SSL Preferences.cpp Sprache: C

/* -*- 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/. */

// Documentation for libpref is in modules/libpref/docs/index.rst.

#include <ctype.h>
#include <stdlib.h>
#include <string.h>

#include "SharedPrefMap.h"

#include "base/basictypes.h"
#include "MainThreadUtils.h"
#include "mozilla/AppShutdown.h"
#include "mozilla/ArenaAllocatorExtensions.h"
#include "mozilla/ArenaAllocator.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/Attributes.h"
#include "mozilla/Components.h"
#include "mozilla/dom/PContent.h"
#include "mozilla/dom/Promise.h"
#include "mozilla/dom/RemoteType.h"
#include "mozilla/glean/LibprefMetrics.h"
#include "mozilla/HashFunctions.h"
#include "mozilla/HashTable.h"
#include "mozilla/Logging.h"
#include "mozilla/Maybe.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Omnijar.h"
#include "mozilla/Preferences.h"
#include "mozilla/ProfilerLabels.h"
#include "mozilla/ProfilerMarkers.h"
#include "mozilla/ResultExtensions.h"
#include "mozilla/SchedulerGroup.h"
#include "mozilla/ScopeExit.h"
#include "mozilla/ServoStyleSet.h"
#include "mozilla/SpinEventLoopUntil.h"
#include "mozilla/StaticMutex.h"
#include "mozilla/StaticPrefsAll.h"
#include "mozilla/StaticPtr.h"
#include "mozilla/SyncRunnable.h"
#include "mozilla/Try.h"
#include "mozilla/UniquePtrExtensions.h"
#include "mozilla/URLPreloader.h"
#include "mozilla/Variant.h"
#include "mozilla/Vector.h"
#include "nsAppDirectoryServiceDefs.h"
#include "nsCategoryManagerUtils.h"
#include "nsClassHashtable.h"
#include "nsCOMArray.h"
#include "nsCOMPtr.h"
#include "nsComponentManagerUtils.h"
#include "nsContentUtils.h"
#include "nsCRT.h"
#include "nsTHashMap.h"
#include "nsDirectoryServiceDefs.h"
#include "nsIConsoleService.h"
#include "nsIFile.h"
#include "nsIMemoryReporter.h"
#include "nsIObserver.h"
#include "nsIObserverService.h"
#include "nsIOutputStream.h"
#include "nsIPrefBranch.h"
#include "nsIPrefLocalizedString.h"
#include "nsIRelativeFilePref.h"
#include "nsISafeOutputStream.h"
#include "nsISimpleEnumerator.h"
#include "nsIStringBundle.h"
#include "nsISupportsImpl.h"
#include "nsISupportsPrimitives.h"
#include "nsIZipReader.h"
#include "nsNetUtil.h"
#include "nsPrintfCString.h"
#include "nsProxyRelease.h"
#include "nsReadableUtils.h"
#include "nsRefPtrHashtable.h"
#include "nsRelativeFilePref.h"
#include "nsString.h"
#include "nsTArray.h"
#include "nsThreadUtils.h"
#include "nsUTF8Utils.h"
#include "nsWeakReference.h"
#include "nsXPCOMCID.h"
#include "nsXPCOM.h"
#include "nsXULAppAPI.h"
#include "nsZipArchive.h"
#include "plbase64.h"
#include "PLDHashTable.h"
#include "prdtoa.h"
#include "prlink.h"
#include "xpcpublic.h"
#include "js/RootingAPI.h"
#ifdef MOZ_BACKGROUNDTASKS
#  include "mozilla/BackgroundTasks.h"
#endif

#ifdef DEBUG
#  include <map>
#endif

#ifdef MOZ_MEMORY
#  include "mozmemory.h"
#endif

#ifdef XP_WIN
#  include "windows.h"
#endif

#if defined(MOZ_WIDGET_GTK)
#  include "mozilla/WidgetUtilsGtk.h"
#endif  // defined(MOZ_WIDGET_GTK)

#ifdef MOZ_WIDGET_COCOA
#  include "ChannelPrefsUtil.h"
#endif

using namespace mozilla;

using dom::Promise;
using ipc::FileDescriptor;

#ifdef DEBUG

#  define ENSURE_PARENT_PROCESS(func, pref)                                   \
    do {                                                                      \
      if (MOZ_UNLIKELY(!XRE_IsParentProcess())) {                             \
        nsPrintfCString msg(                                                  \
            "ENSURE_PARENT_PROCESS: called %s on %s in a non-parent process", \
            func, pref);                                                      \
        NS_ERROR(msg.get());                                                  \
        return NS_ERROR_NOT_AVAILABLE;                                        \
      }                                                                       \
    } while (0)

#else  // DEBUG

#  define ENSURE_PARENT_PROCESS(func, pref)     \
    if (MOZ_UNLIKELY(!XRE_IsParentProcess())) { \
      return NS_ERROR_NOT_AVAILABLE;            \
    }

#endif  // DEBUG

// Forward declarations.
namespace mozilla::StaticPrefs {

static void InitAll();
static void StartObservingAlwaysPrefs();
static void InitOncePrefs();
static void InitStaticPrefsFromShared();
static void RegisterOncePrefs(SharedPrefMapBuilder& aBuilder);
static void ShutdownAlwaysPrefs();

}  // namespace mozilla::StaticPrefs

//===========================================================================
// Low-level types and operations
//===========================================================================

typedef nsTArray<nsCString> PrefSaveData;

// 1 MB should be enough for everyone.
static const uint32_t MAX_PREF_LENGTH = 1 * 1024 * 1024;
// Actually, 4kb should be enough for everyone.
static const uint32_t MAX_ADVISABLE_PREF_LENGTH = 4 * 1024;

// This is used for pref names and string pref values. We encode the string
// length, then a '/', then the string chars. This encoding means there are no
// special chars that are forbidden or require escaping.
static void SerializeAndAppendString(const nsCString& aChars, nsCString& aStr) {
  aStr.AppendInt(uint64_t(aChars.Length()));
  aStr.Append('/');
  aStr.Append(aChars);
}

static char* DeserializeString(char* aChars, nsCString& aStr) {
  char* p = aChars;
  uint32_t length = strtol(p, &p, 10);
  MOZ_ASSERT(p[0] == '/');
  p++;  // move past the '/'
  aStr.Assign(p, length);
  p += length;  // move past the string itself
  return p;
}

// Keep this in sync with PrefValue in parser/src/lib.rs.
union PrefValue {
  // PrefValues within Pref objects own their chars. PrefValues passed around
  // as arguments don't own their chars.
  const char* mStringVal;
  int32_t mIntVal;
  bool mBoolVal;

  PrefValue() = default;

  explicit PrefValue(bool aVal) : mBoolVal(aVal) {}

  explicit PrefValue(int32_t aVal) : mIntVal(aVal) {}

  explicit PrefValue(const char* aVal) : mStringVal(aVal) {}

  bool Equals(PrefType aType, PrefValue aValue) {
    switch (aType) {
      case PrefType::String: {
        if (mStringVal && aValue.mStringVal) {
          return strcmp(mStringVal, aValue.mStringVal) == 0;
        }
        if (!mStringVal && !aValue.mStringVal) {
          return true;
        }
        return false;
      }

      case PrefType::Int:
        return mIntVal == aValue.mIntVal;

      case PrefType::Bool:
        return mBoolVal == aValue.mBoolVal;

      default:
        MOZ_CRASH("Unhandled enum value");
    }
  }

  template <typename T>
  T Get() const;

  void Init(PrefType aNewType, PrefValue aNewValue) {
    if (aNewType == PrefType::String) {
      MOZ_ASSERT(aNewValue.mStringVal);
      aNewValue.mStringVal = moz_xstrdup(aNewValue.mStringVal);
    }
    *this = aNewValue;
  }

  void Clear(PrefType aType) {
    if (aType == PrefType::String) {
      free(const_cast<char*>(mStringVal));
    }

