desktop-packaging

Desktop Packaging

slack-desktop uses Electron Forge for packaging, with platform-specific makers and a multi-stage code signing pipeline.

Quick Reference

# Development build + launch
yarn start

# Package for current platform
yarn package

# Package with options
yarn package --override-arch=arm64
yarn package --dmg=true
yarn package --msi=true
yarn package --appx=true
yarn package --installers=false  # output folder only, no installers

Forge Config (forge.config.ts)

The config is an async function returning ForgeConfig:

• packagerConfig — delegates to getPackagerOpts() in build/make-package.ts
• rebuildConfig — { disablePreGypCopy: true, mode: 'parallel' }
• makers — Windows makers (dynamic), @electron-forge/maker-dmg, @electron-forge/maker-zip
• plugins — empty (webpack runs manually in generateAssets hook)
• hooks — generateAssets, postPackage, postMake

Platform Packaging

macOS

Makers: DMG (UDBZ format, 600x440 window, custom background) + ZIP (for darwin and mas)

App bundle:

• appBundleId: com.tinyspeck.slackmacgap
• ElectronTeamID: BQR82RBBHL
• LSMinimumSystemVersion: 12.0
• URL protocol: slack://

Icons: slack.icns (prod), slack-dogfood.icns (dogfood), slack-prototype.icns (prototype branches)

MAS builds: Set SLACK_DARWIN_PLATFORM=mas env var.

Windows

x64 makers (4):

1. MSQ — Standalone MSI via electron-wix-msi
2. Winstaller — Squirrel.Windows installer (.exe + .msi + .nupkg + RELEASES)
3. MSIX DDL — Direct download MSIX, signed via CI
4. MSIX Store — Windows Store AppX

arm64 makers (2): Only the two MSIX makers (no Squirrel or standalone MSI)

Linux

No Forge makers. Custom createDistroPackage() from build/linux-packaging.ts.

Code Signing

macOS

Signing is done after Forge's package step (not via osxSign). This is intentional — post-package hooks add binaries that need signing.

Flow:

1. Ad-hoc codesign --deep for M1 compatibility (after fuse flipping invalidates Electron's signature)
2. npm run codesign runs:
   • codesignMacApp() via @electron/osx-sign
   • codesignNodeFiles() — signs all .node files individually
   • Optional --notarize triggers notarizeApp() via @electron/notarize

Signing identities:

• DDL: Developer ID Application: SLACK TECHNOLOGIES L.L.C. (BQR82RBBHL)
• MAS: 3rd Party Mac Developer Application: SLACK TECHNOLOGIES L.L.C. (BQR82RBBHL)
• Dev: Apple Development: Desktop Release (44TN467826)

DDL builds: Hardened runtime enabled, custom designated requirements. MAS builds: Per-entitlements signing (separate entitlement files for Plugin, GPU, Renderer, inherit).

Windows

Tool: Jsign (Java-based) with AWS KMS as keystore.

• KMS_REGION: us-east-1
• KMS_ALIAS: alias/code-signing
• Timestamp: http://timestamp.digicert.com

When signing happens:

1. postPackage hook — scans and signs all unsigned .dll, .node, .exe
2. Winstaller — custom Jsign wrapper replaces vendor/signtool.exe for Squirrel releasify
3. MSIX (CI mode) — windows-sign-hook.js calls Jsign
4. MSQ — signs support binaries and final .msi

Skip condition: Prototype builds (version ending .65535) skip signing unless on support-build/ branch.

Webpack Production Build

Triggered by Forge's generateAssets hook calling createCompiledResources().

Architecture:

• Parallelized via jest-worker threads
• src/common pre-bundled with esbuild before webpack runs
• Transpiler: esbuild-loader (target: esnext, JSX factory: h for Preact)
• Minifier: EsbuildPlugin (ES2022 target, replaces Terser)

Build targets (webpack/configs/):

Target	Config	Process
Boot	boot/boot.ts	Startup
Browser	browser/main.ts	Main process
Preload (default)	preload/preload.default.ts	Preload
Preload (main)	preload/preload.main.ts	Main window preload
Renderer (default)	renderer/renderer.default.ts	Renderer
Window Chrome	renderer/windowchrome.ts	Window chrome renderer
Utility	utility/utility.default.ts	Utility process
Vendor DLL	vendor/vendor.dll.ts	Pre-built vendor bundle

Post-build: .map files moved from dist/ to dist_sourcemap/ (uploaded to S3 separately, not shipped).

Security Fuses

Set in build/hooks/common/flip-fuses.ts via @electron/fuses after Electron binary extraction:

Fuse	Value	Purpose
RunAsNode	false	Prevents using the app as a Node.js runtime
EnableCookieEncryption	true	Encrypts cookies at rest
EnableNodeCliInspectArguments	false	Disables --inspect in production
EnableNodeOptionsEnvironmentVariable	false	Ignores NODE_OPTIONS env var
EnableEmbeddedAsarIntegrityValidation	true (except Linux)	Validates ASAR integrity
OnlyLoadAppFromAsar	true	Prevents loading app from plain directories
GrantFileProtocolExtraPrivileges	false	Restricts file:// protocol
WasmTrapHandlers	true	Enables Wasm trap handlers

Build Hooks

afterCopy (after app source copied):

1. stripSourcemapUrlsHook — strips sourcemap references
2. deleteStrayFilesHook — removes unnecessary files
3. copyInLicenseFilesHook — copies license files
4. copyInSoundFilesHook — copies sound assets
5. copyInCRTFilesHook — (Windows) C runtime files
6. copyInVisualElementsFilesHook — (Windows) visual elements manifest
7. deleteUnsupportedLanguageFilesHook — (Darwin) removes unsupported .lproj dirs
8. resetUtimeHook — (Darwin) resets timestamps for reproducible builds

afterExtract: flipFusesHook (see Security Fuses above)

postPackage: signWindowsLibrariesHook (signs unsigned binaries)

postMake: copyOutArtifacts + maybeNotarize (DMG only)

Key Environment Variables

Variable	Purpose
SLACK_OVERRIDE_ARCH	Target architecture (arm64 / x64)
SLACK_DARWIN_PLATFORM	Set to mas for Mac App Store builds
BUILD_TYPE	dogfood or release — changes icons and behavior
BUILD_ONLY	Skip notarization
SLACK_ELECTRON_ZIP_DIR	Custom local Electron zip
WEBPACK_BUNDLE_ANALYZE	Generate bundle analysis .stats.json

Key Files

File	Purpose
forge.config.ts	Top-level Forge config
build/package-cli.ts	Packaging CLI entry point
build/make-package.ts	Packager options, hooks, createInitialPackages()
build/makers/win/index.ts	Windows maker orchestration
build/mac-code-signing.ts	macOS codesign logic
build/windows-code-signing.ts	Windows Jsign + AWS KMS
build/utils/apple-notarize.ts	Apple notarization
build/hooks/common/flip-fuses.ts	Electron fuse configuration
webpack/runner.ts	Webpack build orchestrator
webpack/constants/base-config.ts	Shared webpack base config