openlogi_device/

pairing.rs

//! Wireless device pairing for Logi Bolt and Unifying receivers.
//!
//! The published `hidpp 0.2` can only *read* existing pairings, and its
//! `BoltReceiver` is closed to extension. So OpenLogi drives the receiver's
//! HID++ 1.0 registers directly over the public [`HidppChannel`] primitives,
//! the same way [`crate::write`] and [`crate::session::gesture`] bypass the crate's
//! higher-level abstractions.
//!
//! The register layout and notification framing below are reverse engineered
//! from Solaar (the authoritative open-source reference) and cross-checked
//! against `hidpp 0.2`'s own `0x41` device-connection parser. Two families,
//! two flows:
//!
//! - **Bolt** (`046d:c548`): open *discovery* → the receiver streams nearby
//!   unpaired devices → pick one → pair by its BTLE address → the device
//!   shows a *passkey* the user types (keyboard) or clicks (pointer) →
//!   success carries the assigned slot.
//! - **Unifying** (`046d:c52b`, `046d:c532`): open a pairing *lock*; the next
//!   powered-on unpaired device in range links on its own. No discovery list,
//!   no passkey.
//!
//! Drive a session with [`run_pairing`]: it streams [`PairingEvent`]s out and
//! takes [`PairingCommand`]s in (the Bolt device pick / cancel). [`unpair`]
//! removes a slot; [`list_pairing_receivers`] reports what's connectable.

use std::{collections::HashMap, sync::Arc};

use hidpp::{
    channel::{HidppChannel, HidppMessage},
    receiver::{self, Receiver},
};
use tokio::sync::mpsc;
use tracing::{debug, trace};

pub use hidpp::receiver::bolt::DeviceKind as BoltDeviceKind;
// Click / PasskeyMethod / ReceiverSelector / PairingError are pure data with
// no HID++/backend I/O, so they live in `openlogi_core::hid::pairing`;
// re-exported here unchanged so this module's own API surface doesn't churn.
pub use openlogi_core::hid::pairing::{Click, PairingError, PasskeyMethod, ReceiverSelector};

use crate::backend::HidBackend;

mod notification;
mod registers;

use notification::{Notification, decode, parse_notification, subscribe};
use registers::{
    BOLT_DISCOVERY, BOLT_PAIRING, NOTIFICATION_FLAGS, NOTIFICATIONS, UNIFYING_PAIRING,
    write_long_register, write_register,
};

/// HID++ device index addressing the receiver itself (not a paired device).
const RECEIVER_INDEX: u8 = 0xff;

/// Receiver pairing family. Each uses a different register flow.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum ReceiverFamily {
    /// Logi Bolt receiver.
    Bolt,
    /// Logitech Unifying receiver.
    Unifying,
}

enum SessionState {
    BoltDiscovery(BoltDiscovery),
    BoltPairing(BoltPairing),
    UnifyingPairing,
}

impl From<ReceiverFamily> for SessionState {
    fn from(family: ReceiverFamily) -> Self {
        match family {
            ReceiverFamily::Bolt => Self::BoltDiscovery(BoltDiscovery::default()),
            ReceiverFamily::Unifying => Self::UnifyingPairing,
        }
    }
}

impl SessionState {
    async fn open(&self, channel: &HidppChannel) -> Result<(), PairingError> {
        match self {
            Self::BoltDiscovery(_) => {
                write_register(channel, BOLT_DISCOVERY, [DISCOVERY_TIMEOUT, 0x01, 0x00]).await
            }
            Self::UnifyingPairing => {
                write_register(channel, UNIFYING_PAIRING, [0x01, 0x00, DISCOVERY_TIMEOUT]).await
            }
            Self::BoltPairing(_) => unreachable!("a session starts in receiver-open state"),
        }
    }

    fn select_bolt_device(&mut self, device: &DiscoveredDevice) -> Result<(), PairingError> {
        match self {
            Self::BoltDiscovery(_) | Self::BoltPairing(_) => {
                *self = Self::BoltPairing(BoltPairing {
                    authentication: device.authentication,
                });
                Ok(())
            }
            Self::UnifyingPairing => Err(PairingError::UnsupportedCommand),
        }
    }
}

#[derive(Default)]
struct BoltDiscovery {
    partial: HashMap<u16, PartialDevice>,
}

struct BoltPairing {
    authentication: u8,
}

fn family_for(product_id: u16) -> Option<ReceiverFamily> {
    match crate::find_receiver(crate::LOGITECH_VENDOR_ID, product_id)?.protocol {
        crate::ReceiverProtocol::Bolt => Some(ReceiverFamily::Bolt),
        crate::ReceiverProtocol::Unifying => Some(ReceiverFamily::Unifying),
    }
}

