hidpp/

feature.rs

//! Specific device feature implementations.

use std::{any::Any, sync::Arc};

use crate::{
    channel::{HidppChannel, HidppMessage, LONG_REPORT_LENGTH, MessageListenerGuard},
    event::EventEmitter,
    nibble::U4,
    protocol::v20::{self, Hidpp20Error},
};

pub mod adjustable_dpi;
pub mod backlight;
pub mod battery_status;
pub mod battery_voltage;
pub mod brightness_control;
pub mod change_host;
pub mod color_led_effects;
pub mod crown;
pub mod device_friendly_name;
pub mod device_information;
pub mod device_type_and_name;
pub mod disable_keys;
pub mod disable_keys_by_usage;
pub mod dual_platform;
pub mod equalizer;
pub mod extended_dpi;
pub mod extended_report_rate;
pub mod feature_set;
pub mod fn_inversion;
pub mod gestures2;
pub mod haptic_feedback;
pub mod hires_wheel;
pub mod hosts_info;
pub mod illumination;
pub mod mode_status;
pub mod mouse_pointer;
pub mod multi_platform;
pub mod per_key_lighting;
pub mod persistent_remappable_action;
pub mod registry;
pub mod report_rate;
pub mod reprog_controls;
pub mod rgb_effects;
pub mod root;
pub mod sidetone;
pub mod smartshift;
pub mod smartshift_enhanced;
pub mod solar_dashboard;
pub mod thumbwheel;
pub mod touch_mouse_raw;
pub mod touchpad_raw_xy;
pub mod unified_battery;
pub mod vertical_scrolling;
pub mod wireless_device_status;

/// Represents a concrete implementation of a HID++2.0 device feature.
pub trait Feature: Any + Send + Sync {}

/// Represents a [`Feature`] that can be instantiated automatically.
pub trait CreatableFeature: Feature {
    /// The protocol ID of the implemented feature.
    const ID: u16;

    /// The version of the feature the implementation starts to support.
    const STARTING_VERSION: u8;

    /// Creates a new instance of the feature implementation.
    fn new(chan: Arc<HidppChannel>, device_index: u8, feature_index: u8) -> Self;
}

/// Represents a [`Feature`] that emits events of type `T`.
pub trait EmittingFeature<T>: Feature {
    /// Creates a receiver that is being notified whenever a new event of type
    /// `T` is emitted by the feature.
    fn listen(&self) -> async_channel::Receiver<T>;
}

/// Decodes a feature's event payload from its HID++2.0 event sub-id.
///
/// Implemented by a feature's event enum. [`EventSource::attach`] calls
/// [`Self::decode`] for every unsolicited broadcast addressed to the feature,
/// so this is the only part of a feature's event handling that has to vary —
/// [`EventSource`] owns the listener registration, the [`event_payload`]
/// filtering, and the emitting. Returning `None` drops the report exactly
/// like the hand-rolled per-feature listeners this replaced did on an
/// unrecognised sub-id or an unparsable payload.
pub(crate) trait DecodeEvent: Clone + Send + Sync + 'static {
    /// Decodes `payload` for event sub-id `sub_id`, or returns `None` to drop
    /// the report.
    fn decode(sub_id: u8, payload: &[u8; LONG_REPORT_LENGTH - 4]) -> Option<Self>
    where
        Self: Sized;
}

/// Owns the [`EventEmitter`] and message listener backing an
/// [`EmittingFeature`] implementation.
///
/// Every emitting feature used to hand-roll the same listener ceremony in its
/// `CreatableFeature::new`: build an `Arc<EventEmitter<E>>`, register a
/// guarded message listener, filter the raw report through [`event_payload`],
/// and emit whatever the feature's own decode step produced. A feature now
/// holds one `EventSource<E>` field, builds it with [`Self::attach`], and
/// implements [`EmittingFeature`] with a one-line [`Self::listen`] delegate.
pub(crate) struct EventSource<E: DecodeEvent> {
    emitter: Arc<EventEmitter<E>>,

