From 778382ad3d8f5ecc4535ed44b2cd508475a97beb Mon Sep 17 00:00:00 2001
From: Marc Rousavy <me@mrousavy.com>
Date: Wed, 19 Feb 2025 18:42:51 -0800
Subject: [PATCH] RNGP - Add option to disable bundle compression (was: Make
 all React Native apps start 12% faster) (#49449)
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Summary:
Okay the title is a bit clickbaity, but this is actually true. (on Android)

We (Janic, Szymon, Ruby and Me) discovered something interesting. React Native uses `mmap` for mapping the JS bundle to RAM, to avoid having to load the entire thing instantly at app startup.
Ruby doubted that this was true - so we investigated.

Apparently on Android, resources are **compressed**. And if the JS bundle is stored compressed, it has to be uncompressed before it can be loaded into RAM, hence not allowing it to be mmapp'ed! (see [`_CompressedAsset::getBuffer`](https://cs.android.com/android/platform/superproject/+/master:frameworks/base/libs/androidfw/Asset.cpp;l=903?q=Asset.cpp))

So with this PR, we now add `.bundle` files to `noCompress` in the react-native gradle plugin, which disables compression for the JS bundle.

We discovered while improving the performance of one of our clients: **Discord**.
In our tests, **this improved the TTI of the Discord app by 400ms!! (or 12%)** 🤯🚀

NOTE: Yes, the .apk will now be bigger. But; Google Play compresses it anyways, so the **download size** of your .apk will likely not increase by much. It will be bigger on disk though.

## Changelog:

[ANDROID] [CHANGED] Add option to disable bundle compression to improve startup time

<!-- Help reviewers and the release process by writing your own changelog entry.

Pick one each for the category and type tags:

[ANDROID|GENERAL|IOS|INTERNAL] [BREAKING|ADDED|CHANGED|DEPRECATED|REMOVED|FIXED|SECURITY] - Message

For more details, see:
https://reactnative.dev/contributing/changelogs-in-pull-requests

Pull Request resolved: https://github.com/facebook/react-native/pull/49449

Test Plan:
### 1. Verify compression is disabled

Build two apps, one with this patch and one without. When I did this using the RN community template, the one without this patch was 47,6 MB, and the one with this patch was 48 MB in size. So the .apk got bigger, which is what we expected

### 2. Verify app startup is faster

Use tools like react-native-performance or custom markers to measure TTI. In our tests, we shaved off 400ms from the startup time, which was about 12% of Discord's total TTI. (on a low-end Android device)
In Expensify, we improved the TTI by 14-20% with this change (source: https://github.com/Expensify/App/pull/56930)

Reviewed By: javache, cipolleschi

Differential Revision: D69742221

Pulled By: cortinico

fbshipit-source-id: bd59d77662bd30a3acdbb2e9f8d8f23db922c3f2
---
 .../main/kotlin/com/facebook/react/ReactExtension.kt  | 10 ++++++++++
 .../src/main/kotlin/com/facebook/react/ReactPlugin.kt | 11 +++++++++++
 2 files changed, 21 insertions(+)

diff --git a/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactExtension.kt b/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactExtension.kt
index b67e8826b33..fa9c9373611 100644
--- a/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactExtension.kt
+++ b/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactExtension.kt
@@ -76,6 +76,16 @@ abstract class ReactExtension @Inject constructor(val project: Project) {
   val bundleAssetName: Property<String> =
       objects.property(String::class.java).convention("index.android.bundle")
 
+  /**
+   * Whether the Bundle Asset should be compressed when packaged into a `.apk`, or not. Disabling
+   * compression for the `.bundle` allows it to be directly memory-mapped to RAM, hence improving
+   * startup time - at the cost of a larger resulting `.apk` size.
+   *
+   * Default: false
+   */
+  val enableBundleCompression: Property<Boolean> =
+      objects.property(Boolean::class.java).convention(false)
+
   /**
    * Toggles the .so Cleanup step. If enabled, we will clean up all the unnecessary files before the
    * bundle task. If disabled, the developers will have to manually cleanup the files. Default: true
diff --git a/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt b/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt
index 9cf504539e2..ffcf76ad163 100644
--- a/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt
+++ b/packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt
@@ -81,6 +81,7 @@ class ReactPlugin : Plugin<Project> {
       }
       configureAutolinking(project, extension)
       configureCodegen(project, extension, rootExtension, isLibrary = false)
+      configureResources(project, extension)
     }
 
     // Library Only Configuration
@@ -110,6 +111,16 @@ class ReactPlugin : Plugin<Project> {
     }
   }
 
+  /** This function configures Android resources - in this case just the bundle */
+  private fun configureResources(project: Project, reactExtension: ReactExtension) {
+    project.extensions.getByType(AndroidComponentsExtension::class.java).finalizeDsl { ext ->
+      val bundleFileExtension = reactExtension.bundleAssetName.get().substringAfterLast('.', "")
+      if (!reactExtension.enableBundleCompression.get() && bundleFileExtension.isNotBlank()) {
+        ext.androidResources.noCompress.add(bundleFileExtension)
+      }
+    }
+  }
+
   /** This function sets up `react-native-codegen` in our Gradle plugin. */
   @Suppress("UnstableApiUsage")
   private fun configureCodegen(