gecko-dev/widget/gtk/nsDragService.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=4 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsDragService.h"
#include "nsArrayUtils.h"
#include "nsIObserverService.h"
#include "nsWidgetsCID.h"
#include "nsWindow.h"
#include "nsSystemInfo.h"
#include "nsXPCOM.h"
#include "nsISupportsPrimitives.h"
#include "nsIIOService.h"
#include "nsIFileURL.h"
#include "nsNetUtil.h"
#include "mozilla/Logging.h"
#include "nsTArray.h"
#include "nsPrimitiveHelpers.h"
#include "prtime.h"
#include "prthread.h"
#include <dlfcn.h>
#include <gtk/gtk.h>
#include <gdk/gdkx.h>
#include "nsCRT.h"
#include "mozilla/BasicEvents.h"
#include "mozilla/Services.h"
#include "mozilla/ClearOnShutdown.h"
#include "mozilla/PresShell.h"

#include "gfxXlibSurface.h"
#include "gfxContext.h"
#include "nsImageToPixbuf.h"
#include "nsPresContext.h"
#include "nsIContent.h"
#include "mozilla/dom/Document.h"
#include "nsViewManager.h"
#include "nsIFrame.h"
#include "nsGtkUtils.h"
#include "nsGtkKeyUtils.h"
#include "mozilla/gfx/2D.h"
#include "gfxPlatform.h"
#include "ScreenHelperGTK.h"
#include "nsArrayUtils.h"
#ifdef MOZ_WAYLAND
#  include "nsClipboardWayland.h"
#endif

using namespace mozilla;
using namespace mozilla::gfx;

#define NS_SYSTEMINFO_CONTRACTID "@mozilla.org/system-info;1"

// This sets how opaque the drag image is
#define DRAG_IMAGE_ALPHA_LEVEL 0.5

// These values are copied from GtkDragResult (rather than using GtkDragResult
// directly) so that this code can be compiled against versions of GTK+ that
// do not have GtkDragResult.
// GtkDragResult is available from GTK+ version 2.12.
enum { MOZ_GTK_DRAG_RESULT_SUCCESS, MOZ_GTK_DRAG_RESULT_NO_TARGET };

static LazyLogModule sDragLm("nsDragService");

// data used for synthetic periodic motion events sent to the source widget
// grabbing real events for the drag.
static guint sMotionEventTimerID;
static GdkEvent* sMotionEvent;
static GtkWidget* sGrabWidget;

static const char gMimeListType[] = "application/x-moz-internal-item-list";
static const char gMozUrlType[] = "_NETSCAPE_URL";
static const char gTextUriListType[] = "text/uri-list";
static const char gTextPlainUTF8Type[] = "text/plain;charset=utf-8";
static const char gXdndDirectSaveType[] = "XdndDirectSave0";

static void invisibleSourceDragBegin(GtkWidget* aWidget,
                                     GdkDragContext* aContext, gpointer aData);

static void invisibleSourceDragEnd(GtkWidget* aWidget, GdkDragContext* aContext,
                                   gpointer aData);

static gboolean invisibleSourceDragFailed(GtkWidget* aWidget,
                                          GdkDragContext* aContext,
                                          gint aResult, gpointer aData);

static void invisibleSourceDragDataGet(GtkWidget* aWidget,
                                       GdkDragContext* aContext,
                                       GtkSelectionData* aSelectionData,
                                       guint aInfo, guint32 aTime,
                                       gpointer aData);

nsDragService::nsDragService()
    : mScheduledTask(eDragTaskNone),
      mTaskSource(0)
#ifdef MOZ_WAYLAND
      ,
      mPendingWaylandDragContext(nullptr),
      mTargetWaylandDragContext(nullptr)
#endif
{
  // We have to destroy the hidden widget before the event loop stops
  // running.
  nsCOMPtr<nsIObserverService> obsServ =
      mozilla::services::GetObserverService();
  obsServ->AddObserver(this, "quit-application", false);

  // our hidden source widget
  // Using an offscreen window works around bug 983843.
  mHiddenWidget = gtk_offscreen_window_new();
  // make sure that the widget is realized so that
  // we can use it as a drag source.
  gtk_widget_realize(mHiddenWidget);
  // hook up our internal signals so that we can get some feedback
  // from our drag source
  g_signal_connect(mHiddenWidget, "drag_begin",
                   G_CALLBACK(invisibleSourceDragBegin), this);
  g_signal_connect(mHiddenWidget, "drag_data_get",
                   G_CALLBACK(invisibleSourceDragDataGet), this);
  g_signal_connect(mHiddenWidget, "drag_end",
                   G_CALLBACK(invisibleSourceDragEnd), this);
  // drag-failed is available from GTK+ version 2.12
  guint dragFailedID =
      g_signal_lookup("drag-failed", G_TYPE_FROM_INSTANCE(mHiddenWidget));
  if (dragFailedID) {
    g_signal_connect_closure_by_id(
        mHiddenWidget, dragFailedID, 0,
        g_cclosure_new(G_CALLBACK(invisibleSourceDragFailed), this, nullptr),
        FALSE);
  }

  // set up our logging module
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::nsDragService"));
  mCanDrop = false;
  mTargetDragDataReceived = false;
  mTargetDragData = 0;
  mTargetDragDataLen = 0;
}

nsDragService::~nsDragService() {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::~nsDragService"));
  if (mTaskSource) g_source_remove(mTaskSource);
}

NS_IMPL_ISUPPORTS_INHERITED(nsDragService, nsBaseDragService, nsIObserver)

mozilla::StaticRefPtr<nsDragService> sDragServiceInstance;
/* static */
already_AddRefed<nsDragService> nsDragService::GetInstance() {
  if (gfxPlatform::IsHeadless()) {
    return nullptr;
  }
  if (!sDragServiceInstance) {
    sDragServiceInstance = new nsDragService();
    ClearOnShutdown(&sDragServiceInstance);
  }

  RefPtr<nsDragService> service = sDragServiceInstance.get();
  return service.forget();
}

// nsIObserver

NS_IMETHODIMP
nsDragService::Observe(nsISupports* aSubject, const char* aTopic,
                       const char16_t* aData) {
  if (!nsCRT::strcmp(aTopic, "quit-application")) {
    MOZ_LOG(sDragLm, LogLevel::Debug,
            ("nsDragService::Observe(\"quit-application\")"));
    if (mHiddenWidget) {
      gtk_widget_destroy(mHiddenWidget);
      mHiddenWidget = 0;
    }
    TargetResetData();
  } else {
    MOZ_ASSERT_UNREACHABLE("unexpected topic");
    return NS_ERROR_UNEXPECTED;
  }

  return NS_OK;
}

// Support for periodic drag events

// http://www.whatwg.org/specs/web-apps/current-work/multipage/dnd.html#drag-and-drop-processing-model
// and the Xdnd protocol both recommend that drag events are sent periodically,
// but GTK does not normally provide this.
//
// Here GTK is periodically stimulated by copies of the most recent mouse
// motion events so as to send drag position messages to the destination when
// appropriate (after it has received a status event from the previous
// message).
//
// (If events were sent only on the destination side then the destination
// would have no message to which it could reply with a drag status.  Without
// sending a drag status to the source, the destination would not be able to
// change its feedback re whether it could accept the drop, and so the
// source's behavior on drop will not be consistent.)

static gboolean DispatchMotionEventCopy(gpointer aData) {
  // Clear the timer id before OnSourceGrabEventAfter is called during event
  // dispatch.
  sMotionEventTimerID = 0;

  GdkEvent* event = sMotionEvent;
  sMotionEvent = nullptr;
  // If there is no longer a grab on the widget, then the drag is over and
  // there is no need to continue drag motion.
  if (gtk_widget_has_grab(sGrabWidget)) {
    gtk_propagate_event(sGrabWidget, event);
  }
  gdk_event_free(event);

  // Cancel this timer;
  // We've already started another if the motion event was dispatched.
  return FALSE;
}

static void OnSourceGrabEventAfter(GtkWidget* widget, GdkEvent* event,
                                   gpointer user_data) {
  // If there is no longer a grab on the widget, then the drag motion is
  // over (though the data may not be fetched yet).
  if (!gtk_widget_has_grab(sGrabWidget)) return;

  if (event->type == GDK_MOTION_NOTIFY) {
    if (sMotionEvent) {
      gdk_event_free(sMotionEvent);
    }
    sMotionEvent = gdk_event_copy(event);

    // Update the cursor position.  The last of these recorded gets used for
    // the eDragEnd event.
    nsDragService* dragService = static_cast<nsDragService*>(user_data);
    gint scale = mozilla::widget::ScreenHelperGTK::GetGTKMonitorScaleFactor();
    auto p = LayoutDeviceIntPoint::Round(event->motion.x_root * scale,
                                         event->motion.y_root * scale);
    dragService->SetDragEndPoint(p);
  } else if (sMotionEvent &&
             (event->type == GDK_KEY_PRESS || event->type == GDK_KEY_RELEASE)) {
    // Update modifier state from key events.
    sMotionEvent->motion.state = event->key.state;
  } else {
    return;
  }

  if (sMotionEventTimerID) {
    g_source_remove(sMotionEventTimerID);
  }

  // G_PRIORITY_DEFAULT_IDLE is lower priority than GDK's redraw idle source
  // and lower than GTK's idle source that sends drag position messages after
  // motion-notify signals.
  //
  // http://www.whatwg.org/specs/web-apps/current-work/multipage/dnd.html#drag-and-drop-processing-model
  // recommends an interval of 350ms +/- 200ms.
  sMotionEventTimerID = g_timeout_add_full(
      G_PRIORITY_DEFAULT_IDLE, 350, DispatchMotionEventCopy, nullptr, nullptr);
}

static GtkWindow* GetGtkWindow(dom::Document* aDocument) {
  if (!aDocument) return nullptr;

  PresShell* presShell = aDocument->GetPresShell();
  if (!presShell) {
    return nullptr;
  }

  RefPtr<nsViewManager> vm = presShell->GetViewManager();
  if (!vm) return nullptr;

  nsCOMPtr<nsIWidget> widget;
  vm->GetRootWidget(getter_AddRefs(widget));
  if (!widget) return nullptr;