    // Zero the entire value (regardless of type) via mStringVal.
    mStringVal = nullptr;
  }

  void Replace(bool aHasValue, PrefType aOldType, PrefType aNewType,
               PrefValue aNewValue) {
    if (aHasValue) {
      Clear(aOldType);
    }
    Init(aNewType, aNewValue);
  }

  void ToDomPrefValue(PrefType aType, dom::PrefValue* aDomValue) {
    switch (aType) {
      case PrefType::String:
        *aDomValue = nsDependentCString(mStringVal);
        return;

      case PrefType::Int:
        *aDomValue = mIntVal;
        return;

      case PrefType::Bool:
        *aDomValue = mBoolVal;
        return;

      default:
        MOZ_CRASH();
    }
  }

  PrefType FromDomPrefValue(const dom::PrefValue& aDomValue) {
    switch (aDomValue.type()) {
      case dom::PrefValue::TnsCString:
        mStringVal = aDomValue.get_nsCString().get();
        return PrefType::String;

      case dom::PrefValue::Tint32_t:
        mIntVal = aDomValue.get_int32_t();
        return PrefType::Int;

      case dom::PrefValue::Tbool:
        mBoolVal = aDomValue.get_bool();
        return PrefType::Bool;

      default:
        MOZ_CRASH();
    }
  }

  void SerializeAndAppend(PrefType aType, nsCString& aStr) {
    switch (aType) {
      case PrefType::Bool:
        aStr.Append(mBoolVal ? 'T' : 'F');
        break;

      case PrefType::Int:
        aStr.AppendInt(mIntVal);
        break;

      case PrefType::String: {
        SerializeAndAppendString(nsDependentCString(mStringVal), aStr);
        break;
      }

      case PrefType::None:
      default:
        MOZ_CRASH();
    }
  }

  void ToString(PrefType aType, nsCString& aStr) {
    switch (aType) {
      case PrefType::Bool:
        aStr.Append(mBoolVal ? "true" : "false");
        break;

      case PrefType::Int:
        aStr.AppendInt(mIntVal);
        break;

      case PrefType::String: {
        aStr.Append(nsDependentCString(mStringVal));
        break;
      }

      case PrefType::None:
      default:;
    }
  }

  static char* Deserialize(PrefType aType, char* aStr,
                           Maybe<dom::PrefValue>* aDomValue) {
    char* p = aStr;

    switch (aType) {
      case PrefType::Bool:
        if (*p == 'T') {
          *aDomValue = Some(true);
        } else if (*p == 'F') {
          *aDomValue = Some(false);
        } else {
          *aDomValue = Some(false);
          NS_ERROR("bad bool pref value");
        }
        p++;
        return p;

      case PrefType::Int: {
        *aDomValue = Some(int32_t(strtol(p, &p, 10)));
        return p;
      }

      case PrefType::String: {
        nsCString str;
        p = DeserializeString(p, str);
        *aDomValue = Some(str);
        return p;
      }

      default:
        MOZ_CRASH();
    }
  }
};

template <>
bool PrefValue::Get() const {
  return mBoolVal;
}

template <>
int32_t PrefValue::Get() const {
  return mIntVal;
}

template <>
nsDependentCString PrefValue::Get() const {
  return nsDependentCString(mStringVal);
}

#ifdef DEBUG
const char* PrefTypeToString(PrefType aType) {
  switch (aType) {
    case PrefType::None:
      return "none";
    case PrefType::String:
      return "string";
    case PrefType::Int:
      return "int";
    case PrefType::Bool:
      return "bool";
    default:
      MOZ_CRASH("Unhandled enum value");
  }
}
#endif

// Assign to aResult a quoted, escaped copy of aOriginal.
static void StrEscape(const char* aOriginal, nsCString& aResult) {
  if (aOriginal == nullptr) {
    aResult.AssignLiteral("\"\"");
    return;
  }

  // JavaScript does not allow quotes, slashes, or line terminators inside
  // strings so we must escape them. ECMAScript defines four line terminators,
  // but we're only worrying about \r and \n here.  We currently feed our pref
  // script to the JS interpreter as Latin-1 so  we won't encounter \u2028
  // (line separator) or \u2029 (paragraph separator).
  //
  // WARNING: There are hints that we may be moving to storing prefs as utf8.
  // If we ever feed them to the JS compiler as UTF8 then we'll have to worry
  // about the multibyte sequences that would be interpreted as \u2028 and
  // \u2029.
  const char* p;

  aResult.Assign('"');

  // Paranoid worst case all slashes will free quickly.
  for (p = aOriginal; *p; ++p) {
    switch (*p) {
      case '\n':
        aResult.AppendLiteral("\\n");
        break;

      case '\r':
        aResult.AppendLiteral("\\r");
        break;

      case '\\':
        aResult.AppendLiteral("\\\\");
        break;

      case '\"':
        aResult.AppendLiteral("\\\"");
        break;

      default:
        aResult.Append(*p);
        break;
    }
  }

  aResult.Append('"');
}

// Mimic the behaviour of nsTStringRepr::ToFloat before bug 840706 to preserve
// error case handling for parsing pref strings. Many callers do not check error
// codes, so the returned values may be used even if an error is set.
//
// This method should never return NaN, but may return +-inf if the provided
// number is too large to fit in a float.
static float ParsePrefFloat(const nsCString& aString, nsresult* aError) {
  if (aString.IsEmpty()) {
    *aError = NS_ERROR_ILLEGAL_VALUE;
    return 0.f;
  }

  // PR_strtod does a locale-independent conversion.
  char* stopped = nullptr;
  float result = PR_strtod(aString.get(), &stopped);

  // Defensively avoid potential breakage caused by returning NaN into
  // unsuspecting code. AFAIK this should never happen as PR_strtod cannot
  // return NaN as currently configured.
  if (std::isnan(result)) {
    MOZ_ASSERT_UNREACHABLE("PR_strtod shouldn't return NaN");
    *aError = NS_ERROR_ILLEGAL_VALUE;
    return 0.f;
  }

  *aError = (stopped == aString.EndReading()) ? NS_OK : NS_ERROR_ILLEGAL_VALUE;
  return result;
}

struct PreferenceMarker {
  static constexpr Span<const char> MarkerTypeName() {
    return MakeStringSpan("Preference");
  }
  static void StreamJSONMarkerData(baseprofiler::SpliceableJSONWriter& aWriter,
                                   const ProfilerString8View& aPrefName,
                                   const Maybe<PrefValueKind>& aPrefKind,
                                   PrefType aPrefType,
                                   const ProfilerString8View& aPrefValue) {
    aWriter.StringProperty("prefName", aPrefName);
    aWriter.StringProperty("prefKind", PrefValueKindToString(aPrefKind));
    aWriter.StringProperty("prefType", PrefTypeToString(aPrefType));
    aWriter.StringProperty("prefValue", aPrefValue);
  }
  static MarkerSchema MarkerTypeDisplay() {
    using MS = MarkerSchema;
    MS schema{MS::Location::MarkerChart, MS::Location::MarkerTable};
    schema.AddKeyLabelFormatSearchable("prefName", "Name", MS::Format::String,
                                       MS::Searchable::Searchable);
    schema.AddKeyLabelFormat("prefKind", "Kind", MS::Format::String);
    schema.AddKeyLabelFormat("prefType", "Type", MS::Format::String);
    schema.AddKeyLabelFormat("prefValue", "Value", MS::Format::String);
    schema.SetTableLabel(
        "{marker.name} — {marker.data.prefName}: {marker.data.prefValue} "
        "({marker.data.prefType})");
    return schema;
  }

