init

.gitignore

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+.dart_tool
+.flutter-plugins
+.flutter-plugins-dependencies
+.packages
+/build
+/ios
+/macos
+.DS_Store
+/pubspec.lock
+go.sum

README.md

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+# flap
+
+<p align="center">
+<img width="150" height="150" src="https://raw.githubusercontent.com/capitalpidx/flap/master/art/logo.png"><br/>
+Working proof of the Go server running inside Flutter
+</p>
+
+[Video in action](https://www.youtube.com/watch?v=4DPL5F2DVdc)
+
+## Prerequisites
+
+- [Flutter](https://flutter.dev) >2.0
+- [Go](https://golang.org) >1.16
+
+## Build Go server
+```
+cd go
+```
+macOS:
+```
+make macos
+```
+iOS:
+```
+make ios
+```
+iOS Simulator:
+```
+make ios-simulator
+```
+
+## Run app
+```
+cd ..
+flutter devices
+flutter run -d {target}
+```
+
+## Build app
+```
+flutter build {macos, ios}
+```
+
+
+## Known issues
+
+- Hot reload doesn't work (workaround: run Go server independently in the development phase)
+
+## Q&A
+
+### Why .dylib instead of .a as an iOS library?
+Because I can despite official docs prefer .a. In fact I haven't even tried .a.
+
+## Contribution
+
+I'd like to see stuff working on other platforms.

flap.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/lib" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/test" isTestSource="true" />
+      <excludeFolder url="file://$MODULE_DIR$/.dart_tool" />
+      <excludeFolder url="file://$MODULE_DIR$/.idea" />
+      <excludeFolder url="file://$MODULE_DIR$/.pub" />
+      <excludeFolder url="file://$MODULE_DIR$/build" />
+    </content>
+    <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" name="Dart SDK" level="project" />
+    <orderEntry type="library" name="Flutter Plugins" level="project" />
+    <orderEntry type="library" name="Dart Packages" level="project" />
+  </component>
+</module>

go/.gitignore

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+go.sum
+testdata/

go/Makefile

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+# Todo: fix that these don't work on the apple silicon
+
+all: macos ios
+
+macos:
+	CGO_ENABLED=1 GOOS=darwin GOARCH=amd64 go build -buildmode=c-shared -o ../macos/server-macos.dylib main.go
+ios-simulator:
+	GOOS=darwin GOARCH=amd64 CGO_ENABLED=1 SDK=iphonesimulator CC=`go env GOROOT`/misc/ios/clangwrap.sh go build -tags ios -buildmode=c-shared -o ../ios/server-ios.dylib main.go
+ios:
+	GOOS=darwin GOARCH=arm64 CGO_ENABLED=1 SDK=iphoneos CC=`go env GOROOT`/misc/ios/clangwrap.sh CGO_CFLAGS="-fembed-bitcode" go build -tags ios -buildmode=c-shared -o ../ios/server-ios.dylib main.go
+

go/go.mod

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+module github.com/errtokyo/flap/go
+
+go 1.16
+
+require github.com/cockroachdb/pebble v0.0.0-20210423210359-b62f76615457

go/main.go

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+//go:build !detached
+
+package main
+
+import (
+	"strconv"
+
+	"github.com/1l0/flap/go/server"
+)
+
+import "C"
+
+//export serve
+func serve(port C.int, dir *C.char) {
+	p := strconv.Itoa(int(port))
+	d := C.GoString(dir)
+	server.Serve(p, d)
+}
+
+func main() {}

go/main_detached.go

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+//go:build detached
+
+package main
+
+import (
+	"github.com/1l0/flap/go/server"
+	"log"
+)
+
+func main() {
+	log.Println("Listen on http://localhost:9090")
+	server.Serve("9090", "~/Downloads/")
+}

go/server/server.go

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+package server
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/cockroachdb/pebble"
+)
+
+func Serve(port, libraryPath string) {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		db, err := pebble.Open(libraryPath+"db", &pebble.Options{})
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		key := []byte("now")
+		if err := db.Set(key, []byte(time.Now().String()), pebble.Sync); err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		value, closer, err := db.Get(key)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		dbres := fmt.Sprintf("%s is %s", key, value)
+		if err := closer.Close(); err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		if err := db.Close(); err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		fmt.Fprintf(w, "Hello from Go\n\nport: %s\nfrom local DB:\n%s\n", port, dbres)
+	})
+	http.ListenAndServe(":"+port, mux)
+}

