From d5da1dbc9b9d60ac983730b7f8ce8a53d5219d59 Mon Sep 17 00:00:00 2001
From: Florian Rappl <florian.rappl@skve.de>
Date: Fri, 4 Sep 2026 15:05:55 +0200
Subject: [PATCH] Fixed #1029

---
 Changelog.md                 |  1 +
 docs/Using/Custom_main.md    | 20 ++++++++++++++++
 src/ElectronNET.Host/main.js | 45 ++++++++++++++++++------------------
 3 files changed, 44 insertions(+), 22 deletions(-)

diff --git a/Changelog.md b/Changelog.md
index 6f97b88..11e3fa2 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -11,6 +11,7 @@
 - Fixed resolution of unrelated target (#1099) @epsnm
 - Added target framework customization (#1095) @epsnm
 - Added configurable Electron root directory for custom packaging layouts (#1106) @DYH1319
+- Added ability for `custom_main.js` to modify command line switches (#1029) @AeonSake
 - Added `ElectronExecutableName` to separate the product name from the executable name (#1003) @AeonSake
 - Added build extensibility properties `ElectronSkipExecCommands` and `ElectronIntermediatePublishDir` (#1106) @DYH1319
 
diff --git a/docs/Using/Custom_main.md b/docs/Using/Custom_main.md
index dac300f..7a3f1ec 100644
--- a/docs/Using/Custom_main.md
+++ b/docs/Using/Custom_main.md
@@ -7,6 +7,7 @@ This guide explains how to include and use a `custom_main.js` file in your Elect
 - Register custom protocol handlers (e.g., `myapp://`) — protocols must be registered before the app is fully initialized
 - Integrate Node.js modules (e.g., telemetry, OS APIs)
 - Control startup logic (abort, environment checks)
+- Modify Chromium / Electron.NET command line switches before they are evaluated
 - Set up IPC messaging or preload scripts
 
 ## Step-by-Step Process
@@ -65,10 +66,29 @@ Use environment variables to control features:
   if (env === 'Development') { /* enable dev features */ }
   ```
 
+### Modifying Command Line Switches
+
+`onStartup` is invoked before Electron.NET reads any of its own switches (`manifest`, `unpackedelectron`, `unpackeddotnet`, `dotnetpacked`, `electronforcedport`, `electronurl`), so the hook can append or override them:
+
+```javascript
+module.exports.onStartup = function (host) {
+    const { app } = require('electron');
+
+    // Force a fixed socket bridge port
+    app.commandLine.appendSwitch('electronforcedport', '8000');
+
+    // Chromium switches, e.g. to disable the GPU sandbox
+    app.commandLine.appendSwitch('disable-gpu-sandbox');
+
+    return true;
+};
+```
+
 ## Notes
 
 - `custom_main.js` must use CommonJS syntax (`module.exports.onStartup = ...`).
 - Place the file in your source directory and copy it to `.electron` using `.csproj`.
 - Electron.NET will abort startup if `onStartup` returns `false`.
+- `onStartup` runs before the Electron.NET command line switches are evaluated, so switches set there are picked up by the host.
 
 ### Complete example is available here [ElectronNetSampleApp](https://github.com/niteshsinghal85/ElectronNetSampleApp)
\ No newline at end of file
diff --git a/src/ElectronNET.Host/main.js b/src/ElectronNET.Host/main.js
index d610da8..c182ef3 100644
--- a/src/ElectronNET.Host/main.js
+++ b/src/ElectronNET.Host/main.js
@@ -29,32 +29,11 @@ let electronforcedport;
 let electronUrl;
 let authToken = randomUUID().split('-').join('');
 
-if (app.commandLine.hasSwitch('manifest')) {
-    manifestJsonFileName = app.commandLine.getSwitchValue('manifest');
-}
-
-if (app.commandLine.hasSwitch('unpackedelectron')) {
-    unpackedelectron = true;
-}
-else if (app.commandLine.hasSwitch('unpackeddotnet')) {
-    unpackeddotnet = true;
-}
-else if (app.commandLine.hasSwitch('dotnetpacked')) {
-    dotnetpacked = true;
-}
-
-if (app.commandLine.hasSwitch('electronforcedport')) {
-    electronforcedport = +app.commandLine.getSwitchValue('electronforcedport');
-}
-
 // Store in global for access by browser windows
 global.authToken = authToken;
 
-if (app.commandLine.hasSwitch('electronurl')) {
-    electronUrl = app.commandLine.getSwitchValue('electronurl');
-}
-
 // Custom startup hook: look for custom_main.js and invoke its onStartup(host) if present.
+// Runs before any command line switch is evaluated so the hook can still modify them.
 // If the hook returns false, abort Electron startup.
 try {
     const fs = require('fs');
@@ -77,6 +56,28 @@ try {
     console.error('Error while executing custom_main.js:', err);
 }
 
+if (app.commandLine.hasSwitch('manifest')) {
+    manifestJsonFileName = app.commandLine.getSwitchValue('manifest');
+}
+
+if (app.commandLine.hasSwitch('unpackedelectron')) {
+    unpackedelectron = true;
+}
+else if (app.commandLine.hasSwitch('unpackeddotnet')) {
+    unpackeddotnet = true;
+}
+else if (app.commandLine.hasSwitch('dotnetpacked')) {
+    dotnetpacked = true;
+}
+
+if (app.commandLine.hasSwitch('electronforcedport')) {
+    electronforcedport = +app.commandLine.getSwitchValue('electronforcedport');
+}
+
+if (app.commandLine.hasSwitch('electronurl')) {
+    electronUrl = app.commandLine.getSwitchValue('electronurl');
+}
+
 const currentPath = __dirname;
 let currentBinPath = path.join(currentPath.replace('app.asar', ''), 'bin');
 let manifestJsonFilePath = path.join(currentPath, manifestJsonFileName);