private:
  static Span<const char> PrefValueKindToString(
      const Maybe<PrefValueKind>& aKind) {
    if (aKind) {
      return *aKind == PrefValueKind::Default ? MakeStringSpan("Default")
                                              : MakeStringSpan("User");
    }
    return "Shared";
  }

  static Span<const char> PrefTypeToString(PrefType type) {
    switch (type) {
      case PrefType::None:
        return "None";
      case PrefType::Int:
        return "Int";
      case PrefType::Bool:
        return "Bool";
      case PrefType::String:
        return "String";
      default:
        MOZ_ASSERT_UNREACHABLE("Unknown preference type.");
        return "Unknown";
    }
  }
};

namespace mozilla {
struct PrefsSizes {
  PrefsSizes()
      : mHashTable(0),
        mPrefValues(0),
        mStringValues(0),
        mRootBranches(0),
        mPrefNameArena(0),
        mCallbacksObjects(0),
        mCallbacksDomains(0),
        mMisc(0) {}

  size_t mHashTable;
  size_t mPrefValues;
  size_t mStringValues;
  size_t mRootBranches;
  size_t mPrefNameArena;
  size_t mCallbacksObjects;
  size_t mCallbacksDomains;
  size_t mMisc;
};
}  // namespace mozilla

static StaticRefPtr<SharedPrefMap> gSharedMap;

// Arena for Pref names.
// Never access sPrefNameArena directly, always use PrefNameArena()
// because it must only be accessed on the Main Thread
typedef ArenaAllocator<4096, 1> NameArena;
static NameArena* sPrefNameArena;

static inline NameArena& PrefNameArena() {
  MOZ_ASSERT(NS_IsMainThread());

  if (!sPrefNameArena) {
    sPrefNameArena = new NameArena();
  }
  return *sPrefNameArena;
}

class PrefWrapper;

// Three forward declarations for immediately below
class Pref;
static bool IsPreferenceSanitized(const Pref* const aPref);
static bool ShouldSanitizePreference(const Pref* const aPref);

// Note that this never changes in the parent process, and is only read in
// content processes.
static bool gContentProcessPrefsAreInited = false;

class Pref {
public:
  explicit Pref(const nsACString& aName)
      : mName(ArenaStrdup(aName, PrefNameArena()), aName.Length()),
        mType(static_cast<uint32_t>(PrefType::None)),
        mIsSticky(false),
        mIsLocked(false),
        mIsSanitized(false),
        mHasDefaultValue(false),
        mHasUserValue(false),
        mIsSkippedByIteration(false),
        mDefaultValue(),
        mUserValue() {}

  ~Pref() {
    // There's no need to free mName because it's allocated in memory owned by
    // sPrefNameArena.

    mDefaultValue.Clear(Type());
    mUserValue.Clear(Type());
  }

  const char* Name() const { return mName.get(); }
  const nsDependentCString& NameString() const { return mName; }

  // Types.

  PrefType Type() const { return static_cast<PrefType>(mType); }
  void SetType(PrefType aType) { mType = static_cast<uint32_t>(aType); }

  bool IsType(PrefType aType) const { return Type() == aType; }
  bool IsTypeNone() const { return IsType(PrefType::None); }
  bool IsTypeString() const { return IsType(PrefType::String); }
  bool IsTypeInt() const { return IsType(PrefType::Int); }
  bool IsTypeBool() const { return IsType(PrefType::Bool); }

  // Other properties.

  bool IsLocked() const { return mIsLocked; }
  void SetIsLocked(bool aValue) { mIsLocked = aValue; }
  bool IsSkippedByIteration() const { return mIsSkippedByIteration; }
  void SetIsSkippedByIteration(bool aValue) { mIsSkippedByIteration = aValue; }

  bool IsSticky() const { return mIsSticky; }

  bool IsSanitized() const { return mIsSanitized; }

  bool HasDefaultValue() const { return mHasDefaultValue; }
  bool HasUserValue() const { return mHasUserValue; }

  template <typename T>
  void AddToMap(SharedPrefMapBuilder& aMap) {
    // Sanitized preferences should never be added to the shared pref map
    MOZ_ASSERT(!ShouldSanitizePreference(this));
    aMap.Add(NameString(),
             {HasDefaultValue(), HasUserValue(), IsSticky(), IsLocked(),
              /* isSanitized */ false, IsSkippedByIteration()},
             HasDefaultValue() ? mDefaultValue.Get<T>() : T(),
             HasUserValue() ? mUserValue.Get<T>() : T());
  }

  void AddToMap(SharedPrefMapBuilder& aMap) {
    if (IsTypeBool()) {
      AddToMap<bool>(aMap);
    } else if (IsTypeInt()) {
      AddToMap<int32_t>(aMap);
    } else if (IsTypeString()) {
      AddToMap<nsDependentCString>(aMap);
    } else {
      MOZ_ASSERT_UNREACHABLE("Unexpected preference type");
    }
  }

  // Other operations.

#define CHECK_SANITIZATION()                                                \
  if (IsPreferenceSanitized(this)) {                                        \
    glean::security::pref_usage_content_process.Record(                     \
        Some(glean::security::PrefUsageContentProcessExtra{Some(Name())})); \
    if (sCrashOnBlocklistedPref) {                                          \
      MOZ_CRASH_UNSAFE_PRINTF(                                              \
          "Should not access the preference '%s' in the Content Processes", \
          Name());                                                          \
    }                                                                       \
  }

  bool GetBoolValue(PrefValueKind aKind = PrefValueKind::User) const {
    MOZ_ASSERT(IsTypeBool());
    MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
                                               : HasUserValue());

    CHECK_SANITIZATION();

    return aKind == PrefValueKind::Default ? mDefaultValue.mBoolVal
                                           : mUserValue.mBoolVal;
  }

  int32_t GetIntValue(PrefValueKind aKind = PrefValueKind::User) const {
    MOZ_ASSERT(IsTypeInt());
    MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
                                               : HasUserValue());

    CHECK_SANITIZATION();

    return aKind == PrefValueKind::Default ? mDefaultValue.mIntVal
                                           : mUserValue.mIntVal;
  }

  const char* GetBareStringValue(
      PrefValueKind aKind = PrefValueKind::User) const {
    MOZ_ASSERT(IsTypeString());
    MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
                                               : HasUserValue());

    CHECK_SANITIZATION();

    return aKind == PrefValueKind::Default ? mDefaultValue.mStringVal
                                           : mUserValue.mStringVal;
  }

#undef CHECK_SANITIZATION

  nsDependentCString GetStringValue(
      PrefValueKind aKind = PrefValueKind::User) const {
    return nsDependentCString(GetBareStringValue(aKind));
  }

  void ToDomPref(dom::Pref* aDomPref, bool aIsDestinationWebContentProcess) {
    MOZ_ASSERT(XRE_IsParentProcess());

    aDomPref->name() = mName;

    aDomPref->isLocked() = mIsLocked;

    aDomPref->isSanitized() =
        aIsDestinationWebContentProcess && ShouldSanitizePreference(this);

    if (mHasDefaultValue) {
      aDomPref->defaultValue() = Some(dom::PrefValue());
      mDefaultValue.ToDomPrefValue(Type(), &aDomPref->defaultValue().ref());
    } else {
      aDomPref->defaultValue() = Nothing();
    }

    if (mHasUserValue &&
        !(aDomPref->isSanitized() && sOmitBlocklistedPrefValues)) {
      aDomPref->userValue() = Some(dom::PrefValue());
      mUserValue.ToDomPrefValue(Type(), &aDomPref->userValue().ref());
    } else {
      aDomPref->userValue() = Nothing();
    }

