Merge pull request #115 from Smithay/data_device

Data device implementation

Cargo.toml

@@ -12,6 +12,7 @@ members = [ "anvil" ]
 [dependencies]
 wayland-server = "0.21.1"
 wayland-sys = "0.21.1"
+wayland-commons = "0.21.1"
 nix = "0.11"
 xkbcommon = "0.2.1"
 tempfile = "2.1.5"

anvil/src/shell.rs

@@ -68,9 +68,9 @@ pub fn init_shell(
         compositor_token,
         move |shell_event| match shell_event {
             XdgRequest::NewToplevel { surface } => {
-                // place the window at a random location in the [0;300]x[0;300] square
+                // place the window at a random location in the [0;800]x[0;800] square
                 use rand::distributions::{IndependentSample, Range};
-                let range = Range::new(0, 300);
+                let range = Range::new(0, 800);
                 let mut rng = rand::thread_rng();
                 let x = range.ind_sample(&mut rng);
                 let y = range.ind_sample(&mut rng);

anvil/src/udev.rs

@@ -42,6 +42,7 @@ use smithay::{
     input::Libinput,
     wayland::{
         compositor::CompositorToken,
+        data_device::{default_action_chooser, init_data_device, set_data_device_focus},
         output::{Mode, Output, PhysicalProperties},
         seat::{Seat, XkbConfig},
         shm::init_shm_global,
@@ -107,12 +108,20 @@ pub fn run_udev(mut display: Display, mut event_loop: EventLoop<()>, log: Logger
 
     let udev_session_id = notifier.register(&mut udev_backend);
 
+    init_data_device(
+        &mut display.borrow_mut(),
+        |_| {},
+        default_action_chooser,
+        log.clone(),
+    );
+
     let (mut w_seat, _) = Seat::new(&mut display.borrow_mut(), session.seat(), log.clone());
 
     let pointer = w_seat.add_pointer();
     let keyboard = w_seat
-        .add_keyboard(XkbConfig::default(), 1000, 500)
+        .add_keyboard(XkbConfig::default(), 1000, 500, |seat, focus| {
-        .expect("Failed to initialize the keyboard");
+            set_data_device_focus(seat, focus.and_then(|s| s.client()))
+        }).expect("Failed to initialize the keyboard");
 
     let (output, _output_global) = Output::new(
         &mut display.borrow_mut(),

anvil/src/winit.rs

@@ -11,6 +11,7 @@ use smithay::{
         winit,
     },
     wayland::{
+        data_device::{default_action_chooser, init_data_device, set_data_device_focus},
         output::{Mode, Output, PhysicalProperties},
         seat::{Seat, XkbConfig},
         shm::init_shm_global,
@@ -53,12 +54,16 @@ pub fn run_winit(display: &mut Display, event_loop: &mut EventLoop<()>, log: Log
 
     let (compositor_token, _, _, window_map) = init_shell(display, log.clone());
 
+    init_data_device(display, |_| {}, default_action_chooser, log.clone());
+
     let (mut seat, _) = Seat::new(display, "winit".into(), log.clone());
 
     let pointer = seat.add_pointer();
+
     let keyboard = seat
-        .add_keyboard(XkbConfig::default(), 1000, 500)
+        .add_keyboard(XkbConfig::default(), 1000, 500, |seat, focus| {
-        .expect("Failed to initialize the keyboard");
+            set_data_device_focus(seat, focus.and_then(|s| s.client()))
+        }).expect("Failed to initialize the keyboard");
 
     let (output, _) = Output::new(
         display,

src/lib.rs

@@ -11,6 +11,7 @@ pub extern crate image;
 #[cfg_attr(feature = "backend_session", macro_use)]
 extern crate nix;
 extern crate tempfile;
+pub extern crate wayland_commons;
 pub extern crate wayland_protocols;
 pub extern crate wayland_server;
 extern crate wayland_sys;

src/wayland/data_device/data_source.rs

@@ -0,0 +1,50 @@
+use std::sync::Mutex;
+
+use wayland_server::{
+    protocol::{
+        wl_data_device_manager::DndAction,
+        wl_data_source::{Request, WlDataSource},
+    },
+    NewResource, Resource,
+};
+
+/// The metadata describing a data source
+#[derive(Debug, Clone)]
+pub struct SourceMetadata {
+    /// The MIME types supported by this source
+    pub mime_types: Vec<String>,
+    /// The Drag'n'Drop actions supported by this source
+    pub dnd_action: DndAction,
+}
+
+pub(crate) fn implement_data_source(src: NewResource<WlDataSource>) -> Resource<WlDataSource> {
+    src.implement(
+        |req, me| {
+            let data: &Mutex<SourceMetadata> = me.user_data().unwrap();
+            let mut guard = data.lock().unwrap();
+            match req {
+                Request::Offer { mime_type } => guard.mime_types.push(mime_type),
+                Request::SetActions { dnd_actions } => {
+                    guard.dnd_action = DndAction::from_bits_truncate(dnd_actions);
+                }
+                Request::Destroy => {}
+            }
+        },
+        None::<fn(_)>,
+        Mutex::new(SourceMetadata {
+            mime_types: Vec::new(),
+            dnd_action: DndAction::None,
+        }),
+    )
+}
+
+/// Access the metadata of a data source
+pub fn with_source_metadata<T, F: FnOnce(&SourceMetadata) -> T>(
+    source: &Resource<WlDataSource>,
+    f: F,
+) -> Result<T, ()> {
+    match source.user_data::<Mutex<SourceMetadata>>() {
+        Some(data) => Ok(f(&data.lock().unwrap())),
+        None => Err(()),
+    }
+}

