# Gearslip Bring any app to your car screen. ## What this is Gearslip is a phone-side Android Auto client. It speaks the Android Auto protocol directly to a car head unit over USB and acts as a **Car App Library host**: apps that ship an Android Auto car UI (navigation and media apps) hand Gearslip a template, and Gearslip renders it natively on the car screen, full quality, no phone-screen mirroring. A separate screen-sharing mode is included for apps that don't ship a car UI at all. Built by reverse-engineering the protocol for interoperability - getting a non-Google client talking to a car head unit that only expects Google's own app. ## Status Real progress, with one hard limit that's worth knowing before you build on this: - **Templated app hosting works.** All 16 template types the Car App Library defines are rendered, including a keyboard Gearslip draws itself for search and sign-in. Verified against several real navigation and media apps. - **Media playback works.** Car-enabled media apps are browsable and controllable from the car UI, with lyrics and playback state, over the same host connection. - **The connection to a real head unit needs a certificate Google controls, and Gearslip doesn't ship one.** A head unit only accepts a phone identity that chains to Google's Automotive Link certificate authority - something only Google issues. Without one, Gearslip still runs and renders everything correctly against a debug harness, but a real car will reject the connection outright. See [docs/SPIKE_FINDINGS.md](docs/SPIKE_FINDINGS.md) for what was tested, including one publicly-known leaked certificate that works on some older head units and is rejected by newer firmware and by Google's own reference tooling. - **No adb, root, or Shizuku is required to run it.** Every feature is gated on an ordinary Android permission or an on-device consent dialog - nothing needs privileged access, on the phone or in the car. ## Building ``` ./gradlew :gearslip:assembleDebug ``` The APK lands at `build/Gearslip-debug.apk`. ## Further reading - [docs/BUILDING_APPS.md](docs/BUILDING_APPS.md) - how to write apps Gearslip can render: templated apps, media apps, and the Gearslip app protocol. - [docs/SPIKE_FINDINGS.md](docs/SPIKE_FINDINGS.md) - the certificate investigation in full: what was tried, what a real head unit does and doesn't accept, and why. - [docs/CUSTOM_HEADUNIT_SCOPING.md](docs/CUSTOM_HEADUNIT_SCOPING.md) - the original scoping of what a custom head unit client would need. ## License AGPL-3.0 - see [LICENSE](LICENSE). A separate commercial license is available for private use outside the AGPL's terms; see [NOTICE.md](NOTICE.md).