    MOZ_ASSERT(aDomPref->defaultValue().isNothing() ||
               aDomPref->userValue().isNothing() ||
               (mIsSanitized && sOmitBlocklistedPrefValues) ||
               (aDomPref->defaultValue().ref().type() ==
                aDomPref->userValue().ref().type()));
  }

  void FromDomPref(const dom::Pref& aDomPref, bool* aValueChanged) {
    MOZ_ASSERT(!XRE_IsParentProcess());
    MOZ_ASSERT(mName == aDomPref.name());

    mIsLocked = aDomPref.isLocked();
    mIsSanitized = aDomPref.isSanitized();

    const Maybe<dom::PrefValue>& defaultValue = aDomPref.defaultValue();
    bool defaultValueChanged = false;
    if (defaultValue.isSome()) {
      PrefValue value;
      PrefType type = value.FromDomPrefValue(defaultValue.ref());
      if (!ValueMatches(PrefValueKind::Default, type, value)) {
        // Type() is PrefType::None if it's a newly added pref. This is ok.
        mDefaultValue.Replace(mHasDefaultValue, Type(), type, value);
        SetType(type);
        mHasDefaultValue = true;
        defaultValueChanged = true;
      }
    }
    // Note: we never clear a default value.

    const Maybe<dom::PrefValue>& userValue = aDomPref.userValue();
    bool userValueChanged = false;
    if (userValue.isSome()) {
      PrefValue value;
      PrefType type = value.FromDomPrefValue(userValue.ref());
      if (!ValueMatches(PrefValueKind::User, type, value)) {
        // Type() is PrefType::None if it's a newly added pref. This is ok.
        mUserValue.Replace(mHasUserValue, Type(), type, value);
        SetType(type);
        mHasUserValue = true;
        userValueChanged = true;
      }
    } else if (mHasUserValue) {
      ClearUserValue();
      userValueChanged = true;
    }

    if (userValueChanged || (defaultValueChanged && !mHasUserValue)) {
      *aValueChanged = true;
    }
  }

  void FromWrapper(PrefWrapper& aWrapper);

  bool HasAdvisablySizedValues() {
    MOZ_ASSERT(XRE_IsParentProcess());

    if (!IsTypeString()) {
      return true;
    }

    if (mHasDefaultValue &&
        strlen(mDefaultValue.mStringVal) > MAX_ADVISABLE_PREF_LENGTH) {
      return false;
    }

    if (mHasUserValue &&
        strlen(mUserValue.mStringVal) > MAX_ADVISABLE_PREF_LENGTH) {
      return false;
    }

    return true;
  }

private:
  bool ValueMatches(PrefValueKind aKind, PrefType aType, PrefValue aValue) {
    return IsType(aType) &&
           (aKind == PrefValueKind::Default
                ? mHasDefaultValue && mDefaultValue.Equals(aType, aValue)
                : mHasUserValue && mUserValue.Equals(aType, aValue));
  }

public:
  void ClearUserValue() {
    mUserValue.Clear(Type());
    mHasUserValue = false;
  }

  nsresult SetDefaultValue(PrefType aType, PrefValue aValue, bool aIsSticky,
                           bool aIsLocked, bool* aValueChanged) {
    // Types must always match when setting the default value.
    if (!IsType(aType)) {
      return NS_ERROR_UNEXPECTED;
    }

    // Should we set the default value? Only if the pref is not locked, and
    // doing so would change the default value.
    if (!IsLocked()) {
      if (aIsLocked) {
        SetIsLocked(true);
      }
      if (!ValueMatches(PrefValueKind::Default, aType, aValue)) {
        mDefaultValue.Replace(mHasDefaultValue, Type(), aType, aValue);
        mHasDefaultValue = true;
        if (aIsSticky) {
          mIsSticky = true;
        }
        if (!mHasUserValue) {
          *aValueChanged = true;
        }
        // What if we change the default to be the same as the user value?
        // Should we clear the user value? Currently we don't.
      }
    }
    return NS_OK;
  }

  nsresult SetUserValue(PrefType aType, PrefValue aValue, bool aFromInit,
                        bool* aValueChanged) {
    // If we have a default value, types must match when setting the user
    // value.
    if (mHasDefaultValue && !IsType(aType)) {
      return NS_ERROR_UNEXPECTED;
    }

    // Should we clear the user value, if present? Only if the new user value
    // matches the default value, and the pref isn't sticky, and we aren't
    // force-setting it during initialization.
    if (ValueMatches(PrefValueKind::Default, aType, aValue) && !mIsSticky &&
        !aFromInit) {
      if (mHasUserValue) {
        ClearUserValue();
        if (!IsLocked()) {
          *aValueChanged = true;
        }
      }

      // Otherwise, should we set the user value? Only if doing so would
      // change the user value.
    } else if (!ValueMatches(PrefValueKind::User, aType, aValue)) {
      mUserValue.Replace(mHasUserValue, Type(), aType, aValue);
      SetType(aType);  // needed because we may have changed the type
      mHasUserValue = true;
      if (!IsLocked()) {
        *aValueChanged = true;
      }
    }
    return NS_OK;
  }

  // Prefs are serialized in a manner that mirrors dom::Pref. The two should be
  // kept in sync. E.g. if something is added to one it should also be added to
  // the other. (It would be nice to be able to use the code generated from
  // IPDL for serializing dom::Pref here instead of writing by hand this
  // serialization/deserialization. Unfortunately, that generated code is
  // difficult to use directly, outside of the IPDL IPC code.)
  //
  // The grammar for the serialized prefs has the following form.
  //
  // <pref>         = <type> <locked> <sanitized> ':' <name> ':' <value>? ':'
  //                  <value>? '\n'
  // <type>         = 'B' | 'I' | 'S'
  // <locked>       = 'L' | '-'
  // <sanitized>    = 'S' | '-'
  // <name>         = <string-value>
  // <value>        = <bool-value> | <int-value> | <string-value>
  // <bool-value>   = 'T' | 'F'
  // <int-value>    = an integer literal accepted by strtol()
  // <string-value> = <int-value> '/' <chars>
  // <chars>        = any char sequence of length dictated by the preceding
  //                  <int-value>.
  //
  // No whitespace is tolerated between tokens. <type> must match the types of
  // the values.
  //
  // The serialization is text-based, rather than binary, for the following
  // reasons.
  //
  // - The size difference wouldn't be much different between text-based and
  //   binary. Most of the space is for strings (pref names and string pref
  //   values), which would be the same in both styles. And other differences
  //   would be minimal, e.g. small integers are shorter in text but long
  //   integers are longer in text.
  //
  // - Likewise, speed differences should be negligible.
  //
  // - It's much easier to debug a text-based serialization. E.g. you can
  //   print it and inspect it easily in a debugger.
  //
  // Examples of unlocked boolean prefs:
  // - "B--:8/my.bool1:F:T\n"
  // - "B--:8/my.bool2:F:\n"
  // - "B--:8/my.bool3::T\n"
  //
  // Examples of sanitized, unlocked boolean prefs:
  // - "B-S:8/my.bool1:F:T\n"
  // - "B-S:8/my.bool2:F:\n"
  // - "B-S:8/my.bool3::T\n"
  //
  // Examples of locked integer prefs:
  // - "IL-:7/my.int1:0:1\n"
  // - "IL-:7/my.int2:123:\n"
  // - "IL-:7/my.int3::-99\n"
  //
  // Examples of unlocked string prefs:
  // - "S--:10/my.string1:3/abc:4/wxyz\n"
  // - "S--:10/my.string2:5/1.234:\n"
  // - "S--:10/my.string3::7/string!\n"

  void SerializeAndAppend(nsCString& aStr, bool aSanitizeUserValue) {
    switch (Type()) {
      case PrefType::Bool:
        aStr.Append('B');
        break;

      case PrefType::Int:
        aStr.Append('I');
        break;

      case PrefType::String: {
        aStr.Append('S');
        break;
      }

      case PrefType::None:
      default:
        MOZ_CRASH();
    }

    aStr.Append(mIsLocked ? 'L' : '-');
    aStr.Append(aSanitizeUserValue ? 'S' : '-');
    aStr.Append(':');

