
+const JOINER_LIST = '\0';
+
 class FileStore {
   _root: string;
 
@@ -35,7 +38,14 @@ class FileStore {
 
   get(key: Buffer): ?TransformedCode {
     try {
-      return JSON.parse(fs.readFileSync(this._getFilePath(key), 'utf-8'));
+      const data = fs.readFileSync(this._getFilePath(key), 'utf8');
+      const [code, dependencies, map] = data.split(JOINER_DATA);
+
+      return {
+        code,
+        dependencies: dependencies ? dependencies.split(JOINER_LIST) : [],
+        map: JSON.parse(map),
+      };
     } catch (err) {
       if (err.code === 'ENOENT') {
         return null;
@@ -46,7 +56,13 @@ class FileStore {
   }
 
   set(key: Buffer, value: TransformedCode): void {
-    fs.writeFileSync(this._getFilePath(key), JSON.stringify(value));
+    const data = [
+      value.code,
+      value.dependencies.join(JOINER_LIST),
+      JSON.stringify(value.map),
+    ].join(JOINER_DATA);
+
+    fs.writeFileSync(this._getFilePath(key), data);
   }
 
   _getFilePath(key: Buffer): string {