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# Mob.Bt (mob v0.6.18)

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Bluetooth Classic (BR/EDR) — device-level discovery, pairing, and cross-profile session management.

Profile-specific operations live in submodules:

- `Mob.Bt.Hfp` — Hands-Free Profile (audio + vendor AT commands). Use this for headsets, PTT-equipped earpieces, etc.
- `Mob.Bt.Spp` — Serial Port Profile (RFCOMM byte streams). Use this for legacy serial-over-Bluetooth devices (Arduino HC-05, OBD-II readers, marine GPS, industrial sensors).
- `Mob.Bt.Hid` — Human Interface Device (input reports). Use this for Bluetooth keyboards, mice, gamepads, finger PTTs.

## API style

Same as the rest of Mob: callbacks return `socket` unchanged, results arrive in `handle_info/2` as 4-tuples:

    {:bt, event_atom, session_id_or_nil, payload}

Discovery / pairing events use `nil` for session_id; profile events carry the session_id returned from the matching `connect/2`.

## Permissions

Bluetooth requires runtime permissions on Android 12+ (API 31+):

- `:bluetooth_scan` — for `start_discovery/1`
- `:bluetooth_connect` — for `pair/2`, `connect/*`, `disconnect/2`

Request via `Mob.Permissions.request/2` before calling Mob.Bt functions.

## iOS

Bluetooth Classic on iOS requires Apple's MFi (Made for iPhone) certification — a paid, NDA-gated program. Mob.Bt is Android-only. All functions return `{:error, :unsupported}` synchronously on iOS. For iOS-equivalent custom-hardware connectivity, use `Mob.Ble`.

## Pairing flow

Two pairing modes, auto-selected by whether `:pin` is given:

    # System UI flow — Android shows a system pairing dialog
    socket = Mob.Bt.pair(socket, device)

    # Programmatic — PIN supplied via API, no UI
    socket = Mob.Bt.pair(socket, device, pin: "0000")

If the programmatic PIN fails or the device requires UI confirmation (e.g. numeric comparison), Android falls back to the system UI automatically.

## Disconnect

One canonical disconnect for any profile session:

    Mob.Bt.disconnect(socket, session_id)

The framework looks up which profile owns the session_id and routes to the right profile-disconnect internally. Emits a profile-specific event (`{:bt, :hfp_disconnected, ...}` etc).

## Summary

### Types

device()

A discovered or paired Bluetooth device.

session_id()

An opaque session identifier for an active profile connection.

### Functions

cancel_discovery(socket)

Cancel an in-progress discovery.

disconnect(socket, session_id)

Disconnect a profile session by `session_id`.

list_paired(socket)

List currently paired (bonded) Bluetooth devices.

pair(socket, device, opts \\ [])

Pair (bond) with a Bluetooth device.

start_discovery(socket)

Begin Bluetooth Classic discovery. Discovered devices arrive as individual `{:bt, :device_discovered, nil, device}` messages, terminated by `{:bt, :discovery_finished, nil, nil}`.

unpair(socket, device)

Remove an existing pairing (bond).

## Types

# device()

    @type device() :: %{
      :address => String.t(),
      :name => String.t(),
      optional(:bond_state) => :none | :bonding | :bonded,
      optional(:device_class) => non_neg_integer(),
      optional(:uuids) => [String.t()]
    }

A discovered or paired Bluetooth device.

# session_id()

    @type session_id() :: pos_integer()

An opaque session identifier for an active profile connection.

## Functions

# cancel_discovery(socket)

    @spec cancel_discovery(socket :: term()) :: term()

Cancel an in-progress discovery.

# disconnect(socket, session_id)

    @spec disconnect(socket :: term(), session_id()) :: term()

Disconnect a profile session by `session_id`.

Works for any profile (`Mob.Bt.Hfp`, `Mob.Bt.Spp`, `Mob.Bt.Hid`) — the framework dispatches internally based on which profile owns the session.

Emits a profile-specific disconnect event:

- `{:bt, :hfp_disconnected, session_id, reason}`
- `{:bt, :spp_disconnected, session_id, reason}`
- `{:bt, :hid_disconnected, session_id, reason}`

# list_paired(socket)

    @spec list_paired(socket :: term()) :: term()

List currently paired (bonded) Bluetooth devices.

Result arrives as `{:bt, :paired_devices, nil, [device]}`.

# pair(socket, device, opts \\ [])

    @spec pair(socket :: term(), device(), keyword()) :: term()

Pair (bond) with a Bluetooth device.

Without `:pin`, Android shows the system pairing dialog (user enters PIN). With `:pin`, attempts programmatic pairing using the supplied PIN; falls back to system UI if the device demands user confirmation.

Result arrives as one of:

- `{:bt, :pair_succeeded, nil, device}`
- `{:bt, :pair_failed, nil, %{device: device, reason: atom()}}`

# start_discovery(socket)

    @spec start_discovery(socket :: term()) :: term()

Begin Bluetooth Classic discovery. Discovered devices arrive as individual `{:bt, :device_discovered, nil, device}` messages, terminated by `{:bt, :discovery_finished, nil, nil}`.

Discovery typically runs ~12 seconds on Android.

# unpair(socket, device)

    @spec unpair(socket :: term(), device()) :: term()

Remove an existing pairing (bond).

Result: `{:bt, :unpaired, nil, device}`.