  GtkWidget* gtkWidget =
      static_cast<nsWindow*>(widget.get())->GetMozContainerWidget();
  if (!gtkWidget) return nullptr;

  GtkWidget* toplevel = nullptr;
  toplevel = gtk_widget_get_toplevel(gtkWidget);
  if (!GTK_IS_WINDOW(toplevel)) return nullptr;

  return GTK_WINDOW(toplevel);
}

// nsIDragService

NS_IMETHODIMP
nsDragService::InvokeDragSession(
    nsINode* aDOMNode, nsIPrincipal* aPrincipal, nsIContentSecurityPolicy* aCsp,
    nsIArray* aArrayTransferables, uint32_t aActionType,
    nsContentPolicyType aContentPolicyType = nsIContentPolicy::TYPE_OTHER) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::InvokeDragSession"));

  // If the previous source drag has not yet completed, signal handlers need
  // to be removed from sGrabWidget and dragend needs to be dispatched to
  // the source node, but we can't call EndDragSession yet because we don't
  // know whether or not the drag succeeded.
  if (mSourceNode) return NS_ERROR_NOT_AVAILABLE;

  return nsBaseDragService::InvokeDragSession(aDOMNode, aPrincipal, aCsp,
                                              aArrayTransferables, aActionType,
                                              aContentPolicyType);
}

// nsBaseDragService
nsresult nsDragService::InvokeDragSessionImpl(
    nsIArray* aArrayTransferables, const Maybe<CSSIntRegion>& aRegion,
    uint32_t aActionType) {
  // make sure that we have an array of transferables to use
  if (!aArrayTransferables) return NS_ERROR_INVALID_ARG;
  // set our reference to the transferables.  this will also addref
  // the transferables since we're going to hang onto this beyond the
  // length of this call
  mSourceDataItems = aArrayTransferables;
  // get the list of items we offer for drags
  GtkTargetList* sourceList = GetSourceList();

  if (!sourceList) return NS_OK;

  // save our action type
  GdkDragAction action = GDK_ACTION_DEFAULT;

  if (aActionType & DRAGDROP_ACTION_COPY)
    action = (GdkDragAction)(action | GDK_ACTION_COPY);
  if (aActionType & DRAGDROP_ACTION_MOVE)
    action = (GdkDragAction)(action | GDK_ACTION_MOVE);
  if (aActionType & DRAGDROP_ACTION_LINK)
    action = (GdkDragAction)(action | GDK_ACTION_LINK);

  // Create a fake event for the drag so we can pass the time (so to speak).
  // If we don't do this, then, when the timestamp for the pending button
  // release event is used for the ungrab, the ungrab can fail due to the
  // timestamp being _earlier_ than CurrentTime.
  GdkEvent event;
  memset(&event, 0, sizeof(GdkEvent));
  event.type = GDK_BUTTON_PRESS;
  event.button.window = gtk_widget_get_window(mHiddenWidget);
  event.button.time = nsWindow::GetLastUserInputTime();

  // Put the drag widget in the window group of the source node so that the
  // gtk_grab_add during gtk_drag_begin is effective.
  // gtk_window_get_group(nullptr) returns the default window group.
  GtkWindowGroup* window_group =
      gtk_window_get_group(GetGtkWindow(mSourceDocument));
  gtk_window_group_add_window(window_group, GTK_WINDOW(mHiddenWidget));

#ifdef MOZ_WIDGET_GTK
  // Get device for event source
  GdkDisplay* display = gdk_display_get_default();
  GdkDeviceManager* device_manager = gdk_display_get_device_manager(display);
  event.button.device = gdk_device_manager_get_client_pointer(device_manager);
#endif

  // start our drag.
  GdkDragContext* context =
      gtk_drag_begin(mHiddenWidget, sourceList, action, 1, &event);

  nsresult rv;
  if (context) {
    StartDragSession();

    // GTK uses another hidden window for receiving mouse events.
    sGrabWidget = gtk_window_group_get_current_grab(window_group);
    if (sGrabWidget) {
      g_object_ref(sGrabWidget);
      // Only motion and key events are required but connect to
      // "event-after" as this is never blocked by other handlers.
      g_signal_connect(sGrabWidget, "event-after",
                       G_CALLBACK(OnSourceGrabEventAfter), this);
    }
    // We don't have a drag end point yet.
    mEndDragPoint = LayoutDeviceIntPoint(-1, -1);
    rv = NS_OK;
  } else {
    rv = NS_ERROR_FAILURE;
  }

  gtk_target_list_unref(sourceList);

  return rv;
}

bool nsDragService::SetAlphaPixmap(SourceSurface* aSurface,
                                   GdkDragContext* aContext, int32_t aXOffset,
                                   int32_t aYOffset,
                                   const LayoutDeviceIntRect& dragRect) {
  GdkScreen* screen = gtk_widget_get_screen(mHiddenWidget);

  // Transparent drag icons need, like a lot of transparency-related things,
  // a compositing X window manager
  if (!gdk_screen_is_composited(screen)) return false;

#ifdef cairo_image_surface_create
#  error "Looks like we're including Mozilla's cairo instead of system cairo"
#endif
  // Prior to GTK 3.9.12, cairo surfaces passed into gtk_drag_set_icon_surface
  // had their shape information derived from the alpha channel and used with
  // the X SHAPE extension instead of being displayed as an ARGB window.
  // See bug 1249604.
  if (gtk_check_version(3, 9, 12)) return false;

  // TODO: grab X11 pixmap or image data instead of expensive readback.
  cairo_surface_t* surf = cairo_image_surface_create(
      CAIRO_FORMAT_ARGB32, dragRect.width, dragRect.height);
  if (!surf) return false;

  RefPtr<DrawTarget> dt = gfxPlatform::CreateDrawTargetForData(
      cairo_image_surface_get_data(surf),
      nsIntSize(dragRect.width, dragRect.height),
      cairo_image_surface_get_stride(surf), SurfaceFormat::B8G8R8A8);
  if (!dt) return false;

  dt->ClearRect(Rect(0, 0, dragRect.width, dragRect.height));
  dt->DrawSurface(
      aSurface, Rect(0, 0, dragRect.width, dragRect.height),
      Rect(0, 0, dragRect.width, dragRect.height), DrawSurfaceOptions(),
      DrawOptions(DRAG_IMAGE_ALPHA_LEVEL, CompositionOp::OP_SOURCE));

  cairo_surface_mark_dirty(surf);
  cairo_surface_set_device_offset(surf, -aXOffset, -aYOffset);

  // Ensure that the surface is drawn at the correct scale on HiDPI displays.
  static auto sCairoSurfaceSetDeviceScalePtr =
      (void (*)(cairo_surface_t*, double, double))dlsym(
          RTLD_DEFAULT, "cairo_surface_set_device_scale");
  if (sCairoSurfaceSetDeviceScalePtr) {
    gint scale = mozilla::widget::ScreenHelperGTK::GetGTKMonitorScaleFactor();
    sCairoSurfaceSetDeviceScalePtr(surf, scale, scale);
  }

  gtk_drag_set_icon_surface(aContext, surf);
  cairo_surface_destroy(surf);
  return true;
}

NS_IMETHODIMP
nsDragService::StartDragSession() {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::StartDragSession"));
  return nsBaseDragService::StartDragSession();
}

NS_IMETHODIMP
nsDragService::EndDragSession(bool aDoneDrag, uint32_t aKeyModifiers) {
  MOZ_LOG(sDragLm, LogLevel::Debug,
          ("nsDragService::EndDragSession %d", aDoneDrag));

  if (sGrabWidget) {
    g_signal_handlers_disconnect_by_func(
        sGrabWidget, FuncToGpointer(OnSourceGrabEventAfter), this);
    g_object_unref(sGrabWidget);
    sGrabWidget = nullptr;

    if (sMotionEventTimerID) {
      g_source_remove(sMotionEventTimerID);
      sMotionEventTimerID = 0;
    }
    if (sMotionEvent) {
      gdk_event_free(sMotionEvent);
      sMotionEvent = nullptr;
    }
  }

  // unset our drag action
  SetDragAction(DRAGDROP_ACTION_NONE);

  // We're done with the drag context.
  mTargetDragContextForRemote = nullptr;
#ifdef MOZ_WAYLAND
  mTargetWaylandDragContextForRemote = nullptr;
#endif

  return nsBaseDragService::EndDragSession(aDoneDrag, aKeyModifiers);
}

// nsIDragSession
NS_IMETHODIMP
nsDragService::SetCanDrop(bool aCanDrop) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::SetCanDrop %d", aCanDrop));
  mCanDrop = aCanDrop;
  return NS_OK;
}

NS_IMETHODIMP
nsDragService::GetCanDrop(bool* aCanDrop) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::GetCanDrop"));
  *aCanDrop = mCanDrop;
  return NS_OK;
}

static void UTF16ToNewUTF8(const char16_t* aUTF16, uint32_t aUTF16Len,
                           char** aUTF8, uint32_t* aUTF8Len) {
  nsDependentSubstring utf16(aUTF16, aUTF16Len);
  *aUTF8 = ToNewUTF8String(utf16, aUTF8Len);
}

static void UTF8ToNewUTF16(const char* aUTF8, uint32_t aUTF8Len,
                           char16_t** aUTF16, uint32_t* aUTF16Len) {
  nsDependentCSubstring utf8(aUTF8, aUTF8Len);
  *aUTF16 = UTF8ToNewUnicode(utf8, aUTF16Len);
}

// count the number of URIs in some text/uri-list format data.
static uint32_t CountTextUriListItems(const char* data, uint32_t datalen) {
  const char* p = data;
  const char* endPtr = p + datalen;
  uint32_t count = 0;

  while (p < endPtr) {
    // skip whitespace (if any)
    while (p < endPtr && *p != '\0' && isspace(*p)) p++;
    // if we aren't at the end of the line ...
    if (p != endPtr && *p != '\0' && *p != '\n' && *p != '\r') count++;
    // skip to the end of the line
    while (p < endPtr && *p != '\0' && *p != '\n') p++;
    p++;  // skip the actual newline as well.
  }
  return count;
}

