Adding upstream version 115.8.0esr.upstream/115.8.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1488 insertions, 0 deletions

diff --git a/dom/events/DataTransfer.cpp b/dom/events/DataTransfer.cpp
new file mode 100644
index 0000000000..42edbdf33c
--- /dev/null
+++ b/dom/events/DataTransfer.cpp
@@ -0,0 +1,1488 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 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 "mozilla/ArrayUtils.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/BasicEvents.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/Span.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "DataTransfer.h"
+
+#include "nsISupportsPrimitives.h"
+#include "nsIScriptSecurityManager.h"
+#include "mozilla/dom/DOMStringList.h"
+#include "nsArray.h"
+#include "nsError.h"
+#include "nsIDragService.h"
+#include "nsIClipboard.h"
+#include "nsIXPConnect.h"
+#include "nsContentUtils.h"
+#include "nsIContent.h"
+#include "nsIObjectInputStream.h"
+#include "nsIObjectOutputStream.h"
+#include "nsIStorageStream.h"
+#include "nsStringStream.h"
+#include "nsCRT.h"
+#include "nsIScriptObjectPrincipal.h"
+#include "nsIScriptContext.h"
+#include "mozilla/dom/Document.h"
+#include "nsIScriptGlobalObject.h"
+#include "nsQueryObject.h"
+#include "nsVariant.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/DataTransferBinding.h"
+#include "mozilla/dom/DataTransferItemList.h"
+#include "mozilla/dom/Directory.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/FileList.h"
+#include "mozilla/dom/IPCBlobUtils.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/OSFileSystem.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/WindowContext.h"
+#include "mozilla/Unused.h"
+#include "nsComponentManagerUtils.h"
+#include "nsNetUtil.h"
+#include "nsReadableUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(DataTransfer)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(DataTransfer)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mParent)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mItems)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mDragTarget)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mDragImage)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(DataTransfer)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mParent)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mItems)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDragTarget)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDragImage)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(DataTransfer)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(DataTransfer)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(DataTransfer)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(mozilla::dom::DataTransfer)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+// the size of the array
+const char DataTransfer::sEffects[8][9] = {
+    "none", "copy", "move", "copyMove", "link", "copyLink", "linkMove", "all"};
+
+// Used for custom clipboard types.
+enum CustomClipboardTypeId {
+  eCustomClipboardTypeId_None,
+  eCustomClipboardTypeId_String
+};
+
+static DataTransfer::Mode ModeForEvent(EventMessage aEventMessage) {
+  switch (aEventMessage) {
+    case eCut:
+    case eCopy:
+    case eDragStart:
+      // For these events, we want to be able to add data to the data transfer,
+      // Otherwise, the data is already present.
+      return DataTransfer::Mode::ReadWrite;
+    case eDrop:
+    case ePaste:
+    case ePasteNoFormatting:
+    case eEditorInput:
+      // For these events we want to be able to read the data which is stored in
+      // the DataTransfer, rather than just the type information.
+      return DataTransfer::Mode::ReadOnly;
+    default:
+      return StaticPrefs::dom_events_dataTransfer_protected_enabled()
+                 ? DataTransfer::Mode::Protected
+                 : DataTransfer::Mode::ReadOnly;
+  }
+}
+
+DataTransfer::DataTransfer(nsISupports* aParent, EventMessage aEventMessage,
+                           bool aIsExternal, int32_t aClipboardType)
+    : mParent(aParent),
+      mDropEffect(nsIDragService::DRAGDROP_ACTION_NONE),
+      mEffectAllowed(nsIDragService::DRAGDROP_ACTION_UNINITIALIZED),
+      mEventMessage(aEventMessage),
+      mCursorState(false),
+      mMode(ModeForEvent(aEventMessage)),
+      mIsExternal(aIsExternal),
+      mUserCancelled(false),
+      mIsCrossDomainSubFrameDrop(false),
+      mClipboardType(aClipboardType),
+      mDragImageX(0),
+      mDragImageY(0) {
+  mItems = new DataTransferItemList(this);
+
+  // For external usage, cache the data from the native clipboard or drag.
+  if (mIsExternal && mMode != Mode::ReadWrite) {
+    if (aEventMessage == ePasteNoFormatting) {
+      mEventMessage = ePaste;
+      CacheExternalClipboardFormats(true);
+    } else if (aEventMessage == ePaste) {
+      CacheExternalClipboardFormats(false);
+    } else if (aEventMessage >= eDragDropEventFirst &&
+               aEventMessage <= eDragDropEventLast) {
+      CacheExternalDragFormats();
+    }
+  }
+}
+
+DataTransfer::DataTransfer(nsISupports* aParent, EventMessage aEventMessage,
+                           nsITransferable* aTransferable)
+    : mParent(aParent),
+      mTransferable(aTransferable),
+      mDropEffect(nsIDragService::DRAGDROP_ACTION_NONE),
+      mEffectAllowed(nsIDragService::DRAGDROP_ACTION_UNINITIALIZED),
+      mEventMessage(aEventMessage),
+      mCursorState(false),
+      mMode(ModeForEvent(aEventMessage)),
+      mIsExternal(true),
+      mUserCancelled(false),
+      mIsCrossDomainSubFrameDrop(false),
+      mClipboardType(-1),
+      mDragImageX(0),
+      mDragImageY(0) {
+  mItems = new DataTransferItemList(this);
+
+  // XXX Currently, we cannot make DataTransfer grabs mTransferable for long
+  //     time because nsITransferable is not cycle collectable but this may
+  //     be grabbed by JS.  Additionally, the data initializing path is too
+  //     complicated (too optimized) for D&D and clipboard.  They are cached
+  //     only formats first, then, data of all items will be filled by the
+  //     items later and by themselves.  However, we shouldn't duplicate such
+  //     path for saving the maintenance cost.  Therefore, we need to treat
+  //     that DataTransfer and its items are in external mode.  Finally,
+  //     release mTransferable and make them in internal mode.
+  CacheTransferableFormats();
+  FillAllExternalData();
+  // Now, we have all necessary data of mTransferable.  So, we can work as
+  // internal mode.
+  mIsExternal = false;
+  // Release mTransferable because it won't be referred anymore.