/// A pairing-capable receiver currently connected to the host.
#[derive(Clone, Debug)]
pub struct PairingReceiver {
    /// Bolt unique ID, when readable. `None` for Unifying (no read path yet).
    pub uid: Option<String>,
    /// Receiver protocol family.
    pub family: ReceiverFamily,
    /// USB product ID of the receiver.
    pub product_id: u16,
}

/// A nearby unpaired device surfaced by Bolt discovery.
#[derive(Clone, Debug)]
pub struct DiscoveredDevice {
    /// 6-byte BTLE address used to pair.
    pub address: [u8; 6],
    /// Authentication-method bitfield (bit 0 = passkey typed on keyboard).
    pub authentication: u8,
    /// Device class reported by the receiver discovery notification.
    pub kind: BoltDeviceKind,
    /// Human-readable name advertised by the discovered device.
    pub name: String,
}

impl DiscoveredDevice {
    /// Whether authentication is by typing a passkey on a keyboard (vs. a
    /// pointer click sequence).
    #[must_use]
    pub fn passkey_on_keyboard(&self) -> bool {
        self.authentication & 0x01 != 0
    }

    /// Pairing entropy: keyboards use 20 bits, everything else 10.
    fn entropy(&self) -> u8 {
        if self.kind == BoltDeviceKind::Keyboard {
            20
        } else {
            10
        }
    }
}

/// Renders a Bolt passkey value as a 10-bit MSB-first left/right click sequence.
fn passkey_to_clicks(value: u32) -> Vec<Click> {
    (0..10)
        .rev()
        .map(|bit| {
            if value & (1 << bit) != 0 {
                Click::Right
            } else {
                Click::Left
            }
        })
        .collect()
}

/// Events streamed out of a pairing session.
#[derive(Clone, Debug)]
pub enum PairingEvent {
    /// Discovery (Bolt) or the pairing lock (Unifying) is now open.
    Searching,
    /// Bolt only: a nearby unpaired device was discovered.
    DeviceFound(DiscoveredDevice),
    /// Bolt only: the device asks the user to enter a passkey to authenticate.
    Passkey(PasskeyMethod),
    /// A device was paired and assigned a receiver slot.
    Paired {
        /// Assigned pairing slot.
        slot: u8,
    },
    /// The flow ended without pairing a device.
    Failed(PairingError),
}

/// Commands fed into a pairing session.
#[derive(Clone, Debug)]
pub enum PairingCommand {
    /// Bolt: pair with a previously discovered device.
    Pair(DiscoveredDevice),
    /// Abort the in-progress flow.
    Cancel,
}

/// Lists supported pairing-capable receivers connected to the host.
pub async fn list_pairing_receivers(
    backend: &dyn HidBackend,
) -> Result<Vec<PairingReceiver>, PairingError> {
    let mut out = Vec::new();
    for node in backend.enumerate_hidpp().await? {
        let Some(channel) = backend.open_hidpp(&node).await? else {
            continue;
        };
        let Some(family) = family_for(channel.product_id) else {
            continue;
        };
        let uid = match family {
            ReceiverFamily::Bolt => read_bolt_uid(&channel).await,
            ReceiverFamily::Unifying => None,
        };
        out.push(PairingReceiver {
            uid,
            family,
            product_id: channel.product_id,
        });
    }
    Ok(out)
}

/// Reads a Bolt receiver's unique ID via the crate's `BoltReceiver`.
async fn read_bolt_uid(channel: &Arc<HidppChannel>) -> Option<String> {
    let Some(Receiver::Bolt(bolt)) = receiver::detect(Arc::clone(channel)) else {
        return None;
    };
    bolt.get_unique_id().await.ok()
}

/// Opens the channel for the receiver named by `target`.
async fn open_receiver(
    backend: &dyn HidBackend,
    target: &ReceiverSelector,
) -> Result<(Arc<HidppChannel>, ReceiverFamily), PairingError> {
    for node in backend.enumerate_hidpp().await? {
        let Some(channel) = backend.open_hidpp(&node).await? else {
            continue;
        };
        let Some(family) = family_for(channel.product_id) else {
            continue;
        };
        match target {
            ReceiverSelector::First => return Ok((channel, family)),
            ReceiverSelector::BoltUid(want) => {
                if family == ReceiverFamily::Bolt
                    && read_bolt_uid(&channel)
                        .await
                        .is_some_and(|uid| uid.eq_ignore_ascii_case(want))
                {
                    return Ok((channel, family));
                }
            }
        }
    }
    Err(PairingError::ReceiverNotFound)
}

