metro-buck: getLibrary: precompute asset hashes

Reviewed By: davidaurelio

Differential Revision: D6937279

fbshipit-source-id: 328f06b2b66eeed6fd2f767dab1a03854c4dd28c

packages/metro/src/ModuleGraph/types.flow.js

@@ -196,6 +196,10 @@ export type AssetFile = {|
    * Guessed from the file extension, for example `png` or `html`.
    */
   +contentType: string,
+  /**
+   * Hash of the asset file content.
+   */
+  +hash: string,
   /**
    * The path of the original file for this asset. For example
    * `foo/bar@3x.ios.png`. This is most useful for reporting purposes, such as

packages/metro/src/ModuleGraph/worker/__tests__/__snapshots__/transform-module-test.js.snap

@@ -7,6 +7,7 @@ Object {
     "contentBase64": "eyJfX3NpemUiOnsid2lkdGgiOjMwLCJoZWlnaHQiOjIwfX0=",
     "contentType": "png",
     "filePath": "foo.png",
+    "hash": "AGicIEH/IsIy5t7si/9ocI6Ur8s=",
     "physicalSize": Object {
       "height": 20,
       "width": 30,
@@ -25,6 +26,7 @@ Object {
     "contentBase64": "eyJfX3NpemUiOnsid2lkdGgiOjMwLCJoZWlnaHQiOjIwfX0=",
     "contentType": "png",
     "filePath": "foo@2x.ios.png",
+    "hash": "AGicIEH/IsIy5t7si/9ocI6Ur8s=",
     "physicalSize": Object {
       "height": 20,
       "width": 30,

packages/metro/src/ModuleGraph/worker/transform-module.js

@@ -17,6 +17,7 @@ const JsFileWrapping = require('./JsFileWrapping');
 const Platforms = require('./Platforms');
 
 const collectDependencies = require('./collectDependencies');
+const crypto = require('crypto');
 const defaults = require('../../defaults');
 const docblock = require('jest-docblock');
 const generate = require('./generate');
@@ -173,6 +174,10 @@ function transformAsset(
     assetPath: assetData.assetName,
     contentBase64: content.toString('base64'),
     contentType,
+    hash: crypto
+      .createHash('sha1')
+      .update(content)
+      .digest('base64'),
     filePath,
     physicalSize: getAssetSize(contentType, content, filePath),
     platform: assetData.platform,