src/wayland/data_device/dnd_grab.rs

@@ -0,0 +1,329 @@
+use std::sync::{Arc, Mutex};
+
+use wayland_server::{
+    protocol::{
+        wl_data_device, wl_data_device_manager::DndAction, wl_data_offer, wl_data_source, wl_pointer,
+        wl_surface,
+    },
+    NewResource, Resource,
+};
+
+use wayland::seat::{AxisFrame, PointerGrab, PointerInnerHandle, Seat};
+
+use super::{with_source_metadata, DataDeviceData, SeatData};
+
+pub(crate) struct DnDGrab {
+    data_source: Option<Resource<wl_data_source::WlDataSource>>,
+    current_focus: Option<Resource<wl_surface::WlSurface>>,
+    pending_offers: Vec<Resource<wl_data_offer::WlDataOffer>>,
+    offer_data: Option<Arc<Mutex<OfferData>>>,
+    origin: Resource<wl_surface::WlSurface>,
+    seat: Seat,
+}
+
+impl DnDGrab {
+    pub(crate) fn new(
+        source: Option<Resource<wl_data_source::WlDataSource>>,
+        origin: Resource<wl_surface::WlSurface>,
+        seat: Seat,
+    ) -> DnDGrab {
+        DnDGrab {
+            data_source: source,
+            current_focus: None,
+            pending_offers: Vec::with_capacity(1),
+            offer_data: None,
+            origin,
+            seat,
+        }
+    }
+}
+
+impl PointerGrab for DnDGrab {
+    fn motion(
+        &mut self,
+        _handle: &mut PointerInnerHandle,
+        location: (f64, f64),
+        focus: Option<(Resource<wl_surface::WlSurface>, (f64, f64))>,
+        serial: u32,
+        time: u32,
+    ) {
+        let (x, y) = location;
+        let seat_data = self
+            .seat
+            .user_data()
+            .get::<Mutex<SeatData>>()
+            .unwrap()
+            .lock()
+            .unwrap();
+        if focus.as_ref().map(|&(ref s, _)| s) != self.current_focus.as_ref() {
+            // focus changed, we need to make a leave if appropriate
+            if let Some(surface) = self.current_focus.take() {
+                // only leave if there is a data source or we are on the original client
+                if self.data_source.is_some() || self.origin.same_client_as(&surface) {
+                    for device in &seat_data.known_devices {
+                        if device.same_client_as(&surface) {
+                            device.send(wl_data_device::Event::Leave);
+                        }
+                    }
+                    // disable the offers
+                    self.pending_offers.clear();
+                    if let Some(offer_data) = self.offer_data.take() {
+                        offer_data.lock().unwrap().active = false;
+                    }
+                }
+            }
+        }
+        if let Some((surface, (sx, sy))) = focus {
+            // early return if the surface is no longer valid
+            let client = match surface.client() {
+                Some(c) => c,
+                None => return,
+            };
+            if self.current_focus.is_none() {
+                // We entered a new surface, send the data offer if appropriate
+                if let Some(ref source) = self.data_source {
+                    let offer_data = Arc::new(Mutex::new(OfferData {
+                        active: true,
+                        dropped: false,
+                        accepted: true,
+                        chosen_action: DndAction::empty(),
+                    }));
+                    for device in seat_data
+                        .known_devices
+                        .iter()
+                        .filter(|d| d.same_client_as(&surface))
+                    {
+                        let action_choice = device
+                            .user_data::<DataDeviceData>()
+                            .unwrap()
+                            .action_choice
+                            .clone();
+                        // create a data offer
+                        let offer = client
+                            .create_resource::<wl_data_offer::WlDataOffer>(device.version())
+                            .map(|offer| {
+                                implement_dnd_data_offer(
+                                    offer,
+                                    source.clone(),
+                                    offer_data.clone(),
+                                    action_choice,
+                                )
+                            }).unwrap();
+                        // advertize the offer to the client
+                        device.send(wl_data_device::Event::DataOffer { id: offer.clone() });
+                        with_source_metadata(source, |meta| {
+                            for mime_type in meta.mime_types.iter().cloned() {
+                                offer.send(wl_data_offer::Event::Offer { mime_type })
+                            }
+                            offer.send(wl_data_offer::Event::SourceActions {
+                                source_actions: meta.dnd_action.to_raw(),
+                            });
+                        }).unwrap();
+                        device.send(wl_data_device::Event::Enter {
+                            serial,
+                            x: x - sx,
+                            y: y - sy,
+                            surface: surface.clone(),
+                            id: Some(offer.clone()),
+                        });
+                        self.pending_offers.push(offer);
+                    }
+                    self.offer_data = Some(offer_data);
+                } else {
+                    // only send if we are on a surface of the same client
+                    if self.origin.same_client_as(&surface) {
+                        for device in &seat_data.known_devices {
+                            if device.same_client_as(&surface) {
+                                device.send(wl_data_device::Event::Enter {
+                                    serial,
+                                    x: x - sx,
+                                    y: y - sy,
+                                    surface: surface.clone(),
+                                    id: None,
+                                });
+                            }
+                        }
+                    }
+                }
+                self.current_focus = Some(surface);
+            } else {
+                // make a move
+                if self.data_source.is_some() || self.origin.same_client_as(&surface) {
+                    for device in &seat_data.known_devices {
+                        if device.same_client_as(&surface) {
+                            device.send(wl_data_device::Event::Motion {
+                                time,
+                                x: x - sx,
+                                y: y - sy,
+                            });
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn button(
+        &mut self,
+        handle: &mut PointerInnerHandle,
+        _button: u32,
+        _state: wl_pointer::ButtonState,
+        serial: u32,
+        time: u32,
+    ) {
+        if handle.current_pressed().len() == 0 {
+            // the user dropped, proceed to the drop
+            let seat_data = self
+                .seat
+                .user_data()
+                .get::<Mutex<SeatData>>()
+                .unwrap()
+                .lock()
+                .unwrap();
+            let validated = if let Some(ref data) = self.offer_data {
+                let data = data.lock().unwrap();
+                data.accepted && (!data.chosen_action.is_empty())
+            } else {
+                false
+            };
+            if let Some(ref surface) = self.current_focus {
+                if self.data_source.is_some() || self.origin.same_client_as(&surface) {
+                    for device in &seat_data.known_devices {
+                        if device.same_client_as(surface) {
+                            if validated {
+                                device.send(wl_data_device::Event::Drop);
+                            } else {
+                                device.send(wl_data_device::Event::Leave);
+                            }
+                        }
+                    }
+                }
+            }
+            if let Some(ref offer_data) = self.offer_data {
+                let mut data = offer_data.lock().unwrap();
+                if validated {
+                    data.dropped = true;
+                } else {
+                    data.active = false;
+                }
+            }
+            if let Some(ref source) = self.data_source {
+                source.send(wl_data_source::Event::DndDropPerformed);
+                if !validated {
+                    source.send(wl_data_source::Event::Cancelled);
+                }
+            }
+            // in all cases abandon the drop
+            // no more buttons are pressed, release the grab
+            handle.unset_grab(serial, time);
+        }
+    }
+
+    fn axis(&mut self, handle: &mut PointerInnerHandle, details: AxisFrame) {
+        // we just forward the axis events as is
+        handle.axis(details);
+    }
+}
+
+struct OfferData {
+    active: bool,
+    dropped: bool,
+    accepted: bool,
+    chosen_action: DndAction,
+}
+
+fn implement_dnd_data_offer(
+    offer: NewResource<wl_data_offer::WlDataOffer>,
+    source: Resource<wl_data_source::WlDataSource>,
+    offer_data: Arc<Mutex<OfferData>>,
+    action_choice: Arc<Mutex<FnMut(DndAction, DndAction) -> DndAction + Send + 'static>>,
+) -> Resource<wl_data_offer::WlDataOffer> {
+    use self::wl_data_offer::Request;
+    offer.implement(
+        move |req, offer| {
+            let mut data = offer_data.lock().unwrap();
+            match req {
+                Request::Accept { serial: _, mime_type } => {
+                    if let Some(mtype) = mime_type {
+                        if let Err(()) = with_source_metadata(&source, |meta| {
+                            data.accepted = meta.mime_types.contains(&mtype);
+                        }) {
+                            data.accepted = false;
+                        }
+                    } else {
+                        data.accepted = false;
+                    }
+                }
+                Request::Receive { mime_type, fd } => {
+                    // check if the source and associated mime type is still valid
+                    let valid = with_source_metadata(&source, |meta| meta.mime_types.contains(&mime_type))
+                        .unwrap_or(false)
+                        && source.is_alive()
+                        && data.active;
+                    if valid {
+                        source.send(wl_data_source::Event::Send { mime_type, fd });
+                    }
+                    let _ = ::nix::unistd::close(fd);
+                }
+                Request::Destroy => {}
+                Request::Finish => {
+                    if !data.active {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidFinish as u32,
+                            "Cannot finish a data offer that is no longer active.".into(),
+                        );
+                    }
+                    if !data.accepted {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidFinish as u32,
+                            "Cannot finish a data offer that has not been accepted.".into(),
+                        );
+                    }
+                    if !data.dropped {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidFinish as u32,
+                            "Cannot finish a data offer that has not been dropped.".into(),
+                        );
+                    }
+                    if data.chosen_action.is_empty() {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidFinish as u32,
+                            "Cannot finish a data offer with no valid action.".into(),
+                        );
+                    }
+                    source.send(wl_data_source::Event::DndFinished);
+                    data.active = false;
+                }
+                Request::SetActions {
+                    dnd_actions,
+                    preferred_action,
+                } => {
+                    let preferred_action = DndAction::from_bits_truncate(preferred_action);
+                    if ![DndAction::Move, DndAction::Copy, DndAction::Ask].contains(&preferred_action) {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidAction as u32,
+                            "Invalid preferred action.".into(),
+                        );
+                    }
+                    let source_actions =
+                        with_source_metadata(&source, |meta| meta.dnd_action).unwrap_or(DndAction::empty());
+                    let possible_actions = source_actions & DndAction::from_bits_truncate(dnd_actions);
+                    data.chosen_action =
+                        (&mut *action_choice.lock().unwrap())(possible_actions, preferred_action);
+                    // check that the user provided callback respects that one precise action should be chosen
+                    debug_assert!(
+                        [DndAction::Move, DndAction::Copy, DndAction::Ask].contains(&data.chosen_action)
+                    );
+                    offer.send(wl_data_offer::Event::Action {
+                        dnd_action: data.chosen_action.to_raw(),
+                    });
+                    source.send(wl_data_source::Event::Action {
+                        dnd_action: data.chosen_action.to_raw(),
+                    });
+                }
+            }
+        },
+        None::<fn(_)>,
+        (),
+    )
+}

