cupertino_ffi 0.1.1

Provides C bindings ('dart:ffi') for various APIs by Apple. These include Core Foundation (CFDictionary, etc.), Security (cryptography, biometrics, etc.), and Objective-C runtime.

Overview

This package provides C bindings with various APIs in Apple devices (iOS, Mac OS X, etc.). The package uses dart:ffi. The Dart APIs are currently generated from handwritten definitions and identifiers/signatures are largely identical to the original C libraries.

This package can be used from:

• Flutter (though 'dart:ffi' is an experimental API and not yet fully supported in all platforms)
• OS X command-line applications

Contributing

• Github project
• Instructions for improving definitions of C libraries:
  • Create a fork of the repository in Github.
  • Run git clone https://github.com/your_username/cupertino_ffi.
  • Edit a definition file such as "definitions/core_foundation.dart".
  • Run pub run tool/generate_bindings.dart
  • Run git add -A
  • Run git commit
  • Create a pull request in Github.

Warning

Please consider writing a Flutter plugin instead of using this package.

Flutter plugins are:

• Safer. Swift and Objective-C make all sorts of bugs much less likely.
• Concurrent. Flutter plugin system takes care of creating a separate thread for the plugin.
• Easier to develop. You can use XCode and other tools.

Supported C libraries

Core Foundation

• Documentation: developer.apple.com
• Import: "package:cupertino_ffi/core_foundation.dart"
• Examples:
  • CFArray
  • CFData
  • CFError
  • CFDictionary
  • CFString

Security

• Documentation: developer.apple.com
• Import: "package:cupertino_ffi/security.dart"
• Examples:
  • Cryptographic functions
    • AES
    • RSA
    • etc.
  • Keychain
    • Keys can be stored in secure enclave, a hardware-based key manager that's isolated from the main CPU.

Supported Objective-C libraries

• Objective-C runtime
  • Documentation: developer.apple.com
  • Import: "package:cupertino_ffi/objective_c.dart"
• Foundation
  • Foundation types (NSString, etc.) and Core Foundation types (CFString, etc.) are "toll-free" bridged types. This means that Pointer<CFString> can be used as Pointer<NSString> , and vice-versa.

A missing feature in 'dart:ffi'

Calling Objective-C methods would require calling C function 'objc_msgSend'. Unfortunately it's a variadic C function and 'dart:ffi' doesn't support variadic C functions (yet).

See:

• Dart SDK issue #38578 ("dart:ffi: Support variadic C functions")

Memory management patterns

Calling APIs that return ARC pointers

import 'package:cupertino_ffi/core_foundation.dart';

String example() {
    // Push ARC frame.
    arcPush();
    try {
      // Call some function that returns an ARC pointer.
      Pointer pointer = CFDictionary.fromDart({"key": "value"});

      return "some return value";

    } finally {
      // Pop ARC frame.
      arcPop();
    }
}

Returning ARC pointers

import 'package:cupertino_ffi/core_foundation.dart';

Pointer<CFDictionary> example_that_returns_pointer() {
    arcPush();
    try {
      // Call some function that returns an ARC pointer.
      final result = CFDictionary.fromDart({"key": "value"});

      // You must call function 'arcReturn', which inserts the pointer into caller's reference
      // counting frame and increments the reference count.
      return arcReturn(result);

    } finally {
      arcPop();
    }
}

Storing ARC pointer

import 'package:cupertino_ffi/core_foundation.dart';

Pointer<CFString> _field;
Pointer<CFString> get field => arcFieldGet(_field);
set field(Pointer<CFString> newValue) {
  _field = arcFieldSet(_field, newValue);
}