From 5ecbd2583efdd026b27aceb143c04d85309d1ca3 Mon Sep 17 00:00:00 2001
From: Michael Kaply <mozilla@kaply.com>
Date: Thu, 23 Apr 2020 20:37:25 +0000
Subject: [PATCH] Bug 1415146 - Use getExposedWebLocales for
 navigator.language(s) if there are no accept languages. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D59565
---
 dom/base/Navigator.cpp                        | 30 ++++++++++++-------
 dom/base/test/test_navigator_language.html    |  2 +-
 dom/workers/WorkerNavigator.h                 |  7 ++---
 .../test/test_navigator_languages.html        | 17 +++++++----
 4 files changed, 33 insertions(+), 23 deletions(-)

diff --git a/dom/base/Navigator.cpp b/dom/base/Navigator.cpp
index 9a916aecb138..409cd4cc689d 100644
--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -109,6 +109,8 @@
 #include "mozilla/webgpu/Instance.h"
 #include "mozilla/dom/WindowGlobalChild.h"
 
+#include "mozilla/intl/LocaleService.h"
+
 namespace mozilla {
 namespace dom {
 
@@ -315,7 +317,13 @@ void Navigator::GetAppName(nsAString& aAppName, CallerType aCallerType) const {
  *
  * "en", "en-US" and "i-cherokee" and "" are valid languages tokens.
  *
- * An empty array will be returned if there is no valid languages.
+ * If there is no valid language, the value of getWebExposedLocales is
+ * used to ensure that locale spoofing is honored and to reduce
+ * fingerprinting.
+ *
+ * See RFC 7231, Section 9.7 "Browser Fingerprinting" and
+ * RFC 2616, Section 15.1.4 "Privacy Issues Connected to Accept Headers"
+ * for more detail.
  */
 /* static */
 void Navigator::GetAcceptLanguages(nsTArray<nsString>& aLanguages) {
@@ -361,29 +369,29 @@ void Navigator::GetAcceptLanguages(nsTArray<nsString>& aLanguages) {
 
     aLanguages.AppendElement(lang);
   }
+  if (aLanguages.Length() == 0) {
+    nsTArray<nsCString> locales;
+    mozilla::intl::LocaleService::GetInstance()->GetWebExposedLocales(locales);
+    aLanguages.AppendElement(NS_ConvertUTF8toUTF16(locales[0]));
+  }
 }
 
 /**
- * Do not use UI language (chosen app locale) here but the first value set in
- * the Accept Languages header, see ::GetAcceptLanguages().
+ * Returns the first language from GetAcceptLanguages.
  *
- * See RFC 2616, Section 15.1.4 "Privacy Issues Connected to Accept Headers" for
- * the reasons why.
+ * Full details above in GetAcceptLanguages.
  */
 void Navigator::GetLanguage(nsAString& aLanguage) {
   nsTArray<nsString> languages;
   GetLanguages(languages);
-  if (languages.Length() >= 1) {
-    aLanguage.Assign(languages[0]);
-  } else {
-    aLanguage.Truncate();
-  }
+  MOZ_ASSERT(languages.Length() >= 1);
+  aLanguage.Assign(languages[0]);
 }
 
 void Navigator::GetLanguages(nsTArray<nsString>& aLanguages) {
   GetAcceptLanguages(aLanguages);
 
-  // The returned value is cached by the binding code. The window listen to the
+  // The returned value is cached by the binding code. The window listens to the
   // accept languages change and will clear the cache when needed. It has to
   // take care of dispatching the DOM event already and the invalidation and the
   // event has to be timed correctly.
diff --git a/dom/base/test/test_navigator_language.html b/dom/base/test/test_navigator_language.html
index 7d8cca5fc851..0e0173b5672f 100644
--- a/dom/base/test/test_navigator_language.html
+++ b/dom/base/test/test_navigator_language.html
@@ -28,7 +28,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=889335
 
   var testValues = [
     { accept_languages: 'foo', language: 'foo', languages: ['foo'] },
-    { accept_languages: '', language: '', languages: [] },
+    { accept_languages: '', language: 'en-US', languages: ['en-US'] },
     { accept_languages: 'foo,bar', language: 'foo', languages: [ 'foo', 'bar' ] },
     { accept_languages: '  foo , bar ', language: 'foo', languages: [ 'foo', 'bar' ] },
     { accept_languages: '  foo ; bar ', language: 'foo ; bar', languages: [ 'foo ; bar' ] },
diff --git a/dom/workers/WorkerNavigator.h b/dom/workers/WorkerNavigator.h
index bf186ba1ae36..0b99b02c538b 100644
--- a/dom/workers/WorkerNavigator.h
+++ b/dom/workers/WorkerNavigator.h
@@ -68,11 +68,8 @@ class WorkerNavigator final : public nsWrapperCache {
   bool TaintEnabled() const { return false; }
 
   void GetLanguage(nsString& aLanguage) const {
-    if (mProperties.mLanguages.Length() >= 1) {
-      aLanguage.Assign(mProperties.mLanguages[0]);
-    } else {
-      aLanguage.Truncate();
-    }
+    MOZ_ASSERT(mProperties.mLanguages.Length() >= 1);
+    aLanguage.Assign(mProperties.mLanguages[0]);
   }
 
   void GetLanguages(nsTArray<nsString>& aLanguages) const {
diff --git a/dom/workers/test/test_navigator_languages.html b/dom/workers/test/test_navigator_languages.html
index 1d7426cbdc18..68dab11f2971 100644
--- a/dom/workers/test/test_navigator_languages.html
+++ b/dom/workers/test/test_navigator_languages.html
@@ -20,8 +20,13 @@ Tests of DOM Worker Navigator
 <pre id="test">
 <script class="testbody" language="javascript">
 
-  var tests = [ 'en,it', 'it,en,fr', '', 'en' ];
-  var expectedLanguages;
+  var tests = [
+    { expectedLanguages: 'en,it', inputLanguages: 'en,it' },
+    { expectedLanguages: 'it,en,fr', inputLanguages: 'it,en,fr' },
+    { expectedLanguages: 'en-US', inputLanguages: '' },
+    { expectedLanguages: 'en,it', inputLanguages: 'en,it' },
+  ];
+  var test;
   function runTests() {
     if (!tests.length) {
       worker.postMessage('finish');
@@ -29,8 +34,8 @@ Tests of DOM Worker Navigator
       return;
     }
 
-    expectedLanguages = tests.shift();
-    SpecialPowers.pushPrefEnv({"set": [["intl.accept_languages", expectedLanguages]]}, function() {
+    test = tests.shift();
+    SpecialPowers.pushPrefEnv({"set": [["intl.accept_languages", test.inputLanguages]]}, function() {
       worker.postMessage(true);
     });
   }
@@ -40,8 +45,8 @@ Tests of DOM Worker Navigator
   var worker = new Worker("navigator_languages_worker.js");
 
   worker.onmessage = function(event) {
-    is(event.data.toString(), navigator.languages.toString(), "The languages mach.");
-    is(event.data.toString(), expectedLanguages, "This is the correct result.");
+    is(event.data.toString(), navigator.languages.toString(), "The languages match.");
+    is(event.data.toString(), test.expectedLanguages, "This is the correct result.");
     runTests();
   }