structs.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:ffi';
import 'dart:io' show Directory, Platform;

import 'package:ffi/ffi.dart';
import 'package:path/path.dart' as path;

// Example of handling a simple C struct
final class Coordinate extends Struct {
  @Double()
  external double latitude;

  @Double()
  external double longitude;
}

// Example of a complex struct (contains a string and a nested struct)
final class Place extends Struct {
  external Pointer<Utf8> name;

  external Coordinate coordinate;
}

// C function: char *hello_world();
// There's no need for two typedefs here, as both the
// C and Dart functions have the same signature
typedef HelloWorld = Pointer<Utf8> Function();

// C function: char *reverse(char *str, int length)
typedef ReverseNative = Pointer<Utf8> Function(Pointer<Utf8> str, Int32 length);
typedef Reverse = Pointer<Utf8> Function(Pointer<Utf8> str, int length);

// C function: void free_string(char *str)
typedef FreeStringNative = Void Function(Pointer<Utf8> str);
typedef FreeString = void Function(Pointer<Utf8> str);

// C function: struct Coordinate create_coordinate(double latitude, double longitude)
typedef CreateCoordinateNative =
    Coordinate Function(Double latitude, Double longitude);
typedef CreateCoordinate =
    Coordinate Function(double latitude, double longitude);

// C function: struct Place create_place(char *name, double latitude, double longitude)
typedef CreatePlaceNative =
    Place Function(Pointer<Utf8> name, Double latitude, Double longitude);
typedef CreatePlace =
    Place Function(Pointer<Utf8> name, double latitude, double longitude);

typedef DistanceNative = Double Function(Coordinate p1, Coordinate p2);
typedef Distance = double Function(Coordinate p1, Coordinate p2);

void main() {
  // Open the dynamic library
  var libraryPath = path.join(
    Directory.current.path,
    'structs_library',
    'libstructs.so',
  );
  if (Platform.isMacOS) {
    libraryPath = path.join(
      Directory.current.path,
      'structs_library',
      'libstructs.dylib',
    );
  }
  if (Platform.isWindows) {
    libraryPath = path.join(
      Directory.current.path,
      'structs_library',
      'Debug',
      'structs.dll',
    );
  }
  final dylib = DynamicLibrary.open(libraryPath);

  final helloWorld = dylib.lookupFunction<HelloWorld, HelloWorld>(
    'hello_world',
  );
  final message = helloWorld().toDartString();
  print(message);

  final reverse = dylib.lookupFunction<ReverseNative, Reverse>('reverse');
  final backwards = 'backwards';
  final backwardsUtf8 = backwards.toNativeUtf8();
  final reversedMessageUtf8 = reverse(backwardsUtf8, backwards.length);
  final reversedMessage = reversedMessageUtf8.toDartString();
  calloc.free(backwardsUtf8);
  print('$backwards reversed is $reversedMessage');

  final freeString = dylib.lookupFunction<FreeStringNative, FreeString>(
    'free_string',
  );
  freeString(reversedMessageUtf8);

  final createCoordinate = dylib
      .lookupFunction<CreateCoordinateNative, CreateCoordinate>(
        'create_coordinate',
      );
  final coordinate = createCoordinate(3.5, 4.6);
  print(
    'Coordinate is lat ${coordinate.latitude}, long ${coordinate.longitude}',
  );

  final myHomeUtf8 = 'My Home'.toNativeUtf8();
  final createPlace = dylib.lookupFunction<CreatePlaceNative, CreatePlace>(
    'create_place',
  );
  final place = createPlace(myHomeUtf8, 42.0, 24.0);
  final name = place.name.toDartString();
  calloc.free(myHomeUtf8);
  final coord = place.coordinate;
  print(
    'The name of my place is $name at ${coord.latitude}, ${coord.longitude}',
  );
  final distance = dylib.lookupFunction<DistanceNative, Distance>('distance');
  final dist = distance(createCoordinate(2.0, 2.0), createCoordinate(5.0, 6.0));
  print("distance between (2,2) and (5,6) = $dist");
}