Rework injection to shadow Discord's app.asar

README.md

@@ -45,8 +45,8 @@ This repository contains the source code for the BetterDiscord installer. The ap
 Linux install support:
 
 - Native Discord install: ✅ Supported
-- Flatpak Discord install: ✅ Supported
-- Snap Discord install: ❌ Unsupported due to upstream Snap packaging/runtime changes
+- Flatpak Discord install: ✅ Supported for per-user installs; ⚠️ system-wide/global installs need elevated write access and aren't supported yet
+- Snap Discord install: ❌ Unsupported — Snap mounts Discord's files read-only, so the installer can't modify the app
 
 ## Downloads
 
@@ -85,11 +85,15 @@ xattr -d com.apple.quarantine "/Applications/BetterDiscord Installer.app"
 
 ### Does the installer support Flatpak Discord on Linux?
 
-Yes. Flatpak Discord installs are supported.
+Yes, for **per-user** Flatpak installs (the default `flatpak install --user …`). **System-wide/global** Flatpak installs live under `/var/lib/flatpak`, which is root-owned; the installer needs to write into the app to inject BetterDiscord, and it doesn't request elevation yet, so global Flatpak installs aren't supported for now.
 
 ### Why is Snap Discord unsupported on Linux?
 
-Discord Snap packaging/runtime changes prevent the installer from supporting Snap installs.
+Snap mounts Discord's application files as a read-only squashfs. The installer injects BetterDiscord by modifying files inside the Discord app, which isn't possible on a read-only mount — so Snap can't be supported.
+
+### How does the installer add BetterDiscord to Discord?
+
+It places a small loader inside Discord's own app files (a `resources/app` folder) and preserves Discord's original `app.asar` next to it. Because this loads before Discord's updater runs, BetterDiscord can keep itself injected across Discord updates — so you generally only need to run the installer once. Uninstalling restores Discord's original files.
 
 ### How can I use the global BetterDiscord folder with Flatpak?
 

api/controller.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"log"
-	"os"
 
 	"installer/discord"
 	"installer/types"
@@ -37,9 +36,9 @@ func (d *Controller) GetDiscordPath(channel string) string {
 }
 
 // #region Actions
-func (action *Controller) Install(corePaths []string, options types.InstallOptions) {
-	for i := range corePaths {
-		install := discord.ResolvePath(corePaths[i])
+func (action *Controller) Install(resourcePaths []string, options types.InstallOptions) {
+	for i := range resourcePaths {
+		install := discord.ResolvePath(resourcePaths[i])
 		if install == nil {
 			continue
 		}
@@ -56,9 +55,9 @@ func (action *Controller) Install(corePaths []string, options types.InstallOptio
 	runtime.EventsEmit(action.ctx, "success")
 }
 
-func (action *Controller) Uninstall(corePaths []string, options types.UninstallOptions) {
-	for i := range corePaths {
-		install := discord.ResolvePath(corePaths[i])
+func (action *Controller) Uninstall(resourcePaths []string, options types.UninstallOptions) {
+	for i := range resourcePaths {
+		install := discord.ResolvePath(resourcePaths[i])
 		if install == nil {
 			continue
 		}
@@ -73,9 +72,9 @@ func (action *Controller) Uninstall(corePaths []string, options types.UninstallO
 	runtime.EventsEmit(action.ctx, "success")
 }
 
-func (action *Controller) Repair(corePaths []string, options types.RepairOptions) {
-	for i := range corePaths {
-		install := discord.ResolvePath(corePaths[i])
+func (action *Controller) Repair(resourcePaths []string, options types.RepairOptions) {
+	for i := range resourcePaths {
+		install := discord.ResolvePath(resourcePaths[i])
 		if install == nil {
 			continue
 		}
@@ -119,17 +118,11 @@ func (action *Controller) Repair(corePaths []string, options types.RepairOptions
 
 // #region Dialogs
 func (d *Controller) BrowseForDiscord(schannel string) string {
-	var browsePath string
-	browsePath, err := os.UserConfigDir()
-	if err != nil {
-		browsePath = os.Getenv("HOME")
-	}
-
 	channel := types.ParseChannel(schannel)
 
 	selection, err := runtime.OpenDirectoryDialog(d.ctx, runtime.OpenDialogOptions{
 		Title:                      "Browsing to " + channel.Name(),
-		DefaultDirectory:           browsePath,
+		DefaultDirectory:           discord.DefaultBrowseDir(),
 		ShowHiddenFiles:            true,
 		TreatPackagesAsDirectories: true,
 	})
@@ -139,7 +132,7 @@ func (d *Controller) BrowseForDiscord(schannel string) string {
 	}
 
 	if result := discord.ResolvePath(selection); result != nil {
-		return result.CorePath
+		return result.ResourcesPath
 	}
 
 	return ""

discord/assets/injection.js → discord/assets/app_index.js

@@ -1,9 +1,9 @@
-// BetterDiscord's Injection Script
+// BetterDiscord's Injection Script (app.asar method)
 const path = require("path");
 const electron = require("electron");
 