+  mTransferable = nullptr;
+}
+
+DataTransfer::DataTransfer(nsISupports* aParent, EventMessage aEventMessage,
+                           const nsAString& aString)
+    : mParent(aParent),
+      mDropEffect(nsIDragService::DRAGDROP_ACTION_NONE),
+      mEffectAllowed(nsIDragService::DRAGDROP_ACTION_UNINITIALIZED),
+      mEventMessage(aEventMessage),
+      mCursorState(false),
+      mMode(ModeForEvent(aEventMessage)),
+      mIsExternal(false),
+      mUserCancelled(false),
+      mIsCrossDomainSubFrameDrop(false),
+      mClipboardType(-1),
+      mDragImageX(0),
+      mDragImageY(0) {
+  mItems = new DataTransferItemList(this);
+
+  nsCOMPtr<nsIPrincipal> sysPrincipal = nsContentUtils::GetSystemPrincipal();
+
+  RefPtr<nsVariantCC> variant = new nsVariantCC();
+  variant->SetAsAString(aString);
+  DebugOnly<nsresult> rvIgnored =
+      SetDataWithPrincipal(u"text/plain"_ns, variant, 0, sysPrincipal, false);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rvIgnored),
+                       "Failed to set given string to the DataTransfer object");
+}
+
+DataTransfer::DataTransfer(nsISupports* aParent, EventMessage aEventMessage,
+                           const uint32_t aEffectAllowed, bool aCursorState,
+                           bool aIsExternal, bool aUserCancelled,
+                           bool aIsCrossDomainSubFrameDrop,
+                           int32_t aClipboardType, DataTransferItemList* aItems,
+                           Element* aDragImage, uint32_t aDragImageX,
+                           uint32_t aDragImageY, bool aShowFailAnimation)
+    : mParent(aParent),
+      mDropEffect(nsIDragService::DRAGDROP_ACTION_NONE),
+      mEffectAllowed(aEffectAllowed),
+      mEventMessage(aEventMessage),
+      mCursorState(aCursorState),
+      mMode(ModeForEvent(aEventMessage)),
+      mIsExternal(aIsExternal),
+      mUserCancelled(aUserCancelled),
+      mIsCrossDomainSubFrameDrop(aIsCrossDomainSubFrameDrop),
+      mClipboardType(aClipboardType),
+      mDragImage(aDragImage),
+      mDragImageX(aDragImageX),
+      mDragImageY(aDragImageY),
+      mShowFailAnimation(aShowFailAnimation) {
+  MOZ_ASSERT(mParent);
+  MOZ_ASSERT(aItems);
+
+  // We clone the items array after everything else, so that it has a valid
+  // mParent value
+  mItems = aItems->Clone(this);
+  // The items are copied from aItems into mItems. There is no need to copy
+  // the actual data in the items as the data transfer will be read only. The
+  // dragstart event is the only time when items are
+  // modifiable, but those events should have been using the first constructor
+  // above.
+  NS_ASSERTION(aEventMessage != eDragStart,
+               "invalid event type for DataTransfer constructor");
+}
+
+DataTransfer::~DataTransfer() = default;
+
+// static
+already_AddRefed<DataTransfer> DataTransfer::Constructor(
+    const GlobalObject& aGlobal) {
+  RefPtr<DataTransfer> transfer =
+      new DataTransfer(aGlobal.GetAsSupports(), eCopy, /* is external */ false,
+                       /* clipboard type */ -1);
+  transfer->mEffectAllowed = nsIDragService::DRAGDROP_ACTION_NONE;
+  return transfer.forget();
+}
+
+JSObject* DataTransfer::WrapObject(JSContext* aCx,
+                                   JS::Handle<JSObject*> aGivenProto) {
+  return DataTransfer_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+void DataTransfer::SetDropEffect(const nsAString& aDropEffect) {
+  // the drop effect can only be 'none', 'copy', 'move' or 'link'.
+  for (uint32_t e = 0; e <= nsIDragService::DRAGDROP_ACTION_LINK; e++) {
+    if (aDropEffect.EqualsASCII(sEffects[e])) {
+      // don't allow copyMove
+      if (e != (nsIDragService::DRAGDROP_ACTION_COPY |
+                nsIDragService::DRAGDROP_ACTION_MOVE)) {
+        mDropEffect = e;
+      }
+      break;
+    }
+  }
+}
+
+void DataTransfer::SetEffectAllowed(const nsAString& aEffectAllowed) {
+  if (aEffectAllowed.EqualsLiteral("uninitialized")) {
+    mEffectAllowed = nsIDragService::DRAGDROP_ACTION_UNINITIALIZED;
+    return;
+  }
+
+  static_assert(nsIDragService::DRAGDROP_ACTION_NONE == 0,
+                "DRAGDROP_ACTION_NONE constant is wrong");
+  static_assert(nsIDragService::DRAGDROP_ACTION_COPY == 1,
+                "DRAGDROP_ACTION_COPY constant is wrong");
+  static_assert(nsIDragService::DRAGDROP_ACTION_MOVE == 2,
+                "DRAGDROP_ACTION_MOVE constant is wrong");
+  static_assert(nsIDragService::DRAGDROP_ACTION_LINK == 4,
+                "DRAGDROP_ACTION_LINK constant is wrong");
+
+  for (uint32_t e = 0; e < ArrayLength(sEffects); e++) {
+    if (aEffectAllowed.EqualsASCII(sEffects[e])) {
+      mEffectAllowed = e;
+      break;
+    }
+  }
+}
+
+void DataTransfer::GetMozTriggeringPrincipalURISpec(
+    nsAString& aPrincipalURISpec) {
+  nsCOMPtr<nsIDragSession> dragSession = nsContentUtils::GetDragSession();
+  if (!dragSession) {
+    aPrincipalURISpec.Truncate(0);
+    return;
+  }
+
+  nsCOMPtr<nsIPrincipal> principal;
+  dragSession->GetTriggeringPrincipal(getter_AddRefs(principal));
+  if (!principal) {
+    aPrincipalURISpec.Truncate(0);
+    return;
+  }
+
+  nsAutoCString spec;
+  principal->GetAsciiSpec(spec);
+  CopyUTF8toUTF16(spec, aPrincipalURISpec);
+}
+
+nsIContentSecurityPolicy* DataTransfer::GetMozCSP() {
+  nsCOMPtr<nsIDragSession> dragSession = nsContentUtils::GetDragSession();
+  if (!dragSession) {
+    return nullptr;
+  }
+  nsCOMPtr<nsIContentSecurityPolicy> csp;
+  dragSession->GetCsp(getter_AddRefs(csp));
+  return csp;
+}
+
+already_AddRefed<FileList> DataTransfer::GetFiles(
+    nsIPrincipal& aSubjectPrincipal) {
+  return mItems->Files(&aSubjectPrincipal);
+}
+
+void DataTransfer::GetTypes(nsTArray<nsString>& aTypes,
+                            CallerType aCallerType) const {
+  // When called from bindings, aTypes will be empty, but since we might have
+  // Gecko-internal callers too, clear it to be safe.
