gecko-dev/widget/gtk/nsClipboard.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:expandtab:shiftwidth=4:tabstop=4:
 */
/* 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 "nsArrayUtils.h"
#include "nsClipboard.h"
#include "nsClipboardX11.h"
#if defined(MOZ_WAYLAND)
#  include "nsClipboardWayland.h"
#endif
#include "nsContentUtils.h"
#include "HeadlessClipboard.h"
#include "nsSupportsPrimitives.h"
#include "nsString.h"
#include "nsReadableUtils.h"
#include "nsPrimitiveHelpers.h"
#include "nsIServiceManager.h"
#include "nsImageToPixbuf.h"
#include "nsStringStream.h"
#include "nsIObserverService.h"
#include "mozilla/Services.h"
#include "mozilla/RefPtr.h"
#include "mozilla/TimeStamp.h"

#include "imgIContainer.h"

#include <gtk/gtk.h>
#include <gtk/gtkx.h>

#include "mozilla/Encoding.h"

using namespace mozilla;

// Idle timeout for receiving selection and property notify events (microsec)
const int kClipboardTimeout = 500000;

// We add this prefix to HTML markup, so that GetHTMLCharset can correctly
// detect the HTML as UTF-8 encoded.
static const char kHTMLMarkupPrefix[] =
    R"(<meta http-equiv="content-type" content="text/html; charset=utf-8">)";

// Callback when someone asks us for the data
void clipboard_get_cb(GtkClipboard* aGtkClipboard,
                      GtkSelectionData* aSelectionData, guint info,
                      gpointer user_data);

// Callback when someone asks us to clear a clipboard
void clipboard_clear_cb(GtkClipboard* aGtkClipboard, gpointer user_data);

static void ConvertHTMLtoUCS2(const char* data, int32_t dataLength,
                              char16_t** unicodeData, int32_t& outUnicodeLen);

static void GetHTMLCharset(const char* data, int32_t dataLength,
                           nsCString& str);

GdkAtom GetSelectionAtom(int32_t aWhichClipboard) {
  if (aWhichClipboard == nsIClipboard::kGlobalClipboard)
    return GDK_SELECTION_CLIPBOARD;

  return GDK_SELECTION_PRIMARY;
}

int GetGeckoClipboardType(GtkClipboard* aGtkClipboard) {
  if (aGtkClipboard == gtk_clipboard_get(GDK_SELECTION_PRIMARY))
    return nsClipboard::kSelectionClipboard;
  else if (aGtkClipboard == gtk_clipboard_get(GDK_SELECTION_CLIPBOARD))
    return nsClipboard::kGlobalClipboard;
  else
    return -1;  // THAT AIN'T NO CLIPBOARD I EVER HEARD OF
}

nsClipboard::nsClipboard() {}

nsClipboard::~nsClipboard() {
  // We have to clear clipboard before gdk_display_close() call.
  // See bug 531580 for details.
  if (mGlobalTransferable) {
    gtk_clipboard_clear(gtk_clipboard_get(GDK_SELECTION_CLIPBOARD));
  }
  if (mSelectionTransferable) {
    gtk_clipboard_clear(gtk_clipboard_get(GDK_SELECTION_PRIMARY));
  }
}

NS_IMPL_ISUPPORTS(nsClipboard, nsIClipboard, nsIObserver)

nsresult nsClipboard::Init(void) {
  GdkDisplay* display = gdk_display_get_default();

  // Create a nsRetrievalContext. If there's no default display
  // create the X11 one as a fallback.
  if (!display || GDK_IS_X11_DISPLAY(display)) {
    mContext = new nsRetrievalContextX11();
#if defined(MOZ_WAYLAND)
  } else {
    mContext = new nsRetrievalContextWayland();
#endif
  }
  NS_ASSERTION(mContext, "Missing nsRetrievalContext for nsClipboard!");

  nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
  if (os) {
    os->AddObserver(this, "quit-application", false);
    os->AddObserver(this, "xpcom-shutdown", false);
  }

  return NS_OK;
}

nsresult nsClipboard::Store(void) {
  LOGCLIP(("nsClipboard::Store\n"));

  if (mGlobalTransferable) {
    GtkClipboard* clipboard = gtk_clipboard_get(GDK_SELECTION_CLIPBOARD);
    gtk_clipboard_store(clipboard);
  }
  return NS_OK;
}