src/wayland/data_device/mod.rs

@@ -0,0 +1,468 @@
+//! Utilities for manipulating the data devices
+//!
+//! The data device is wayland's abstraction to represent both selection (copy/paste) and
+//! drag'n'drop actions. This module provides logic to handle this part of the protocol.
+//! Selection and drag'n'drop are per-seat notions.
+//!
+//! This module provides 2 main freestanding functions:
+//!
+//! - `init_data_device`: this function must be called during the compositor startup to initialize
+//!   the data device logic
+//! - `set_data_device_focus`: this function sets the data device focus for a given seat; you'd
+//!   typically call it whenever the keyboard focus changes, to follow it (for example in the focus
+//!   hook of your keyboards)
+//!
+//! Using these two functions is enough for your clients to be able to interact with each other using
+//! the data devices.
+//!
+//! The module also provides additionnal mechanisms allowing your compositor to see and interact with
+//! the contents of the data device:
+//!
+//! - You can provide a callback closure to `init_data_device` to peek into the the actions of your clients
+//! - the freestanding function `set_data_device_selection` allows you to set the contents of the selection
+//!   for your clients
+//! - the freestanding function `start_dnd` allows you to initiate a drag'n'drop event from the compositor
+//!   itself and receive interactions of clients with it via an other dedicated callback.
+//!
+//! ## Initialization
+//!
+//! ```
+//! # extern crate wayland_server;
+//! # #[macro_use] extern crate smithay;
+//! use smithay::wayland::data_device::{init_data_device, default_action_chooser};
+//!
+//! # fn main(){
+//! # let mut event_loop = wayland_server::calloop::EventLoop::<()>::new().unwrap();
+//! # let mut display = wayland_server::Display::new(event_loop.handle());
+//! // init the data device:
+//! init_data_device(
+//!     &mut display,           // the display
+//!     |dnd_event| { /* a callback to react to client DnD/selection actions */ },
+//!     default_action_chooser, // a closure to choose the DnD action depending on clients
+//!                             // negociation
+//!     None                    // insert a logger here
+//! );
+//! # }
+//! ```
+
+use std::os::unix::io::RawFd;
+use std::sync::{Arc, Mutex};
+
+use wayland_server::{
+    protocol::{
+        wl_data_device,
+        wl_data_device_manager::{self, DndAction},
+        wl_data_offer, wl_data_source,
+    },
+    Client, Display, Global, NewResource, Resource,
+};
+
+use wayland::seat::Seat;
+
+mod data_source;
+mod dnd_grab;
+mod server_dnd_grab;
+
+pub use self::data_source::{with_source_metadata, SourceMetadata};
+pub use self::server_dnd_grab::ServerDndEvent;
+
+/// Events that are generated by interactions of the clients with the data device
+pub enum DataDeviceEvent {
+    /// A client has set the selection
+    NewSelection(Option<Resource<wl_data_source::WlDataSource>>),
+    /// A client started a drag'n'drop as response to a user pointer action
+    DnDStarted(Option<Resource<wl_data_source::WlDataSource>>),
+    /// A client requested to read the server-set selection
+    SendSelection {
+        /// the requested mime type
+        mime_type: String,
+        /// the fd to write into
+        fd: RawFd,
+    },
+}
+
+enum Selection {
+    Empty,
+    Client(Resource<wl_data_source::WlDataSource>),
+    Compositor(SourceMetadata),
+}
+
+struct SeatData {
+    known_devices: Vec<Resource<wl_data_device::WlDataDevice>>,
+    selection: Selection,
+    log: ::slog::Logger,
+    current_focus: Option<Client>,
+}
+
+impl SeatData {
+    fn set_selection(&mut self, new_selection: Selection) {
+        self.selection = new_selection;
+        self.send_selection();
+    }
+
+    fn set_focus(&mut self, new_focus: Option<Client>) {
+        self.current_focus = new_focus;
+        self.send_selection();
+    }
+
+    fn send_selection(&mut self) {
+        let client = match self.current_focus.as_ref() {
+            Some(c) => c,
+            None => return,
+        };
+        // first sanitize the selection, reseting it to null if the client holding
+        // it dropped it
+        let cleanup = if let Selection::Client(ref data_source) = self.selection {
+            !data_source.is_alive()
+        } else {
+            false
+        };
+        if cleanup {
+            self.selection = Selection::Empty;
+        }
+        // then send it if appropriate
+        match self.selection {
+            Selection::Empty => {
+                // send an empty selection
+                for dd in &self.known_devices {
+                    // skip data devices not belonging to our client
+                    if dd.client().map(|c| !c.equals(client)).unwrap_or(true) {
+                        continue;
+                    }
+                    dd.send(wl_data_device::Event::Selection { id: None });
+                }
+            }
+            Selection::Client(ref data_source) => {
+                for dd in &self.known_devices {
+                    // skip data devices not belonging to our client
+                    if dd.client().map(|c| !c.equals(client)).unwrap_or(true) {
+                        continue;
+                    }
+                    let source = data_source.clone();
+                    let log = self.log.clone();
+                    // create a corresponding data offer
+                    let offer = client
+                        .create_resource::<wl_data_offer::WlDataOffer>(dd.version())
+                        .unwrap()
+                        .implement(
+                            move |req, _offer| match req {
+                                wl_data_offer::Request::Receive { fd, mime_type } => {
+                                    // check if the source and associated mime type is still valid
+                                    let valid = with_source_metadata(&source, |meta| {
+                                        meta.mime_types.contains(&mime_type)
+                                    }).unwrap_or(false)
+                                        && source.is_alive();
+                                    if !valid {
+                                        // deny the receive
+                                        debug!(log, "Denying a wl_data_offer.receive with invalid source.");
+                                    } else {
+                                        source.send(wl_data_source::Event::Send { mime_type, fd });
+                                    }
+                                    let _ = ::nix::unistd::close(fd);
+                                }
+                                _ => { /* seleciton data offers only care about the `receive` event */ }
+                            },
+                            None::<fn(_)>,
+                            (),
+                        );
+                    // advertize the offer to the client
+                    dd.send(wl_data_device::Event::DataOffer { id: offer.clone() });
+                    with_source_metadata(data_source, |meta| {
+                        for mime_type in meta.mime_types.iter().cloned() {
+                            offer.send(wl_data_offer::Event::Offer { mime_type })
+                        }
+                    }).unwrap();
+                    dd.send(wl_data_device::Event::Selection { id: Some(offer) });
+                }
+            }
+            Selection::Compositor(ref meta) => {
+                for dd in &self.known_devices {
+                    // skip data devices not belonging to our client
+                    if dd.client().map(|c| !c.equals(client)).unwrap_or(true) {
+                        continue;
+                    }
+                    let log = self.log.clone();
+                    let offer_meta = meta.clone();
+                    let callback = dd.user_data::<DataDeviceData>().unwrap().callback.clone();
+                    // create a corresponding data offer
+                    let offer = client
+                        .create_resource::<wl_data_offer::WlDataOffer>(dd.version())
+                        .unwrap()
+                        .implement(
+                            move |req, _offer| match req {
+                                wl_data_offer::Request::Receive { fd, mime_type } => {
+                                    // check if the associated mime type is valid
+                                    if !offer_meta.mime_types.contains(&mime_type) {
+                                        // deny the receive
+                                        debug!(log, "Denying a wl_data_offer.receive with invalid source.");
+                                        let _ = ::nix::unistd::close(fd);
+                                    } else {
+                                        (&mut *callback.lock().unwrap())(DataDeviceEvent::SendSelection {
+                                            mime_type,
+                                            fd,
+                                        });
+                                    }
+                                }
+                                _ => { /* seleciton data offers only care about the `receive` event */ }
+                            },
+                            None::<fn(_)>,
+                            (),
+                        );
+                    // advertize the offer to the client
+                    dd.send(wl_data_device::Event::DataOffer { id: offer.clone() });
+                    for mime_type in meta.mime_types.iter().cloned() {
+                        offer.send(wl_data_offer::Event::Offer { mime_type })
+                    }
+                    dd.send(wl_data_device::Event::Selection { id: Some(offer) });
+                }
+            }
+        }
+    }
+}
+
