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How ADBd and Framework communicate

adbd_auth

The recommended way is to use libadbd_auth (frameworks/native/libs/adbd_auth). It is a bidirectional socket originally used to handle authentication messages (hence the name). It has since evolved to carry other categories of messages.

        ┌────────────┐               ┌─────────────────────┐
        │ ADBService ◄───────────────► AdbDebuggingManager │
        └────────────┘               └──────────▲──────────┘
                                                │
                                     ┌──────────▼──────────┐
                                     │  AdbDebuggingThread │
                                     └──────────▲──────────┘
                                                │
   Framework                            ┌───────▼───────┐
   ─────────────────────────────────────┤ "adbd" socket ├─────────
   ADBd                                 └───────▲───────┘
                                                │
           ┌───────┐                     ┌──────▼─────┐
           │ ADBd  ◄─────────────────────► adbd_auth  │
           └───────┘                     └────────────┘

Example of usages (adbd-framework direction, packet header):

  • [>> DD] Upon authentication, prompt user with a window to accept/refuse adb server's public key.
  • [<< OK] Upon authentication, tell adbd the user accepted the key.
  • [<< KO] Upon authentication, tell adbd the user refused the key.
  • [>> DC] When a device disconnects.
  • [>> TP] When the TLS Server starts, advertise its TLS port.
  • [>> WE] When a TLS device connects.
  • [>> WF] When a TLS device disconnects.

System properties

A hacky way which should be avoided as much as possible is to use system property setter + getter. There are threads listening on system property changes in both adbd and framework. See examples as follows.

  • adbd writes service.adb.tls.port, framework uses a thread to monitor it.
  • framework writes persist.adb.tls_server.enable, adbd uses a thread to monitor it.

If you are an ADB maintainer or/and have a few spare cycles, it would not be a bad idea to remove these in favor of using adbd_auth.