    SerializeAndAppendString(mName, aStr);
    aStr.Append(':');

    if (mHasDefaultValue) {
      mDefaultValue.SerializeAndAppend(Type(), aStr);
    }
    aStr.Append(':');

    if (mHasUserValue && !(aSanitizeUserValue && sOmitBlocklistedPrefValues)) {
      mUserValue.SerializeAndAppend(Type(), aStr);
    }
    aStr.Append('\n');
  }

  static char* Deserialize(char* aStr, dom::Pref* aDomPref) {
    char* p = aStr;

    // The type.
    PrefType type;
    if (*p == 'B') {
      type = PrefType::Bool;
    } else if (*p == 'I') {
      type = PrefType::Int;
    } else if (*p == 'S') {
      type = PrefType::String;
    } else {
      NS_ERROR("bad pref type");
      type = PrefType::None;
    }
    p++;  // move past the type char

    // Locked?
    bool isLocked;
    if (*p == 'L') {
      isLocked = true;
    } else if (*p == '-') {
      isLocked = false;
    } else {
      NS_ERROR("bad pref locked status");
      isLocked = false;
    }
    p++;  // move past the isLocked char

    // Sanitize?
    bool isSanitized;
    if (*p == 'S') {
      isSanitized = true;
    } else if (*p == '-') {
      isSanitized = false;
    } else {
      NS_ERROR("bad pref sanitized status");
      isSanitized = false;
    }
    p++;  // move past the isSanitized char

    MOZ_ASSERT(*p == ':');
    p++;  // move past the ':'

    // The pref name.
    nsCString name;
    p = DeserializeString(p, name);

    MOZ_ASSERT(*p == ':');
    p++;  // move past the ':' preceding the default value

    Maybe<dom::PrefValue> maybeDefaultValue;
    if (*p != ':') {
      dom::PrefValue defaultValue;
      p = PrefValue::Deserialize(type, p, &maybeDefaultValue);
    }

    MOZ_ASSERT(*p == ':');
    p++;  // move past the ':' between the default and user values

    Maybe<dom::PrefValue> maybeUserValue;
    if (*p != '\n') {
      dom::PrefValue userValue;
      p = PrefValue::Deserialize(type, p, &maybeUserValue);
    }

    MOZ_ASSERT(*p == '\n');
    p++;  // move past the '\n' following the user value

    *aDomPref = dom::Pref(name, isLocked, isSanitized, maybeDefaultValue,
                          maybeUserValue);

    return p;
  }

  void AddSizeOfIncludingThis(MallocSizeOf aMallocSizeOf, PrefsSizes& aSizes) {
    // Note: mName is allocated in sPrefNameArena, measured elsewhere.
    aSizes.mPrefValues += aMallocSizeOf(this);
    if (IsTypeString()) {
      if (mHasDefaultValue) {
        aSizes.mStringValues += aMallocSizeOf(mDefaultValue.mStringVal);
      }
      if (mHasUserValue) {
        aSizes.mStringValues += aMallocSizeOf(mUserValue.mStringVal);
      }
    }
  }

  void RelocateName(NameArena* aArena) {
    mName.Rebind(ArenaStrdup(mName.get(), *aArena), mName.Length());
  }

private:
  nsDependentCString mName;  // allocated in sPrefNameArena

  uint32_t mType : 2;
  uint32_t mIsSticky : 1;
  uint32_t mIsLocked : 1;
  uint32_t mIsSanitized : 1;
  uint32_t mHasDefaultValue : 1;
  uint32_t mHasUserValue : 1;
  uint32_t mIsSkippedByIteration : 1;

  PrefValue mDefaultValue;
  PrefValue mUserValue;
};

struct PrefHasher {
  using Key = UniquePtr<Pref>;
  using Lookup = const char*;

  static HashNumber hash(const Lookup aLookup) { return HashString(aLookup); }

  static bool match(const Key& aKey, const Lookup aLookup) {
    if (!aLookup || !aKey->Name()) {
      return false;
    }

    return strcmp(aLookup, aKey->Name()) == 0;
  }
};

using PrefWrapperBase = Variant<Pref*, SharedPrefMap::Pref>;
class MOZ_STACK_CLASS PrefWrapper : public PrefWrapperBase {
  using SharedPref = const SharedPrefMap::Pref;

public:
  MOZ_IMPLICIT PrefWrapper(Pref* aPref) : PrefWrapperBase(AsVariant(aPref)) {}

  MOZ_IMPLICIT PrefWrapper(const SharedPrefMap::Pref& aPref)
      : PrefWrapperBase(AsVariant(aPref)) {}

  // Types.

  bool IsType(PrefType aType) const { return Type() == aType; }
  bool IsTypeNone() const { return IsType(PrefType::None); }
  bool IsTypeString() const { return IsType(PrefType::String); }
  bool IsTypeInt() const { return IsType(PrefType::Int); }
  bool IsTypeBool() const { return IsType(PrefType::Bool); }

#define FORWARD(retType, method)                                        \
  retType method() const {                                              \
    struct Matcher {                                                    \
      retType operator()(const Pref* aPref) { return aPref->method(); } \
      retType operator()(SharedPref& aPref) { return aPref.method(); }  \
    };                                                                  \
    return match(Matcher());                                            \
  }

  FORWARD(bool, IsLocked)
  FORWARD(bool, IsSanitized)
  FORWARD(bool, IsSticky)
  FORWARD(bool, HasDefaultValue)
  FORWARD(bool, HasUserValue)
  FORWARD(const char*, Name)
  FORWARD(nsCString, NameString)
  FORWARD(PrefType, Type)
#undef FORWARD

#define FORWARD(retType, method)                                             \
  retType method(PrefValueKind aKind = PrefValueKind::User) const {          \
    struct Matcher {                                                         \
      PrefValueKind mKind;                                                   \
                                                                             \
      retType operator()(const Pref* aPref) { return aPref->method(mKind); } \
      retType operator()(SharedPref& aPref) { return aPref.method(mKind); }  \
    };                                                                       \
    return match(Matcher{aKind});                                            \
  }

  FORWARD(bool, GetBoolValue)
  FORWARD(int32_t, GetIntValue)
  FORWARD(nsCString, GetStringValue)
  FORWARD(const char*, GetBareStringValue)
#undef FORWARD