+impl SeatData {
+    fn new(log: ::slog::Logger) -> SeatData {
+        SeatData {
+            known_devices: Vec::new(),
+            selection: Selection::Empty,
+            log,
+            current_focus: None,
+        }
+    }
+}
+
+/// Initialize the data device global
+///
+/// You can provide a callback to peek into the actions of your clients over the data devices
+/// (allowing you to retrieve the current selection buffer, or intercept DnD data). See the
+/// `DataDeviceEvent` type for details about what notifications you can receive. Note that this
+/// closure will not receive notifications about dnd actions the compositor initiated, see
+/// `start_dnd` for details about that.
+///
+/// You also need to provide a `(DndAction, DndAction) -> DndAction` closure that will arbitrate
+/// the choice of action resulting from a drag'n'drop session. Its first argument is the set of
+/// available actions (which is the intersection of the actions supported by the source and targets)
+/// and the second argument is the preferred action reported by the target. If no action should be
+/// chosen (and thus the drag'n'drop should abort on drop), return `DndAction::empty()`.
+pub fn init_data_device<F, C, L>(
+    display: &mut Display,
+    callback: C,
+    action_choice: F,
+    logger: L,
+) -> Global<wl_data_device_manager::WlDataDeviceManager>
+where
+    F: FnMut(DndAction, DndAction) -> DndAction + Send + 'static,
+    C: FnMut(DataDeviceEvent) + Send + 'static,
+    L: Into<Option<::slog::Logger>>,
+{
+    let log = ::slog_or_stdlog(logger).new(o!("smithay_module" => "data_device_mgr"));
+    let action_choice = Arc::new(Mutex::new(action_choice));
+    let callback = Arc::new(Mutex::new(callback));
+    let global = display.create_global(3, move |new_ddm, _version| {
+        implement_ddm(new_ddm, callback.clone(), action_choice.clone(), log.clone());
+    });
+
+    global
+}
+
+/// Set the data device focus to a certain client for a given seat
+pub fn set_data_device_focus(seat: &Seat, client: Option<Client>) {
+    // ensure the seat user_data is ready
+    // TODO: find a better way to retrieve a logger without requiring the user
+    // to provide one ?
+    // This should be a rare path anyway, it is unlikely that a client gets focus
+    // before initializing its data device, which would already init the user_data.
+    seat.user_data().insert_if_missing(|| {
+        Mutex::new(SeatData::new(
+            seat.arc.log.new(o!("smithay_module" => "data_device_mgr")),
+        ))
+    });
+    let seat_data = seat.user_data().get::<Mutex<SeatData>>().unwrap();
+    seat_data.lock().unwrap().set_focus(client);
+}
+
+/// Set a compositor-provided selection for this seat
+///
+/// You need to provide the available mime types for this selection.
+///
+/// Whenever a client requests to read the selection, your callback will
+/// receive a `DataDeviceEvent::SendSelection` event.
+pub fn set_data_device_selection(seat: &Seat, mime_types: Vec<String>) {
+    // TODO: same question as in set_data_device_focus
+    seat.user_data().insert_if_missing(|| {
+        Mutex::new(SeatData::new(
+            seat.arc.log.new(o!("smithay_module" => "data_device_mgr")),
+        ))
+    });
+    let seat_data = seat.user_data().get::<Mutex<SeatData>>().unwrap();
+    seat_data
+        .lock()
+        .unwrap()
+        .set_selection(Selection::Compositor(SourceMetadata {
+            mime_types,
+            dnd_action: DndAction::empty(),
+        }));
+}
+
+/// Start a drag'n'drop from a ressource controlled by the compositor
+///
+/// You'll receive events generated by the interaction of clients with your
+/// drag'n'drop in the provided callback. See `SeverDndEvent` for details about
+/// which events can be generated and what response is expected from you to them.
+pub fn start_dnd<C>(seat: &Seat, serial: u32, metadata: SourceMetadata, callback: C)
+where
+    C: FnMut(ServerDndEvent) + Send + 'static,
+{
+    // TODO: same question as in set_data_device_focus
+    seat.user_data().insert_if_missing(|| {
+        Mutex::new(SeatData::new(
+            seat.arc.log.new(o!("smithay_module" => "data_device_mgr")),
+        ))
+    });
+    if let Some(pointer) = seat.get_pointer() {
+        pointer.set_grab(
+            server_dnd_grab::ServerDnDGrab::new(metadata, seat.clone(), Arc::new(Mutex::new(callback))),
+            serial,
+        );
+        return;
+    }
+}
+
+fn implement_ddm<F, C>(
+    new_ddm: NewResource<wl_data_device_manager::WlDataDeviceManager>,
+    callback: Arc<Mutex<C>>,
+    action_choice: Arc<Mutex<F>>,
+    log: ::slog::Logger,
+) -> Resource<wl_data_device_manager::WlDataDeviceManager>
+where
+    F: FnMut(DndAction, DndAction) -> DndAction + Send + 'static,
+    C: FnMut(DataDeviceEvent) + Send + 'static,
+{
+    use self::wl_data_device_manager::Request;
+    new_ddm.implement(
+        move |req, _ddm| match req {
+            Request::CreateDataSource { id } => {
+                self::data_source::implement_data_source(id);
+            }
+            Request::GetDataDevice { id, seat } => match Seat::from_resource(&seat) {
+                Some(seat) => {
+                    // ensure the seat user_data is ready
+                    seat.user_data()
+                        .insert_if_missing(|| Mutex::new(SeatData::new(log.clone())));
+                    let seat_data = seat.user_data().get::<Mutex<SeatData>>().unwrap();
+                    let data_device = implement_data_device(
+                        id,
+                        seat.clone(),
+                        callback.clone(),
+                        action_choice.clone(),
+                        log.clone(),
+                    );
+                    seat_data.lock().unwrap().known_devices.push(data_device);
+                }
+                None => {
+                    error!(log, "Unmanaged seat given to a data device.");
+                }
+            },
+        },
+        None::<fn(_)>,
+        (),
+    )
+}
+
+struct DataDeviceData {
+    callback: Arc<Mutex<FnMut(DataDeviceEvent) + Send + 'static>>,
+    action_choice: Arc<Mutex<FnMut(DndAction, DndAction) -> DndAction + Send + 'static>>,
+}
+
+fn implement_data_device<F, C>(
+    new_dd: NewResource<wl_data_device::WlDataDevice>,
+    seat: Seat,
+    callback: Arc<Mutex<C>>,
+    action_choice: Arc<Mutex<F>>,
+    log: ::slog::Logger,
+) -> Resource<wl_data_device::WlDataDevice>
+where
+    F: FnMut(DndAction, DndAction) -> DndAction + Send + 'static,
+    C: FnMut(DataDeviceEvent) + Send + 'static,
+{
+    use self::wl_data_device::Request;
+    let dd_data = DataDeviceData {
+        callback: callback.clone(),
+        action_choice,
+    };
+    new_dd.implement(
+        move |req, dd| match req {
+            Request::StartDrag {
+                source,
+                origin,
+                icon: _,
+                serial,
+            } => {
+                /* TODO: handle the icon */
+                if let Some(pointer) = seat.get_pointer() {
+                    if pointer.has_grab(serial) {
+                        // The StartDrag is in response to a pointer implicit grab, all is good
+                        (&mut *callback.lock().unwrap())(DataDeviceEvent::DnDStarted(source.clone()));
+                        pointer.set_grab(dnd_grab::DnDGrab::new(source, origin, seat.clone()), serial);
+                        return;
+                    }
+                }
+                debug!(log, "denying drag from client without implicit grab");
+            }
+            Request::SetSelection { source, serial: _ } => {
+                if let Some(keyboard) = seat.get_keyboard() {
+                    if dd
+                        .client()
+                        .as_ref()
+                        .map(|c| keyboard.has_focus(c))
+                        .unwrap_or(false)
+                    {
+                        let seat_data = seat.user_data().get::<Mutex<SeatData>>().unwrap();
+                        (&mut *callback.lock().unwrap())(DataDeviceEvent::NewSelection(source.clone()));
+                        // The client has kbd focus, it can set the selection
+                        seat_data
+                            .lock()
+                            .unwrap()
+                            .set_selection(source.map(Selection::Client).unwrap_or(Selection::Empty));
+                        return;
+                    }
+                }
+                debug!(log, "denying setting selection by a non-focused client");
+            }
+            Request::Release => {
+                // Clean up the known devices
+                seat.user_data()
+                    .get::<Mutex<SeatData>>()
+                    .unwrap()
+                    .lock()
+                    .unwrap()
+                    .known_devices
+                    .retain(|ndd| ndd.is_alive() && (!ndd.equals(&dd)))
+            }
+        },
+        None::<fn(_)>,
+        dd_data,
+    )
+}
+
+/// A simple action chooser for DnD negociation
+///
+/// If the preferred action is available, it'll pick it. Otherwise, it'll pick the first
+/// available in the following order: Ask, Copy, Move.
+pub fn default_action_chooser(available: DndAction, preferred: DndAction) -> DndAction {
+    // if the preferred action is valid (a single action) and in the available actions, use it
+    // otherwise, follow a fallback stategy
+    if [DndAction::Move, DndAction::Copy, DndAction::Ask].contains(&preferred)
+        && available.contains(preferred)
+    {
+        preferred
+    } else if available.contains(DndAction::Ask) {
+        DndAction::Ask
+    } else if available.contains(DndAction::Copy) {
+        DndAction::Copy
+    } else if available.contains(DndAction::Move) {
+        DndAction::Move
+    } else {
+        DndAction::empty()
+    }
+}