+  aTypes.Clear();
+
+  return mItems->GetTypes(aTypes, aCallerType);
+}
+
+bool DataTransfer::HasType(const nsAString& aType) const {
+  return mItems->HasType(aType);
+}
+
+bool DataTransfer::HasFile() const { return mItems->HasFile(); }
+
+void DataTransfer::GetData(const nsAString& aFormat, nsAString& aData,
+                           nsIPrincipal& aSubjectPrincipal,
+                           ErrorResult& aRv) const {
+  // return an empty string if data for the format was not found
+  aData.Truncate();
+
+  nsCOMPtr<nsIVariant> data;
+  nsresult rv =
+      GetDataAtInternal(aFormat, 0, &aSubjectPrincipal, getter_AddRefs(data));
+  if (NS_FAILED(rv)) {
+    if (rv != NS_ERROR_DOM_INDEX_SIZE_ERR) {
+      aRv.Throw(rv);
+    }
+    return;
+  }
+
+  if (data) {
+    nsAutoString stringdata;
+    data->GetAsAString(stringdata);
+
+    // for the URL type, parse out the first URI from the list. The URIs are
+    // separated by newlines
+    nsAutoString lowercaseFormat;
+    nsContentUtils::ASCIIToLower(aFormat, lowercaseFormat);
+
+    if (lowercaseFormat.EqualsLiteral("url")) {
+      int32_t lastidx = 0, idx;
+      int32_t length = stringdata.Length();
+      while (lastidx < length) {
+        idx = stringdata.FindChar('\n', lastidx);
+        // lines beginning with # are comments
+        if (stringdata[lastidx] == '#') {
+          if (idx == -1) {
+            break;
+          }
+        } else {
+          if (idx == -1) {
+            aData.Assign(Substring(stringdata, lastidx));
+          } else {
+            aData.Assign(Substring(stringdata, lastidx, idx - lastidx));
+          }
+          aData =
+              nsContentUtils::TrimWhitespace<nsCRT::IsAsciiSpace>(aData, true);
+          return;
+        }
+        lastidx = idx + 1;
+      }
+    } else {
+      aData = stringdata;
+    }
+  }
+}
+
+void DataTransfer::SetData(const nsAString& aFormat, const nsAString& aData,
+                           nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+  RefPtr<nsVariantCC> variant = new nsVariantCC();
+  variant->SetAsAString(aData);
+
+  aRv = SetDataAtInternal(aFormat, variant, 0, &aSubjectPrincipal);
+}
+
+void DataTransfer::ClearData(const Optional<nsAString>& aFormat,
+                             nsIPrincipal& aSubjectPrincipal,
+                             ErrorResult& aRv) {
+  if (IsReadOnly()) {
+    aRv.Throw(NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR);
+    return;
+  }
+
+  if (MozItemCount() == 0) {
+    return;
+  }
+
+  if (aFormat.WasPassed()) {
+    MozClearDataAtHelper(aFormat.Value(), 0, aSubjectPrincipal, aRv);
+  } else {
+    MozClearDataAtHelper(u""_ns, 0, aSubjectPrincipal, aRv);
+  }
+}
+
+void DataTransfer::SetMozCursor(const nsAString& aCursorState) {
+  // Lock the cursor to an arrow during the drag.
+  mCursorState = aCursorState.EqualsLiteral("default");
+}
+
+already_AddRefed<nsINode> DataTransfer::GetMozSourceNode() {
+  nsCOMPtr<nsIDragSession> dragSession = nsContentUtils::GetDragSession();
+  if (!dragSession) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsINode> sourceNode;
+  dragSession->GetSourceNode(getter_AddRefs(sourceNode));
+  if (sourceNode && !nsContentUtils::LegacyIsCallerNativeCode() &&
+      !nsContentUtils::CanCallerAccess(sourceNode)) {
+    return nullptr;
+  }
+
+  return sourceNode.forget();
+}
+
+already_AddRefed<WindowContext> DataTransfer::GetSourceTopWindowContext() {
+  nsCOMPtr<nsIDragSession> dragSession = nsContentUtils::GetDragSession();
+  if (!dragSession) {
+    return nullptr;
+  }
+
+  RefPtr<WindowContext> sourceTopWindowContext;
+  dragSession->GetSourceTopWindowContext(
+      getter_AddRefs(sourceTopWindowContext));
+  return sourceTopWindowContext.forget();
+}
+
+already_AddRefed<DOMStringList> DataTransfer::MozTypesAt(
+    uint32_t aIndex, ErrorResult& aRv) const {
+  // Only the first item is valid for clipboard events
+  if (aIndex > 0 && (mEventMessage == eCut || mEventMessage == eCopy ||
+                     mEventMessage == ePaste)) {
+    aRv.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+    return nullptr;
+  }
+
+  RefPtr<DOMStringList> types = new DOMStringList();
+  if (aIndex < MozItemCount()) {
+    // note that you can retrieve the types regardless of their principal
+    const nsTArray<RefPtr<DataTransferItem>>& items =
+        *mItems->MozItemsAt(aIndex);
+
+    bool addFile = false;
+    for (uint32_t i = 0; i < items.Length(); i++) {
+      // NOTE: The reason why we get the internal type here is because we want
+      // kFileMime to appear in the types list for backwards compatibility
+      // reasons.
+      nsAutoString type;
+      items[i]->GetInternalType(type);
+      if (NS_WARN_IF(!types->Add(type))) {
+        aRv.Throw(NS_ERROR_FAILURE);
+        return nullptr;
+      }
+
+      if (items[i]->Kind() == DataTransferItem::KIND_FILE) {
+        addFile = true;
+      }
+    }
+
+    if (addFile) {
+      types->Add(u"Files"_ns);
+    }
+  }
+
+  return types.forget();
+}
+
+nsresult DataTransfer::GetDataAtNoSecurityCheck(const nsAString& aFormat,
+                                                uint32_t aIndex,
+                                                nsIVariant** aData) const {
+  return GetDataAtInternal(aFormat, aIndex,
+                           nsContentUtils::GetSystemPrincipal(), aData);
+}
+
+nsresult DataTransfer::GetDataAtInternal(const nsAString& aFormat,
+                                         uint32_t aIndex,
+                                         nsIPrincipal* aSubjectPrincipal,
+                                         nsIVariant** aData) const {
+  *aData = nullptr;
+
+  if (aFormat.IsEmpty()) {
+    return NS_OK;
+  }
+
+  if (aIndex >= MozItemCount()) {
+    return NS_ERROR_DOM_INDEX_SIZE_ERR;
+  }
+
+  // Only the first item is valid for clipboard events
+  if (aIndex > 0 && (mEventMessage == eCut || mEventMessage == eCopy ||
+                     mEventMessage == ePaste)) {
+    return NS_ERROR_DOM_INDEX_SIZE_ERR;
+  }
+
+  nsAutoString format;
+  GetRealFormat(aFormat, format);
+
+  MOZ_ASSERT(aSubjectPrincipal);
+
+  RefPtr<DataTransferItem> item = mItems->MozItemByTypeAt(format, aIndex);
+  if (!item) {
+    // The index exists but there's no data for the specified format, in this
+    // case we just return undefined
+    return NS_OK;
+  }
+
+  // If we have chrome only content, and we aren't chrome, don't allow access
+  if (!aSubjectPrincipal->IsSystemPrincipal() && item->ChromeOnly()) {
+    return NS_OK;
+  }
+
+  // DataTransferItem::Data() handles the principal checks
+  ErrorResult result;
+  nsCOMPtr<nsIVariant> data = item->Data(aSubjectPrincipal, result);
+  if (NS_WARN_IF(!data || result.Failed())) {
+    return result.StealNSResult();
+  }
+
+  data.forget(aData);
+  return NS_OK;
+}
+
+void DataTransfer::MozGetDataAt(JSContext* aCx, const nsAString& aFormat,
+                                uint32_t aIndex,
+                                JS::MutableHandle<JS::Value> aRetval,
+                                mozilla::ErrorResult& aRv) {
+  nsCOMPtr<nsIVariant> data;
+  aRv = GetDataAtInternal(aFormat, aIndex, nsContentUtils::GetSystemPrincipal(),
+                          getter_AddRefs(data));
+  if (aRv.Failed()) {
+    return;
+  }
+
+  if (!data) {
+    aRetval.setNull();
+    return;
+  }
+
+  JS::Rooted<JS::Value> result(aCx);
+  if (!VariantToJsval(aCx, data, aRetval)) {
+    aRv = NS_ERROR_FAILURE;
+    return;
+  }
+}
+
+/* static */
+bool DataTransfer::PrincipalMaySetData(const nsAString& aType,
+                                       nsIVariant* aData,
+                                       nsIPrincipal* aPrincipal) {
+  if (!aPrincipal->IsSystemPrincipal()) {
+    DataTransferItem::eKind kind = DataTransferItem::KindFromData(aData);
+    if (kind == DataTransferItem::KIND_OTHER) {
+      NS_WARNING("Disallowing adding non string/file types to DataTransfer");
+      return false;
+    }
+
+    // Don't allow adding internal types of the form */x-moz-*, but
+    // special-case the url types as they are simple variations of urls.