// extract an item from text/uri-list formatted data and convert it to
// unicode.
static void GetTextUriListItem(const char* data, uint32_t datalen,
                               uint32_t aItemIndex, char16_t** convertedText,
                               uint32_t* convertedTextLen) {
  const char* p = data;
  const char* endPtr = p + datalen;
  unsigned int count = 0;

  *convertedText = nullptr;
  while (p < endPtr) {
    // skip whitespace (if any)
    while (p < endPtr && *p != '\0' && isspace(*p)) p++;
    // if we aren't at the end of the line, we have a url
    if (p != endPtr && *p != '\0' && *p != '\n' && *p != '\r') count++;
    // this is the item we are after ...
    if (aItemIndex + 1 == count) {
      const char* q = p;
      while (q < endPtr && *q != '\0' && *q != '\n' && *q != '\r') q++;
      UTF8ToNewUTF16(p, q - p, convertedText, convertedTextLen);
      break;
    }
    // skip to the end of the line
    while (p < endPtr && *p != '\0' && *p != '\n') p++;
    p++;  // skip the actual newline as well.
  }

  // didn't find the desired item, so just pass the whole lot
  if (!*convertedText) {
    UTF8ToNewUTF16(data, datalen, convertedText, convertedTextLen);
  }
}

NS_IMETHODIMP
nsDragService::GetNumDropItems(uint32_t* aNumItems) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::GetNumDropItems"));

  if (!mTargetWidget) {
    MOZ_LOG(sDragLm, LogLevel::Debug, ("*** warning: GetNumDropItems \
               called without a valid target widget!\n"));
    *aNumItems = 0;
    return NS_OK;
  }

#ifdef MOZ_WAYLAND
  // TODO: Wayland implementation of text/uri-list.
  if (!mTargetDragContext) {
    *aNumItems = 1;
    return NS_OK;
  }
#endif

  bool isList = IsTargetContextList();
  if (isList)
    mSourceDataItems->GetLength(aNumItems);
  else {
    GdkAtom gdkFlavor = gdk_atom_intern(gTextUriListType, FALSE);
    GetTargetDragData(gdkFlavor);
    if (mTargetDragData) {
      const char* data = reinterpret_cast<char*>(mTargetDragData);
      *aNumItems = CountTextUriListItems(data, mTargetDragDataLen);
    } else
      *aNumItems = 1;
  }
  MOZ_LOG(sDragLm, LogLevel::Debug, ("%d items", *aNumItems));
  return NS_OK;
}

NS_IMETHODIMP
nsDragService::GetData(nsITransferable* aTransferable, uint32_t aItemIndex) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::GetData %d", aItemIndex));

  // make sure that we have a transferable
  if (!aTransferable) return NS_ERROR_INVALID_ARG;

  if (!mTargetWidget) {
    MOZ_LOG(sDragLm, LogLevel::Debug, ("*** warning: GetData \
               called without a valid target widget!\n"));
    return NS_ERROR_FAILURE;
  }

  // get flavor list that includes all acceptable flavors (including
  // ones obtained through conversion).
  nsTArray<nsCString> flavors;
  nsresult rv = aTransferable->FlavorsTransferableCanImport(flavors);
  if (NS_FAILED(rv)) return rv;

  // check to see if this is an internal list
  bool isList = IsTargetContextList();

  if (isList) {
    MOZ_LOG(sDragLm, LogLevel::Debug, ("it's a list..."));
    // find a matching flavor
    for (uint32_t i = 0; i < flavors.Length(); ++i) {
      nsCString& flavorStr = flavors[i];
      MOZ_LOG(sDragLm, LogLevel::Debug, ("flavor is %s\n", flavorStr.get()));
      // get the item with the right index
      nsCOMPtr<nsITransferable> item =
          do_QueryElementAt(mSourceDataItems, aItemIndex);
      if (!item) continue;

      nsCOMPtr<nsISupports> data;
      MOZ_LOG(sDragLm, LogLevel::Debug,
              ("trying to get transfer data for %s\n", flavorStr.get()));
      rv = item->GetTransferData(flavorStr.get(), getter_AddRefs(data));
      if (NS_FAILED(rv)) {
        MOZ_LOG(sDragLm, LogLevel::Debug, ("failed.\n"));
        continue;
      }
      MOZ_LOG(sDragLm, LogLevel::Debug, ("succeeded.\n"));
      rv = aTransferable->SetTransferData(flavorStr.get(), data);
      if (NS_FAILED(rv)) {
        MOZ_LOG(sDragLm, LogLevel::Debug,
                ("fail to set transfer data into transferable!\n"));
        continue;
      }
      // ok, we got the data
      return NS_OK;
    }
    // if we got this far, we failed
    return NS_ERROR_FAILURE;
  }

  // Now walk down the list of flavors. When we find one that is
  // actually present, copy out the data into the transferable in that
  // format. SetTransferData() implicitly handles conversions.
  for (uint32_t i = 0; i < flavors.Length(); ++i) {
    nsCString& flavorStr = flavors[i];
    GdkAtom gdkFlavor = gdk_atom_intern(flavorStr.get(), FALSE);
    MOZ_LOG(sDragLm, LogLevel::Debug,
            ("looking for data in type %s, gdk flavor %p\n", flavorStr.get(),
             gdkFlavor));
    bool dataFound = false;
    if (gdkFlavor) {
      GetTargetDragData(gdkFlavor);
    }
    if (mTargetDragData) {
      MOZ_LOG(sDragLm, LogLevel::Debug, ("dataFound = true\n"));
      dataFound = true;
    } else {
      MOZ_LOG(sDragLm, LogLevel::Debug, ("dataFound = false\n"));

      // Dragging and dropping from the file manager would cause us
      // to parse the source text as a nsIFile URL.
      if (flavorStr.EqualsLiteral(kFileMime)) {
        gdkFlavor = gdk_atom_intern(kTextMime, FALSE);
        GetTargetDragData(gdkFlavor);
        if (!mTargetDragData) {
          gdkFlavor = gdk_atom_intern(gTextUriListType, FALSE);
          GetTargetDragData(gdkFlavor);
        }
        if (mTargetDragData) {
          const char* text = static_cast<char*>(mTargetDragData);
          char16_t* convertedText = nullptr;
          uint32_t convertedTextLen = 0;

          GetTextUriListItem(text, mTargetDragDataLen, aItemIndex,
                             &convertedText, &convertedTextLen);

          if (convertedText) {
            nsCOMPtr<nsIIOService> ioService = do_GetIOService(&rv);
            nsCOMPtr<nsIURI> fileURI;
            rv = ioService->NewURI(NS_ConvertUTF16toUTF8(convertedText),
                                   nullptr, nullptr, getter_AddRefs(fileURI));
            if (NS_SUCCEEDED(rv)) {
              nsCOMPtr<nsIFileURL> fileURL = do_QueryInterface(fileURI, &rv);
              if (NS_SUCCEEDED(rv)) {
                nsCOMPtr<nsIFile> file;
                rv = fileURL->GetFile(getter_AddRefs(file));
                if (NS_SUCCEEDED(rv)) {
                  // The common wrapping code at the end of
                  // this function assumes the data is text
                  // and calls text-specific operations.
                  // Make a secret hideout here for nsIFile
                  // objects and return early.
                  aTransferable->SetTransferData(flavorStr.get(), file);
                  g_free(convertedText);
                  return NS_OK;
                }
              }
            }
            g_free(convertedText);
          }
          continue;
        }
      }

      // if we are looking for text/unicode and we fail to find it
      // on the clipboard first, try again with text/plain. If that
      // is present, convert it to unicode.
      if (flavorStr.EqualsLiteral(kUnicodeMime)) {
        MOZ_LOG(sDragLm, LogLevel::Debug,
                ("we were looking for text/unicode... \
                       trying with text/plain;charset=utf-8\n"));
        gdkFlavor = gdk_atom_intern(gTextPlainUTF8Type, FALSE);
        GetTargetDragData(gdkFlavor);
        if (mTargetDragData) {
          MOZ_LOG(sDragLm, LogLevel::Debug, ("Got textplain data\n"));
          const char* castedText = reinterpret_cast<char*>(mTargetDragData);
          char16_t* convertedText = nullptr;
          NS_ConvertUTF8toUTF16 ucs2string(castedText, mTargetDragDataLen);
          convertedText = ToNewUnicode(ucs2string);
          if (convertedText) {
            MOZ_LOG(sDragLm, LogLevel::Debug,
                    ("successfully converted plain text \
                               to unicode.\n"));
            // out with the old, in with the new
            g_free(mTargetDragData);
            mTargetDragData = convertedText;
            mTargetDragDataLen = ucs2string.Length() * 2;
            dataFound = true;
          }  // if plain text data on clipboard
        } else {
          MOZ_LOG(sDragLm, LogLevel::Debug,
                  ("we were looking for text/unicode... \
                           trying again with text/plain\n"));
          gdkFlavor = gdk_atom_intern(kTextMime, FALSE);
          GetTargetDragData(gdkFlavor);
          if (mTargetDragData) {
            MOZ_LOG(sDragLm, LogLevel::Debug, ("Got textplain data\n"));
            const char* castedText = reinterpret_cast<char*>(mTargetDragData);
            char16_t* convertedText = nullptr;
            uint32_t convertedTextLen = 0;
            UTF8ToNewUTF16(castedText, mTargetDragDataLen, &convertedText,
                           &convertedTextLen);
            if (convertedText) {
              MOZ_LOG(sDragLm, LogLevel::Debug,
                      ("successfully converted plain text \
                                   to unicode.\n"));
              // out with the old, in with the new
              g_free(mTargetDragData);
              mTargetDragData = convertedText;
              mTargetDragDataLen = convertedTextLen * 2;
              dataFound = true;
            }  // if plain text data on clipboard
          }    // if plain text flavor present
        }      // if plain text charset=utf-8 flavor present
      }        // if looking for text/unicode