  PrefValue GetValue(PrefValueKind aKind = PrefValueKind::User) const {
    switch (Type()) {
      case PrefType::Bool:
        return PrefValue{GetBoolValue(aKind)};
      case PrefType::Int:
        return PrefValue{GetIntValue(aKind)};
      case PrefType::String:
        return PrefValue{GetBareStringValue(aKind)};
      case PrefType::None:
        // This check will be performed in the above functions; but for NoneType
        // we need to do it explicitly, then fall-through.
        if (IsPreferenceSanitized(Name())) {
          glean::security::pref_usage_content_process.Record(Some(
              glean::security::PrefUsageContentProcessExtra{Some(Name())}));

          if (sCrashOnBlocklistedPref) {
            MOZ_CRASH_UNSAFE_PRINTF(
                "Should not access the preference '%s' in the Content "
                "Processes",
                Name());
          }
        }
        [[fallthrough]];
      default:
        MOZ_ASSERT_UNREACHABLE("Unexpected pref type");
        return PrefValue{};
    }
  }

  Result<PrefValueKind, nsresult> WantValueKind(PrefType aType,
                                                PrefValueKind aKind) const {
    // WantValueKind may short-circuit GetValue functions and cause them to
    // return early, before this check occurs in GetFooValue()
    if (this->is<Pref*>() && IsPreferenceSanitized(this->as<Pref*>())) {
      glean::security::pref_usage_content_process.Record(
          Some(glean::security::PrefUsageContentProcessExtra{Some(Name())}));

      if (sCrashOnBlocklistedPref) {
        MOZ_CRASH_UNSAFE_PRINTF(
            "Should not access the preference '%s' in the Content Processes",
            Name());
      }
    } else if (!this->is<Pref*>()) {
      // While we could use Name() above, and avoid the Variant checks, it
      // would less efficient than needed and we can instead do a debug-only
      // assert here to limit the inefficientcy
      MOZ_ASSERT(!IsPreferenceSanitized(Name()),
                 "We should never have a sanitized SharedPrefMap::Pref.");
    }

    if (Type() != aType) {
      return Err(NS_ERROR_UNEXPECTED);
    }

    if (aKind == PrefValueKind::Default || IsLocked() || !HasUserValue()) {
      if (!HasDefaultValue()) {
        return Err(NS_ERROR_UNEXPECTED);
      }
      return PrefValueKind::Default;
    }
    return PrefValueKind::User;
  }

  nsresult GetValue(PrefValueKind aKind, bool* aResult) const {
    PrefValueKind kind;
    MOZ_TRY_VAR(kind, WantValueKind(PrefType::Bool, aKind));

    *aResult = GetBoolValue(kind);
    return NS_OK;
  }

  nsresult GetValue(PrefValueKind aKind, int32_t* aResult) const {
    PrefValueKind kind;
    MOZ_TRY_VAR(kind, WantValueKind(PrefType::Int, aKind));

    *aResult = GetIntValue(kind);
    return NS_OK;
  }

  nsresult GetValue(PrefValueKind aKind, uint32_t* aResult) const {
    return GetValue(aKind, reinterpret_cast<int32_t*>(aResult));
  }

  nsresult GetValue(PrefValueKind aKind, float* aResult) const {
    nsAutoCString result;
    nsresult rv = GetValue(aKind, result);
    if (NS_SUCCEEDED(rv)) {
      // ParsePrefFloat() does a locale-independent conversion.
      // FIXME: Other `GetValue` overloads don't clobber `aResult` on error.
      *aResult = ParsePrefFloat(result, &rv);
    }
    return rv;
  }

  nsresult GetValue(PrefValueKind aKind, nsACString& aResult) const {
    PrefValueKind kind;
    MOZ_TRY_VAR(kind, WantValueKind(PrefType::String, aKind));

    aResult = GetStringValue(kind);
    return NS_OK;
  }

  nsresult GetValue(PrefValueKind aKind, nsACString* aResult) const {
    return GetValue(aKind, *aResult);
  }

  // Returns false if this pref doesn't have a user value worth saving.
  bool UserValueToStringForSaving(nsCString& aStr) {
    // Should we save the user value, if present? Only if it does not match the
    // default value, or it is sticky.
    if (HasUserValue() &&
        (!ValueMatches(PrefValueKind::Default, Type(), GetValue()) ||
         IsSticky())) {
      if (IsTypeString()) {
        StrEscape(GetStringValue().get(), aStr);

      } else if (IsTypeInt()) {
        aStr.AppendInt(GetIntValue());

      } else if (IsTypeBool()) {
        aStr = GetBoolValue() ? "true" : "false";
      }
      return true;
    }

    // Do not save default prefs that haven't changed.
    return false;
  }

  bool Matches(PrefType aType, PrefValueKind aKind, PrefValue& aValue,
               bool aIsSticky, bool aIsLocked) const {
    return (ValueMatches(aKind, aType, aValue) && aIsSticky == IsSticky() &&
            aIsLocked == IsLocked());
  }

  bool ValueMatches(PrefValueKind aKind, PrefType aType,
                    const PrefValue& aValue) const {
    if (!IsType(aType)) {
      return false;
    }
    if (!(aKind == PrefValueKind::Default ? HasDefaultValue()
                                          : HasUserValue())) {
      return false;
    }
    switch (aType) {
      case PrefType::Bool:
        return GetBoolValue(aKind) == aValue.mBoolVal;
      case PrefType::Int:
        return GetIntValue(aKind) == aValue.mIntVal;
      case PrefType::String:
        return strcmp(GetBareStringValue(aKind), aValue.mStringVal) == 0;
      default:
        MOZ_ASSERT_UNREACHABLE("Unexpected preference type");
        return false;
    }
  }
};

void Pref::FromWrapper(PrefWrapper& aWrapper) {
  MOZ_ASSERT(aWrapper.is<SharedPrefMap::Pref>());
  auto pref = aWrapper.as<SharedPrefMap::Pref>();

  MOZ_ASSERT(IsTypeNone());
  MOZ_ASSERT(mName == pref.NameString());

  mType = uint32_t(pref.Type());

  mIsLocked = pref.IsLocked();
  mIsSanitized = pref.IsSanitized();
  mIsSticky = pref.IsSticky();

  mHasDefaultValue = pref.HasDefaultValue();
  mHasUserValue = pref.HasUserValue();

  if (mHasDefaultValue) {
    mDefaultValue.Init(Type(), aWrapper.GetValue(PrefValueKind::Default));
  }
  if (mHasUserValue) {
    mUserValue.Init(Type(), aWrapper.GetValue(PrefValueKind::User));
  }
}

class CallbackNode {
public:
  CallbackNode(const nsACString& aDomain, PrefChangedFunc aFunc, void* aData,
               Preferences::MatchKind aMatchKind)
      : mDomain(AsVariant(nsCString(aDomain))),
        mFunc(aFunc),
        mData(aData),
        mNextAndMatchKind(aMatchKind) {}

  CallbackNode(const char* const* aDomains, PrefChangedFunc aFunc, void* aData,
               Preferences::MatchKind aMatchKind)
      : mDomain(AsVariant(aDomains)),
        mFunc(aFunc),
        mData(aData),
        mNextAndMatchKind(aMatchKind) {}

  // mDomain is a UniquePtr<>, so any uses of Domain() should only be temporary
  // borrows.
  const Variant<nsCString, const char* const*>& Domain() const {
    return mDomain;
  }