+    // In addition, allow x-moz-place flavors to be added by WebExtensions.
+    if (FindInReadable(kInternal_Mimetype_Prefix, aType) &&
+        !StringBeginsWith(aType, u"text/x-moz-url"_ns)) {
+      auto principal = BasePrincipal::Cast(aPrincipal);
+      if (!principal->AddonPolicy() ||
+          !StringBeginsWith(aType, u"text/x-moz-place"_ns)) {
+        NS_WARNING("Disallowing adding this type to DataTransfer");
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+void DataTransfer::TypesListMayHaveChanged() {
+  DataTransfer_Binding::ClearCachedTypesValue(this);
+}
+
+already_AddRefed<DataTransfer> DataTransfer::MozCloneForEvent(
+    const nsAString& aEvent, ErrorResult& aRv) {
+  RefPtr<nsAtom> atomEvt = NS_Atomize(aEvent);
+  if (!atomEvt) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return nullptr;
+  }
+  EventMessage eventMessage = nsContentUtils::GetEventMessage(atomEvt);
+
+  RefPtr<DataTransfer> dt;
+  nsresult rv = Clone(mParent, eventMessage, false, false, getter_AddRefs(dt));
+  if (NS_FAILED(rv)) {
+    aRv.Throw(rv);
+    return nullptr;
+  }
+  return dt.forget();
+}
+
+// The order of the types matters. `kFileMime` needs to be one of the first two
+// types.
+static const char* kNonPlainTextExternalFormats[] = {
+    kCustomTypesMime, kFileMime, kHTMLMime,     kRTFMime,  kURLMime,
+    kURLDataMime,     kTextMime, kPNGImageMime, kPDFJSMime};
+
+/* static */
+void DataTransfer::GetExternalClipboardFormats(const int32_t& aWhichClipboard,
+                                               const bool& aPlainTextOnly,
+                                               nsTArray<nsCString>* aResult) {
+  MOZ_ASSERT(aResult);
+
+  // NOTE: When you change this method, you may need to change
+  //       GetExternalTransferableFormats() too since those methods should
+  //       work similarly.
+
+  nsCOMPtr<nsIClipboard> clipboard =
+      do_GetService("@mozilla.org/widget/clipboard;1");
+  if (!clipboard || aWhichClipboard < 0) {
+    return;
+  }
+
+  if (aPlainTextOnly) {
+    bool hasType;
+    AutoTArray<nsCString, 1> textMime = {nsDependentCString(kTextMime)};
+    nsresult rv =
+        clipboard->HasDataMatchingFlavors(textMime, aWhichClipboard, &hasType);
+    NS_SUCCEEDED(rv);
+    if (hasType) {
+      aResult->AppendElement(kTextMime);
+    }
+    return;
+  }
+
+  // If not plain text only, then instead check all the other types
+  for (uint32_t f = 0; f < mozilla::ArrayLength(kNonPlainTextExternalFormats);
+       ++f) {
+    bool hasType;
+    AutoTArray<nsCString, 1> format = {
+        nsDependentCString(kNonPlainTextExternalFormats[f])};
+    nsresult rv =
+        clipboard->HasDataMatchingFlavors(format, aWhichClipboard, &hasType);
+    NS_SUCCEEDED(rv);
+    if (hasType) {
+      aResult->AppendElement(kNonPlainTextExternalFormats[f]);
+    }
+  }
+}
+
+/* static */
+void DataTransfer::GetExternalTransferableFormats(
+    nsITransferable* aTransferable, bool aPlainTextOnly,
+    nsTArray<nsCString>* aResult) {
+  MOZ_ASSERT(aTransferable);
+  MOZ_ASSERT(aResult);
+
+  aResult->Clear();
+
+  // NOTE: When you change this method, you may need to change
+  //       GetExternalClipboardFormats() too since those methods should
+  //       work similarly.
+
+  AutoTArray<nsCString, 10> flavors;
+  aTransferable->FlavorsTransferableCanExport(flavors);
+
+  if (aPlainTextOnly) {
+    auto index = flavors.IndexOf(nsLiteralCString(kTextMime));
+    if (index != flavors.NoIndex) {
+      aResult->AppendElement(nsLiteralCString(kTextMime));
+    }
+    return;
+  }
+
+  // If not plain text only, then instead check all the other types
+  for (const char* format : kNonPlainTextExternalFormats) {
+    auto index = flavors.IndexOf(nsCString(format));
+    if (index != flavors.NoIndex) {
+      aResult->AppendElement(nsCString(format));
+    }
+  }
+}
+
+nsresult DataTransfer::SetDataAtInternal(const nsAString& aFormat,
+                                         nsIVariant* aData, uint32_t aIndex,
+                                         nsIPrincipal* aSubjectPrincipal) {
+  if (aFormat.IsEmpty()) {
+    return NS_OK;
+  }
+
+  if (IsReadOnly()) {
+    return NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR;
+  }
+
+  // Specifying an index less than the current length will replace an existing
+  // item. Specifying an index equal to the current length will add a new item.
+  if (aIndex > MozItemCount()) {
+    return NS_ERROR_DOM_INDEX_SIZE_ERR;
+  }
+
+  // Only the first item is valid for clipboard events
+  if (aIndex > 0 && (mEventMessage == eCut || mEventMessage == eCopy ||
+                     mEventMessage == ePaste)) {
+    return NS_ERROR_DOM_INDEX_SIZE_ERR;
+  }
+
+  // Don't allow the custom type to be assigned.