lib/main.dart

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+import 'package:flutter/material.dart';
+import 'dart:io';
+import 'dart:ffi' as ffi;
+import 'package:path_provider/path_provider.dart';
+import 'package:ffi/ffi.dart';
+import 'dart:developer';
+import 'dart:isolate';
+import 'package:http/http.dart' as http;
+
+void main() {
+  runApp(MyApp());
+}
+
+class Config {
+  static const bool localDev = false;
+}
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Flutter Demo',
+      theme: ThemeData(
+        primarySwatch: Colors.blue,
+      ),
+      home: MyHomePage(title: 'local Go server'),
+    );
+  }
+}
+
+class MyHomePage extends StatefulWidget {
+  MyHomePage({Key key, this.title}) : super(key: key);
+  final String title;
+
+  @override
+  _MyHomePageState createState() => _MyHomePageState();
+}
+
+typedef serve_func = ffi.Void Function(ffi.Int32, ffi.Pointer<Utf8>);
+typedef Serve = void Function(int, ffi.Pointer<Utf8>);
+
+class _MyHomePageState extends State<MyHomePage> {
+  int _port = 9090;
+  bool _running = false;
+  String _body = "";
+
+  void _startServer() async {
+    if (_running || Config.localDev) return;
+    Directory supportDir = await getApplicationSupportDirectory();
+    String dir = supportDir.path;
+    log('application support directory: $dir');
+    int p = await getUnusedPort();
+    setState(() {
+      _port = p;
+      _running = true;
+    });
+    await Isolate.spawn(_launchServer, [p, dir]);
+  }
+
+  static void _launchServer(List<Object> args) async {
+    int p = args[0];
+    String dir = args[1];
+
+    final dylib = () {
+      if (Platform.isIOS) {
+        return ffi.DynamicLibrary.open('server-ios.dylib');
+      }
+      return ffi.DynamicLibrary.open('server-macos.dylib');
+    }();
+    final Serve serve =
+        dylib.lookup<ffi.NativeFunction<serve_func>>('serve').asFunction();
+    serve(p, dir.toNativeUtf8());
+    log('finished go server');
+  }
+
+  Future<int> getUnusedPort() async {
+    ServerSocket socket = await ServerSocket.bind(
+        InternetAddress.loopbackIPv4 ?? InternetAddress.anyIPv4, 0);
+    var port = socket.port;
+    socket.close();
+    log('go server listening on port: $port');
+    return port;
+  }
+
+  void _fetch() async {
+    final res = await http.get(Uri.http('localhost:$_port', '/'));
+    if (res.statusCode == 200) {
+      setState(() {
+        _body = res.body;
+      });
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(widget.title),
+      ),
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: <Widget>[
+            if (_running || Config.localDev) Text('server port: $_port'),
+            if (_running || Config.localDev)
+              TextButton(onPressed: _fetch, child: Text('fetch')),
+            Text('$_body'),
+          ],
+        ),
+      ),
+      floatingActionButton: FloatingActionButton(
+        onPressed: _startServer,
+        tooltip: 'Launch server',
+        child: Icon(Icons.launch),
+      ),
+    );
+  }
+}

pubspec.yaml

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+name: flap
+description: A new Flutter project.
+
+# The following line prevents the package from being accidentally published to
+# pub.dev using `pub publish`. This is preferred for private packages.
+publish_to: 'none' # Remove this line if you wish to publish to pub.dev
+
+# The following defines the version and build number for your application.
+# A version number is three numbers separated by dots, like 1.2.43
+# followed by an optional build number separated by a +.
+# Both the version and the builder number may be overridden in flutter
+# build by specifying --build-name and --build-number, respectively.
+# In Android, build-name is used as versionName while build-number used as versionCode.
+# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
+# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
+# Read more about iOS versioning at
+# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
+version: 1.0.0+1
+
+environment:
+  sdk: ">=2.7.0 <3.0.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+  ffi:
+  path_provider:
+  http:
+
+
+  # The following adds the Cupertino Icons font to your application.
+  # Use with the CupertinoIcons class for iOS style icons.
+  cupertino_icons: ^1.0.2
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+
+# For information on the generic Dart part of this file, see the
+# following page: https://dart.dev/tools/pub/pubspec
+
+# The following section is specific to Flutter.
+flutter:
+
+  # The following line ensures that the Material Icons font is
+  # included with your application, so that you can use the icons in
+  # the material Icons class.
+  uses-material-design: true
+
+  # To add assets to your application, add an assets section, like this:
+  # assets:
+  #   - images/a_dot_burr.jpeg
+  #   - images/a_dot_ham.jpeg
+
+  # An image asset can refer to one or more resolution-specific "variants", see
+  # https://flutter.dev/assets-and-images/#resolution-aware.
+
+  # For details regarding adding assets from package dependencies, see
+  # https://flutter.dev/assets-and-images/#from-packages
+
+  # To add custom fonts to your application, add a fonts section here,
+  # in this "flutter" section. Each entry in this list should have a
+  # "family" key with the font family name, and a "fonts" key with a
+  # list giving the asset and other descriptors for the font. For
+  # example:
+  # fonts:
+  #   - family: Schyler
+  #     fonts:
+  #       - asset: fonts/Schyler-Regular.ttf
+  #       - asset: fonts/Schyler-Italic.ttf
+  #         style: italic
+  #   - family: Trajan Pro
+  #     fonts:
+  #       - asset: fonts/TrajanPro.ttf
+  #       - asset: fonts/TrajanPro_Bold.ttf
+  #         weight: 700
+  #
+  # For details regarding fonts from package dependencies,
+  # see https://flutter.dev/custom-fonts/#from-packages