Allow users to override library opening behavior

extras/integration_tests/vm/pubspec.yaml

@@ -8,8 +8,14 @@ environment:
   sdk: '>=2.4.0 <3.0.0'
 
 dependencies:
+  moor_ffi:
+    path: ../../../moor_ffi
   tests:
     path: ../tests
 
 dev_dependencies:
   test: ^1.5.0
+
+dependency_overrides:
+  moor:
+    path: ../../../moor

extras/integration_tests/vm/test/vm_test.dart

@@ -1,6 +1,6 @@
 import 'dart:io';
 
-import 'package:moor/moor_vm.dart';
+import 'package:moor_ffi/moor_ffi.dart';
 import 'package:tests/tests.dart';
 
 import 'package:path/path.dart' show join;

moor_ffi/README.md

@@ -5,10 +5,10 @@ Moor backend that uses the new `dart:ffi` apis.
 ## Supported platforms
 At the moment, this plugin supports Android natively. However, it's also going to run on all
 platforms that expose `sqlite3` as a shared native library (macOS and virtually all Linux
-distros).
+distros, I'm not sure about Windows). Native iOS support is planned.
 
 ## Notes
 
 Using `flutter run` or `flutter build` when this library is imported is going to take very long for
 the first time. The reason is that we compile sqlite. Subsequent builds should take an acceptable
-time execute.
+time execute.

moor_ffi/lib/moor_ffi.dart

@@ -1,3 +1,4 @@
+import 'dart:ffi';
 import 'dart:io';
 
 import 'package:moor/backends.dart';
@@ -5,3 +6,4 @@ import 'package:moor/moor.dart';
 import 'package:moor_ffi/src/api/database.dart';
 
 part 'src/vm_database.dart';
+part 'src/load_library.dart';

moor_ffi/lib/src/bindings/bindings.dart

@@ -4,8 +4,9 @@
 
 import 'dart:ffi';
 
+import 'package:moor_ffi/moor_ffi.dart';
+
 import '../ffi/blob.dart';
-import '../ffi/open_platform_specific.dart';
 
 import 'signatures.dart';
 import 'types.dart';
@@ -93,7 +94,7 @@ class _SQLiteBindings {
   int Function(Pointer<Statement> statement, int columnIndex) sqlite3_bind_null;
 
   _SQLiteBindings() {
-    sqlite = dlopenPlatformSpecific('sqlite3');
+    sqlite = moorSqliteOpener();
 
     sqlite3_bind_double = sqlite
         .lookup<NativeFunction<sqlite3_bind_double_native>>(

moor_ffi/lib/src/ffi/open_platform_specific.dart

@@ -1,23 +0,0 @@
-import 'dart:ffi';
-import 'dart:io';
-
-String _platformPath(String name, {String path}) {
-  final resolvedPath = path ?? '';
-
-  if (Platform.isLinux || Platform.isAndroid) {
-    return '${resolvedPath}lib$name.so';
-  }
-  if (Platform.isMacOS) {
-    return '${resolvedPath}lib$name.dylib';
-  }
-  if (Platform.isWindows) {
-    return '$resolvedPath$name.dll';
-  }
-
-  throw UnsupportedError('Platform not implemented');
-}
-
-DynamicLibrary dlopenPlatformSpecific(String name, {String path}) {
-  final resolvedPath = _platformPath(name, path: path);
-  return DynamicLibrary.open(resolvedPath);
-}

moor_ffi/lib/src/load_library.dart

@@ -0,0 +1,26 @@
+part of 'package:moor_ffi/moor_ffi.dart';
+
+/// Signature responsible for loading the dynamic sqlite3 library that moor will
+/// use.
+typedef OpenLibrary = DynamicLibrary Function();
+
+/// The [OpenLibrary] function that will be used for the first time the native
+/// library is requested. This can be overridden, but won't have an effect after
+/// the library has been opened once (which happens when a `VmDatabase` is
+/// instantiated).
+OpenLibrary moorSqliteOpener = _defaultOpen;
+
+DynamicLibrary _defaultOpen() {
+  if (Platform.isLinux || Platform.isAndroid) {
+    return DynamicLibrary.open('libsqlite3.so');
+  }
+  if (Platform.isMacOS) {
+    return DynamicLibrary.open('libsqlite3.dylib');
+  }
+  if (Platform.isWindows) {
+    return DynamicLibrary.open('sqlite3.dll');
+  }
+
+  throw UnsupportedError(
+      'moor_ffi does not support ${Platform.operatingSystem} yet');
+}