+  if (aFormat.EqualsLiteral(kCustomTypesMime)) {
+    return NS_ERROR_DOM_NOT_SUPPORTED_ERR;
+  }
+
+  if (!PrincipalMaySetData(aFormat, aData, aSubjectPrincipal)) {
+    return NS_ERROR_DOM_SECURITY_ERR;
+  }
+
+  return SetDataWithPrincipal(aFormat, aData, aIndex, aSubjectPrincipal);
+}
+
+void DataTransfer::MozSetDataAt(JSContext* aCx, const nsAString& aFormat,
+                                JS::Handle<JS::Value> aData, uint32_t aIndex,
+                                ErrorResult& aRv) {
+  nsCOMPtr<nsIVariant> data;
+  aRv = nsContentUtils::XPConnect()->JSValToVariant(aCx, aData,
+                                                    getter_AddRefs(data));
+  if (!aRv.Failed()) {
+    aRv = SetDataAtInternal(aFormat, data, aIndex,
+                            nsContentUtils::GetSystemPrincipal());
+  }
+}
+
+void DataTransfer::MozClearDataAt(const nsAString& aFormat, uint32_t aIndex,
+                                  ErrorResult& aRv) {
+  if (IsReadOnly()) {
+    aRv.Throw(NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR);
+    return;
+  }
+
+  if (aIndex >= MozItemCount()) {
+    aRv.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+    return;
+  }
+
+  // Only the first item is valid for clipboard events
+  if (aIndex > 0 && (mEventMessage == eCut || mEventMessage == eCopy ||
+                     mEventMessage == ePaste)) {
+    aRv.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+    return;
+  }
+
+  MozClearDataAtHelper(aFormat, aIndex, *nsContentUtils::GetSystemPrincipal(),
+                       aRv);
+
+  // If we just cleared the 0-th index, and there are still more than 1 indexes
+  // remaining, MozClearDataAt should cause the 1st index to become the 0th
+  // index. This should _only_ happen when the MozClearDataAt function is
+  // explicitly called by script, as this behavior is inconsistent with spec.
+  // (however, so is the MozClearDataAt API)
+
+  if (aIndex == 0 && mItems->MozItemCount() > 1 &&
+      mItems->MozItemsAt(0)->Length() == 0) {
+    mItems->PopIndexZero();
+  }
+}
+
+void DataTransfer::MozClearDataAtHelper(const nsAString& aFormat,
+                                        uint32_t aIndex,
+                                        nsIPrincipal& aSubjectPrincipal,
+                                        ErrorResult& aRv) {
+  MOZ_ASSERT(!IsReadOnly());
+  MOZ_ASSERT(aIndex < MozItemCount());
+  MOZ_ASSERT(aIndex == 0 || (mEventMessage != eCut && mEventMessage != eCopy &&
+                             mEventMessage != ePaste));
+
+  nsAutoString format;
+  GetRealFormat(aFormat, format);
+
+  mItems->MozRemoveByTypeAt(format, aIndex, aSubjectPrincipal, aRv);
+}
+
+void DataTransfer::SetDragImage(Element& aImage, int32_t aX, int32_t aY) {
+  if (!IsReadOnly()) {
+    mDragImage = &aImage;
+    mDragImageX = aX;
+    mDragImageY = aY;
+  }
+}
+
+void DataTransfer::UpdateDragImage(Element& aImage, int32_t aX, int32_t aY) {
+  if (mEventMessage < eDragDropEventFirst ||
+      mEventMessage > eDragDropEventLast) {
+    return;
+  }
+
+  nsCOMPtr<nsIDragSession> dragSession = nsContentUtils::GetDragSession();
+  if (dragSession) {
+    dragSession->UpdateDragImage(&aImage, aX, aY);
+  }
+}
+
+void DataTransfer::AddElement(Element& aElement, ErrorResult& aRv) {
+  if (IsReadOnly()) {
+    aRv.Throw(NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR);
+    return;
+  }
+
+  mDragTarget = &aElement;
+}
+
+nsresult DataTransfer::Clone(nsISupports* aParent, EventMessage aEventMessage,
+                             bool aUserCancelled,
+                             bool aIsCrossDomainSubFrameDrop,
+                             DataTransfer** aNewDataTransfer) {
+  RefPtr<DataTransfer> newDataTransfer = new DataTransfer(
+      aParent, aEventMessage, mEffectAllowed, mCursorState, mIsExternal,
+      aUserCancelled, aIsCrossDomainSubFrameDrop, mClipboardType, mItems,
+      mDragImage, mDragImageX, mDragImageY, mShowFailAnimation);
+
+  newDataTransfer.forget(aNewDataTransfer);
+  return NS_OK;
+}
+
+already_AddRefed<nsIArray> DataTransfer::GetTransferables(
+    nsINode* aDragTarget) {
+  MOZ_ASSERT(aDragTarget);
+
+  Document* doc = aDragTarget->GetComposedDoc();
+  if (!doc) {
+    return nullptr;
+  }
+
+  return GetTransferables(doc->GetLoadContext());
+}
+
+already_AddRefed<nsIArray> DataTransfer::GetTransferables(
+    nsILoadContext* aLoadContext) {
+  nsCOMPtr<nsIMutableArray> transArray = nsArray::Create();
+  if (!transArray) {
+    return nullptr;
+  }
+
+  uint32_t count = MozItemCount();
+  for (uint32_t i = 0; i < count; i++) {
+    nsCOMPtr<nsITransferable> transferable = GetTransferable(i, aLoadContext);
+    if (transferable) {
+      transArray->AppendElement(transferable);
+    }
+  }
+
+  return transArray.forget();
+}
+
+already_AddRefed<nsITransferable> DataTransfer::GetTransferable(
+    uint32_t aIndex, nsILoadContext* aLoadContext) {
+  if (aIndex >= MozItemCount()) {
+    return nullptr;
+  }
+
+  const nsTArray<RefPtr<DataTransferItem>>& item = *mItems->MozItemsAt(aIndex);
+  uint32_t count = item.Length();
+  if (!count) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsITransferable> transferable =
+      do_CreateInstance("@mozilla.org/widget/transferable;1");
+  if (!transferable) {
+    return nullptr;
+  }
+  transferable->Init(aLoadContext);
+
+  nsCOMPtr<nsIStorageStream> storageStream;
+  nsCOMPtr<nsIObjectOutputStream> stream;
+
+  bool added = false;
+  bool handlingCustomFormats = true;
+
+  // When writing the custom data, we need to ensure that there is sufficient
+  // space for a (uint32_t) data ending type, and the null byte character at
+  // the end of the nsCString. We claim that space upfront and store it in
+  // baseLength. This value will be set to zero if a write error occurs
+  // indicating that the data and length are no longer valid.
+  const uint32_t baseLength = sizeof(uint32_t) + 1;
+  uint32_t totalCustomLength = baseLength;
+
+  /*
+   * Two passes are made here to iterate over all of the types. First, look for
+   * any types that are not in the list of known types. For this pass,
+   * handlingCustomFormats will be true. Data that corresponds to unknown types
+   * will be pulled out and inserted into a single type (kCustomTypesMime) by
+   * writing the data into a stream.
+   *
+   * The second pass will iterate over the formats looking for known types.
+   * These are added as is. The unknown types are all then inserted as a single
+   * type (kCustomTypesMime) in the same position of the first custom type. This
+   * model is used to maintain the format order as best as possible.
+   *
+   * The format of the kCustomTypesMime type is one or more of the following
+   * stored sequentially:
+   *   <32-bit> type (only none or string is supported)
+   *   <32-bit> length of format
+   *   <wide string> format
+   *   <32-bit> length of data
+   *   <wide string> data
+   * A type of eCustomClipboardTypeId_None ends the list, without any following
+   * data.
+   */
+  do {
+    for (uint32_t f = 0; f < count; f++) {
+      RefPtr<DataTransferItem> formatitem = item[f];
+      nsCOMPtr<nsIVariant> variant = formatitem->DataNoSecurityCheck();
+      if (!variant) {  // skip empty items
+        continue;
+      }
+
+      nsAutoString type;
+      formatitem->GetInternalType(type);
+
+      // If the data is of one of the well-known formats, use it directly.