      // if we are looking for text/x-moz-url and we failed to find
      // it on the clipboard, try again with text/uri-list, and then
      // _NETSCAPE_URL
      if (flavorStr.EqualsLiteral(kURLMime)) {
        MOZ_LOG(sDragLm, LogLevel::Debug,
                ("we were looking for text/x-moz-url...\
                       trying again with text/uri-list\n"));
        gdkFlavor = gdk_atom_intern(gTextUriListType, FALSE);
        GetTargetDragData(gdkFlavor);
        if (mTargetDragData) {
          MOZ_LOG(sDragLm, LogLevel::Debug, ("Got text/uri-list data\n"));
          const char* data = reinterpret_cast<char*>(mTargetDragData);
          char16_t* convertedText = nullptr;
          uint32_t convertedTextLen = 0;

          GetTextUriListItem(data, mTargetDragDataLen, aItemIndex,
                             &convertedText, &convertedTextLen);

          if (convertedText) {
            MOZ_LOG(sDragLm, LogLevel::Debug, ("successfully converted \
                               _NETSCAPE_URL to unicode.\n"));
            // out with the old, in with the new
            g_free(mTargetDragData);
            mTargetDragData = convertedText;
            mTargetDragDataLen = convertedTextLen * 2;
            dataFound = true;
          }
        } else {
          MOZ_LOG(sDragLm, LogLevel::Debug,
                  ("failed to get text/uri-list data\n"));
        }
        if (!dataFound) {
          MOZ_LOG(sDragLm, LogLevel::Debug,
                  ("we were looking for text/x-moz-url...\
                           trying again with _NETSCAP_URL\n"));
          gdkFlavor = gdk_atom_intern(gMozUrlType, FALSE);
          GetTargetDragData(gdkFlavor);
          if (mTargetDragData) {
            MOZ_LOG(sDragLm, LogLevel::Debug, ("Got _NETSCAPE_URL data\n"));
            const char* castedText = reinterpret_cast<char*>(mTargetDragData);
            char16_t* convertedText = nullptr;
            uint32_t convertedTextLen = 0;
            UTF8ToNewUTF16(castedText, mTargetDragDataLen, &convertedText,
                           &convertedTextLen);
            if (convertedText) {
              MOZ_LOG(sDragLm, LogLevel::Debug,
                      ("successfully converted _NETSCAPE_URL \
                                   to unicode.\n"));
              // out with the old, in with the new
              g_free(mTargetDragData);
              mTargetDragData = convertedText;
              mTargetDragDataLen = convertedTextLen * 2;
              dataFound = true;
            }
          } else {
            MOZ_LOG(sDragLm, LogLevel::Debug,
                    ("failed to get _NETSCAPE_URL data\n"));
          }
        }
      }

    }  // else we try one last ditch effort to find our data

    if (dataFound) {
      if (!flavorStr.EqualsLiteral(kCustomTypesMime)) {
        // the DOM only wants LF, so convert from MacOS line endings
        // to DOM line endings.
        nsLinebreakHelpers::ConvertPlatformToDOMLinebreaks(
            flavorStr, &mTargetDragData,
            reinterpret_cast<int*>(&mTargetDragDataLen));
      }

      // put it into the transferable.
      nsCOMPtr<nsISupports> genericDataWrapper;
      nsPrimitiveHelpers::CreatePrimitiveForData(
          flavorStr, mTargetDragData, mTargetDragDataLen,
          getter_AddRefs(genericDataWrapper));
      aTransferable->SetTransferData(flavorStr.get(), genericDataWrapper);
      // we found one, get out of this loop!
      MOZ_LOG(sDragLm, LogLevel::Debug, ("dataFound and converted!\n"));
      break;
    }
  }

  return NS_OK;
}

NS_IMETHODIMP
nsDragService::IsDataFlavorSupported(const char* aDataFlavor, bool* _retval) {
  MOZ_LOG(sDragLm, LogLevel::Debug,
          ("nsDragService::IsDataFlavorSupported %s", aDataFlavor));
  if (!_retval) return NS_ERROR_INVALID_ARG;

  // set this to no by default
  *_retval = false;

  // check to make sure that we have a drag object set, here
  if (!mTargetWidget) {
    MOZ_LOG(sDragLm, LogLevel::Debug, ("*** warning: IsDataFlavorSupported \
               called without a valid target widget!\n"));
    return NS_OK;
  }

  // check to see if the target context is a list.
  bool isList = IsTargetContextList();
  // if it is, just look in the internal data since we are the source
  // for it.
  if (isList) {
    MOZ_LOG(sDragLm, LogLevel::Debug, ("It's a list.."));
    uint32_t numDragItems = 0;
    // if we don't have mDataItems we didn't start this drag so it's
    // an external client trying to fool us.
    if (!mSourceDataItems) return NS_OK;
    mSourceDataItems->GetLength(&numDragItems);
    for (uint32_t itemIndex = 0; itemIndex < numDragItems; ++itemIndex) {
      nsCOMPtr<nsITransferable> currItem =
          do_QueryElementAt(mSourceDataItems, itemIndex);
      if (currItem) {
        nsTArray<nsCString> flavors;
        currItem->FlavorsTransferableCanExport(flavors);
        for (uint32_t i = 0; i < flavors.Length(); ++i) {
          MOZ_LOG(sDragLm, LogLevel::Debug,
                  ("checking %s against %s\n", flavors[i].get(), aDataFlavor));
          if (flavors[i].Equals(aDataFlavor)) {
            MOZ_LOG(sDragLm, LogLevel::Debug, ("boioioioiooioioioing!\n"));
            *_retval = true;
          }
        }
      }
    }
    return NS_OK;
  }

  // check the target context vs. this flavor, one at a time
  GList* tmp = nullptr;
  if (mTargetDragContext) {
    tmp = gdk_drag_context_list_targets(mTargetDragContext);
  }
#ifdef MOZ_WAYLAND
  else if (mTargetWaylandDragContext) {
    tmp = mTargetWaylandDragContext->GetTargets();
  }
  GList* tmp_head = tmp;
#endif

  for (; tmp; tmp = tmp->next) {
    /* Bug 331198 */
    GdkAtom atom = GDK_POINTER_TO_ATOM(tmp->data);
    gchar* name = nullptr;
    name = gdk_atom_name(atom);
    MOZ_LOG(sDragLm, LogLevel::Debug,
            ("checking %s against %s\n", name, aDataFlavor));
    if (name && (strcmp(name, aDataFlavor) == 0)) {
      MOZ_LOG(sDragLm, LogLevel::Debug, ("good!\n"));
      *_retval = true;
    }
    // check for automatic text/uri-list -> text/x-moz-url mapping
    if (!*_retval && name && (strcmp(name, gTextUriListType) == 0) &&
        (strcmp(aDataFlavor, kURLMime) == 0 ||
         strcmp(aDataFlavor, kFileMime) == 0)) {
      MOZ_LOG(sDragLm, LogLevel::Debug, ("good! ( it's text/uri-list and \
                   we're checking against text/x-moz-url )\n"));
      *_retval = true;
    }
    // check for automatic _NETSCAPE_URL -> text/x-moz-url mapping
    if (!*_retval && name && (strcmp(name, gMozUrlType) == 0) &&
        (strcmp(aDataFlavor, kURLMime) == 0)) {
      MOZ_LOG(sDragLm, LogLevel::Debug, ("good! ( it's _NETSCAPE_URL and \
                   we're checking against text/x-moz-url )\n"));
      *_retval = true;
    }
    // check for auto text/plain -> text/unicode mapping
    if (!*_retval && name && (strcmp(name, kTextMime) == 0) &&
        ((strcmp(aDataFlavor, kUnicodeMime) == 0) ||
         (strcmp(aDataFlavor, kFileMime) == 0))) {
      MOZ_LOG(sDragLm, LogLevel::Debug,
              ("good! ( it's text plain and we're checking \
                   against text/unicode or application/x-moz-file)\n"));
      *_retval = true;
    }
    g_free(name);
  }

#ifdef MOZ_WAYLAND
  // mTargetWaylandDragContext->GetTargets allocates the list
  // so we need to free it here.
  if (!mTargetDragContext && tmp_head) {
    g_list_free(tmp_head);
  }
#endif

  return NS_OK;
}

void nsDragService::ReplyToDragMotion(GdkDragContext* aDragContext) {
  MOZ_LOG(sDragLm, LogLevel::Debug,
          ("nsDragService::ReplyToDragMotion %d", mCanDrop));

  GdkDragAction action = (GdkDragAction)0;
  if (mCanDrop) {
    // notify the dragger if we can drop
    switch (mDragAction) {
      case DRAGDROP_ACTION_COPY:
        action = GDK_ACTION_COPY;
        break;
      case DRAGDROP_ACTION_LINK:
        action = GDK_ACTION_LINK;
        break;
      case DRAGDROP_ACTION_NONE:
        action = (GdkDragAction)0;
        break;
      default:
        action = GDK_ACTION_MOVE;
        break;
    }
  }

  gdk_drag_status(aDragContext, action, mTargetTime);
}

#ifdef MOZ_WAYLAND
void nsDragService::ReplyToDragMotion(nsWaylandDragContext* aDragContext) {
  MOZ_LOG(sDragLm, LogLevel::Debug,
          ("nsDragService::ReplyToDragMotion %d", mCanDrop));

  GdkDragAction action = (GdkDragAction)0;
  if (mCanDrop) {
    // notify the dragger if we can drop
    switch (mDragAction) {
      case DRAGDROP_ACTION_COPY:
        action = GDK_ACTION_COPY;
        break;
      case DRAGDROP_ACTION_LINK:
        action = GDK_ACTION_LINK;
        break;
      case DRAGDROP_ACTION_NONE:
        action = (GdkDragAction)0;
        break;
      default:
        action = GDK_ACTION_MOVE;
        break;
    }
  }

  aDragContext->SetDragStatus(action);
}
#endif

void nsDragService::TargetDataReceived(GtkWidget* aWidget,
                                       GdkDragContext* aContext, gint aX,
                                       gint aY,
                                       GtkSelectionData* aSelectionData,
                                       guint aInfo, guint32 aTime) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::TargetDataReceived"));
  TargetResetData();
  mTargetDragDataReceived = true;
  gint len = gtk_selection_data_get_length(aSelectionData);
  const guchar* data = gtk_selection_data_get_data(aSelectionData);
  if (len > 0 && data) {
    mTargetDragDataLen = len;
    mTargetDragData = g_malloc(mTargetDragDataLen);
    memcpy(mTargetDragData, data, mTargetDragDataLen);
  } else {
    MOZ_LOG(sDragLm, LogLevel::Debug,
            ("Failed to get data.  selection data len was %d\n",
             mTargetDragDataLen));
  }
}

bool nsDragService::IsTargetContextList(void) {
  bool retval = false;