-// Windows and macOS both use the fixed global BetterDiscord folder but
-// Electron gives the postfixed version of userData, so go up a directory
+// The global BetterDiscord folder lives one directory above userData (the
+// appData root). Electron gives the postfixed userData, so go up a directory.
 let userConfig = path.join(electron.app.getPath("userData"), "..");
 
 // If we're on Linux there are a couple cases to deal with
@@ -14,5 +14,5 @@ if (process.platform !== "win32" && process.platform !== "darwin") {
 
 require(path.join(userConfig, "BetterDiscord", "data", "betterdiscord.asar"));
 
-// Discord's Default Export
-module.exports = require("./core.asar");
+// Hand off to Discord's real (renamed) app entry point
+module.exports = require("../betterdiscord.app.asar");

discord/assets/app_package.json

@@ -0,0 +1 @@
+{"main": "./index.js"}

discord/injection.go

@@ -2,61 +2,180 @@ package discord
 
 import (
 	_ "embed"
+	"fmt"
 	"log"
 	"os"
 	"path/filepath"
-	"strings"
 
 	"installer/betterdiscord"
+	"installer/utils"
 )
 
-//go:embed assets/injection.js
-var injectionScript string
+//go:embed assets/app_index.js
+var appIndexScript string
 
+//go:embed assets/app_package.json
+var appPackageJSON string
+
+// probeWritable verifies dir accepts writes before we perform any destructive
+// operation, by creating and removing a unique throwaway file. This is the
+// elevation trigger: a failure here means we abort before touching the bundle.
+// A unique name (os.CreateTemp) avoids colliding with or clobbering an existing
+// file and is safe under concurrent probes.
+func probeWritable(dir string) error {
+	f, err := os.CreateTemp(dir, ".bd-write-probe-*")
+	if err != nil {
+		return err
+	}
+	// Writability is already proven by the successful create; cleanup is
+	// best-effort and must not turn a writable dir into a probe failure.
+	_ = f.Close()
+	_ = os.Remove(f.Name())
+	return nil
+}
+
+// inject shadows Discord's app.asar: it preserves the original as
+// betterdiscord.app.asar and drops an `app/` entry directory that loads
+// BetterDiscord and then the preserved app. The operation is transactional —
+// any failure after the rename rolls back to the original state.
+//
+// bd is accepted for call-site symmetry with the install flow but unused: the
+// injection script resolves the BetterDiscord folder at runtime.
 func (discord *DiscordInstall) inject(bd *betterdiscord.BDInstall) error {
+	resources := discord.ResourcesPath
+	originalAsar := filepath.Join(resources, "app.asar")
+	preservedAsar := filepath.Join(resources, "betterdiscord.app.asar")
+	appDir := filepath.Join(resources, "app")
 
-	// 0o644: index.js is a require target, it doesn't need the executable bit
-	// (matches the mode uninject writes).
-	if err := os.WriteFile(filepath.Join(discord.CorePath, "index.js"), []byte(injectionScript), 0o644); err != nil {
-		log.Printf("❌ Unable to write index.js in %s\n", discord.CorePath)
+	// Probe writability before the destructive rename so we never leave a
+	// half-modified bundle on a read-only/permission-denied target.
+	if err := probeWritable(resources); err != nil {
+		log.Printf("❌ Cannot write to %s\n", resources)
 		log.Printf("   %s\n", err.Error())
 		return err
 	}
 