src/wayland/data_device/server_dnd_grab.rs

@@ -0,0 +1,320 @@
+use std::os::unix::io::RawFd;
+use std::sync::{Arc, Mutex};
+
+use wayland_server::{
+    protocol::{wl_data_device, wl_data_device_manager::DndAction, wl_data_offer, wl_pointer, wl_surface},
+    NewResource, Resource,
+};
+
+use wayland::seat::{AxisFrame, PointerGrab, PointerInnerHandle, Seat};
+
+use super::{DataDeviceData, SeatData};
+
+/// Event generated by the interactions of clients with a server innitiated drag'n'drop
+pub enum ServerDndEvent {
+    /// The client chose an action
+    Action(DndAction),
+    /// The DnD resource was dropped by the user
+    ///
+    /// After that, the client can still interract with your ressource
+    Dropped,
+    /// The Dnd was cancelled
+    ///
+    /// The client can no longer interact
+    Cancelled,
+    /// The client requested for data to be sent
+    Send {
+        /// The requested mime type
+        mime_type: String,
+        /// The FD to write into
+        fd: RawFd,
+    },
+    /// The client has finished interacting with the resource
+    ///
+    /// This can only happen after the resource was dropped.
+    Finished,
+}
+
+pub(crate) struct ServerDnDGrab<C: 'static> {
+    metadata: super::SourceMetadata,
+    current_focus: Option<Resource<wl_surface::WlSurface>>,
+    pending_offers: Vec<Resource<wl_data_offer::WlDataOffer>>,
+    offer_data: Option<Arc<Mutex<OfferData>>>,
+    seat: Seat,
+    callback: Arc<Mutex<C>>,
+}
+
+impl<C: 'static> ServerDnDGrab<C> {
+    pub(crate) fn new(
+        metadata: super::SourceMetadata,
+        seat: Seat,
+        callback: Arc<Mutex<C>>,
+    ) -> ServerDnDGrab<C> {
+        ServerDnDGrab {
+            metadata,
+            current_focus: None,
+            pending_offers: Vec::with_capacity(1),
+            offer_data: None,
+            seat,
+            callback,
+        }
+    }
+}
+
+impl<C> PointerGrab for ServerDnDGrab<C>
+where
+    C: FnMut(ServerDndEvent) + Send + 'static,
+{
+    fn motion(
+        &mut self,
+        _handle: &mut PointerInnerHandle,
+        location: (f64, f64),
+        focus: Option<(Resource<wl_surface::WlSurface>, (f64, f64))>,
+        serial: u32,
+        time: u32,
+    ) {
+        let (x, y) = location;
+        let seat_data = self
+            .seat
+            .user_data()
+            .get::<Mutex<SeatData>>()
+            .unwrap()
+            .lock()
+            .unwrap();
+        if focus.as_ref().map(|&(ref s, _)| s) != self.current_focus.as_ref() {
+            // focus changed, we need to make a leave if appropriate
+            if let Some(surface) = self.current_focus.take() {
+                for device in &seat_data.known_devices {
+                    if device.same_client_as(&surface) {
+                        device.send(wl_data_device::Event::Leave);
+                    }
+                }
+                // disable the offers
+                self.pending_offers.clear();
+                if let Some(offer_data) = self.offer_data.take() {
+                    offer_data.lock().unwrap().active = false;
+                }
+            }
+        }
+        if let Some((surface, (sx, sy))) = focus {
+            // early return if the surface is no longer valid
+            let client = match surface.client() {
+                Some(c) => c,
+                None => return,
+            };
+            if self.current_focus.is_none() {
+                // We entered a new surface, send the data offer
+                let offer_data = Arc::new(Mutex::new(OfferData {
+                    active: true,
+                    dropped: false,
+                    accepted: true,
+                    chosen_action: DndAction::empty(),
+                }));
+                for device in seat_data
+                    .known_devices
+                    .iter()
+                    .filter(|d| d.same_client_as(&surface))
+                {
+                    let action_choice = device
+                        .user_data::<DataDeviceData>()
+                        .unwrap()
+                        .action_choice
+                        .clone();
+                    // create a data offer
+                    let offer = client
+                        .create_resource::<wl_data_offer::WlDataOffer>(device.version())
+                        .map(|offer| {
+                            implement_dnd_data_offer(
+                                offer,
+                                self.metadata.clone(),
+                                offer_data.clone(),
+                                self.callback.clone(),
+                                action_choice,
+                            )
+                        }).unwrap();
+                    // advertize the offer to the client
+                    device.send(wl_data_device::Event::DataOffer { id: offer.clone() });
+                    for mime_type in self.metadata.mime_types.iter().cloned() {
+                        offer.send(wl_data_offer::Event::Offer { mime_type })
+                    }
+                    offer.send(wl_data_offer::Event::SourceActions {
+                        source_actions: self.metadata.dnd_action.to_raw(),
+                    });
+                    device.send(wl_data_device::Event::Enter {
+                        serial,
+                        x: x - sx,
+                        y: y - sy,
+                        surface: surface.clone(),
+                        id: Some(offer.clone()),
+                    });
+                    self.pending_offers.push(offer);
+                }
+                self.offer_data = Some(offer_data);
+                self.current_focus = Some(surface);
+            } else {
+                // make a move
+                for device in &seat_data.known_devices {
+                    if device.same_client_as(&surface) {
+                        device.send(wl_data_device::Event::Motion {
+                            time,
+                            x: x - sx,
+                            y: y - sy,
+                        });
+                    }
+                }
+            }
+        }
+    }
+
+    fn button(
+        &mut self,
+        handle: &mut PointerInnerHandle,
+        _button: u32,
+        _state: wl_pointer::ButtonState,
+        serial: u32,
+        time: u32,
+    ) {
+        if handle.current_pressed().len() == 0 {
+            // the user dropped, proceed to the drop
+            let seat_data = self
+                .seat
+                .user_data()
+                .get::<Mutex<SeatData>>()
+                .unwrap()
+                .lock()
+                .unwrap();
+            let validated = if let Some(ref data) = self.offer_data {
+                let data = data.lock().unwrap();
+                data.accepted && (!data.chosen_action.is_empty())
+            } else {
+                false
+            };