NS_IMETHODIMP
nsClipboard::Observe(nsISupports* aSubject, const char* aTopic,
                     const char16_t* aData) {
  Store();
  return NS_OK;
}

NS_IMETHODIMP
nsClipboard::SetData(nsITransferable* aTransferable, nsIClipboardOwner* aOwner,
                     int32_t aWhichClipboard) {
  // See if we can short cut
  if ((aWhichClipboard == kGlobalClipboard &&
       aTransferable == mGlobalTransferable.get() &&
       aOwner == mGlobalOwner.get()) ||
      (aWhichClipboard == kSelectionClipboard &&
       aTransferable == mSelectionTransferable.get() &&
       aOwner == mSelectionOwner.get())) {
    return NS_OK;
  }

  LOGCLIP(("nsClipboard::SetData (%s)\n",
           aWhichClipboard == kSelectionClipboard ? "primary" : "clipboard"));

  // Clear out the clipboard in order to set the new data
  EmptyClipboard(aWhichClipboard);

  // List of suported targets
  GtkTargetList* list = gtk_target_list_new(nullptr, 0);

  // Get the types of supported flavors
  nsTArray<nsCString> flavors;
  nsresult rv = aTransferable->FlavorsTransferableCanExport(flavors);
  if (NS_FAILED(rv)) {
    LOGCLIP(("    FlavorsTransferableCanExport failed!\n"));
    return rv;
  }

  // Add all the flavors to this widget's supported type.
  bool imagesAdded = false;
  for (uint32_t i = 0; i < flavors.Length(); i++) {
    nsCString& flavorStr = flavors[i];

    // Special case text/unicode since we can handle all of the string types.
    if (flavorStr.EqualsLiteral(kUnicodeMime)) {
      LOGCLIP(("    text targets\n"));
      gtk_target_list_add_text_targets(list, 0);
      continue;
    }

    if (nsContentUtils::IsFlavorImage(flavorStr)) {
      // Don't bother adding image targets twice
      if (!imagesAdded) {
        // accept any writable image type
        LOGCLIP(("    image targets\n"));
        gtk_target_list_add_image_targets(list, 0, TRUE);
        imagesAdded = true;
      }
      continue;
    }

    // Add this to our list of valid targets
    GdkAtom atom = gdk_atom_intern(flavorStr.get(), FALSE);
    gtk_target_list_add(list, atom, 0, 0);
  }

  // Get GTK clipboard (CLIPBOARD or PRIMARY)
  GtkClipboard* gtkClipboard =
      gtk_clipboard_get(GetSelectionAtom(aWhichClipboard));

  gint numTargets;
  GtkTargetEntry* gtkTargets =
      gtk_target_table_new_from_list(list, &numTargets);

  LOGCLIP(("    gtk_target_table_new_from_list() = %p\n", (void*)gtkTargets));

  // Set getcallback and request to store data after an application exit
  if (gtkTargets &&
      gtk_clipboard_set_with_data(gtkClipboard, gtkTargets, numTargets,
                                  clipboard_get_cb, clipboard_clear_cb, this)) {
    LOGCLIP(("    gtk_clipboard_set_with_data() is ok\n"));
    // We managed to set-up the clipboard so update internal state
    // We have to set it now because gtk_clipboard_set_with_data() calls
    // clipboard_clear_cb() which reset our internal state
    if (aWhichClipboard == kSelectionClipboard) {
      mSelectionOwner = aOwner;
      mSelectionTransferable = aTransferable;
    } else {
      mGlobalOwner = aOwner;
      mGlobalTransferable = aTransferable;
      gtk_clipboard_set_can_store(gtkClipboard, gtkTargets, numTargets);
    }