+      bool isCustomFormat = true;
+      for (const char* format : kKnownFormats) {
+        if (type.EqualsASCII(format)) {
+          isCustomFormat = false;
+          break;
+        }
+      }
+
+      uint32_t lengthInBytes;
+      nsCOMPtr<nsISupports> convertedData;
+
+      if (handlingCustomFormats) {
+        if (!ConvertFromVariant(variant, getter_AddRefs(convertedData),
+                                &lengthInBytes)) {
+          continue;
+        }
+
+        // When handling custom types, add the data to the stream if this is a
+        // custom type. If totalCustomLength is 0, then a write error occurred
+        // on a previous item, so ignore any others.
+        if (isCustomFormat && totalCustomLength > 0) {
+          // If it isn't a string, just ignore it. The dataTransfer is cached in
+          // the drag sesion during drag-and-drop, so non-strings will be
+          // available when dragging locally.
+          nsCOMPtr<nsISupportsString> str(do_QueryInterface(convertedData));
+          if (str) {
+            nsAutoString data;
+            str->GetData(data);
+
+            if (!stream) {
+              // Create a storage stream to write to.
+              NS_NewStorageStream(1024, UINT32_MAX,
+                                  getter_AddRefs(storageStream));
+
+              nsCOMPtr<nsIOutputStream> outputStream;
+              storageStream->GetOutputStream(0, getter_AddRefs(outputStream));
+
+              stream = NS_NewObjectOutputStream(outputStream);
+            }
+
+            CheckedInt<uint32_t> formatLength =
+                CheckedInt<uint32_t>(type.Length()) *
+                sizeof(nsString::char_type);
+
+            // The total size of the stream is the format length, the data
+            // length, two integers to hold the lengths and one integer for
+            // the string flag. Guard against large data by ignoring any that
+            // don't fit.
+            CheckedInt<uint32_t> newSize = formatLength + totalCustomLength +
+                                           lengthInBytes +
+                                           (sizeof(uint32_t) * 3);
+            if (newSize.isValid()) {
+              // If a write error occurs, set totalCustomLength to 0 so that
+              // further processing gets ignored.
+              nsresult rv = stream->Write32(eCustomClipboardTypeId_String);
+              if (NS_WARN_IF(NS_FAILED(rv))) {
+                totalCustomLength = 0;
+                continue;
+              }
+              rv = stream->Write32(formatLength.value());
+              if (NS_WARN_IF(NS_FAILED(rv))) {
+                totalCustomLength = 0;
+                continue;
+              }
+              MOZ_ASSERT(formatLength.isValid() &&
+                             formatLength.value() ==
+                                 type.Length() * sizeof(nsString::char_type),
+                         "Why is formatLength off?");
+              rv = stream->WriteBytes(
+                  AsBytes(Span(type.BeginReading(), type.Length())));
+              if (NS_WARN_IF(NS_FAILED(rv))) {
+                totalCustomLength = 0;
+                continue;
+              }
+              rv = stream->Write32(lengthInBytes);
+              if (NS_WARN_IF(NS_FAILED(rv))) {
+                totalCustomLength = 0;
+                continue;
+              }
+              // XXXbz it's not obvious to me that lengthInBytes is the actual
+              // length of "data" if the variant contained an nsISupportsString
+              // as VTYPE_INTERFACE, say.  We used lengthInBytes above for
+              // sizing, so just keep doing that.
+              rv = stream->WriteBytes(
+                  Span(reinterpret_cast<const uint8_t*>(data.BeginReading()),
+                       lengthInBytes));
+              if (NS_WARN_IF(NS_FAILED(rv))) {
+                totalCustomLength = 0;
+                continue;
+              }
+
+              totalCustomLength = newSize.value();
+            }
+          }
+        }
+      } else if (isCustomFormat && stream) {
+        // This is the second pass of the loop (handlingCustomFormats is false).
+        // When encountering the first custom format, append all of the stream
+        // at this position. If totalCustomLength is 0 indicating a write error
+        // occurred, or no data has been added to it, don't output anything,
+        if (totalCustomLength > baseLength) {
+          // Write out an end of data terminator.
+          nsresult rv = stream->Write32(eCustomClipboardTypeId_None);
+          if (NS_SUCCEEDED(rv)) {
+            nsCOMPtr<nsIInputStream> inputStream;
+            storageStream->NewInputStream(0, getter_AddRefs(inputStream));
+
+            RefPtr<nsStringBuffer> stringBuffer =
+                nsStringBuffer::Alloc(totalCustomLength);
+
+            // Subtract off the null terminator when reading.
+            totalCustomLength--;
+
+            // Read the data from the stream and add a null-terminator as
+            // ToString needs it.
+            uint32_t amountRead;
+            rv = inputStream->Read(static_cast<char*>(stringBuffer->Data()),
+                                   totalCustomLength, &amountRead);
+            if (NS_SUCCEEDED(rv)) {
+              static_cast<char*>(stringBuffer->Data())[amountRead] = 0;
+
+              nsCString str;
+              stringBuffer->ToString(totalCustomLength, str);
+              nsCOMPtr<nsISupportsCString> strSupports(
+                  do_CreateInstance(NS_SUPPORTS_CSTRING_CONTRACTID));
+              strSupports->SetData(str);
+
+              nsresult rv =
+                  transferable->SetTransferData(kCustomTypesMime, strSupports);
+              if (NS_FAILED(rv)) {
+                return nullptr;
+              }
+
+              added = true;
+            }
+          }
+        }
+
+        // Clear the stream so it doesn't get used again.
+        stream = nullptr;
+      } else {
+        // This is the second pass of the loop and a known type is encountered.
+        // Add it as is.
+        if (!ConvertFromVariant(variant, getter_AddRefs(convertedData),
+                                &lengthInBytes)) {
+          continue;
+        }
+
+        NS_ConvertUTF16toUTF8 format(type);
+
+        // If a converter is set for a format, set the converter for the
+        // transferable and don't add the item
+        nsCOMPtr<nsIFormatConverter> converter =
+            do_QueryInterface(convertedData);
+        if (converter) {
+          transferable->AddDataFlavor(format.get());
+          transferable->SetConverter(converter);
+          continue;
+        }
+
+        nsresult rv =
+            transferable->SetTransferData(format.get(), convertedData);
+        if (NS_FAILED(rv)) {
+          return nullptr;
+        }
+
+        added = true;
+      }
+    }
+
+    handlingCustomFormats = !handlingCustomFormats;
+  } while (!handlingCustomFormats);
+
+  // only return the transferable if data was successfully added to it
+  if (added) {
+    return transferable.forget();
+  }
+
+  return nullptr;
+}
+
+bool DataTransfer::ConvertFromVariant(nsIVariant* aVariant,
+                                      nsISupports** aSupports,
+                                      uint32_t* aLength) const {
+  *aSupports = nullptr;
+  *aLength = 0;
+
+  uint16_t type = aVariant->GetDataType();
+  if (type == nsIDataType::VTYPE_INTERFACE ||
+      type == nsIDataType::VTYPE_INTERFACE_IS) {
+    nsCOMPtr<nsISupports> data;
+    if (NS_FAILED(aVariant->GetAsISupports(getter_AddRefs(data)))) {
+      return false;
+    }
+
+    // For flavour data providers, use 0 as the length.