  PrefChangedFunc Func() const { return mFunc; }
  void ClearFunc() { mFunc = nullptr; }

  void* Data() const { return mData; }

  Preferences::MatchKind MatchKind() const {
    return static_cast<Preferences::MatchKind>(mNextAndMatchKind &
                                               kMatchKindMask);
  }

  bool DomainIs(const nsACString& aDomain) const {
    return mDomain.is<nsCString>() && mDomain.as<nsCString>() == aDomain;
  }

  bool DomainIs(const char* const* aPrefs) const {
    return mDomain == AsVariant(aPrefs);
  }

  bool Matches(const nsACString& aPrefName) const {
    auto match = [&](const nsACString& aStr) {
      return MatchKind() == Preferences::ExactMatch
                 ? aPrefName == aStr
                 : StringBeginsWith(aPrefName, aStr);
    };

    if (mDomain.is<nsCString>()) {
      return match(mDomain.as<nsCString>());
    }
    for (const char* const* ptr = mDomain.as<const char* const*>(); *ptr;
         ptr++) {
      if (match(nsDependentCString(*ptr))) {
        return true;
      }
    }
    return false;
  }

  CallbackNode* Next() const {
    return reinterpret_cast<CallbackNode*>(mNextAndMatchKind & kNextMask);
  }

  void SetNext(CallbackNode* aNext) {
    uintptr_t matchKind = mNextAndMatchKind & kMatchKindMask;
    mNextAndMatchKind = reinterpret_cast<uintptr_t>(aNext);
    MOZ_ASSERT((mNextAndMatchKind & kMatchKindMask) == 0);
    mNextAndMatchKind |= matchKind;
  }

  void AddSizeOfIncludingThis(MallocSizeOf aMallocSizeOf, PrefsSizes& aSizes) {
    aSizes.mCallbacksObjects += aMallocSizeOf(this);
    if (mDomain.is<nsCString>()) {
      aSizes.mCallbacksDomains +=
          mDomain.as<nsCString>().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
    }
  }

private:
  static const uintptr_t kMatchKindMask = uintptr_t(0x1);
  static const uintptr_t kNextMask = ~kMatchKindMask;

  Variant<nsCString, const char* const*> mDomain;

  // If someone attempts to remove the node from the callback list while
  // NotifyCallbacks() is running, |func| is set to nullptr. Such nodes will
  // be removed at the end of NotifyCallbacks().
  PrefChangedFunc mFunc;
  void* mData;

  // Conceptually this is two fields:
  // - CallbackNode* mNext;
  // - Preferences::MatchKind mMatchKind;
  // They are combined into a tagged pointer to save memory.
  uintptr_t mNextAndMatchKind;
};

using PrefsHashTable = HashSet<UniquePtr<Pref>, PrefHasher>;

// The main prefs hash table. Inside a function so we can assert it's only
// accessed on the main thread. (That assertion can be avoided but only do so
// with great care!)
static inline PrefsHashTable*& HashTable(bool aOffMainThread = false) {
  MOZ_ASSERT(NS_IsMainThread() || ServoStyleSet::IsInServoTraversal());
  static PrefsHashTable* sHashTable = nullptr;
  return sHashTable;
}

#ifdef DEBUG
// This defines the type used to store our `once` mirrors checker. We can't use
// HashMap for now due to alignment restrictions when dealing with
// std::function<void()> (see bug 1557617).
typedef std::function<void()> AntiFootgunCallback;
struct CompareStr {
  bool operator()(char const* a, char const* b) const {
    return std::strcmp(a, b) < 0;
  }
};
typedef std::map<const char*, AntiFootgunCallback, CompareStr> AntiFootgunMap;
static StaticAutoPtr<AntiFootgunMap> gOnceStaticPrefsAntiFootgun;
#endif

// The callback list contains all the priority callbacks followed by the
// non-priority callbacks. gLastPriorityNode records where the first part ends.
static CallbackNode* gFirstCallback = nullptr;
static CallbackNode* gLastPriorityNode = nullptr;

#ifdef DEBUG
#  define ACCESS_COUNTS
#endif

#ifdef ACCESS_COUNTS
using AccessCountsHashTable = nsTHashMap<nsCStringHashKey, uint32_t>;
static StaticAutoPtr<AccessCountsHashTable> gAccessCounts;

static void AddAccessCount(const nsACString& aPrefName) {
  // FIXME: Servo reads preferences from background threads in unsafe ways (bug
  // 1474789), and triggers assertions here if we try to add usage count entries
  // from background threads.
  if (NS_IsMainThread()) {
    JS::AutoSuppressGCAnalysis nogc;  // Hash functions will not GC.
    uint32_t& count = gAccessCounts->LookupOrInsert(aPrefName);
    count++;
  }
}

static void AddAccessCount(const char* aPrefName) {
  AddAccessCount(nsDependentCString(aPrefName));
}
#else
static void MOZ_MAYBE_UNUSED AddAccessCount(const nsACString& aPrefName) {}

static void AddAccessCount(const char* aPrefName) {}
#endif

// These are only used during the call to NotifyCallbacks().
static bool gCallbacksInProgress = false;
static bool gShouldCleanupDeadNodes = false;

class PrefsHashIter {
  using Iterator = decltype(HashTable()->modIter());
  using ElemType = Pref*;

  Iterator mIter;

public:
  explicit PrefsHashIter(PrefsHashTable* aTable) : mIter(aTable->modIter()) {}

  class Elem {
    friend class PrefsHashIter;

    PrefsHashIter& mParent;
    bool mDone;

    Elem(PrefsHashIter& aIter, bool aDone) : mParent(aIter), mDone(aDone) {}

    Iterator& Iter() { return mParent.mIter; }

   public:
    Elem& operator*() { return *this; }

    ElemType get() {
      if (mDone) {
        return nullptr;
      }
      return Iter().get().get();
    }
    ElemType get() const { return const_cast<Elem*>(this)->get(); }

    ElemType operator->() { return get(); }
    ElemType operator->() const { return get(); }

    operator ElemType() { return get(); }

    void Remove() { Iter().remove(); }

    Elem& operator++() {
      MOZ_ASSERT(!mDone);
      Iter().next();
      mDone = Iter().done();
      return *this;
    }

    bool operator!=(Elem& other) {
      return mDone != other.mDone || this->get() != other.get();
    }
  };

  Elem begin() { return Elem(*this, mIter.done()); }

  Elem end() { return Elem(*this, true); }
};

class PrefsIter {
  using Iterator = decltype(HashTable()->iter());
  using ElemType = PrefWrapper;

  using HashElem = PrefsHashIter::Elem;
  using SharedElem = SharedPrefMap::Pref;

  using ElemTypeVariant = Variant<HashElem, SharedElem>;

  SharedPrefMap* mSharedMap;
  PrefsHashTable* mHashTable;
  PrefsHashIter mIter;

  ElemTypeVariant mPos;
  ElemTypeVariant mEnd;