#ifdef MOZ_WAYLAND
  // TODO: We need a wayland implementation here.
  if (!mTargetDragContext) return retval;
#endif

  // gMimeListType drags only work for drags within a single process. The
  // gtk_drag_get_source_widget() function will return nullptr if the source
  // of the drag is another app, so we use it to check if a gMimeListType
  // drop will work or not.
  if (gtk_drag_get_source_widget(mTargetDragContext) == nullptr) return retval;

  GList* tmp;

  // walk the list of context targets and see if one of them is a list
  // of items.
  for (tmp = gdk_drag_context_list_targets(mTargetDragContext); tmp;
       tmp = tmp->next) {
    /* Bug 331198 */
    GdkAtom atom = GDK_POINTER_TO_ATOM(tmp->data);
    gchar* name = nullptr;
    name = gdk_atom_name(atom);
    if (name && strcmp(name, gMimeListType) == 0) retval = true;
    g_free(name);
    if (retval) break;
  }
  return retval;
}

// Maximum time to wait for a "drag_received" arrived, in microseconds
#define NS_DND_TIMEOUT 500000

void nsDragService::GetTargetDragData(GdkAtom aFlavor) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("getting data flavor %p\n", aFlavor));
  MOZ_LOG(sDragLm, LogLevel::Debug,
          ("mLastWidget is %p and mLastContext is %p\n", mTargetWidget.get(),
           mTargetDragContext.get()));
  // reset our target data areas
  TargetResetData();

  if (mTargetDragContext) {
    gtk_drag_get_data(mTargetWidget, mTargetDragContext, aFlavor, mTargetTime);

    MOZ_LOG(sDragLm, LogLevel::Debug, ("about to start inner iteration."));
    PRTime entryTime = PR_Now();
    while (!mTargetDragDataReceived && mDoingDrag) {
      // check the number of iterations
      MOZ_LOG(sDragLm, LogLevel::Debug, ("doing iteration...\n"));
      PR_Sleep(20 * PR_TicksPerSecond() / 1000); /* sleep for 20 ms/iteration */
      if (PR_Now() - entryTime > NS_DND_TIMEOUT) break;
      gtk_main_iteration();
    }
  }
#ifdef MOZ_WAYLAND
  else {
    mTargetDragData = mTargetWaylandDragContext->GetData(gdk_atom_name(aFlavor),
                                                         &mTargetDragDataLen);
    mTargetDragDataReceived = true;
  }
#endif
  MOZ_LOG(sDragLm, LogLevel::Debug, ("finished inner iteration\n"));
}

void nsDragService::TargetResetData(void) {
  mTargetDragDataReceived = false;
  // make sure to free old data if we have to
  g_free(mTargetDragData);
  mTargetDragData = 0;
  mTargetDragDataLen = 0;
}

GtkTargetList* nsDragService::GetSourceList(void) {
  if (!mSourceDataItems) return nullptr;
  nsTArray<GtkTargetEntry*> targetArray;
  GtkTargetEntry* targets;
  GtkTargetList* targetList = 0;
  uint32_t targetCount = 0;
  unsigned int numDragItems = 0;

  mSourceDataItems->GetLength(&numDragItems);

  // Check to see if we're dragging > 1 item.
  if (numDragItems > 1) {
    // as the Xdnd protocol only supports a single item (or is it just
    // gtk's implementation?), we don't advertise all flavours listed
    // in the nsITransferable.

    // the application/x-moz-internal-item-list format, which preserves
    // all information for drags within the same mozilla instance.
    GtkTargetEntry* listTarget =
        (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry));
    listTarget->target = g_strdup(gMimeListType);
    listTarget->flags = 0;
    MOZ_LOG(sDragLm, LogLevel::Debug,
            ("automatically adding target %s\n", listTarget->target));
    targetArray.AppendElement(listTarget);

    // check what flavours are supported so we can decide what other
    // targets to advertise.
    nsCOMPtr<nsITransferable> currItem = do_QueryElementAt(mSourceDataItems, 0);

    if (currItem) {
      nsTArray<nsCString> flavors;
      currItem->FlavorsTransferableCanExport(flavors);
      for (uint32_t i = 0; i < flavors.Length(); ++i) {
        // check if text/x-moz-url is supported.
        // If so, advertise
        // text/uri-list.
        if (flavors[i].EqualsLiteral(kURLMime)) {
          listTarget = (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry));
          listTarget->target = g_strdup(gTextUriListType);
          listTarget->flags = 0;
          MOZ_LOG(sDragLm, LogLevel::Debug,
                  ("automatically adding target %s\n", listTarget->target));
          targetArray.AppendElement(listTarget);
        }
      }
    }  // if item is a transferable
  } else if (numDragItems == 1) {
    nsCOMPtr<nsITransferable> currItem = do_QueryElementAt(mSourceDataItems, 0);
    if (currItem) {
      nsTArray<nsCString> flavors;
      currItem->FlavorsTransferableCanExport(flavors);
      for (uint32_t i = 0; i < flavors.Length(); ++i) {
        nsCString& flavorStr = flavors[i];

        GtkTargetEntry* target =
            (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry));
        target->target = g_strdup(flavorStr.get());
        target->flags = 0;
        MOZ_LOG(sDragLm, LogLevel::Debug,
                ("adding target %s\n", target->target));
        targetArray.AppendElement(target);

        // If there is a file, add the text/uri-list type.
        if (flavorStr.EqualsLiteral(kFileMime)) {
          GtkTargetEntry* urilistTarget =
              (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry));
          urilistTarget->target = g_strdup(gTextUriListType);
          urilistTarget->flags = 0;
          MOZ_LOG(sDragLm, LogLevel::Debug,
                  ("automatically adding target %s\n", urilistTarget->target));
          targetArray.AppendElement(urilistTarget);
        }
        // Check to see if this is text/unicode.
        // If it is, add text/plain
        // since we automatically support text/plain
        // if we support text/unicode.
        else if (flavorStr.EqualsLiteral(kUnicodeMime)) {
          GtkTargetEntry* plainUTF8Target =
              (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry));
          plainUTF8Target->target = g_strdup(gTextPlainUTF8Type);
          plainUTF8Target->flags = 0;
          MOZ_LOG(
              sDragLm, LogLevel::Debug,
              ("automatically adding target %s\n", plainUTF8Target->target));
          targetArray.AppendElement(plainUTF8Target);

          GtkTargetEntry* plainTarget =
              (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry));
          plainTarget->target = g_strdup(kTextMime);
          plainTarget->flags = 0;
          MOZ_LOG(sDragLm, LogLevel::Debug,
                  ("automatically adding target %s\n", plainTarget->target));
          targetArray.AppendElement(plainTarget);
        }
        // Check to see if this is the x-moz-url type.
        // If it is, add _NETSCAPE_URL
        // this is a type used by everybody.
        else if (flavorStr.EqualsLiteral(kURLMime)) {
          GtkTargetEntry* urlTarget =
              (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry));
          urlTarget->target = g_strdup(gMozUrlType);
          urlTarget->flags = 0;
          MOZ_LOG(sDragLm, LogLevel::Debug,
                  ("automatically adding target %s\n", urlTarget->target));
          targetArray.AppendElement(urlTarget);
        }
        // XdndDirectSave
        else if (flavorStr.EqualsLiteral(kFilePromiseMime)) {
          GtkTargetEntry* directsaveTarget =
              (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry));
          directsaveTarget->target = g_strdup(gXdndDirectSaveType);
          directsaveTarget->flags = 0;
          MOZ_LOG(
              sDragLm, LogLevel::Debug,
              ("automatically adding target %s\n", directsaveTarget->target));
          targetArray.AppendElement(directsaveTarget);
        }
      }
    }
  }

  // get all the elements that we created.
  targetCount = targetArray.Length();
  if (targetCount) {
    // allocate space to create the list of valid targets
    targets = (GtkTargetEntry*)g_malloc(sizeof(GtkTargetEntry) * targetCount);
    uint32_t targetIndex;
    for (targetIndex = 0; targetIndex < targetCount; ++targetIndex) {
      GtkTargetEntry* disEntry = targetArray.ElementAt(targetIndex);
      // this is a string reference but it will be freed later.
      targets[targetIndex].target = disEntry->target;
      targets[targetIndex].flags = disEntry->flags;
      targets[targetIndex].info = 0;
    }
    targetList = gtk_target_list_new(targets, targetCount);
    // clean up the target list
    for (uint32_t cleanIndex = 0; cleanIndex < targetCount; ++cleanIndex) {
      GtkTargetEntry* thisTarget = targetArray.ElementAt(cleanIndex);
      g_free(thisTarget->target);
      g_free(thisTarget);
    }
    g_free(targets);
  } else {
    // We need to create a dummy target list to be able initialize dnd.
    targetList = gtk_target_list_new(nullptr, 0);
  }
  return targetList;
}

void nsDragService::SourceEndDragSession(GdkDragContext* aContext,
                                         gint aResult) {
  // this just releases the list of data items that we provide
  mSourceDataItems = nullptr;