/// Overall guard so a wedged receiver can't hang the session forever.
const SESSION_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(90);
/// Discovery / lock window opened on the receiver, in seconds.
const DISCOVERY_TIMEOUT: u8 = 30;

/// Runs a pairing session against `target`, streaming [`PairingEvent`]s to
/// `events` and consuming [`PairingCommand`]s from `commands`. Returns when the
/// flow finishes (paired, failed, cancelled, or timed out).
///
/// The caller owns the orchestration: spawn this on a runtime, hold the command
/// sender to forward the user's device pick / cancel, and read events to drive
/// the UI.
pub async fn run_pairing(
    backend: &dyn HidBackend,
    target: ReceiverSelector,
    mut commands: mpsc::UnboundedReceiver<PairingCommand>,
    events: mpsc::UnboundedSender<PairingEvent>,
) -> Result<(), PairingError> {
    let (channel, family) = match open_receiver(backend, &target).await {
        Ok(receiver) => receiver,
        Err(e) => {
            let _ = events.send(PairingEvent::Failed(e.clone()));
            return Err(e);
        }
    };
    let (listener, mut notifications) = subscribe(&channel);

    let result = run_session(&channel, family, &mut commands, &mut notifications, &events).await;

    drop(listener);
    // Best-effort restore: clear notification flags we set.
    let _ = channel
        .write_register(RECEIVER_INDEX, NOTIFICATIONS, [0, 0, 0])
        .await;

    if let Err(ref e) = result {
        let _ = events.send(PairingEvent::Failed(e.clone()));
    }
    result
}

/// Runs the core flow and phase-correct cancellation on every unsuccessful exit.
async fn run_session(
    channel: &HidppChannel,
    family: ReceiverFamily,
    commands: &mut mpsc::UnboundedReceiver<PairingCommand>,
    notifications: &mut mpsc::UnboundedReceiver<HidppMessage>,
    events: &mpsc::UnboundedSender<PairingEvent>,
) -> Result<(), PairingError> {
    let mut state = SessionState::from(family);
    let result = drive(channel, &mut state, commands, notifications, events).await;
    if result.is_err() {
        cancel(channel, &state).await;
    }
    result
}

/// Core session loop.
async fn drive(
    channel: &HidppChannel,
    state: &mut SessionState,
    commands: &mut mpsc::UnboundedReceiver<PairingCommand>,
    notifications: &mut mpsc::UnboundedReceiver<HidppMessage>,
    events: &mpsc::UnboundedSender<PairingEvent>,
) -> Result<(), PairingError> {
    write_register(channel, NOTIFICATIONS, NOTIFICATION_FLAGS).await?;
    state.open(channel).await?;
    let _ = events.send(PairingEvent::Searching);

    let deadline = tokio::time::sleep(SESSION_TIMEOUT);
    tokio::pin!(deadline);

    loop {
        tokio::select! {
            () = &mut deadline => return Err(PairingError::Timeout),

            cmd = commands.recv() => match cmd {
                Some(PairingCommand::Pair(device)) => {
                    state.select_bolt_device(&device)?;
                    pair_bolt_device(channel, &device).await?;
                }
                Some(PairingCommand::Cancel) | None => {
                    return Err(PairingError::Cancelled);
                }
            },