+    if (nsCOMPtr<nsIFlavorDataProvider> fdp = do_QueryInterface(data)) {
+      fdp.forget(aSupports);
+      *aLength = 0;
+      return true;
+    }
+
+    // Only use the underlying BlobImpl for transferables.
+    if (RefPtr<Blob> blob = do_QueryObject(data)) {
+      RefPtr<BlobImpl> blobImpl = blob->Impl();
+      blobImpl.forget(aSupports);
+    } else {
+      data.forget(aSupports);
+    }
+
+    *aLength = sizeof(nsISupports*);
+    return true;
+  }
+
+  nsAutoString str;
+  nsresult rv = aVariant->GetAsAString(str);
+  if (NS_FAILED(rv)) {
+    return false;
+  }
+
+  nsCOMPtr<nsISupportsString> strSupports(
+      do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID));
+  if (!strSupports) {
+    return false;
+  }
+
+  strSupports->SetData(str);
+
+  strSupports.forget(aSupports);
+
+  // each character is two bytes
+  *aLength = str.Length() * 2;
+
+  return true;
+}
+
+void DataTransfer::Disconnect() {
+  SetMode(Mode::Protected);
+  if (StaticPrefs::dom_events_dataTransfer_protected_enabled()) {
+    ClearAll();
+  }
+}
+
+void DataTransfer::ClearAll() { mItems->ClearAllItems(); }
+
+uint32_t DataTransfer::MozItemCount() const { return mItems->MozItemCount(); }
+
+nsresult DataTransfer::SetDataWithPrincipal(const nsAString& aFormat,
+                                            nsIVariant* aData, uint32_t aIndex,
+                                            nsIPrincipal* aPrincipal,
+                                            bool aHidden) {
+  nsAutoString format;
+  GetRealFormat(aFormat, format);
+
+  ErrorResult rv;
+  RefPtr<DataTransferItem> item =
+      mItems->SetDataWithPrincipal(format, aData, aIndex, aPrincipal,
+                                   /* aInsertOnly = */ false, aHidden, rv);
+  return rv.StealNSResult();
+}
+
+void DataTransfer::SetDataWithPrincipalFromOtherProcess(
+    const nsAString& aFormat, nsIVariant* aData, uint32_t aIndex,
+    nsIPrincipal* aPrincipal, bool aHidden) {
+  if (aFormat.EqualsLiteral(kCustomTypesMime)) {
+    FillInExternalCustomTypes(aData, aIndex, aPrincipal);
+  } else {
+    nsAutoString format;
+    GetRealFormat(aFormat, format);
+
+    ErrorResult rv;
+    RefPtr<DataTransferItem> item =
+        mItems->SetDataWithPrincipal(format, aData, aIndex, aPrincipal,
+                                     /* aInsertOnly = */ false, aHidden, rv);
+    if (NS_WARN_IF(rv.Failed())) {
+      rv.SuppressException();
+    }
+  }
+}
+
+void DataTransfer::GetRealFormat(const nsAString& aInFormat,
+                                 nsAString& aOutFormat) const {
+  // For compatibility, treat text/unicode as equivalent to text/plain
+  nsAutoString lowercaseFormat;
+  nsContentUtils::ASCIIToLower(aInFormat, lowercaseFormat);
+  if (lowercaseFormat.EqualsLiteral("text") ||
+      lowercaseFormat.EqualsLiteral("text/unicode")) {
+    aOutFormat.AssignLiteral("text/plain");
+    return;
+  }
+
+  if (lowercaseFormat.EqualsLiteral("url")) {
+    aOutFormat.AssignLiteral("text/uri-list");
+    return;
+  }
+
+  aOutFormat.Assign(lowercaseFormat);
+}
+
+nsresult DataTransfer::CacheExternalData(const char* aFormat, uint32_t aIndex,
+                                         nsIPrincipal* aPrincipal,
+                                         bool aHidden) {
+  ErrorResult rv;
+  RefPtr<DataTransferItem> item;
+
+  if (strcmp(aFormat, kTextMime) == 0) {
+    item = mItems->SetDataWithPrincipal(u"text/plain"_ns, nullptr, aIndex,
+                                        aPrincipal, false, aHidden, rv);
+    if (NS_WARN_IF(rv.Failed())) {
+      return rv.StealNSResult();
+    }
+    return NS_OK;
+  }
+
+  if (strcmp(aFormat, kURLDataMime) == 0) {
+    item = mItems->SetDataWithPrincipal(u"text/uri-list"_ns, nullptr, aIndex,
+                                        aPrincipal, false, aHidden, rv);
+    if (NS_WARN_IF(rv.Failed())) {
+      return rv.StealNSResult();
+    }
+    return NS_OK;
+  }
+
+  nsAutoString format;
+  GetRealFormat(NS_ConvertUTF8toUTF16(aFormat), format);
+  item = mItems->SetDataWithPrincipal(format, nullptr, aIndex, aPrincipal,
+                                      false, aHidden, rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    return rv.StealNSResult();
+  }
+  return NS_OK;
+}
+
+void DataTransfer::CacheExternalDragFormats() {
+  // Called during the constructor to cache the formats available from an
+  // external drag. The data associated with each format will be set to null.
+  // This data will instead only be retrieved in FillInExternalDragData when
+  // asked for, as it may be time consuming for the source application to
+  // generate it.
+
+  nsCOMPtr<nsIDragSession> dragSession = nsContentUtils::GetDragSession();
+  if (!dragSession) {
+    return;
+  }
+
+  // make sure that the system principal is used for external drags
+  nsIScriptSecurityManager* ssm = nsContentUtils::GetSecurityManager();
+  nsCOMPtr<nsIPrincipal> sysPrincipal;
+  ssm->GetSystemPrincipal(getter_AddRefs(sysPrincipal));
+
+  // there isn't a way to get a list of the formats that might be available on
+  // all platforms, so just check for the types that can actually be imported
+  // XXXndeakin there are some other formats but those are platform specific.
+  // NOTE: kFileMime must have index 0
+  // TODO: should this be `kNonPlainTextExternalFormats` instead?
+  static const char* formats[] = {kFileMime,    kHTMLMime, kURLMime,
+                                  kURLDataMime, kTextMime, kPNGImageMime};
+
+  uint32_t count;
+  dragSession->GetNumDropItems(&count);
+  for (uint32_t c = 0; c < count; c++) {
+    bool hasFileData = false;
+    dragSession->IsDataFlavorSupported(kFileMime, &hasFileData);
+
+    // First, check for the special format that holds custom types.
+    bool supported;
+    dragSession->IsDataFlavorSupported(kCustomTypesMime, &supported);
+    if (supported) {
+      FillInExternalCustomTypes(c, sysPrincipal);
+    }
+
+    for (uint32_t f = 0; f < ArrayLength(formats); f++) {
+      // IsDataFlavorSupported doesn't take an index as an argument and just
+      // checks if any of the items support a particular flavor, even though
+      // the GetData method does take an index. Here, we just assume that
+      // every item being dragged has the same set of flavors.