    /// Removes the message listener when the source is dropped.
    _listener: MessageListenerGuard,
}

impl<E: DecodeEvent> EventSource<E> {
    /// Registers a listener on `chan` that decodes broadcasts addressed to
    /// `(device_index, feature_index)` via [`DecodeEvent::decode`] and emits
    /// them to receivers created by [`Self::listen`].
    pub(crate) fn attach(chan: &Arc<HidppChannel>, device_index: u8, feature_index: u8) -> Self {
        let emitter = Arc::new(EventEmitter::new());

        let listener = chan.add_msg_listener_guarded({
            let emitter = Arc::clone(&emitter);

            move |raw, matched| {
                let Some((func, payload)) =
                    event_payload(raw, matched, device_index, feature_index)
                else {
                    return;
                };
                if let Some(event) = E::decode(func.to_lo(), &payload) {
                    emitter.emit(event);
                }
            }
        });

        Self {
            emitter,
            _listener: listener,
        }
    }

    /// Creates a receiver notified of every event this source decodes.
    pub(crate) fn listen(&self) -> async_channel::Receiver<E> {
        self.emitter.create_receiver()
    }
}

/// A feature's addressable `(device, feature)` endpoint on a channel.
///
/// Embedding this in a feature replaces the three loose `chan` / `device_index`
/// / `feature_index` fields every implementation used to carry, and centralises
/// the HID++2.0 request framing that was otherwise hand-written at every call
/// site.
#[derive(Clone)]
pub(crate) struct FeatureEndpoint {
    /// The underlying HID++ channel.
    chan: Arc<HidppChannel>,

    /// The index of the device the feature belongs to.
    device_index: u8,

    /// The index of the feature in the device's feature table.
    feature_index: u8,
}

impl FeatureEndpoint {
    /// Binds an endpoint to `feature_index` on `device_index` of `chan`.
    pub(crate) fn new(chan: Arc<HidppChannel>, device_index: u8, feature_index: u8) -> Self {
        Self {
            chan,
            device_index,
            feature_index,
        }
    }

    /// The request header addressing `function` on this endpoint, stamped with
    /// the channel's next software id.
    ///
    /// `function` is a HID++2.0 function id, which is 4-bit; only the low nibble
    /// is sent. The assert keeps a stray out-of-range id from silently routing
    /// to a different function in debug builds.
    fn header(&self, function: u8) -> v20::MessageHeader {
        debug_assert!(
            function < 16,
            "HID++2.0 function id {function} exceeds 4 bits"
        );
        v20::MessageHeader {
            device_index: self.device_index,
            feature_index: self.feature_index,
            function_id: U4::from_lo(function),
            software_id: self.chan.get_sw_id(),
        }
    }

    /// Calls `function` with a 3-byte short-report payload and waits for the
    /// matching response.
    pub(crate) async fn call(
        &self,
        function: u8,
        args: [u8; 3],
    ) -> Result<v20::Message, Hidpp20Error> {
        self.chan
            .send_v20(v20::Message::Short(self.header(function), args))
            .await
    }

    /// Calls `function` with a 16-byte long-report payload and waits for the
    /// matching response.
    pub(crate) async fn call_long(
        &self,
        function: u8,
        args: [u8; 16],
    ) -> Result<v20::Message, Hidpp20Error> {
        self.chan
            .send_v20(v20::Message::Long(self.header(function), args))
            .await
    }

    /// Sends `function` with a 3-byte short-report payload without waiting for a
    /// response.
    ///
    /// For functions the device answers normally use [`Self::call`]; this is for
    /// the rare function whose side effect (e.g. a host switch that resets the
    /// device) prevents a response from ever arriving.
    pub(crate) async fn notify(&self, function: u8, args: [u8; 3]) -> Result<(), Hidpp20Error> {
        self.chan
            .send_and_forget(v20::Message::Short(self.header(function), args).into())
            .await?;
        Ok(())
    }
}