    rv = NS_OK;
  } else {
    LOGCLIP(("    gtk_clipboard_set_with_data() failed!\n"));
    rv = NS_ERROR_FAILURE;
  }

  gtk_target_table_free(gtkTargets, numTargets);
  gtk_target_list_unref(list);

  return rv;
}

void nsClipboard::SetTransferableData(nsITransferable* aTransferable,
                                      nsCString& aFlavor,
                                      const char* aClipboardData,
                                      uint32_t aClipboardDataLength) {
  LOGCLIP(("nsClipboard::SetTransferableData MIME %s\n", aFlavor.get()));

  nsCOMPtr<nsISupports> wrapper;
  nsPrimitiveHelpers::CreatePrimitiveForData(
      aFlavor, aClipboardData, aClipboardDataLength, getter_AddRefs(wrapper));
  aTransferable->SetTransferData(aFlavor.get(), wrapper);
}

NS_IMETHODIMP
nsClipboard::GetData(nsITransferable* aTransferable, int32_t aWhichClipboard) {
  if (!aTransferable) return NS_ERROR_FAILURE;

  LOGCLIP(("nsClipboard::GetData (%s)\n",
           aWhichClipboard == kSelectionClipboard ? "primary" : "clipboard"));

  // Get a list of flavors this transferable can import
  nsTArray<nsCString> flavors;
  nsresult rv = aTransferable->FlavorsTransferableCanImport(flavors);
  if (NS_FAILED(rv)) {
    LOGCLIP(("    FlavorsTransferableCanImport falied!\n"));
    return rv;
  }

  for (uint32_t i = 0; i < flavors.Length(); i++) {
    nsCString& flavorStr = flavors[i];

    if (flavorStr.EqualsLiteral(kJPEGImageMime) ||
        flavorStr.EqualsLiteral(kJPGImageMime) ||
        flavorStr.EqualsLiteral(kPNGImageMime) ||
        flavorStr.EqualsLiteral(kGIFImageMime)) {
      // Emulate support for image/jpg
      if (flavorStr.EqualsLiteral(kJPGImageMime)) {
        flavorStr.Assign(kJPEGImageMime);
      }

      uint32_t clipboardDataLength;
      const char* clipboardData = mContext->GetClipboardData(
          flavorStr.get(), aWhichClipboard, &clipboardDataLength);
      if (!clipboardData) {
        LOGCLIP(("    %s type is missing\n", flavorStr.get()));
        continue;
      }

      nsCOMPtr<nsIInputStream> byteStream;
      NS_NewByteInputStream(getter_AddRefs(byteStream),
                            MakeSpan(clipboardData, clipboardDataLength),
                            NS_ASSIGNMENT_COPY);
      aTransferable->SetTransferData(flavorStr.get(), byteStream);
      LOGCLIP(("    got %s MIME data\n", flavorStr.get()));

      mContext->ReleaseClipboardData(clipboardData);
      return NS_OK;
    }

    // Special case text/unicode since we can convert any
    // string into text/unicode
    if (flavorStr.EqualsLiteral(kUnicodeMime)) {
      const char* clipboardData = mContext->GetClipboardText(aWhichClipboard);
      if (!clipboardData) {
        LOGCLIP(("    failed to get unicode data\n"));
        // If the type was text/unicode and we couldn't get
        // text off the clipboard, run the next loop
        // iteration.
        continue;
      }

      // Convert utf-8 into our unicode format.
      NS_ConvertUTF8toUTF16 ucs2string(clipboardData);
      const char* unicodeData = (const char*)ToNewUnicode(ucs2string);
      uint32_t unicodeDataLength = ucs2string.Length() * 2;
      SetTransferableData(aTransferable, flavorStr, unicodeData,
                          unicodeDataLength);
      free((void*)unicodeData);

      LOGCLIP(("    got unicode data, length %d\n", ucs2string.Length()));

      mContext->ReleaseClipboardData(clipboardData);
      return NS_OK;
    }

    uint32_t clipboardDataLength;
    const char* clipboardData = mContext->GetClipboardData(
        flavorStr.get(), aWhichClipboard, &clipboardDataLength);