+      bool supported;
+      dragSession->IsDataFlavorSupported(formats[f], &supported);
+      // if the format is supported, add an item to the array with null as
+      // the data. When retrieved, GetRealData will read the data.
+      if (supported) {
+        CacheExternalData(formats[f], c, sysPrincipal,
+                          /* hidden = */ f && hasFileData);
+      }
+    }
+  }
+}
+
+void DataTransfer::CacheExternalClipboardFormats(bool aPlainTextOnly) {
+  // Called during the constructor for paste events to cache the formats
+  // available on the clipboard. As with CacheExternalDragFormats, the
+  // data will only be retrieved when needed.
+  NS_ASSERTION(mEventMessage == ePaste,
+               "caching clipboard data for invalid event");
+
+  nsCOMPtr<nsIPrincipal> sysPrincipal = nsContentUtils::GetSystemPrincipal();
+
+  nsTArray<nsCString> typesArray;
+
+  if (XRE_IsContentProcess()) {
+    ContentChild::GetSingleton()->SendGetExternalClipboardFormats(
+        mClipboardType, aPlainTextOnly, &typesArray);
+  } else {
+    GetExternalClipboardFormats(mClipboardType, aPlainTextOnly, &typesArray);
+  }
+
+  if (aPlainTextOnly) {
+    // The only thing that will be in types is kTextMime
+    MOZ_ASSERT(typesArray.IsEmpty() || typesArray.Length() == 1);
+    if (typesArray.Length() == 1) {
+      CacheExternalData(kTextMime, 0, sysPrincipal, false);
+    }
+    return;
+  }
+
+  CacheExternalData(typesArray, sysPrincipal);
+}
+
+void DataTransfer::CacheTransferableFormats() {
+  nsCOMPtr<nsIPrincipal> sysPrincipal = nsContentUtils::GetSystemPrincipal();
+
+  AutoTArray<nsCString, 10> typesArray;
+  GetExternalTransferableFormats(mTransferable, false, &typesArray);
+
+  CacheExternalData(typesArray, sysPrincipal);
+}
+
+void DataTransfer::CacheExternalData(const nsTArray<nsCString>& aTypes,
+                                     nsIPrincipal* aPrincipal) {
+  bool hasFileData = false;
+  for (const nsCString& type : aTypes) {
+    if (type.EqualsLiteral(kCustomTypesMime)) {
+      FillInExternalCustomTypes(0, aPrincipal);
+    } else if (type.EqualsLiteral(kFileMime) && XRE_IsContentProcess() &&
+               !StaticPrefs::dom_events_dataTransfer_mozFile_enabled()) {
+      // We will be ignoring any application/x-moz-file files found in the paste
+      // datatransfer within e10s, as they will fail top be sent over IPC.
+      // Because of that, we will unset hasFileData, whether or not it would
+      // have been set. (bug 1308007)
+      hasFileData = false;
+      continue;
+    } else {
+      // We expect that if kFileMime is supported, then it will be the either at
+      // index 0 or at index 1 in the aTypes returned by
+      // GetExternalClipboardFormats
+      if (type.EqualsLiteral(kFileMime)) {
+        hasFileData = true;
+      }
+
+      // If we aren't the file data, and we have file data, we want to be hidden
+      CacheExternalData(
+          type.get(), 0, aPrincipal,
+          /* hidden = */ !type.EqualsLiteral(kFileMime) && hasFileData);
+    }
+  }
+}
+
+void DataTransfer::FillAllExternalData() {
+  if (mIsExternal) {
+    for (uint32_t i = 0; i < MozItemCount(); ++i) {
+      const nsTArray<RefPtr<DataTransferItem>>& items = *mItems->MozItemsAt(i);
+      for (uint32_t j = 0; j < items.Length(); ++j) {
+        MOZ_ASSERT(items[j]->Index() == i);
+
+        items[j]->FillInExternalData();
+      }
+    }
+  }
+}
+
+void DataTransfer::FillInExternalCustomTypes(uint32_t aIndex,
+                                             nsIPrincipal* aPrincipal) {
+  RefPtr<DataTransferItem> item = new DataTransferItem(
+      this, NS_LITERAL_STRING_FROM_CSTRING(kCustomTypesMime),
+      DataTransferItem::KIND_STRING);
+  item->SetIndex(aIndex);
+
+  nsCOMPtr<nsIVariant> variant = item->DataNoSecurityCheck();
+  if (!variant) {
+    return;
+  }
+
+  FillInExternalCustomTypes(variant, aIndex, aPrincipal);
+}
+
+void DataTransfer::FillInExternalCustomTypes(nsIVariant* aData, uint32_t aIndex,
+                                             nsIPrincipal* aPrincipal) {
+  char* chrs;
+  uint32_t len = 0;
+  nsresult rv = aData->GetAsStringWithSize(&len, &chrs);
+  if (NS_FAILED(rv)) {
+    return;
+  }
+
+  CheckedInt<int32_t> checkedLen(len);
+  if (!checkedLen.isValid()) {
+    return;
+  }
+
+  nsCOMPtr<nsIInputStream> stringStream;
+  NS_NewByteInputStream(getter_AddRefs(stringStream),
+                        Span(chrs, checkedLen.value()), NS_ASSIGNMENT_ADOPT);
+
+  nsCOMPtr<nsIObjectInputStream> stream = NS_NewObjectInputStream(stringStream);
+
+  uint32_t type;
+  do {
+    rv = stream->Read32(&type);
+    NS_ENSURE_SUCCESS_VOID(rv);
+    if (type == eCustomClipboardTypeId_String) {
+      uint32_t formatLength;
+      rv = stream->Read32(&formatLength);
+      NS_ENSURE_SUCCESS_VOID(rv);
+      char* formatBytes;
+      rv = stream->ReadBytes(formatLength, &formatBytes);
+      NS_ENSURE_SUCCESS_VOID(rv);
+      nsAutoString format;
+      format.Adopt(reinterpret_cast<char16_t*>(formatBytes),
+                   formatLength / sizeof(char16_t));
+
+      uint32_t dataLength;
+      rv = stream->Read32(&dataLength);
+      NS_ENSURE_SUCCESS_VOID(rv);
+      char* dataBytes;
+      rv = stream->ReadBytes(dataLength, &dataBytes);
+      NS_ENSURE_SUCCESS_VOID(rv);
+      nsAutoString data;
+      data.Adopt(reinterpret_cast<char16_t*>(dataBytes),
+                 dataLength / sizeof(char16_t));
+
+      RefPtr<nsVariantCC> variant = new nsVariantCC();
+      rv = variant->SetAsAString(data);
+      NS_ENSURE_SUCCESS_VOID(rv);
+
+      SetDataWithPrincipal(format, variant, aIndex, aPrincipal);
+    }
+  } while (type != eCustomClipboardTypeId_None);
+}
+
+void DataTransfer::SetMode(DataTransfer::Mode aMode) {
+  if (!StaticPrefs::dom_events_dataTransfer_protected_enabled() &&
+      aMode == Mode::Protected) {
+    mMode = Mode::ReadOnly;
+  } else {
+    mMode = aMode;
+  }
+}
+
+}  // namespace mozilla::dom