-	log.Printf("✅ Injected into %s\n", discord.CorePath)
+	// Preserve the original app.asar (idempotent, guarded).
+	//
+	// A live app.asar is always Discord's current app and takes priority: it
+	// must be renamed away or it would shadow our app/ folder (Electron loads
+	// app.asar before app/), silently disabling BetterDiscord. If a preserved
+	// copy is also present — e.g. Discord repaired/reinstalled over a previous
+	// injection — that copy is stale, so we discard it and re-preserve the live
+	// app. Only when there is no live app.asar do we treat an existing preserved
+	// copy as the (already-injected) source of truth and leave it be.
+	renamed := false
+	switch {
+	case utils.Exists(originalAsar):
+		if utils.Exists(preservedAsar) {
+			if err := os.Remove(preservedAsar); err != nil {
+				log.Printf("❌ Unable to replace stale %s\n", preservedAsar)
+				log.Printf("   %s\n", err.Error())
+				return err
+			}
+		}
+		if err := os.Rename(originalAsar, preservedAsar); err != nil {
+			log.Printf("❌ Unable to preserve app.asar in %s\n", resources)
+			log.Printf("   %s\n", err.Error())
+			return err
+		}
+		renamed = true
+	case utils.Exists(preservedAsar):
+		// Already preserved from a prior injection and no live app.asar; the
+		// archive is correct — only the shadow app/ needs (re)writing below.
+	default:
+		return fmt.Errorf("no app.asar found in %s", resources)
+	}
+
+	// Roll back anything done after the rename so a partial failure never
+	// leaves Discord without a loadable app.
+	rollback := func() {
+		os.RemoveAll(appDir)
+		if renamed && !utils.Exists(originalAsar) {
+			if err := os.Rename(preservedAsar, originalAsar); err != nil {
+				// If this fails, Discord is left with no app.asar and no app/ —
+				// surface it so the user can restore manually.
+				log.Printf("❌ Rollback failed: unable to restore app.asar in %s\n", resources)
+				log.Printf("   %s\n", err.Error())
+			}
+		}
+	}
+
+	if err := os.MkdirAll(appDir, 0755); err != nil {
+		log.Printf("❌ Unable to create %s\n", appDir)
+		log.Printf("   %s\n", err.Error())
+		rollback()
+		return err
+	}
+
+	if err := os.WriteFile(filepath.Join(appDir, "package.json"), []byte(appPackageJSON), 0o644); err != nil {
+		log.Printf("❌ Unable to write package.json in %s\n", appDir)
+		log.Printf("   %s\n", err.Error())
+		rollback()
+		return err
+	}
+
+	if err := os.WriteFile(filepath.Join(appDir, "index.js"), []byte(appIndexScript), 0o644); err != nil {
+		log.Printf("❌ Unable to write index.js in %s\n", appDir)
+		log.Printf("   %s\n", err.Error())
+		rollback()
+		return err
+	}
+
+	if !utils.Exists(filepath.Join(appDir, "index.js")) ||
+		!utils.Exists(filepath.Join(appDir, "package.json")) ||
+		!utils.Exists(preservedAsar) {
+		rollback()
+		return fmt.Errorf("injection verification failed in %s", resources)
+	}
+
+	log.Printf("✅ Injected into %s\n", resources)
 	return nil
 }
 
+// uninject reverses inject: it removes the shadow `app/` directory and restores
+// Discord's original app.asar from the preserved copy.
 func (discord *DiscordInstall) uninject() error {
-	indexFile := filepath.Join(discord.CorePath, "index.js")
+	resources := discord.ResourcesPath
+	originalAsar := filepath.Join(resources, "app.asar")
+	preservedAsar := filepath.Join(resources, "betterdiscord.app.asar")
+	appDir := filepath.Join(resources, "app")
 
-	contents, err := os.ReadFile(indexFile)
-
-	// First try to check the file, but if there's an issue we try to blindly overwrite below
-	if err == nil {
-		if !strings.Contains(strings.ToLower(string(contents)), "betterdiscord") {
-			log.Printf("✅ No injection found for %s\n", discord.Channel.Name())
-			return nil
+	if utils.Exists(appDir) {
+		if err := os.RemoveAll(appDir); err != nil {
+			log.Printf("❌ Unable to remove %s\n", appDir)
+			log.Printf("   %s\n", err.Error())
+			return err
 		}
 	}
 
-	if err := os.WriteFile(indexFile, []byte(`module.exports = require("./core.asar");`), 0o644); err != nil {
-		log.Printf("❌ Unable to write file %s\n", indexFile)
-		log.Printf("   %s\n", err.Error())
-		return err
+	switch {
+	case utils.Exists(preservedAsar) && !utils.Exists(originalAsar):
+		// Normal revert: restore Discord's original app from the preserved copy.
+		if err := os.Rename(preservedAsar, originalAsar); err != nil {
+			log.Printf("❌ Unable to restore app.asar in %s\n", resources)
+			log.Printf("   %s\n", err.Error())
+			return err
+		}
+	case utils.Exists(preservedAsar):
+		// A live app.asar is already present (e.g. Discord repaired/reinstalled
+		// over the injection), so the preserved copy is stale. Remove it to fully
+		// revert and reclaim the space (100MB+). A failure here only leaves a
+		// harmless leftover — Discord still launches — so don't fail the uninstall.
+		if err := os.Remove(preservedAsar); err != nil {
+			log.Printf("⚠️  Unable to remove stale %s\n", preservedAsar)
+			log.Printf("   %s\n", err.Error())
+		}
 	}
-	log.Printf("✅ Removed from %s\n", discord.Channel.Name())
 
+	log.Printf("✅ Removed from %s\n", discord.Channel.Name())
 	return nil
 }
 
-// TODO: consider putting this in the betterdiscord package
+// IsInjected reports whether this install currently has the app.asar shadow in
+// place: both our `app/index.js` entry and the preserved original must exist.
 func (discord *DiscordInstall) IsInjected() bool {
-	indexFile := filepath.Join(discord.CorePath, "index.js")
-	contents, err := os.ReadFile(indexFile)
-	if err != nil {
-		return false
-	}
-	lower := strings.ToLower(string(contents))
-	return strings.Contains(lower, "betterdiscord")
+	resources := discord.ResourcesPath
+	return utils.Exists(filepath.Join(resources, "app", "index.js")) &&
+		utils.Exists(filepath.Join(resources, "betterdiscord.app.asar"))
 }