Dart Setup Ffi Assets

Compiling C Code into Code Assets with Native Assets Hooks

Integrate and automate the compilation and packaging of native C/C++ source code into Code Assets under Dart's overarching Native Assets feature using build and link hooks.

Contents

• Introduction
• Constraints
• Native Interop Packages
• Step-by-Step Workflow
• Choosing an Integration Approach
• Method 1: Local Compilation with Linker Tree-Shaking (Recommended)
• Prerequisite Host Compiler Toolchains
• C Source and Bindings Setup
• Defining the C Library Build Spec
• Implementing hook/build.dart
• Implementing hook/link.dart
• Method 2: Downloading Precompiled Dynamic Libraries
• Why Download Precompiled Binaries?
• Implementing Precompiled Dynamic Downloads
• Verification Checklist
• 1. Local Execution Sandbox
• 2. Verify Target Outputs
• 3. Verify Tree-Shaking Stripping
• 4. Verify Offline Compliance (User Defines)

Introduction

Under Dart's Native Assets feature, packages can package native code (like C/C++ libraries) as Code Assets and bundle them automatically during standard development cycles (e.g., dart run, dart test, dart build, and flutter run). The packaging of Code Assets is driven by two programmatic hook scripts placed inside a package's hook/ folder:

1. hook/build.dart: Compiles local C sources to machine code or bundles prebuilt native binaries as code assets for a specific host/target architecture.
2. hook/link.dart: Links built code assets, applying advanced tree-shaking optimizations to strip unused native symbols and compress the runtime binary size.

Constraints

[!IMPORTANT] Keep all file resolving platform-independent. Never hardcode absolute target paths, shell scripts, or system command variables. Always use Platform.script.resolve() or Uri-based resolution to ensure scripts are fully portable.

• Hook Locations: Compiling and packaging hooks must reside strictly inside the hook/ directory at the package's root:
• hook/build.dart (Build execution phase)
• hook/link.dart (Optional packaging/linking/tree-shaking phase)
• Compile Toolchain Standard: Use the programmatic APIs from package:native_toolchain_c (e.g. CBuilder and CLibrary) to run compile toolchains. Never invoke raw gcc, clang, or msvc via shell commands.
• Preamble & License Headers: Every handcrafted and generated source file (including bindings, helpers, and hooks) must strictly contain the target package's copyright and licensing header.
• Tree Shaking Mapping: If utilizing compiler tree-shaking, you must map the target Dart method names (e.g. Method.name) back to their raw native C symbol names using a record use mapping generated by FFIgen. The mapping file must reside under lib/src/third_party/ and strictly use the .g.dart extension (e.g., sqlite3.record_use_mapping.g.dart).
• Integrity Safeguards for Precompiled Libraries: If adopting the dynamic download pattern:
• Cryptographic Verification: Downloaded prebuilt binaries must be checked against preconfigured lookup tables containing MD5 or SHA-256 hashes to guarantee binary integrity and prevent tampering.
• Graceful Recovery: Support offline developers by providing fallbacks (such as local compiler execution via flags like local_build).

Native Interop Packages

Programmatic build and link hooks for Code Assets leverage three specialized native interop packages:

Step-by-Step Workflow

Step 1: Add Dependencies

Add Code Assets hook and toolchain dependencies to your package. You must fetch these dependencies directly from pub.dev.

You can add it automatically using the CLI:

dart pub add code_assets hooks native_toolchain_c record_use dev:ffigen

Or manually declare them in your target package's pubspec.yaml:

dependencies:
  code_assets: ^1.0.0
  hooks: ^0.1.0
  native_toolchain_c: ^0.1.0
  record_use: ^0.6.0

dev_dependencies:
  ffigen: ^20.1.1

Step 2: Define C Specifications

Define your target C library compilation metadata inside lib/src/c_library.dart. This lets both the build and link hooks share a single source of truth for assets, names, and sources.

Step 3: Implement Build and Link Hook Scripts

Write the compilation orchestration script inside hook/build.dart and the dead-code elimination logic inside hook/link.dart.

Step 4: Run the Hook Cycle

Running standard test suites dynamically launches the build and link hook lifecycle in the background:

dart test

Choosing an Integration Approach

There are two primary methods for integrating and delivering C/C++ native assets in Dart. Select the one that matches your project requirements:

Method 1: Local Compilation with Linker Tree-Shaking (Recommended)

In this approach, the build hook invokes local toolchains (GCC, Clang, MSVC) to compile source files directly. The link hook subsequently filters output symbols utilizing compiler options, retaining only target methods invoked in user code. This represents the standard, robust SQLite pattern under pkgs/code_assets/example/sqlite.

Prerequisite Host Compiler Toolchains

Since package:native_toolchain_c delegates actual dynamic compilation to the host operating system's default toolchain, the development machine must have one of the following compiler packages pre-installed:

• macOS: Xcode Command Line Tools. Install via: ``bash xcode-select --install ``
• Linux: GCC or Clang. Install via: ``bash sudo apt install build-essential ``
• Windows: MSVC (Microsoft Visual C++). Install the Visual Studio Installer and select the Desktop development with C++ workload.