#ifdef MOZ_LOGGING
    if (!clipboardData) {
      LOGCLIP(("    %s type is missing\n", flavorStr.get()));
    }
#endif

    if (clipboardData) {
      LOGCLIP(("    got %s mime type data.\n", flavorStr.get()));

      // Special case text/html since we can convert into UCS2
      if (flavorStr.EqualsLiteral(kHTMLMime)) {
        char16_t* htmlBody = nullptr;
        int32_t htmlBodyLen = 0;
        // Convert text/html into our unicode format
        ConvertHTMLtoUCS2(clipboardData, clipboardDataLength, &htmlBody,
                          htmlBodyLen);

        // Try next data format?
        if (!htmlBodyLen) {
          mContext->ReleaseClipboardData(clipboardData);
          continue;
        }

        SetTransferableData(aTransferable, flavorStr, (const char*)htmlBody,
                            htmlBodyLen * 2);
        free(htmlBody);
      } else {
        SetTransferableData(aTransferable, flavorStr, clipboardData,
                            clipboardDataLength);
      }

      mContext->ReleaseClipboardData(clipboardData);
      return NS_OK;
    }
  }

  LOGCLIP(("    failed to get clipboard content.\n"));
  return NS_OK;
}

NS_IMETHODIMP
nsClipboard::EmptyClipboard(int32_t aWhichClipboard) {
  LOGCLIP(("nsClipboard::EmptyClipboard (%s)\n",
           aWhichClipboard == kSelectionClipboard ? "primary" : "clipboard"));

  if (aWhichClipboard == kSelectionClipboard) {
    if (mSelectionOwner) {
      mSelectionOwner->LosingOwnership(mSelectionTransferable);
      mSelectionOwner = nullptr;
    }
    mSelectionTransferable = nullptr;
  } else {
    if (mGlobalOwner) {
      mGlobalOwner->LosingOwnership(mGlobalTransferable);
      mGlobalOwner = nullptr;
    }
    mGlobalTransferable = nullptr;
  }

  return NS_OK;
}

NS_IMETHODIMP
nsClipboard::HasDataMatchingFlavors(const nsTArray<nsCString>& aFlavorList,
                                    int32_t aWhichClipboard, bool* _retval) {
  if (!_retval) {
    return NS_ERROR_NULL_POINTER;
  }

  LOGCLIP(("nsClipboard::HasDataMatchingFlavors (%s)\n",
           aWhichClipboard == kSelectionClipboard ? "primary" : "clipboard"));

  *_retval = false;

  int targetNums;
  GdkAtom* targets = mContext->GetTargets(aWhichClipboard, &targetNums);
  if (!targets) {
    LOGCLIP(("    no targes at clipboard (null)\n"));
    return NS_OK;
  }

  // Walk through the provided types and try to match it to a
  // provided type.
  for (auto& flavor : aFlavorList) {
    // We special case text/unicode here.
    if (flavor.EqualsLiteral(kUnicodeMime) &&
        gtk_targets_include_text(targets, targetNums)) {
      *_retval = true;
      LOGCLIP(("    has kUnicodeMime\n"));
      break;
    }

    for (int32_t j = 0; j < targetNums; j++) {
      gchar* atom_name = gdk_atom_name(targets[j]);
      if (!atom_name) continue;

      if (flavor.Equals(atom_name)) {
        *_retval = true;
        LOGCLIP(("    has %s\n", atom_name));
      }
      // X clipboard supports image/jpeg, but we want to emulate support
      // for image/jpg as well
      else if (flavor.EqualsLiteral(kJPGImageMime) &&
               !strcmp(atom_name, kJPEGImageMime)) {
        *_retval = true;
        LOGCLIP(("    has image/jpg\n"));
      }

      g_free(atom_name);

      if (*_retval) break;
    }
  }

#ifdef MOZ_LOGGING
  if (!(*_retval)) {
    LOGCLIP(("    no targes at clipboard (bad match)\n"));
  }
#endif

  g_free(targets);
  return NS_OK;
}

NS_IMETHODIMP
nsClipboard::SupportsSelectionClipboard(bool* _retval) {
  *_retval = mContext->HasSelectionSupport();
  return NS_OK;
}