  // Remove this property, if it exists, to satisfy the Direct Save Protocol.
  GdkAtom property = gdk_atom_intern(gXdndDirectSaveType, FALSE);
  gdk_property_delete(gdk_drag_context_get_source_window(aContext), property);

  if (!mDoingDrag || mScheduledTask == eDragTaskSourceEnd)
    // EndDragSession() was already called on drop
    // or SourceEndDragSession on drag-failed
    return;

  if (mEndDragPoint.x < 0) {
    // We don't have a drag end point, so guess
    gint x, y;
    GdkDisplay* display = gdk_display_get_default();
    if (display) {
      gint scale = mozilla::widget::ScreenHelperGTK::GetGTKMonitorScaleFactor();
      gdk_display_get_pointer(display, nullptr, &x, &y, nullptr);
      SetDragEndPoint(LayoutDeviceIntPoint(x * scale, y * scale));
    }
  }

  // Either the drag was aborted or the drop occurred outside the app.
  // The dropEffect of mDataTransfer is not updated for motion outside the
  // app, but is needed for the dragend event, so set it now.

  uint32_t dropEffect;

  if (aResult == MOZ_GTK_DRAG_RESULT_SUCCESS) {
    // With GTK+ versions 2.10.x and prior the drag may have been
    // cancelled (but no drag-failed signal would have been sent).
    // aContext->dest_window will be non-nullptr only if the drop was
    // sent.
    GdkDragAction action = gdk_drag_context_get_dest_window(aContext)
                               ? gdk_drag_context_get_actions(aContext)
                               : (GdkDragAction)0;

    // Only one bit of action should be set, but, just in case someone
    // does something funny, erring away from MOVE, and not recording
    // unusual action combinations as NONE.
    if (!action)
      dropEffect = DRAGDROP_ACTION_NONE;
    else if (action & GDK_ACTION_COPY)
      dropEffect = DRAGDROP_ACTION_COPY;
    else if (action & GDK_ACTION_LINK)
      dropEffect = DRAGDROP_ACTION_LINK;
    else if (action & GDK_ACTION_MOVE)
      dropEffect = DRAGDROP_ACTION_MOVE;
    else
      dropEffect = DRAGDROP_ACTION_COPY;

  } else {
    dropEffect = DRAGDROP_ACTION_NONE;

    if (aResult != MOZ_GTK_DRAG_RESULT_NO_TARGET) {
      mUserCancelled = true;
    }
  }

  if (mDataTransfer) {
    mDataTransfer->SetDropEffectInt(dropEffect);
  }

  // Schedule the appropriate drag end dom events.
  Schedule(eDragTaskSourceEnd, nullptr, nullptr, nullptr,
           LayoutDeviceIntPoint(), 0);
}

static void CreateURIList(nsIArray* aItems, nsACString& aURIList) {
  uint32_t length = 0;
  aItems->GetLength(&length);

  for (uint32_t i = 0; i < length; ++i) {
    nsCOMPtr<nsITransferable> item = do_QueryElementAt(aItems, i);
    if (!item) {
      continue;
    }

    nsCOMPtr<nsISupports> data;
    nsresult rv = item->GetTransferData(kURLMime, getter_AddRefs(data));
    if (NS_SUCCEEDED(rv)) {
      nsCOMPtr<nsISupportsString> string = do_QueryInterface(data);

      nsAutoString text;
      if (string) {
        string->GetData(text);
      }

      // text/x-moz-url is of form url + "\n" + title.
      // We just want the url.
      int32_t separatorPos = text.FindChar(u'\n');
      if (separatorPos >= 0) {
        text.Truncate(separatorPos);
      }

      AppendUTF16toUTF8(text, aURIList);
      aURIList.AppendLiteral("\r\n");
      continue;
    }

    // There is no URI available. If there is a file available, create
    // a URI from the file.
    rv = item->GetTransferData(kFileMime, getter_AddRefs(data));
    if (NS_SUCCEEDED(rv)) {
      if (nsCOMPtr<nsIFile> file = do_QueryInterface(data)) {
        nsCOMPtr<nsIURI> fileURI;
        NS_NewFileURI(getter_AddRefs(fileURI), file);
        if (fileURI) {
          nsAutoCString spec;
          fileURI->GetSpec(spec);

          aURIList.Append(spec);
          aURIList.AppendLiteral("\r\n");
        }
      }
    }
  }
}

void nsDragService::SourceDataGet(GtkWidget* aWidget, GdkDragContext* aContext,
                                  GtkSelectionData* aSelectionData,
                                  guint32 aTime) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("nsDragService::SourceDataGet"));
  GdkAtom target = gtk_selection_data_get_target(aSelectionData);
  gchar* typeName = gdk_atom_name(target);
  if (!typeName) {
    MOZ_LOG(sDragLm, LogLevel::Debug, ("failed to get atom name.\n"));
    return;
  }


  MOZ_LOG(sDragLm, LogLevel::Debug, ("Type is %s\n", typeName));
  auto freeTypeName = mozilla::MakeScopeExit([&] {
    g_free(typeName);
  });
  // check to make sure that we have data items to return.
  if (!mSourceDataItems) {
    MOZ_LOG(sDragLm, LogLevel::Debug, ("Failed to get our data items\n"));
    return;
  }

  nsDependentCSubstring mimeFlavor(typeName, strlen(typeName));
  nsCOMPtr<nsITransferable> item;
  item = do_QueryElementAt(mSourceDataItems, 0);
  if (item) {
    // if someone was asking for text/plain, lookup unicode instead so
    // we can convert it.
    bool needToDoConversionToPlainText = false;
    const char* actualFlavor;
    if (mimeFlavor.EqualsLiteral(kTextMime) ||
        mimeFlavor.EqualsLiteral(gTextPlainUTF8Type)) {
      actualFlavor = kUnicodeMime;
      needToDoConversionToPlainText = true;
    }
    // if someone was asking for _NETSCAPE_URL we need to convert to
    // plain text but we also need to look for x-moz-url
    else if (mimeFlavor.EqualsLiteral(gMozUrlType)) {
      actualFlavor = kURLMime;
      needToDoConversionToPlainText = true;
    }
    // if someone was asking for text/uri-list we need to convert to
    // plain text.
    else if (mimeFlavor.EqualsLiteral(gTextUriListType)) {
      actualFlavor = gTextUriListType;
      needToDoConversionToPlainText = true;
    }
    // Someone is asking for the special Direct Save Protocol type.
    else if (mimeFlavor.EqualsLiteral(gXdndDirectSaveType)) {
      // Indicate failure by default.
      gtk_selection_data_set(aSelectionData, target, 8, (guchar*)"E", 1);

      GdkAtom property = gdk_atom_intern(gXdndDirectSaveType, FALSE);
      GdkAtom type = gdk_atom_intern(kTextMime, FALSE);

      guchar* data;
      gint length;
      if (!gdk_property_get(gdk_drag_context_get_source_window(aContext),
                            property, type, 0, INT32_MAX, FALSE, nullptr,
                            nullptr, &length, &data)) {
        return;
      }

      // Zero-terminate the string.
      data = (guchar*)g_realloc(data, length + 1);
      if (!data) return;
      data[length] = '\0';

      gchar* hostname;
      char* gfullpath =
          g_filename_from_uri((const gchar*)data, &hostname, nullptr);
      g_free(data);
      if (!gfullpath) return;

      nsCString fullpath(gfullpath);
      g_free(gfullpath);

      MOZ_LOG(sDragLm, LogLevel::Debug,
              ("XdndDirectSave filepath is %s\n", fullpath.get()));

      // If there is no hostname in the URI, NULL will be stored.
      // We should not accept uris with from a different host.
      if (hostname) {
        nsCOMPtr<nsIPropertyBag2> infoService =
            do_GetService(NS_SYSTEMINFO_CONTRACTID);
        if (!infoService) return;

        nsAutoCString host;
        if (NS_SUCCEEDED(infoService->GetPropertyAsACString(
                NS_LITERAL_STRING("host"), host))) {
          if (!host.Equals(hostname)) {
            MOZ_LOG(sDragLm, LogLevel::Debug,
                    ("ignored drag because of different host.\n"));

            // Special error code "F" for this case.
            gtk_selection_data_set(aSelectionData, target, 8, (guchar*)"F", 1);
            g_free(hostname);
            return;
          }
        }

        g_free(hostname);
      }

      nsCOMPtr<nsIFile> file;
      if (NS_FAILED(
              NS_NewNativeLocalFile(fullpath, false, getter_AddRefs(file)))) {
        return;
      }

      // We have to split the path into a directory and filename,
      // because our internal file-promise API is based on these.

      nsCOMPtr<nsIFile> directory;
      file->GetParent(getter_AddRefs(directory));

      item->SetTransferData(kFilePromiseDirectoryMime, directory);

      nsCOMPtr<nsISupportsString> filenamePrimitive =
          do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID);
      if (!filenamePrimitive) return;

      nsAutoString leafName;
      file->GetLeafName(leafName);
      filenamePrimitive->SetData(leafName);

      item->SetTransferData(kFilePromiseDestFilename, filenamePrimitive);

