SideCar - Deep Dive

SideCar manages pre-compiled, platform-specific runtime binaries (primarily Node.js) so the Land editor can bundle vendored runtimes without requiring users to install them separately.

Architecture 🏗️

Two binaries: a download tool that fetches official distributions and organizes them by target triple, and a spawn helper used by Mountain to launch sidecars from the vendored store.

Modules

Path
`Source/Download.rs` - Download binary: fetches distributions, resolves versions, organizes by target triple
`Source/Spawn.rs` - Spawn helper: launches a sidecar binary from the vendored store
`Source/Library.rs` - Shared utilities: version resolution, path helpers, cache types
`Cache.json` - Tracks downloaded versions per target triple
`.gitattributes` - Auto-updated by download tool for Git LFS tracking

Directory Structure 📂

[target-triple]/
  [SIDECAR_NAME]/
    [version]/
      bin/
        node

Example: aarch64-apple-darwin/NODE/22/bin/node

Download Flow ⬇️

Developer runs ./Target/release/Download
Tool reads Cache.json for existing versions
Fetches version manifest from nodejs.org
Downloads binary archive for latest patch version
Extracts to target-triple directory
Updates Cache.json and .gitattributes for Git LFS

Build-Time Selection 🎯

Mountain’s build.rs reads the SideCar directory, selects the binary matching the current Tauri target triple, and copies it into the Tauri sidecar resource path for bundling.

Configuration ⚙️

Parameter	Convention
Directory layout	`[target-triple]/[NAME]/[version]/bin/`
Target triples	All Tauri-supported platform identifiers
Node.js version	`22` (default, controlled by `--node-version`)
Cache file	`Cache.json` mapping triple/name/major to resolved version
Git LFS	Auto-updated `.gitattributes` for all binary files

The SideCar directory is not committed in its populated form. Run Download during initial setup or CI release pipeline.

Integration 🔗

Element	Direction	Mechanism
Mountain	Consumer	`build.rs` file copy by target triple
Tauri	Consumer	Sidecar resource bundling in installer
Cocoon	Runtime dependency	Mountain spawns Cocoon using vendored Node.js
Air	Potential consumer	Same target-triple convention

SideCar overview