NS_IMETHODIMP
nsClipboard::SupportsFindClipboard(bool* _retval) {
  *_retval = false;
  return NS_OK;
}

nsITransferable* nsClipboard::GetTransferable(int32_t aWhichClipboard) {
  nsITransferable* retval;

  if (aWhichClipboard == kSelectionClipboard)
    retval = mSelectionTransferable.get();
  else
    retval = mGlobalTransferable.get();

  return retval;
}

void nsClipboard::SelectionGetEvent(GtkClipboard* aClipboard,
                                    GtkSelectionData* aSelectionData) {
  // Someone has asked us to hand them something.  The first thing
  // that we want to do is see if that something includes text.  If
  // it does, try to give it text/unicode after converting it to
  // utf-8.

  int32_t whichClipboard;

  // which clipboard?
  GdkAtom selection = gtk_selection_data_get_selection(aSelectionData);
  if (selection == GDK_SELECTION_PRIMARY)
    whichClipboard = kSelectionClipboard;
  else if (selection == GDK_SELECTION_CLIPBOARD)
    whichClipboard = kGlobalClipboard;
  else
    return;  // THAT AIN'T NO CLIPBOARD I EVER HEARD OF

  LOGCLIP(("nsClipboard::SelectionGetEvent (%s)\n",
           whichClipboard == kSelectionClipboard ? "primary" : "clipboard"));

  nsCOMPtr<nsITransferable> trans = GetTransferable(whichClipboard);
  if (!trans) {
    // We have nothing to serve
    LOGCLIP(("nsClipboard::SelectionGetEvent() - %s clipboard is empty!\n",
             whichClipboard == kSelectionClipboard ? "Primary" : "Clipboard"));
    return;
  }

  nsresult rv;
  nsCOMPtr<nsISupports> item;

  GdkAtom selectionTarget = gtk_selection_data_get_target(aSelectionData);

  // Check to see if the selection data is some text type.
  if (gtk_targets_include_text(&selectionTarget, 1)) {
    // Try to convert our internal type into a text string.  Get
    // the transferable for this clipboard and try to get the
    // text/unicode type for it.
    rv = trans->GetTransferData("text/unicode", getter_AddRefs(item));
    if (NS_FAILED(rv) || !item) {
      return;
    }

    nsCOMPtr<nsISupportsString> wideString;
    wideString = do_QueryInterface(item);
    if (!wideString) return;

    nsAutoString ucs2string;
    wideString->GetData(ucs2string);
    NS_ConvertUTF16toUTF8 utf8string(ucs2string);

    gtk_selection_data_set_text(aSelectionData, utf8string.get(),
                                utf8string.Length());
    return;
  }

  // Check to see if the selection data is an image type
  if (gtk_targets_include_image(&selectionTarget, 1, TRUE)) {
    // Look through our transfer data for the image
    static const char* const imageMimeTypes[] = {kNativeImageMime,
                                                 kPNGImageMime, kJPEGImageMime,
                                                 kJPGImageMime, kGIFImageMime};
    nsCOMPtr<nsISupports> imageItem;
    nsCOMPtr<imgIContainer> image;
    for (uint32_t i = 0; i < ArrayLength(imageMimeTypes); i++) {
      rv = trans->GetTransferData(imageMimeTypes[i], getter_AddRefs(imageItem));
      if (NS_FAILED(rv)) {
        continue;
      }

      image = do_QueryInterface(imageItem);
      if (image) {
        break;
      }
    }

    if (!image) {  // Not getting an image for an image mime type!?
      return;
    }