      // Request a different type in GetTransferData.
      actualFlavor = kFilePromiseMime;
    } else {
      actualFlavor = typeName;
    }
    nsresult rv;
    nsCOMPtr<nsISupports> data;
    rv = item->GetTransferData(actualFlavor, getter_AddRefs(data));

    if (strcmp(actualFlavor, kFilePromiseMime) == 0) {
      if (NS_SUCCEEDED(rv)) {
        // Indicate success.
        gtk_selection_data_set(aSelectionData, target, 8, (guchar*)"S", 1);
      }
      return;
    }

    if (NS_SUCCEEDED(rv)) {
      void* tmpData = nullptr;
      uint32_t tmpDataLen = 0;
      nsPrimitiveHelpers::CreateDataFromPrimitive(
          nsDependentCString(actualFlavor), data, &tmpData, &tmpDataLen);
      // if required, do the extra work to convert unicode to plain
      // text and replace the output values with the plain text.
      if (needToDoConversionToPlainText) {
        char* plainTextData = nullptr;
        char16_t* castedUnicode = reinterpret_cast<char16_t*>(tmpData);
        uint32_t plainTextLen = 0;
        UTF16ToNewUTF8(castedUnicode, tmpDataLen / 2, &plainTextData,
                       &plainTextLen);
        if (tmpData) {
          // this was not allocated using glib
          free(tmpData);
          tmpData = plainTextData;
          tmpDataLen = plainTextLen;
        }
      }
      if (tmpData) {
        // this copies the data
        gtk_selection_data_set(aSelectionData, target, 8, (guchar*)tmpData,
                               tmpDataLen);
        // this wasn't allocated with glib
        free(tmpData);
      }
    } else {
      if (mimeFlavor.EqualsLiteral(gTextUriListType)) {
        // fall back for text/uri-list
        nsAutoCString list;
        CreateURIList(mSourceDataItems, list);
        gtk_selection_data_set(aSelectionData, target, 8, (guchar*)list.get(),
                               list.Length());
        return;
      }
    }
  }
}

void nsDragService::SourceBeginDrag(GdkDragContext* aContext) {
  nsCOMPtr<nsITransferable> transferable =
      do_QueryElementAt(mSourceDataItems, 0);
  if (!transferable) return;

  nsTArray<nsCString> flavors;
  nsresult rv = transferable->FlavorsTransferableCanImport(flavors);
  NS_ENSURE_SUCCESS(rv, );

  for (uint32_t i = 0; i < flavors.Length(); ++i) {
    if (flavors[i].EqualsLiteral(kFilePromiseDestFilename)) {
      nsCOMPtr<nsISupports> data;
      rv = transferable->GetTransferData(kFilePromiseDestFilename,
                                         getter_AddRefs(data));
      if (NS_FAILED(rv)) {
        return;
      }

      nsCOMPtr<nsISupportsString> fileName = do_QueryInterface(data);
      if (!fileName) {
        return;
      }

      nsAutoString fileNameStr;
      fileName->GetData(fileNameStr);

      nsCString fileNameCStr;
      CopyUTF16toUTF8(fileNameStr, fileNameCStr);

      GdkAtom property = gdk_atom_intern(gXdndDirectSaveType, FALSE);
      GdkAtom type = gdk_atom_intern(kTextMime, FALSE);

      gdk_property_change(gdk_drag_context_get_source_window(aContext),
                          property, type, 8, GDK_PROP_MODE_REPLACE,
                          (const guchar*)fileNameCStr.get(),
                          fileNameCStr.Length());
    }
  }
}

void nsDragService::SetDragIcon(GdkDragContext* aContext) {
  if (!mHasImage && !mSelection) return;

  LayoutDeviceIntRect dragRect;
  nsPresContext* pc;
  RefPtr<SourceSurface> surface;
  DrawDrag(mSourceNode, mRegion, mScreenPosition, &dragRect, &surface, &pc);
  if (!pc) return;

  LayoutDeviceIntPoint screenPoint =
      ConvertToUnscaledDevPixels(pc, mScreenPosition);
  int32_t offsetX = screenPoint.x - dragRect.x;
  int32_t offsetY = screenPoint.y - dragRect.y;

  // If a popup is set as the drag image, use its widget. Otherwise, use
  // the surface that DrawDrag created.
  //
  // XXX: Disable drag popups on GTK 3.19.4 and above: see bug 1264454.
  //      Fix this once a new GTK version ships that does not destroy our
  //      widget in gtk_drag_set_icon_widget.
  if (mDragPopup && gtk_check_version(3, 19, 4)) {
    GtkWidget* gtkWidget = nullptr;
    nsIFrame* frame = mDragPopup->GetPrimaryFrame();
    if (frame) {
      // DrawDrag ensured that this is a popup frame.
      nsCOMPtr<nsIWidget> widget = frame->GetNearestWidget();
      if (widget) {
        gtkWidget = (GtkWidget*)widget->GetNativeData(NS_NATIVE_SHELLWIDGET);
        if (gtkWidget) {
          OpenDragPopup();
          gtk_drag_set_icon_widget(aContext, gtkWidget, offsetX, offsetY);
        }
      }
    }
  } else if (surface) {
    if (!SetAlphaPixmap(surface, aContext, offsetX, offsetY, dragRect)) {
      GdkPixbuf* dragPixbuf = nsImageToPixbuf::SourceSurfaceToPixbuf(
          surface, dragRect.width, dragRect.height);
      if (dragPixbuf) {
        gtk_drag_set_icon_pixbuf(aContext, dragPixbuf, offsetX, offsetY);
        g_object_unref(dragPixbuf);
      }
    }
  }
}

static void invisibleSourceDragBegin(GtkWidget* aWidget,
                                     GdkDragContext* aContext, gpointer aData) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("invisibleSourceDragBegin"));
  nsDragService* dragService = (nsDragService*)aData;

  dragService->SourceBeginDrag(aContext);
  dragService->SetDragIcon(aContext);
}

static void invisibleSourceDragDataGet(GtkWidget* aWidget,
                                       GdkDragContext* aContext,
                                       GtkSelectionData* aSelectionData,
                                       guint aInfo, guint32 aTime,
                                       gpointer aData) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("invisibleSourceDragDataGet"));
  nsDragService* dragService = (nsDragService*)aData;
  dragService->SourceDataGet(aWidget, aContext, aSelectionData, aTime);
}

static gboolean invisibleSourceDragFailed(GtkWidget* aWidget,
                                          GdkDragContext* aContext,
                                          gint aResult, gpointer aData) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("invisibleSourceDragFailed %i", aResult));
  nsDragService* dragService = (nsDragService*)aData;
  // End the drag session now (rather than waiting for the drag-end signal)
  // so that operations performed on dropEffect == none can start immediately
  // rather than waiting for the drag-failed animation to finish.
  dragService->SourceEndDragSession(aContext, aResult);

  // We should return TRUE to disable the drag-failed animation iff the
  // source performed an operation when dropEffect was none, but the handler
  // of the dragend DOM event doesn't provide this information.
  return FALSE;
}

static void invisibleSourceDragEnd(GtkWidget* aWidget, GdkDragContext* aContext,
                                   gpointer aData) {
  MOZ_LOG(sDragLm, LogLevel::Debug, ("invisibleSourceDragEnd"));
  nsDragService* dragService = (nsDragService*)aData;

  // The drag has ended.  Release the hostages!
  dragService->SourceEndDragSession(aContext, MOZ_GTK_DRAG_RESULT_SUCCESS);
}

// The following methods handle responding to GTK drag signals and
// tracking state between these signals.
//
// In general, GTK does not expect us to run the event loop while handling its
// drag signals, however our drag event handlers may run the
// event loop, most often to fetch information about the drag data.
//
// GTK, for example, uses the return value from drag-motion signals to
// determine whether drag-leave signals should be sent.  If an event loop is
// run during drag-motion the XdndLeave message can get processed but when GTK
// receives the message it does not yet know that it needs to send the
// drag-leave signal to our widget.
//
// After a drag-drop signal, we need to reply with gtk_drag_finish().
// However, gtk_drag_finish should happen after the drag-drop signal handler
// returns so that when the Motif drag protocol is used, the
// XmTRANSFER_SUCCESS during gtk_drag_finish is sent after the XmDROP_START
// reply sent on return from the drag-drop signal handler.
//
// Similarly drag-end for a successful drag and drag-failed are not good
// times to run a nested event loop as gtk_drag_drop_finished() and
// gtk_drag_source_info_destroy() don't gtk_drag_clear_source_info() or remove
// drop_timeout until after at least the first of these signals is sent.
// Processing other events (e.g. a slow GDK_DROP_FINISHED reply, or the drop
// timeout) could cause gtk_drag_drop_finished to be called again with the
// same GtkDragSourceInfo, which won't like being destroyed twice.
//
// Therefore we reply to the signals immediately and schedule a task to
// dispatch the Gecko events, which may run the event loop.
//
// Action in response to drag-leave signals is also delayed until the event
// loop runs again so that we find out whether a drag-drop signal follows.
//
// A single task is scheduled to manage responses to all three GTK signals.
// If further signals are received while the task is scheduled, the scheduled
// response is updated, sometimes effectively compressing successive signals.
//
// No Gecko drag events are dispatched (during nested event loops) while other
// Gecko drag events are in flight.  This helps event handlers that may not
// expect nested events, while accessing an event's dataTransfer for example.

gboolean nsDragService::ScheduleMotionEvent(
    nsWindow* aWindow, GdkDragContext* aDragContext,
    nsWaylandDragContext* aWaylandDragContext,
    LayoutDeviceIntPoint aWindowPoint, guint aTime) {
  if (aDragContext && mScheduledTask == eDragTaskMotion) {
    // The drag source has sent another motion message before we've
    // replied to the previous.  That shouldn't happen with Xdnd.  The
    // spec for Motif drags is less clear, but we'll just update the
    // scheduled task with the new position reply only to the most
    // recent message.
    NS_WARNING("Drag Motion message received before previous reply was sent");
  }

  // Returning TRUE means we'll reply with a status message, unless we first
  // get a leave.
  return Schedule(eDragTaskMotion, aWindow, aDragContext, aWaylandDragContext,
                  aWindowPoint, aTime);
}

void nsDragService::ScheduleLeaveEvent() {
  // We don't know at this stage whether a drop signal will immediately
  // follow.  If the drop signal gets sent it will happen before we return
  // to the main loop and the scheduled leave task will be replaced.
  if (!Schedule(eDragTaskLeave, nullptr, nullptr, nullptr,
                LayoutDeviceIntPoint(), 0)) {
    NS_WARNING("Drag leave after drop");
  }
}

gboolean nsDragService::ScheduleDropEvent(
    nsWindow* aWindow, GdkDragContext* aDragContext,
    nsWaylandDragContext* aWaylandDragContext,
    LayoutDeviceIntPoint aWindowPoint, guint aTime) {
  if (!Schedule(eDragTaskDrop, aWindow, aDragContext, aWaylandDragContext,
                aWindowPoint, aTime)) {
    NS_WARNING("Additional drag drop ignored");
    return FALSE;
  }

  SetDragEndPoint(aWindowPoint + aWindow->WidgetToScreenOffset());

  // We'll reply with gtk_drag_finish().
  return TRUE;
}

gboolean nsDragService::Schedule(DragTask aTask, nsWindow* aWindow,
                                 GdkDragContext* aDragContext,
                                 nsWaylandDragContext* aWaylandDragContext,
                                 LayoutDeviceIntPoint aWindowPoint,
                                 guint aTime) {
  // If there is an existing leave or motion task scheduled, then that
  // will be replaced.  When the new task is run, it will dispatch
  // any necessary leave or motion events.

