Commit 8600097d authored by igt0's avatar igt0 Committed by Georg Koppen
Browse files

bug 23104 - Add a default line height compensation 

Many fonts have issues with their vertical metrics. they
are used to influence the height of ascenders and depth
of descenders. Gecko uses it to calculate the line height
(font height + ascender + descender), however because of
that idiosyncratic behavior across multiple operating
systems, it can be used to identify the user's OS.

The solution proposed in the patch uses a default factor
to be multiplied with the font size, simulating the concept
of ascender and descender. This way all operating
systems will have the same line height.
parent 694e7dea

layout/generic/ReflowInput.cpp

+6 −0
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ 
#include "CounterStyleManager.h"

#include <algorithm>

#include "mozilla/dom/HTMLInputElement.h"

#include "nsContentUtils.h"



#ifdef DEBUG

#undef NOISY_VERTICAL_ALIGN
@@ -2768,6 +2769,11 @@ GetNormalLineHeight(nsFontMetrics* aFontMetrics) 
  nscoord externalLeading = aFontMetrics->ExternalLeading();

  nscoord internalLeading = aFontMetrics->InternalLeading();

  nscoord emHeight = aFontMetrics->EmHeight();



  if (nsContentUtils::ShouldResistFingerprinting()) {

    return NSToCoordRound(emHeight * NORMAL_LINE_HEIGHT_FACTOR);

  }



  switch (GetNormalLineHeightCalcControl()) {

  case eIncludeExternalLeading:

    normalLineHeight = emHeight+ internalLeading + externalLeading;

tbb-tests/mochitest.ini

+1 −0
Original line number Diff line number Diff line
@@ -10,3 +10,4 @@ support-files = 
[test_tor_bug2875.html]

[test_tor_bug4755.html]

[test_tor_bug5856.html]

[test_tor_bug23104.html]

tbb-tests/test_tor_bug23104.html

0 → 100644
+51 −0
Original line number Diff line number Diff line 
<!DOCTYPE HTML>

<meta charset="UTF-8">

<html>

<head>

  <title>Test for Tor Bug #23104: CSS line-height reveals the platform Tor browser is running</title>

  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>

  <script type="application/javascript" src="/tests/SimpleTest/SpawnTask.js"></script>

  <style type="text/css">

    span {

      background-color: #000;

      color: #fff;

      font-size: 16.5px;

    }

  </style>

</head>

<body>

<span id="test1">Test1</span>

<span id="test2">كلمة</span>

<span id="test3">ação</span>

<script type="application/javascript;version=1.7">



let setPref = function* (key, value) {

  return new Promise(function(resolve, reject) {

    SpecialPowers.pushPrefEnv({"set": [[key, value]]}, resolve);

  });

}



function getStyle(el, styleprop) {

  el = document.getElementById(el);

  return document.defaultView.getComputedStyle(el, null).getPropertyValue(styleprop);

}



function validateElement(elementName, isFingerprintResistent) {

  var fontSize = getStyle(elementName, 'font-size');

  var lineHeight = getStyle(elementName, 'line-height');

  var validationCb = isFingerprintResistent ? is : isnot;

  validationCb(parseFloat(lineHeight), Math.ceil(parseFloat(fontSize)) * 1.2, 'Line Height validation');

}



add_task(function* () {

  for (let resistFingerprintingValue of [true, false]) {

  yield setPref("privacy.resistFingerprinting", resistFingerprintingValue);

    for (let elementId of ['test1', 'test2', 'test3']) {

      validateElement(elementId, resistFingerprintingValue);

    }

  }

});



</script>

</body>

</html>