    GdkPixbuf* pixbuf = nsImageToPixbuf::ImageToPixbuf(image);
    if (!pixbuf) return;

    gtk_selection_data_set_pixbuf(aSelectionData, pixbuf);
    g_object_unref(pixbuf);
    return;
  }

  if (selectionTarget == gdk_atom_intern(kHTMLMime, FALSE)) {
    rv = trans->GetTransferData(kHTMLMime, getter_AddRefs(item));
    if (NS_FAILED(rv) || !item) {
      return;
    }

    nsCOMPtr<nsISupportsString> wideString;
    wideString = do_QueryInterface(item);
    if (!wideString) {
      return;
    }

    nsAutoString ucs2string;
    wideString->GetData(ucs2string);

    nsAutoCString html;
    // Add the prefix so the encoding is correctly detected.
    html.AppendLiteral(kHTMLMarkupPrefix);
    AppendUTF16toUTF8(ucs2string, html);

    gtk_selection_data_set(aSelectionData, selectionTarget, 8,
                           (const guchar*)html.get(), html.Length());
    return;
  }

  // Try to match up the selection data target to something our
  // transferable provides.
  gchar* target_name = gdk_atom_name(selectionTarget);
  if (!target_name) return;

  rv = trans->GetTransferData(target_name, getter_AddRefs(item));
  // nothing found?
  if (NS_FAILED(rv) || !item) {
    g_free(target_name);
    return;
  }

  void* primitive_data = nullptr;
  uint32_t dataLen = 0;
  nsPrimitiveHelpers::CreateDataFromPrimitive(nsDependentCString(target_name),
                                              item, &primitive_data, &dataLen);

  if (primitive_data) {
    gtk_selection_data_set(aSelectionData, selectionTarget,
                           8, /* 8 bits in a unit */
                           (const guchar*)primitive_data, dataLen);
    free(primitive_data);
  }

  g_free(target_name);
}

void nsClipboard::SelectionClearEvent(GtkClipboard* aGtkClipboard) {
  int32_t whichClipboard = GetGeckoClipboardType(aGtkClipboard);
  if (whichClipboard < 0) {
    return;
  }

  LOGCLIP(("nsClipboard::SelectionClearEvent (%s)\n",
           whichClipboard == kSelectionClipboard ? "primary" : "clipboard"));

  EmptyClipboard(whichClipboard);
}

void clipboard_get_cb(GtkClipboard* aGtkClipboard,
                      GtkSelectionData* aSelectionData, guint info,
                      gpointer user_data) {
  LOGCLIP(("clipboard_get_cb() callback\n"));
  nsClipboard* aClipboard = static_cast<nsClipboard*>(user_data);
  aClipboard->SelectionGetEvent(aGtkClipboard, aSelectionData);
}

void clipboard_clear_cb(GtkClipboard* aGtkClipboard, gpointer user_data) {
  LOGCLIP(("clipboard_clear_cb() callback\n"));
  nsClipboard* aClipboard = static_cast<nsClipboard*>(user_data);
  aClipboard->SelectionClearEvent(aGtkClipboard);
}

/*
 * when copy-paste, mozilla wants data encoded using UCS2,
 * other app such as StarOffice use "text/html"(RFC2854).
 * This function convert data(got from GTK clipboard)
 * to data mozilla wanted.
 *
 * data from GTK clipboard can be 3 forms:
 *  1. From current mozilla
 *     "text/html", charset = utf-16
 *  2. From old version mozilla or mozilla-based app
 *     content("body" only), charset = utf-16
 *  3. From other app who use "text/html" when copy-paste
 *     "text/html", has "charset" info
 *
 * data      : got from GTK clipboard
 * dataLength: got from GTK clipboard
 * body      : pass to Mozilla
 * bodyLength: pass to Mozilla
 */
void ConvertHTMLtoUCS2(const char* data, int32_t dataLength,
                       char16_t** unicodeData, int32_t& outUnicodeLen) {
  nsAutoCString charset;
  GetHTMLCharset(data, dataLength, charset);  // get charset of HTML
  if (charset.EqualsLiteral("UTF-16")) {      // current mozilla
    outUnicodeLen = (dataLength / 2) - 1;
    *unicodeData = reinterpret_cast<char16_t*>(
        moz_xmalloc((outUnicodeLen + sizeof('\0')) * sizeof(char16_t)));
    memcpy(*unicodeData, data + sizeof(char16_t),
           outUnicodeLen * sizeof(char16_t));
    (*unicodeData)[outUnicodeLen] = '\0';
  } else if (charset.EqualsLiteral("UNKNOWN")) {
    outUnicodeLen = 0;
    return;
  } else {
    // app which use "text/html" to copy&paste
    // get the decoder
    auto encoding = Encoding::ForLabelNoReplacement(charset);
    if (!encoding) {
#ifdef DEBUG_CLIPBOARD
      g_print("        get unicode decoder error\n");
#endif
      outUnicodeLen = 0;
      return;
    }