  // If aTask is eDragTaskSourceEnd, then it will replace even a scheduled
  // drop event (which could happen if the drop event has not been processed
  // within the allowed time).  Otherwise, if we haven't yet run a scheduled
  // drop or end task, just say that we are not ready to receive another
  // drop.
  if (mScheduledTask == eDragTaskSourceEnd ||
      (mScheduledTask == eDragTaskDrop && aTask != eDragTaskSourceEnd))
    return FALSE;

  mScheduledTask = aTask;
  mPendingWindow = aWindow;
  mPendingDragContext = aDragContext;
#ifdef MOZ_WAYLAND
  mPendingWaylandDragContext = aWaylandDragContext;
#endif
  mPendingWindowPoint = aWindowPoint;
  mPendingTime = aTime;

  if (!mTaskSource) {
    // High priority is used here because the native events involved have
    // already waited at default priority.  Perhaps a lower than default
    // priority could be used for motion tasks because there is a chance
    // that a leave or drop is waiting, but managing different priorities
    // may not be worth the effort.  Motion tasks shouldn't queue up as
    // they should be throttled based on replies.
    mTaskSource =
        g_idle_add_full(G_PRIORITY_HIGH, TaskDispatchCallback, this, nullptr);
  }
  return TRUE;
}

gboolean nsDragService::TaskDispatchCallback(gpointer data) {
  RefPtr<nsDragService> dragService = static_cast<nsDragService*>(data);
  return dragService->RunScheduledTask();
}

gboolean nsDragService::RunScheduledTask() {
  if (mTargetWindow && mTargetWindow != mPendingWindow) {
    MOZ_LOG(sDragLm, LogLevel::Debug,
            ("nsDragService: dispatch drag leave (%p)\n", mTargetWindow.get()));
    mTargetWindow->DispatchDragEvent(eDragExit, mTargetWindowPoint, 0);

    if (!mSourceNode) {
      // The drag that was initiated in a different app. End the drag
      // session, since we're done with it for now (until the user drags
      // back into this app).
      EndDragSession(false, GetCurrentModifiers());
    }
  }

  // It is possible that the pending state has been updated during dispatch
  // of the leave event.  That's fine.

  // Now we collect the pending state because, from this point on, we want
  // to use the same state for all events dispatched.  All state is updated
  // so that when other tasks are scheduled during dispatch here, this
  // task is considered to have already been run.
  bool positionHasChanged = mPendingWindow != mTargetWindow ||
                            mPendingWindowPoint != mTargetWindowPoint;
  DragTask task = mScheduledTask;
  mScheduledTask = eDragTaskNone;
  mTargetWindow = std::move(mPendingWindow);
  mTargetWindowPoint = mPendingWindowPoint;

  if (task == eDragTaskLeave || task == eDragTaskSourceEnd) {
    if (task == eDragTaskSourceEnd) {
      // Dispatch drag end events.
      EndDragSession(true, GetCurrentModifiers());
    }

    // Nothing more to do
    // Returning false removes the task source from the event loop.
    mTaskSource = 0;
    return FALSE;
  }

  // This may be the start of a destination drag session.
  StartDragSession();

  // mTargetWidget may be nullptr if the window has been destroyed.
  // (The leave event is not scheduled if a drop task is still scheduled.)
  // We still reply appropriately to indicate that the drop will or didn't
  // succeeed.
  mTargetWidget = mTargetWindow->GetMozContainerWidget();
  mTargetDragContext.steal(mPendingDragContext);
#ifdef MOZ_WAYLAND
  mTargetWaylandDragContext = std::move(mPendingWaylandDragContext);
#endif
  mTargetTime = mPendingTime;

  // http://www.whatwg.org/specs/web-apps/current-work/multipage/dnd.html#drag-and-drop-processing-model
  // (as at 27 December 2010) indicates that a "drop" event should only be
  // fired (at the current target element) if the current drag operation is
  // not none.  The current drag operation will only be set to a non-none
  // value during a "dragover" event.
  //
  // If the user has ended the drag before any dragover events have been
  // sent, then the spec recommends skipping the drop (because the current
  // drag operation is none).  However, here we assume that, by releasing
  // the mouse button, the user has indicated that they want to drop, so we
  // proceed with the drop where possible.
  //
  // In order to make the events appear to content in the same way as if the
  // spec is being followed we make sure to dispatch a "dragover" event with
  // appropriate coordinates and check canDrop before the "drop" event.
  //
  // When the Xdnd protocol is used for source/destination communication (as
  // should be the case with GTK source applications) a dragover event
  // should have already been sent during the drag-motion signal, which
  // would have already been received because XdndDrop messages do not
  // contain a position.  However, we can't assume the same when the Motif
  // protocol is used.
  if (task == eDragTaskMotion || positionHasChanged) {
    UpdateDragAction();
    TakeDragEventDispatchedToChildProcess();  // Clear the old value.
    DispatchMotionEvents();
    if (task == eDragTaskMotion) {
      if (TakeDragEventDispatchedToChildProcess()) {
        mTargetDragContextForRemote = mTargetDragContext;
#ifdef MOZ_WAYLAND
        mTargetWaylandDragContextForRemote = mTargetWaylandDragContext;
#endif
      } else {
        // Reply to tell the source whether we can drop and what
        // action would be taken.
        if (mTargetDragContext) {
          ReplyToDragMotion(mTargetDragContext);
        }
#ifdef MOZ_WAYLAND
        else if (mTargetWaylandDragContext) {
          ReplyToDragMotion(mTargetWaylandDragContext);
        }
#endif
      }
    }
  }

  if (task == eDragTaskDrop) {
    gboolean success = DispatchDropEvent();

    // Perhaps we should set the del parameter to TRUE when the drag
    // action is move, but we don't know whether the data was successfully
    // transferred.
    if (mTargetDragContext) {
      gtk_drag_finish(mTargetDragContext, success,
                      /* del = */ FALSE, mTargetTime);
    }

    // This drag is over, so clear out our reference to the previous
    // window.
    mTargetWindow = nullptr;
    // Make sure to end the drag session. If this drag started in a
    // different app, we won't get a drag_end signal to end it from.
    EndDragSession(true, GetCurrentModifiers());
  }

  // We're done with the drag context.
  mTargetWidget = nullptr;
  mTargetDragContext = nullptr;
#ifdef MOZ_WAYLAND
  mTargetWaylandDragContext = nullptr;
#endif

  // If we got another drag signal while running the sheduled task, that
  // must have happened while running a nested event loop.  Leave the task
  // source on the event loop.
  if (mScheduledTask != eDragTaskNone) return TRUE;

  // We have no task scheduled.
  // Returning false removes the task source from the event loop.
  mTaskSource = 0;
  return FALSE;
}

// This will update the drag action based on the information in the
// drag context.  Gtk gets this from a combination of the key settings
// and what the source is offering.

void nsDragService::UpdateDragAction() {
  // This doesn't look right.  dragSession.dragAction is used by
  // nsContentUtils::SetDataTransferInEvent() to set the initial
  // dataTransfer.dropEffect, so GdkDragContext::suggested_action would be
  // more appropriate.  GdkDragContext::actions should be used to set
  // dataTransfer.effectAllowed, which doesn't currently happen with
  // external sources.

  // default is to do nothing
  int action = nsIDragService::DRAGDROP_ACTION_NONE;
  GdkDragAction gdkAction = GDK_ACTION_DEFAULT;
  if (mTargetDragContext) {
    gdkAction = gdk_drag_context_get_actions(mTargetDragContext);
  }
#ifdef MOZ_WAYLAND
  else if (mTargetWaylandDragContext) {
    gdkAction = mTargetWaylandDragContext->GetAvailableDragActions();
  }
#endif

  // set the default just in case nothing matches below
  if (gdkAction & GDK_ACTION_DEFAULT)
    action = nsIDragService::DRAGDROP_ACTION_MOVE;

  // first check to see if move is set
  if (gdkAction & GDK_ACTION_MOVE)
    action = nsIDragService::DRAGDROP_ACTION_MOVE;

  // then fall to the others
  else if (gdkAction & GDK_ACTION_LINK)
    action = nsIDragService::DRAGDROP_ACTION_LINK;

  // copy is ctrl
  else if (gdkAction & GDK_ACTION_COPY)
    action = nsIDragService::DRAGDROP_ACTION_COPY;

  // update the drag information
  SetDragAction(action);
}

NS_IMETHODIMP
nsDragService::UpdateDragEffect() {
  if (mTargetDragContextForRemote) {
    ReplyToDragMotion(mTargetDragContextForRemote);
    mTargetDragContextForRemote = nullptr;
  }
#ifdef MOZ_WAYLAND
  else if (mTargetWaylandDragContextForRemote) {
    ReplyToDragMotion(mTargetWaylandDragContextForRemote);
    mTargetWaylandDragContextForRemote = nullptr;
  }
#endif
  return NS_OK;
}

void nsDragService::DispatchMotionEvents() {
  mCanDrop = false;

  FireDragEventAtSource(eDrag, GetCurrentModifiers());

  mTargetWindow->DispatchDragEvent(eDragOver, mTargetWindowPoint, mTargetTime);
}

// Returns true if the drop was successful
gboolean nsDragService::DispatchDropEvent() {
  // We need to check IsDestroyed here because the nsRefPtr
  // only protects this from being deleted, it does NOT protect
  // against nsView::~nsView() calling Destroy() on it, bug 378273.
  if (mTargetWindow->IsDestroyed()) return FALSE;

  EventMessage msg = mCanDrop ? eDrop : eDragExit;

  mTargetWindow->DispatchDragEvent(msg, mTargetWindowPoint, mTargetTime);

  return mCanDrop;
}

/* static */
uint32_t nsDragService::GetCurrentModifiers() {
  return mozilla::widget::KeymapWrapper::ComputeCurrentKeyModifiers();
}