+            if let Some(ref surface) = self.current_focus {
+                for device in &seat_data.known_devices {
+                    if device.same_client_as(surface) {
+                        if validated {
+                            device.send(wl_data_device::Event::Drop);
+                        } else {
+                            device.send(wl_data_device::Event::Leave);
+                        }
+                    }
+                }
+            }
+            if let Some(ref offer_data) = self.offer_data {
+                let mut data = offer_data.lock().unwrap();
+                if validated {
+                    data.dropped = true;
+                } else {
+                    data.active = false;
+                }
+            }
+            let mut callback = self.callback.lock().unwrap();
+            (&mut *callback)(ServerDndEvent::Dropped);
+            if !validated {
+                (&mut *callback)(ServerDndEvent::Cancelled);
+            }
+            // in all cases abandon the drop
+            // no more buttons are pressed, release the grab
+            handle.unset_grab(serial, time);
+        }
+    }
+
+    fn axis(&mut self, handle: &mut PointerInnerHandle, details: AxisFrame) {
+        // we just forward the axis events as is
+        handle.axis(details);
+    }
+}
+
+struct OfferData {
+    active: bool,
+    dropped: bool,
+    accepted: bool,
+    chosen_action: DndAction,
+}
+
+fn implement_dnd_data_offer<C>(
+    offer: NewResource<wl_data_offer::WlDataOffer>,
+    metadata: super::SourceMetadata,
+    offer_data: Arc<Mutex<OfferData>>,
+    callback: Arc<Mutex<C>>,
+    action_choice: Arc<Mutex<FnMut(DndAction, DndAction) -> DndAction + Send + 'static>>,
+) -> Resource<wl_data_offer::WlDataOffer>
+where
+    C: FnMut(ServerDndEvent) + Send + 'static,
+{
+    use self::wl_data_offer::Request;
+    offer.implement(
+        move |req, offer| {
+            let mut data = offer_data.lock().unwrap();
+            match req {
+                Request::Accept { serial: _, mime_type } => {
+                    if let Some(mtype) = mime_type {
+                        data.accepted = metadata.mime_types.contains(&mtype);
+                    } else {
+                        data.accepted = false;
+                    }
+                }
+                Request::Receive { mime_type, fd } => {
+                    // check if the source and associated mime type is still valid
+                    if metadata.mime_types.contains(&mime_type) && data.active {
+                        (&mut *callback.lock().unwrap())(ServerDndEvent::Send { mime_type, fd });
+                    }
+                }
+                Request::Destroy => {}
+                Request::Finish => {
+                    if !data.active {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidFinish as u32,
+                            "Cannot finish a data offer that is no longer active.".into(),
+                        );
+                    }
+                    if !data.accepted {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidFinish as u32,
+                            "Cannot finish a data offer that has not been accepted.".into(),
+                        );
+                    }
+                    if !data.dropped {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidFinish as u32,
+                            "Cannot finish a data offer that has not been dropped.".into(),
+                        );
+                    }
+                    if data.chosen_action.is_empty() {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidFinish as u32,
+                            "Cannot finish a data offer with no valid action.".into(),
+                        );
+                    }
+                    (&mut *callback.lock().unwrap())(ServerDndEvent::Finished);
+                    data.active = false;
+                }
+                Request::SetActions {
+                    dnd_actions,
+                    preferred_action,
+                } => {
+                    let preferred_action = DndAction::from_bits_truncate(preferred_action);
+                    if ![DndAction::Move, DndAction::Copy, DndAction::Ask].contains(&preferred_action) {
+                        offer.post_error(
+                            wl_data_offer::Error::InvalidAction as u32,
+                            "Invalid preferred action.".into(),
+                        );
+                    }
+                    let possible_actions = metadata.dnd_action & DndAction::from_bits_truncate(dnd_actions);
+                    data.chosen_action =
+                        (&mut *action_choice.lock().unwrap())(possible_actions, preferred_action);
+                    // check that the user provided callback respects that one precise action should be chosen
+                    debug_assert!(
+                        [DndAction::Move, DndAction::Copy, DndAction::Ask].contains(&data.chosen_action)
+                    );
+                    offer.send(wl_data_offer::Event::Action {
+                        dnd_action: data.chosen_action.to_raw(),
+                    });
+                    (&mut *callback.lock().unwrap())(ServerDndEvent::Action(data.chosen_action));
+                }
+            }
+        },
+        None::<fn(_)>,
+        (),
+    )
+}

src/wayland/mod.rs

@@ -15,6 +15,7 @@
 use std::sync::atomic::{AtomicUsize, Ordering};
 
 pub mod compositor;
+pub mod data_device;
 pub mod output;
 pub mod seat;
 pub mod shell;

src/wayland/seat/keyboard.rs

@@ -11,7 +11,7 @@ use wayland_server::{
         wl_keyboard::{Event, KeyState as WlKeyState, KeymapFormat, Request, WlKeyboard},
         wl_surface::WlSurface,
     },
-    NewResource, Resource,
+    Client, NewResource, Resource,
 };
 use xkbcommon::xkb;
 pub use xkbcommon::xkb::{keysyms, Keysym};
@@ -112,6 +112,7 @@ struct KbdInternal {
     state: xkb::State,
     repeat_rate: i32,
     repeat_delay: i32,
+    focus_hook: Box<FnMut(Option<&Resource<WlSurface>>)>,
 }
 
 // This is OK because all parts of `xkb` will remain on the
@@ -119,7 +120,12 @@ struct KbdInternal {
 unsafe impl Send for KbdInternal {}
 
 impl KbdInternal {
-    fn new(xkb_config: XkbConfig, repeat_rate: i32, repeat_delay: i32) -> Result<KbdInternal, ()> {
+    fn new(
+        xkb_config: XkbConfig,
+        repeat_rate: i32,
+        repeat_delay: i32,
+        focus_hook: Box<FnMut(Option<&Resource<WlSurface>>)>,
+    ) -> Result<KbdInternal, ()> {
         // we create a new contex for each keyboard because libxkbcommon is actually NOT threadsafe
         // so confining it inside the KbdInternal allows us to use Rusts mutability rules to make
         // sure nothing goes wrong.
@@ -146,6 +152,7 @@ impl KbdInternal {
             state,
             repeat_rate,
             repeat_delay,
+            focus_hook,
         })
     }
 
