Code Push

Code Push lets you push Dart code changes to deployed Flutter apps without going through app store review. Users get updates within hours instead of days.

How It Works

Code Push uses Approach B (Engine Swap):

1. Developers use a standard Flutter SDK from flutter.dev.
2. The fcp CLI downloads a custom gen_snapshot and engine library that include the code push runtime (C++ patch loader, updater, signature verification).
3. At build time, fcp codepush release compiles the app with the custom engine and uploads the AOT snapshot as a baseline.
4. For patches, fcp codepush patch computes a binary diff (BSDIFF50) between the baseline and the new snapshot, signs it, and uploads it.
5. At runtime, the app uses the flutterplaza_code_push package to check for updates, download patches, and apply them on next restart.

Prerequisites

• Flutter SDK 3.24.0 or later
• fcp CLI installed: dart pub global activate flutter_compile
• A FlutterPlaza account at codepush.flutterplaza.com

Quick Start

1. Authenticate

fcp codepush login --api-key YOUR_API_KEY

2. Download engine artifacts

# Auto-detects your Flutter version
fcp codepush setup

# Or specify version and platform
fcp codepush setup --flutter-version 3.24.0 --platform android-arm64

Artifacts are cached at ~/.flutter_compile/cache/codepush-engine/ and verified with SHA-256 checksums.

3. Register your app

cd my_flutter_app
fcp codepush init

This creates an app on the server and stores the app ID in ~/.flutter_compilerc.

4. Add the runtime package

flutter pub add flutterplaza_code_push

Add the update check to your app:

import 'package:flutterplaza_code_push/flutterplaza_code_push.dart';

Future<void> checkForUpdates() async {
  final update = await CodePush.checkForUpdate();
  if (update.isUpdateAvailable) {
    await CodePush.downloadAndApply(
      onProgress: (p) => print('${(p * 100).toInt()}%'),
    );
    // Patch takes effect on next restart.
  }
}

5. Create a release

# Build and upload baseline
fcp codepush release --build --platform apk

This runs flutter build, swaps the engine library in the build output, and uploads the AOT snapshot to the server.

6. Push a patch

# Make code changes, then:
fcp codepush patch --build --release-id RELEASE_ID --rollout 25

The CLI compiles the patched source, computes a binary diff against the baseline, signs it with your RSA key, packages it as a .vmcode file, and uploads it. Use --rollout for staged rollout (1-100%).

7. Roll back if needed

fcp codepush rollback --patch-id PATCH_ID

CLI Commands

Engine Artifacts

The fcp codepush setup command downloads pre-built engine binaries from Google Cloud Storage. Each Flutter version has its own set of artifacts:

Artifacts are cached at ~/.flutter_compile/cache/codepush-engine/flutter-<version>/<platform>/ and verified via SHA-256 checksums.

Engine Swap

When you run fcp codepush release --build, the CLI:

1. Runs flutter build <platform> --release using the standard SDK.
2. Replaces the engine library in the build output with the code-push-enabled version:
   • Android: libflutter.so in stripped_native_libs/
   • iOS: Flutter.framework from the xcframework archive
   • macOS: FlutterMacOS in Frameworks/
   • Linux: libflutter_linux_gtk.so in bundle/lib/
   • Windows: flutter_windows.dll in runner/Release/
3. Optionally re-runs gen_snapshot with --deterministic for stable binary diffs.

Original files are backed up with a .original suffix.

Runtime API

The flutterplaza_code_push package provides the runtime API. Key methods:

Security

• Patch signing: Patches are signed with RSA-SHA256 using the developer's private key. The engine verifies the signature before applying.
• Integrity verification: SHA-256 hashes are embedded in the .vmcode header and checked on both the CLI and engine side.
• Artifact verification: Engine artifacts downloaded via fcp codepush setup are verified against SHA-256 checksums from the server.
• TLS: All server communication uses HTTPS. Optional certificate pinning is supported via codepush_pinned_cert in ~/.flutter_compilerc.
• App store compliance: Code push uses native AOT compilation, not interpretation. This complies with Apple's App Store Review Guidelines (3.3.2) and Google Play policies.

IDE Integration

Both the VS Code and IntelliJ / Android Studio extensions include a Code Push panel showing:

• Account status (email, subscription tier)
• App configuration
• Releases with version, platform, and creation date
• Patches with rollout percentage and active/inactive status

Actions like Login, Release, Patch, and Rollback are available directly from the IDE toolbar and context menus.

Pricing

Code push operations (release, patch) require a paid FlutterPlaza subscription. See codepush.flutterplaza.com/pricing for tiers and limits. The fcp codepush account command shows your current tier and subscription status.

Supported Flutter Versions

Run fcp codepush setup --list-versions to see all Flutter versions with available code push engine artifacts.