test_transferable_overflow.xhtml

<?xml version="1.0"?>
<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
<window title="nsTransferable with large string"
        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
        onload="RunTest();">
  <title>nsTransferable with large string</title>
  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>

  <script type="application/javascript">
  <![CDATA[
  // This value is chosen such that the size of the memory for the string exceeds
  // the kLargeDatasetSize threshold in nsTransferable.h (one million).
  // Each character of a JS string is internally represented by two bytes,
  // so the following string of length 500 001 uses 1 000 002 bytes.
  const BIG_STRING = "x" + "BIGGY".repeat(100000);

  // Some value with a length that is exactly kLargeDatasetSize (1 000 000).
  const SMALL_STRING = "small".repeat(100000);

  const nsTransferable = Components.Constructor("@mozilla.org/widget/transferable;1", "nsITransferable");
  const nsSupportsString = Components.Constructor("@mozilla.org/supports-string;1", "nsISupportsString");

  function assignTextToTransferable(transferable, string) {
    var Suppstr = nsSupportsString();
    Suppstr.data = string;
    transferable.setTransferData("text/plain", Suppstr);
  }

  function checkTransferableText(transferable, expectedString, description) {
    var data = {};
    transferable.getTransferData("text/plain", data);
    var actualValue = data.value.QueryInterface(Ci.nsISupportsString).data;
    // Use ok + shortenString instead of is(...) to avoid dumping millions of characters in the output.
    ok(actualValue === expectedString, description + ": text should match. " +
       "Expected " + shortenString(expectedString)  + ", got " + shortenString(actualValue));

    function shortenString(str) {
      return str && str.length > 30 ? str.slice(0, 10) + "..." + str.slice(-10) : String(str);
    }
  }

  function isFDCountingSupported() {
    // On on-Windows we can count the number of file handles for the current process,
    // while on Windows we need to count the number of files in ${TempD}\mozilla-temp-files\,
    // which can be unreliable, especially because nsAnonymousTemporaryFile has documented
    // that the deletion might not be immediate.
    //
    // To avoid intermittents, we only check the file descriptor counts on non-Windows.
    // test_bug1123480.xhtml will do some basic testing for Windows.
    const {AppConstants} = ChromeUtils.importESModule(
      "resource://gre/modules/AppConstants.sys.mjs"
    );
    return AppConstants.platform !== 'win';
  }

  function getClipboardCacheFDCount() {
    var dir = Cc["@mozilla.org/file/local;1"].createInstance(Ci.nsIFile);
    dir.initWithPath("/dev/fd");
    var count = 0;
    for (var de = dir.directoryEntries; de.hasMoreElements(); ) {
      var fdFile = de.nextFile;
      var fileSize;
      try {
        fileSize = fdFile.fileSize;
      } catch (e) {
        // This can happen on macOS.
        continue;
      }
      if (fileSize === BIG_STRING.length * 2 ||
          // We are not expecting files of this small size,
          // but include them in the count anyway
          // in case the files are unexpectedly created.
          fileSize === SMALL_STRING.length * 2) {
        // Assume that the file was created by us if the size matches.
        ++count;
      }
    }
    return count;
  }

  function RunTest() {
    const {PrivateBrowsingUtils} = ChromeUtils.importESModule(
      "resource://gre/modules/PrivateBrowsingUtils.sys.mjs"
    );

    var win = window.browsingContext.topChromeWindow.open("about:blank", "_blank", "chrome, width=500, height=200");
    ok(win, "should open window");
    is(PrivateBrowsingUtils.isContentWindowPrivate(win), false, "used correct window context");

    // ### Part 1 - Writing to the clipboard.

    var Loadctx = PrivateBrowsingUtils.privacyContextFromWindow(win);
    var Transfer = nsTransferable();
    Transfer.init(Loadctx);
    Transfer.addDataFlavor("text/plain");
    var initialFdCount = isFDCountingSupported() ? getClipboardCacheFDCount() : -1;

    assignTextToTransferable(Transfer, BIG_STRING);
    checkTransferableText(Transfer, BIG_STRING, "transferable after assigning BIG_STRING");
    if (isFDCountingSupported()) {
      is(getClipboardCacheFDCount(), initialFdCount + 1, "should use a file for BIG_STRING");
    }

    // Share the transferable with the system.
    Services.clipboard.setData(Transfer, null, Services.clipboard.kGlobalClipboard);

    // Sanity check: Copying to the clipboard should not have altered the transferable.
    checkTransferableText(Transfer, BIG_STRING, "transferable after copying to clipboard");
    if (isFDCountingSupported()) {
      // We are only counting file descriptors for the current process,
      // so even if the test were to be multi-process and the parent process creates another
      // nsTransferable, then the count should still be the same.
      is(getClipboardCacheFDCount(), initialFdCount + 1, "should still be using files for previously stored BIG_STRING");

      // Re-establish baseline for the second part of the test below.
      initialFdCount = getClipboardCacheFDCount();
    }

    // ### Part 2 - Reading from the clipboard.

    var Transfer2 = nsTransferable();
    Transfer2.init(Loadctx);
    Transfer2.addDataFlavor("text/plain");

    // Iniitalize with a small string, so we can see that mData -> mCacheFD works.
    assignTextToTransferable(Transfer2, SMALL_STRING);
    checkTransferableText(Transfer2, SMALL_STRING, "transferable after assigning SMALL_STRING");
    if (isFDCountingSupported()) {
      is(getClipboardCacheFDCount(), initialFdCount, "should not use file to store SMALL_STRING.");
    }

    // Check whether the clipboard data can be read, and simulatenously trigger mData -> mCacheFD.
    Services.clipboard.getData(Transfer2, Services.clipboard.kGlobalClipboard);
    checkTransferableText(Transfer2, BIG_STRING, "transferable after retrieving from clipboard");
    if (isFDCountingSupported()) {
      is(getClipboardCacheFDCount(), initialFdCount + 1, "should use a file for BIG_STRING (read from clipboard).");
    }

    // Store a small string, to exercise the code path from mCacheFD -> mData.
    assignTextToTransferable(Transfer2, SMALL_STRING);
    checkTransferableText(Transfer2, SMALL_STRING, "transferable after assigning SMALL_STRING");
    if (isFDCountingSupported()) {
      is(getClipboardCacheFDCount(), initialFdCount, "should release the file after clearing the transferable.");
    }
  }
  ]]>
  </script>

  <!-- test results are displayed in the html:body -->
  <body xmlns="http://www.w3.org/1999/xhtml">
    This test checks whether a big string can be copied to the clipboard, and then retrieved in the same form.
    On non-Windows, the test also checks whether the data of the transferable is really stored in a file.
  </body>
</window>