@@ -219,18 +226,23 @@ pub enum Error {
 }
 
 /// Create a keyboard handler from a set of RMLVO rules
-pub(crate) fn create_keyboard_handler(
+pub(crate) fn create_keyboard_handler<F>(
     xkb_config: XkbConfig,
     repeat_delay: i32,
     repeat_rate: i32,
     logger: &::slog::Logger,
-) -> Result<KeyboardHandle, Error> {
+    focus_hook: F,
+) -> Result<KeyboardHandle, Error>
+where
+    F: FnMut(Option<&Resource<WlSurface>>) + 'static,
+{
     let log = logger.new(o!("smithay_module" => "xkbcommon_handler"));
     info!(log, "Initializing a xkbcommon handler with keymap query";
         "rules" => xkb_config.rules, "model" => xkb_config.model, "layout" => xkb_config.layout,
         "variant" => xkb_config.variant, "options" => &xkb_config.options
     );
-    let internal = KbdInternal::new(xkb_config, repeat_rate, repeat_delay).map_err(|_| {
+    let internal =
+        KbdInternal::new(xkb_config, repeat_rate, repeat_delay, Box::new(focus_hook)).map_err(|_| {
             debug!(log, "Loading keymap failed");
             Error::BadKeymap
         })?;
@@ -382,6 +394,14 @@ impl KeyboardHandle {
                     keys: keys.clone(),
                 });
             });
+            {
+                let KbdInternal {
+                    ref focus,
+                    ref mut focus_hook,
+                    ..
+                } = *guard;
+                focus_hook(focus.as_ref());
+            }
             if guard.focus.is_some() {
                 trace!(self.arc.logger, "Focus set to new surface");
             } else {
@@ -392,6 +412,19 @@ impl KeyboardHandle {
         }
     }
 
+    /// Check if given client currently has keyboard focus
+    pub fn has_focus(&self, client: &Client) -> bool {
+        self.arc
+            .internal
+            .lock()
+            .unwrap()
+            .focus
+            .as_ref()
+            .and_then(|f| f.client())
+            .map(|c| c.equals(client))
+            .unwrap_or(false)
+    }
+
     /// Register a new keyboard to this handler
     ///
     /// The keymap will automatically be sent to it

src/wayland/seat/mod.rs

@@ -64,16 +64,26 @@ pub use self::{
     pointer::{AxisFrame, PointerGrab, PointerHandle, PointerInnerHandle},
 };
 
-use wayland_server::{protocol::wl_seat, Display, Global, NewResource, Resource};
+use wayland_commons::utils::UserDataMap;
+
+use wayland_server::{
+    protocol::{wl_seat, wl_surface},
+    Display, Global, NewResource, Resource,
+};
 
 struct Inner {
-    log: ::slog::Logger,
-    name: String,
     pointer: Option<PointerHandle>,
     keyboard: Option<KeyboardHandle>,
     known_seats: Vec<Resource<wl_seat::WlSeat>>,
 }
 
+pub(crate) struct SeatArc {
+    inner: Mutex<Inner>,
+    user_data: UserDataMap,
+    pub(crate) log: ::slog::Logger,
+    name: String,
+}
+
 impl Inner {
     fn compute_caps(&self) -> wl_seat::Capability {
         let mut caps = wl_seat::Capability::empty();
@@ -101,9 +111,13 @@ impl Inner {
 ///
 /// It is directly inserted in the event loop by its `new` method.
 ///
+/// This is an handle to the inner logic, it can be cloned and shared accross
+/// threads.
+///
 /// See module-level documentation for details of use.
+#[derive(Clone)]
 pub struct Seat {
-    inner: Arc<Mutex<Inner>>,
+    pub(crate) arc: Arc<SeatArc>,
 }
 
 impl Seat {
@@ -120,20 +134,23 @@ impl Seat {
         L: Into<Option<::slog::Logger>>,
     {
         let log = ::slog_or_stdlog(logger);
-        let inner = Arc::new(Mutex::new(Inner {
+        let arc = Arc::new(SeatArc {
-            log: log.new(o!("smithay_module" => "seat_handler", "seat_name" => name.clone())),
+            inner: Mutex::new(Inner {
-            name,
                 pointer: None,
                 keyboard: None,
                 known_seats: Vec::new(),
-        }));
+            }),
-        let seat = Seat { inner: inner.clone() };
+            log: log.new(o!("smithay_module" => "seat_handler", "seat_name" => name.clone())),
+            name,
+            user_data: UserDataMap::new(),
+        });
+        let seat = Seat { arc: arc.clone() };
         let global = display.create_global(5, move |new_seat, _version| {
-            let seat = implement_seat(new_seat, inner.clone());
+            let seat = implement_seat(new_seat, arc.clone());
-            let mut inner = inner.lock().unwrap();
+            let mut inner = arc.inner.lock().unwrap();
             if seat.version() >= 2 {
                 seat.send(wl_seat::Event::Name {
-                    name: inner.name.clone(),
+                    name: arc.name.clone(),
                 });
             }
             seat.send(wl_seat::Event::Capabilities {
@@ -144,6 +161,16 @@ impl Seat {
         (seat, global)
     }
 
+    /// Attempt to retrieve a `Seat` from an existing resource
+    pub fn from_resource(seat: &Resource<wl_seat::WlSeat>) -> Option<Seat> {
+        seat.user_data::<Arc<SeatArc>>().cloned().map(|arc| Seat { arc })
+    }
+
+    /// Acces the `UserDataMap` associated with this `Seat`
+    pub fn user_data(&self) -> &UserDataMap {
+        &self.arc.user_data
+    }
+
     /// Adds the pointer capability to this seat
     ///
     /// You are provided a `PointerHandle`, which allows you to send input events
@@ -153,7 +180,7 @@ impl Seat {
     /// will overwrite it, and will be seen by the clients as if the
     /// mouse was unplugged and a new one was plugged.
     pub fn add_pointer(&mut self) -> PointerHandle {
-        let mut inner = self.inner.lock().unwrap();
+        let mut inner = self.arc.inner.lock().unwrap();
         let pointer = self::pointer::create_pointer_handler();
         if inner.pointer.is_some() {
             // there is already a pointer, remove it and notify the clients
@@ -166,11 +193,16 @@ impl Seat {
         pointer
     }
 
+    /// Access the pointer of this seat if any
+    pub fn get_pointer(&self) -> Option<PointerHandle> {
+        self.arc.inner.lock().unwrap().pointer.clone()
+    }
+
     /// Remove the pointer capability from this seat
     ///
     /// Clients will be appropriately notified.
     pub fn remove_pointer(&mut self) {
-        let mut inner = self.inner.lock().unwrap();
+        let mut inner = self.arc.inner.lock().unwrap();
         if inner.pointer.is_some() {
             inner.pointer = None;
             inner.send_all_caps();
@@ -205,18 +237,32 @@ impl Seat {
     ///         },
     ///         1000,
     ///         500,
+    ///         |seat, focus| {
+    ///             /* This closure is called whenever the keyboard focus
+    ///              * changes, with the new focus as argument */
+    ///         }
     ///     )
     ///     .expect("Failed to initialize the keyboard");
     /// ```
-    pub fn add_keyboard(
+    pub fn add_keyboard<F>(
         &mut self,
         xkb_config: keyboard::XkbConfig,
         repeat_delay: i32,
         repeat_rate: i32,
-    ) -> Result<KeyboardHandle, KeyboardError> {
+        mut focus_hook: F,
-        let mut inner = self.inner.lock().unwrap();
+    ) -> Result<KeyboardHandle, KeyboardError>
-        let keyboard =
+    where
-            self::keyboard::create_keyboard_handler(xkb_config, repeat_delay, repeat_rate, &inner.log)?;
+        F: FnMut(&Seat, Option<&Resource<wl_surface::WlSurface>>) + 'static,
+    {
+        let me = self.clone();
+        let mut inner = self.arc.inner.lock().unwrap();
+        let keyboard = self::keyboard::create_keyboard_handler(
+            xkb_config,
+            repeat_delay,
+            repeat_rate,
+            &self.arc.log,
+            move |focus| focus_hook(&me, focus),
+        )?;
         if inner.keyboard.is_some() {
             // there is already a keyboard, remove it and notify the clients
             // of the change
@@ -228,11 +274,16 @@ impl Seat {
         Ok(keyboard)
     }
 
