include shared library in the app

client/electron/app_paths.ts

@@ -56,6 +56,17 @@ export function pathToEmbeddedTun2socksBinary() {
   );
 }
 
+export function pathToBackendLibrary() {
+  return path.join(
+    unpackedAppPath(),
+    'client',
+    'output',
+    'build',
+    isWindows ? 'windows' : 'linux',
+    isWindows ? 'backend.dll' : 'libbackend.so'
+  );
+}
+
 /**
  * Get the parent directory path containing the background service binaries.
  * On Windows, this folder contains `OutlineService.exe`.

client/electron/go_helpers.ts

@@ -19,6 +19,7 @@
  */
 
 import {pathToEmbeddedTun2socksBinary} from './app_paths';
+import {goFetchResource} from './go_plugin';
 import {ChildProcessHelper} from './process';
 import {TransportConfigJson} from '../src/www/app/outline_server_repository/vpn';
 
@@ -66,13 +67,15 @@ export async function checkUDPConnectivity(
  * @returns A Promise that resolves to the fetched content as a string.
  * @throws ProcessTerminatedExitCodeError if tun2socks failed to run.
  */
-export function fetchResource(
+export async function fetchResource(
   url: string,
   debugMode: boolean = false
 ): Promise<string> {
-  const tun2socks = new ChildProcessHelper(pathToEmbeddedTun2socksBinary());
-  tun2socks.isDebugModeEnabled = debugMode;
-
-  console.debug('[tun2socks] - fetching resource ...');
-  return tun2socks.launch(['-fetchUrl', url]);
+  console.debug('[tun2socks] - preparing library calls ...');
+  const result = await goFetchResource(url);
+  console.debug('[tun2socks] - result: ', result);
+  if (result.Error) {
+    throw new Error(`Returned error handle: ${result.Error}`);
+  }
+  return result.Content;
 }

client/electron/go_plugin.ts

@@ -0,0 +1,57 @@
+// Copyright 2024 The Outline Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import {promisify} from 'node:util';
+import koffi from 'koffi';
+import {pathToBackendLibrary} from './app_paths';
+
+export type GoPlatformErrorHandle = number;
+
+export interface GoFetchResourceResult {
+  Content: string;
+  Error: GoPlatformErrorHandle;
+}
+
+var goFetchResourceFunc: koffi.KoffiFunction | undefined;
+
+export function goFetchResource(url: string): Promise<GoFetchResourceResult> {
+  if (!goFetchResourceFunc) {
+    const lib = ensureBackendLibraryLoaded();
+    const resultStruct = koffi.struct('FetchResourceResult', {
+      Content: 'CStr',
+      Error: 'GoPlatformErrorHandle',
+    });
+    goFetchResourceFunc = lib.func('FetchResource', resultStruct, ['str']);
+  }
+  return promisify(goFetchResourceFunc.async)(url);
+}
+
+var backendLib: koffi.IKoffiLib | undefined;
+
+function ensureBackendLibraryLoaded(): koffi.IKoffiLib {
+  if (!backendLib) {
+    backendLib = koffi.load(pathToBackendLibrary());
+    defineCommonFunctions(backendLib);
+  }
+  return backendLib;
+}
+
+var goStr: koffi.IKoffiCType | undefined;
+var goFreeString: koffi.KoffiFunction | undefined;
+
+function defineCommonFunctions(lib: koffi.IKoffiLib) {
+  goFreeString = lib.func('FreeString', koffi.types.void, [koffi.types.str]);
+  goStr = koffi.disposable('CStr', koffi.types.str, goFreeString);
+  koffi.alias('GoPlatformErrorHandle', koffi.types.uintptr_t);
+}