/// Shared prelude for a feature's event listener.
///
/// Drops reports already matched to an outgoing request, parses the raw report
/// as a HID++2.0 message, and keeps only unsolicited broadcasts addressed to
/// this `(device_index, feature_index)` with a zero software id. Returns the
/// event's function id (its sub-id) and extended payload, leaving sub-id
/// dispatch to the caller — so a multi-event feature filters its sub-ids
/// explicitly rather than folding the check into the header guard.
pub(crate) fn event_payload(
    raw: HidppMessage,
    matched: bool,
    device_index: u8,
    feature_index: u8,
) -> Option<(U4, [u8; LONG_REPORT_LENGTH - 4])> {
    if matched {
        return None;
    }

    let msg = v20::Message::from(raw);
    let header = msg.header();
    if header.device_index != device_index
        || header.feature_index != feature_index
        || header.software_id.to_lo() != 0
    {
        return None;
    }

    Some((header.function_id, msg.extend_payload()))
}

bitflags::bitflags! {
    /// A bitfield describing some properties of a feature.
    ///
    /// Documentation is taken from <https://drive.google.com/file/d/1ULmw9uJL8b8iwwUo5xjSS9F5Zvno-86y/view>.
    #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
    #[cfg_attr(feature = "serde", derive(serde::Serialize))]
    pub struct FeatureType: u8 {
        /// An obsolete feature is a feature that has been replaced by a newer
        /// one, but is advertised in order for older SWs to still be able to
        /// support the feature (in case the old SW does not know yet the newer
        /// one).
        const OBSOLETE = 1 << 7;

        /// A SW hidden feature is a feature that should not be
        /// known/managed/used by end user configuration SW. The host should
        /// ignore this type of features.
        const HIDDEN = 1 << 6;

        /// A hidden feature that has been disabled for user software. Used for
        /// internal testing and manufacturing.
        const ENGINEERING = 1 << 5;

        /// A manufacturing feature that can be permanently deactivated. It is
        /// usually also hidden and engineering.
        ///
        /// This flag was added in feature version 2 and is never set by older
        /// versions.
        const MANUFACTURING_DEACTIVATABLE = 1 << 4;

        /// A compliance feature that can be permanently deactivated. It is
        /// usually also hidden and engineering.
        ///
        /// This flag was added in feature version 2 and is never set by older
        /// versions.
        const COMPLIANCE_DEACTIVATABLE = 1 << 3;
    }
}

#[cfg(test)]
#[allow(
    clippy::unwrap_used,
    clippy::expect_used,
    reason = "expect/unwrap are idiomatic in tests"
)]
mod tests {
    use super::event_payload;
    use crate::{
        channel::HidppMessage,
        nibble::U4,
        protocol::v20::{Message, MessageHeader},
    };

    /// Builds a raw long report carrying a HID++2.0 broadcast with the given
    /// header fields and a recognisable payload.
    fn broadcast(device_index: u8, feature_index: u8, function: u8, software: u8) -> HidppMessage {
        Message::Long(
            MessageHeader {
                device_index,
                feature_index,
                function_id: U4::from_lo(function),
                software_id: U4::from_lo(software),
            },
            [0xab; 16],
        )
        .into()
    }

    #[test]
    fn accepts_matching_broadcast_and_returns_sub_id() {
        let (func, payload) =
            event_payload(broadcast(2, 5, 1, 0), false, 2, 5).expect("broadcast should pass");
        assert_eq!(func.to_lo(), 1);
        assert_eq!(payload, [0xab; 16]);
    }

    #[test]
    fn rejects_request_matched_report() {
        // A report already matched to an outgoing request is a response, not an
        // event.
        assert!(event_payload(broadcast(2, 5, 0, 0), true, 2, 5).is_none());
    }

    #[test]
    fn rejects_other_device_or_feature() {
        assert!(event_payload(broadcast(9, 5, 0, 0), false, 2, 5).is_none());
        assert!(event_payload(broadcast(2, 9, 0, 0), false, 2, 5).is_none());
    }

    #[test]
    fn gates_on_software_id_only_not_sub_id() {
        // Only the software id gates a broadcast: a nonzero one is rejected, but
        // a nonzero function id is a valid event sub-id the caller dispatches on
        // and must still pass. This is the invariant the old per-feature
        // `nibble::combine(software_id, function_id) != 0` guard got right only
        // by accident (those features happened to emit a single sub-id 0 event).
        assert!(event_payload(broadcast(2, 5, 0, 1), false, 2, 5).is_none());
        assert!(event_payload(broadcast(2, 5, 7, 0), false, 2, 5).is_some());
    }
}