+    /// Access the keyboard of this seat if any
+    pub fn get_keyboard(&self) -> Option<KeyboardHandle> {
+        self.arc.inner.lock().unwrap().keyboard.clone()
+    }
+
     /// Remove the keyboard capability from this seat
     ///
     /// Clients will be appropriately notified.
     pub fn remove_keyboard(&mut self) {
-        let mut inner = self.inner.lock().unwrap();
+        let mut inner = self.arc.inner.lock().unwrap();
         if inner.keyboard.is_some() {
             inner.keyboard = None;
             inner.send_all_caps();
@@ -241,19 +292,23 @@ impl Seat {
 
     /// Checks whether a given `WlSeat` is associated with this `Seat`
     pub fn owns(&self, seat: &Resource<wl_seat::WlSeat>) -> bool {
-        let inner = self.inner.lock().unwrap();
+        let inner = self.arc.inner.lock().unwrap();
         inner.known_seats.iter().any(|s| s.equals(seat))
     }
 }
 
-fn implement_seat(
+impl ::std::cmp::PartialEq for Seat {
-    new_seat: NewResource<wl_seat::WlSeat>,
+    fn eq(&self, other: &Seat) -> bool {
-    inner: Arc<Mutex<Inner>>,
+        Arc::ptr_eq(&self.arc, &other.arc)
-) -> Resource<wl_seat::WlSeat> {
+    }
-    let dest_inner = inner.clone();
+}
+
+fn implement_seat(new_seat: NewResource<wl_seat::WlSeat>, arc: Arc<SeatArc>) -> Resource<wl_seat::WlSeat> {
+    let dest_arc = arc.clone();
     new_seat.implement(
-        move |request, _seat| {
+        move |request, seat| {
-            let inner = inner.lock().unwrap();
+            let arc = seat.user_data::<Arc<SeatArc>>().unwrap();
+            let inner = arc.inner.lock().unwrap();
             match request {
                 wl_seat::Request::GetPointer { id } => {
                     let pointer = self::pointer::implement_pointer(id, inner.pointer.as_ref());
@@ -281,12 +336,13 @@ fn implement_seat(
             }
         },
         Some(move |seat| {
-            dest_inner
+            dest_arc
+                .inner
                 .lock()
                 .unwrap()
                 .known_seats
                 .retain(|s| !s.equals(&seat));
         }),
-        (),
+        arc,
     )
 }

src/wayland/seat/pointer.rs

@@ -18,8 +18,10 @@ enum GrabStatus {
 struct PointerInternal {
     known_pointers: Vec<Resource<WlPointer>>,
     focus: Option<(Resource<WlSurface>, (f64, f64))>,
+    pending_focus: Option<(Resource<WlSurface>, (f64, f64))>,
     location: (f64, f64),
     grab: GrabStatus,
+    pressed_buttons: Vec<u32>,
 }
 
 impl PointerInternal {
@@ -27,8 +29,10 @@ impl PointerInternal {
         PointerInternal {
             known_pointers: Vec::new(),
             focus: None,
+            pending_focus: None,
             location: (0.0, 0.0),
             grab: GrabStatus::None,
+            pressed_buttons: Vec::new(),
         }
     }
 
@@ -136,7 +140,9 @@ impl PointerHandle {
         serial: u32,
         time: u32,
     ) {
-        self.inner.lock().unwrap().with_grab(move |mut handle, grab| {
+        let mut inner = self.inner.lock().unwrap();
+        inner.pending_focus = focus.clone();
+        inner.with_grab(move |mut handle, grab| {
             grab.motion(&mut handle, location, focus, serial, time);
         });
     }
@@ -146,7 +152,16 @@ impl PointerHandle {
     /// This will internally send the appropriate button event to the client
     /// objects matching with the currently focused surface.
     pub fn button(&self, button: u32, state: ButtonState, serial: u32, time: u32) {
-        self.inner.lock().unwrap().with_grab(|mut handle, grab| {
+        let mut inner = self.inner.lock().unwrap();
+        match state {
+            ButtonState::Pressed => {
+                inner.pressed_buttons.push(button);
+            }
+            ButtonState::Released => {
+                inner.pressed_buttons.retain(|b| *b != button);
+            }
+        }
+        inner.with_grab(|mut handle, grab| {
             grab.button(&mut handle, button, state, serial, time);
         });
     }
@@ -215,8 +230,14 @@ impl<'a> PointerInnerHandle<'a> {
     }
 
     /// Remove any current grab on this pointer, resetting it to the default behavior
-    pub fn unset_grab(&mut self) {
+    ///
+    /// This will also restore the focus of the underlying pointer
+    pub fn unset_grab(&mut self, serial: u32, time: u32) {
         self.inner.grab = GrabStatus::None;
+        // restore the focus
+        let location = self.current_location();
+        let focus = self.inner.pending_focus.take();
+        self.motion(location, focus, serial, time);
     }
 
     /// Access the current focus of this pointer
@@ -229,6 +250,14 @@ impl<'a> PointerInnerHandle<'a> {
         self.inner.location
     }
 
+    /// A list of the currently physically pressed buttons
+    ///
+    /// This still includes buttons that your grab have intercepted and not sent
+    /// to the client.
+    pub fn current_pressed(&self) -> &[u32] {
+        &self.inner.pressed_buttons
+    }
+
     /// Notify that the pointer moved
     ///
     /// You provide the new location of the pointer, in the form of:
@@ -542,7 +571,6 @@ impl PointerGrab for DefaultGrab {
         handle.set_grab(
             serial,
             ClickGrab {
-                buttons: vec![button],
                 current_focus,
                 pending_focus: None,
             },
@@ -559,7 +587,6 @@ impl PointerGrab for DefaultGrab {
 // In case the user maintains several simultaneous clicks, release
 // the grab once all are released.
 struct ClickGrab {
-    buttons: Vec<u32>,
     current_focus: Option<(Resource<WlSurface>, (f64, f64))>,
     pending_focus: Option<(Resource<WlSurface>, (f64, f64))>,
 }
@@ -585,17 +612,10 @@ impl PointerGrab for ClickGrab {
         serial: u32,
         time: u32,
     ) {
-        match state {
-            ButtonState::Pressed => self.buttons.push(button),
-            ButtonState::Released => self.buttons.retain(|b| *b != button),
-        }
         handle.button(button, state, serial, time);
-        if self.buttons.is_empty() {
+        if handle.current_pressed().len() == 0 {
             // no more buttons are pressed, release the grab
-            handle.unset_grab();
+            handle.unset_grab(serial, time);
-            // restore the focus
-            let location = handle.current_location();
-            handle.motion(location, self.pending_focus.clone(), serial, time);
         }
     }
     fn axis(&mut self, handle: &mut PointerInnerHandle, details: AxisFrame) {