    auto dataSpan = MakeSpan(data, dataLength);
    // Remove kHTMLMarkupPrefix again, it won't necessarily cause any
    // issues, but might confuse other users.
    const size_t prefixLen = ArrayLength(kHTMLMarkupPrefix) - 1;
    if (dataSpan.Length() >= prefixLen &&
        Substring(data, prefixLen).EqualsLiteral(kHTMLMarkupPrefix)) {
      dataSpan = dataSpan.From(prefixLen);
    }

    auto decoder = encoding->NewDecoder();
    CheckedInt<size_t> needed =
        decoder->MaxUTF16BufferLength(dataSpan.Length());
    if (!needed.isValid() || needed.value() > INT32_MAX) {
      outUnicodeLen = 0;
      return;
    }

    outUnicodeLen = 0;
    if (needed.value()) {
      *unicodeData = reinterpret_cast<char16_t*>(
          moz_xmalloc((needed.value() + 1) * sizeof(char16_t)));
      uint32_t result;
      size_t read;
      size_t written;
      bool hadErrors;
      Tie(result, read, written, hadErrors) = decoder->DecodeToUTF16(
          AsBytes(dataSpan), MakeSpan(*unicodeData, needed.value()), true);
      MOZ_ASSERT(result == kInputEmpty);
      MOZ_ASSERT(read == size_t(dataSpan.Length()));
      MOZ_ASSERT(written <= needed.value());
      Unused << hadErrors;
      outUnicodeLen = written;
      // null terminate.
      (*unicodeData)[outUnicodeLen] = '\0';
    }  // if valid length
  }
}

/*
 * get "charset" information from clipboard data
 * return value can be:
 *  1. "UTF-16":      mozilla or "text/html" with "charset=utf-16"
 *  2. "UNKNOWN":     mozilla can't detect what encode it use
 *  3. other:         "text/html" with other charset than utf-16
 */
void GetHTMLCharset(const char* data, int32_t dataLength, nsCString& str) {
  // if detect "FFFE" or "FEFF", assume UTF-16
  char16_t* beginChar = (char16_t*)data;
  if ((beginChar[0] == 0xFFFE) || (beginChar[0] == 0xFEFF)) {
    str.AssignLiteral("UTF-16");
    return;
  }
  // no "FFFE" and "FEFF", assume ASCII first to find "charset" info
  const nsDependentCSubstring htmlStr(data, dataLength);
  nsACString::const_iterator start, end;
  htmlStr.BeginReading(start);
  htmlStr.EndReading(end);
  nsACString::const_iterator valueStart(start), valueEnd(start);

  if (CaseInsensitiveFindInReadable(NS_LITERAL_CSTRING("CONTENT=\"text/html;"),
                                    start, end)) {
    start = end;
    htmlStr.EndReading(end);

    if (CaseInsensitiveFindInReadable(NS_LITERAL_CSTRING("charset="), start,
                                      end)) {
      valueStart = end;
      start = end;
      htmlStr.EndReading(end);

      if (FindCharInReadable('"', start, end)) valueEnd = start;
    }
  }
  // find "charset" in HTML
  if (valueStart != valueEnd) {
    str = Substring(valueStart, valueEnd);
    ToUpperCase(str);
#ifdef DEBUG_CLIPBOARD
    printf("Charset of HTML = %s\n", charsetUpperStr.get());
#endif
    return;
  }
  str.AssignLiteral("UNKNOWN");
}