            msg = notifications.recv() => {
                let Some(msg) = msg else {
                    return Err(PairingError::Hid("receiver channel closed".into()));
                };
                let (device_index, sub_id, payload) = decode(&msg);
                // Reverse-engineered wire format — log every notification so a
                // mis-parse can be diagnosed against real hardware.
                trace!(sub_id = format_args!("{sub_id:#04x}"), ?payload, "pairing notification");
                let Some(note) = parse_notification(sub_id, device_index, payload) else {
                    continue;
                };
                // Discovery is phase-bound: a late DeviceFound would move the
                // event owner back from Pairing to Found after selection.
                match note {
                    Notification::DiscoveryInfo { counter, kind, address, authentication } => {
                        let SessionState::BoltDiscovery(discovery) = state else {
                            continue;
                        };
                        let entry = discovery.partial.entry(counter).or_default();
                        entry.kind = Some(kind);
                        entry.address = Some(address);
                        entry.authentication = Some(authentication);
                        if let Some(device) = entry.build() {
                            let _ = events.send(PairingEvent::DeviceFound(device));
                        }
                    }
                    Notification::DiscoveryName { counter, name } => {
                        let SessionState::BoltDiscovery(discovery) = state else {
                            continue;
                        };
                        let entry = discovery.partial.entry(counter).or_default();
                        entry.name = Some(name);
                        if let Some(device) = entry.build() {
                            let _ = events.send(PairingEvent::DeviceFound(device));
                        }
                    }
                    Notification::Passkey { digits, value } => {
                        let method = match state {
                            SessionState::BoltPairing(pairing)
                                if pairing.authentication & 0x01 != 0 =>
                            {
                                PasskeyMethod::Keyboard(digits)
                            }
                            _ => PasskeyMethod::Pointer {
                                clicks: passkey_to_clicks(value),
                                passkey: digits,
                            },
                        };
                        let _ = events.send(PairingEvent::Passkey(method));
                    }
                    Notification::MalformedPasskey => {
                        return Err(PairingError::MalformedNotification("passkey digits"));
                    }
                    Notification::PairingSucceeded { slot } => {
                        let _ = events.send(PairingEvent::Paired { slot });
                        return Ok(());
                    }
                    Notification::PairingError(code) => return Err(PairingError::Device(code)),
                    Notification::Connected { slot, established }
                        if matches!(state, SessionState::UnifyingPairing) => {
                        if established {
                            let _ = events.send(PairingEvent::Paired { slot });
                            return Ok(());
                        }
                    }
                    Notification::Connected { .. } => {}
                    Notification::UnifyingLock { open, error } => {
                        if error != 0 {
                            return Err(PairingError::Device(error));
                        }
                        if !open {
                            // Lock closed without a connection notification: nothing paired.
                            return Err(PairingError::Timeout);
                        }
                    }
                }
            }
        }
    }
}

/// Accumulates the two Bolt discovery frames for one device.
#[derive(Default)]
struct PartialDevice {
    kind: Option<u8>,
    address: Option<[u8; 6]>,
    authentication: Option<u8>,
    name: Option<String>,
    emitted: bool,
}

impl PartialDevice {
    /// Builds a [`DiscoveredDevice`] once both frames have arrived, exactly once.
    fn build(&mut self) -> Option<DiscoveredDevice> {
        if self.emitted {
            return None;
        }
        let (kind, address, authentication, name) = (
            self.kind?,
            self.address?,
            self.authentication?,
            self.name.clone()?,
        );
        self.emitted = true;
        Some(DiscoveredDevice {
            address,
            authentication,
            kind: BoltDeviceKind::from(kind & 0x0f),
            name,
        })
    }
}

/// Sends the Bolt pair command (action `0x01`, auto slot) for `device`.
async fn pair_bolt_device(
    channel: &HidppChannel,
    device: &DiscoveredDevice,
) -> Result<(), PairingError> {
    let mut payload = [0u8; 16];
    payload[0] = 0x01; // action: pair
    payload[1] = 0x00; // slot: auto-assign
    payload[2..8].copy_from_slice(&device.address);
    payload[8] = device.authentication;
    payload[9] = device.entropy();
    write_long_register(channel, BOLT_PAIRING, payload).await
}

/// Best-effort cancel of an in-progress flow.
async fn cancel(channel: &HidppChannel, state: &SessionState) {
    let res = match state {
        SessionState::BoltDiscovery(_) => {
            write_register(channel, BOLT_DISCOVERY, [DISCOVERY_TIMEOUT, 0x02, 0x00]).await
        }
        SessionState::BoltPairing(_) => {
            let mut payload = [0u8; 16];
            payload[0] = 0x02;
            write_long_register(channel, BOLT_PAIRING, payload).await
        }
        SessionState::UnifyingPairing => {
            write_register(channel, UNIFYING_PAIRING, [0x02, 0x00, 0x00]).await
        }
    };
    if let Err(e) = res {
        let phase = match state {
            SessionState::BoltDiscovery(_) => "Bolt discovery",
            SessionState::BoltPairing(_) => "Bolt pairing",
            SessionState::UnifyingPairing => "Unifying pairing",
        };
        debug!(phase, ?e, "cancel write failed");
    }
}

/// Removes the device on `slot` from the receiver named by `target`.
pub async fn unpair(
    backend: &dyn HidBackend,
    target: ReceiverSelector,
    slot: u8,
) -> Result<(), PairingError> {
    let (channel, family) = open_receiver(backend, &target).await?;
    match family {
        ReceiverFamily::Bolt => {
            let mut payload = [0u8; 16];
            payload[0] = 0x03; // action: unpair
            payload[1] = slot;
            write_long_register(&channel, BOLT_PAIRING, payload).await
        }
        ReceiverFamily::Unifying => {
            write_register(&channel, UNIFYING_PAIRING, [0x03, slot, 0x00]).await
        }
    }
}

#[cfg(test)]
mod tests;