  Maybe<PrefWrapper> mEntry;

public:
  PrefsIter(PrefsHashTable* aHashTable, SharedPrefMap* aSharedMap)
      : mSharedMap(aSharedMap),
        mHashTable(aHashTable),
        mIter(aHashTable),
        mPos(AsVariant(mIter.begin())),
        mEnd(AsVariant(mIter.end())) {
    if (Done()) {
      NextIterator();
    }
  }

private:
#define MATCH(type, ...)                                                \
  do {                                                                  \
    struct Matcher {                                                    \
      PrefsIter& mIter;                                                 \
      type operator()(HashElem& pos) {                                  \
        HashElem& end MOZ_MAYBE_UNUSED = mIter.mEnd.as<HashElem>();     \
        __VA_ARGS__;                                                    \
      }                                                                 \
      type operator()(SharedElem& pos) {                                \
        SharedElem& end MOZ_MAYBE_UNUSED = mIter.mEnd.as<SharedElem>(); \
        __VA_ARGS__;                                                    \
      }                                                                 \
    };                                                                  \
    return mPos.match(Matcher{*this});                                  \
  } while (0);

  bool Done() { MATCH(bool, return pos == end); }

  PrefWrapper MakeEntry() { MATCH(PrefWrapper, return PrefWrapper(pos)); }

  void NextEntry() {
    mEntry.reset();
    MATCH(void, ++pos);
  }
#undef MATCH

  bool Next() {
    NextEntry();
    return !Done() || NextIterator();
  }

  bool NextIterator() {
    if (mPos.is<HashElem>() && mSharedMap) {
      mPos = AsVariant(mSharedMap->begin());
      mEnd = AsVariant(mSharedMap->end());
      return !Done();
    }
    return false;
  }

  bool IteratingBase() { return mPos.is<SharedElem>(); }

  PrefWrapper& Entry() {
    MOZ_ASSERT(!Done());

    if (!mEntry.isSome()) {
      mEntry.emplace(MakeEntry());
    }
    return mEntry.ref();
  }

public:
  class Elem {
    friend class PrefsIter;

    PrefsIter& mParent;
    bool mDone;

    Elem(PrefsIter& aIter, bool aDone) : mParent(aIter), mDone(aDone) {
      SkipDuplicates();
    }

    void Next() { mDone = !mParent.Next(); }

    void SkipDuplicates() {
      while (!mDone &&
             (mParent.IteratingBase() ? mParent.mHashTable->has(ref().Name())
                                      : ref().IsTypeNone())) {
        Next();
      }
    }

   public:
    Elem& operator*() { return *this; }

    ElemType& ref() { return mParent.Entry(); }
    const ElemType& ref() const { return const_cast<Elem*>(this)->ref(); }

    ElemType* operator->() { return &ref(); }
    const ElemType* operator->() const { return &ref(); }

    operator ElemType() { return ref(); }

    Elem& operator++() {
      MOZ_ASSERT(!mDone);
      Next();
      SkipDuplicates();
      return *this;
    }

    bool operator!=(Elem& other) {
      if (mDone != other.mDone) {
        return true;
      }
      if (mDone) {
        return false;
      }
      return &this->ref() != &other.ref();
    }
  };

  Elem begin() { return {*this, Done()}; }

  Elem end() { return {*this, true}; }
};

static Pref* pref_HashTableLookup(const char* aPrefName);

static void NotifyCallbacks(const nsCString& aPrefName,
                            const PrefWrapper* aPref = nullptr);

static void NotifyCallbacks(const nsCString& aPrefName,
                            const PrefWrapper& aPref) {
  NotifyCallbacks(aPrefName, &aPref);
}

// The approximate number of preferences in the dynamic hashtable for the parent
// and content processes, respectively. These numbers are used to determine the
// initial size of the dynamic preference hashtables, and should be chosen to
// avoid rehashing during normal usage. The actual number of preferences will,
// or course, change over time, but these numbers only need to be within a
// binary order of magnitude of the actual values to remain effective.
//
// The number for the parent process should reflect the total number of
// preferences in the database, since the parent process needs to initially
// build a dynamic hashtable of the entire preference database. The number for
// the child process should reflect the number of preferences which are likely
// to change after the startup of the first content process, since content
// processes only store changed preferences on top of a snapshot of the database
// created at startup.
//
// Note: The capacity of a hashtable doubles when its length reaches an exact
// power of two. A table with an initial length of 64 is twice as large as one
// with an initial length of 63. This is important in content processes, where
// lookup speed is less critical and we pay the price of the additional overhead
// for each content process. So the initial content length should generally be
// *under* the next power-of-two larger than its expected length.
constexpr size_t kHashTableInitialLengthParent = 3000;
constexpr size_t kHashTableInitialLengthContent = 64;

static PrefSaveData pref_savePrefs() {
  MOZ_ASSERT(NS_IsMainThread());

  PrefSaveData savedPrefs(HashTable()->count());

  for (auto& pref : PrefsIter(HashTable(), gSharedMap)) {
    nsAutoCString prefValueStr;
    if (!pref->UserValueToStringForSaving(prefValueStr)) {
      continue;
    }

    nsAutoCString prefNameStr;
    StrEscape(pref->Name(), prefNameStr);

    nsPrintfCString str("user_pref(%s, %s);", prefNameStr.get(),
                        prefValueStr.get());

    savedPrefs.AppendElement(str);
  }

  return savedPrefs;
}

static Pref* pref_HashTableLookup(const char* aPrefName) {
  MOZ_ASSERT(NS_IsMainThread() || ServoStyleSet::IsInServoTraversal());

  MOZ_ASSERT_IF(!XRE_IsParentProcess(), gContentProcessPrefsAreInited);

  // We use readonlyThreadsafeLookup() because we often have concurrent lookups
  // from multiple Stylo threads. This is safe because those threads cannot
  // modify sHashTable, and the main thread is blocked while Stylo threads are
  // doing these lookups.
  auto p = HashTable()->readonlyThreadsafeLookup(aPrefName);
  return p ? p->get() : nullptr;
}

// While notifying preference callbacks, this holds the wrapper for the
// preference being notified, in order to optimize lookups.
//
// Note: Callbacks and lookups only happen on the main thread, so this is safe
// to use without locking.
static const PrefWrapper* gCallbackPref;

Maybe<PrefWrapper> pref_SharedLookup(const char* aPrefName) {
  MOZ_DIAGNOSTIC_ASSERT(gSharedMap, "gSharedMap must be initialized");
  if (Maybe<SharedPrefMap::Pref> pref = gSharedMap->Get(aPrefName)) {
    return Some(*pref);
  }
  return Nothing();
}

Maybe<PrefWrapper> pref_Lookup(const char* aPrefName,
                               bool aIncludeTypeNone = false) {
  MOZ_ASSERT(NS_IsMainThread() || ServoStyleSet::IsInServoTraversal());

  AddAccessCount(aPrefName);

  if (gCallbackPref && strcmp(aPrefName, gCallbackPref->Name()) == 0) {
    return Some(*gCallbackPref);
  }
  if (Pref* pref = pref_HashTableLookup(aPrefName)) {
    if (aIncludeTypeNone || !pref->IsTypeNone() || pref->IsSanitized()) {
      return Some(pref);
    }
  } else if (gSharedMap) {
    return pref_SharedLookup(aPrefName);
  }

  return Nothing();
}

static Result<Pref*, nsresult> pref_LookupForModify(
    const nsCString& aPrefName,
    const std::function<bool(const PrefWrapper&)>& aCheckFn) {
  Maybe<PrefWrapper> wrapper =
      pref_Lookup(aPrefName.get(), /* includeTypeNone */ true);
  if (wrapper.isNothing()) {
    return Err(NS_ERROR_INVALID_ARG);
  }
  if (!aCheckFn(*wrapper)) {
    return nullptr;
  }
  if (wrapper->is<Pref*>()) {
    return wrapper->as<Pref*>();
  }

  Pref* pref = new Pref(aPrefName);
  if (!HashTable()->putNew(aPrefName.get(), pref)) {
    delete pref;
    return Err(NS_ERROR_OUT_OF_MEMORY);
  }
  pref->FromWrapper(*wrapper);
  return pref;
}

static nsresult pref_SetPref(const nsCString& aPrefName, PrefType aType,
                             PrefValueKind aKind, PrefValue aValue,
                             bool aIsSticky, bool aIsLocked, bool aFromInit) {
  MOZ_ASSERT(XRE_IsParentProcess());
  MOZ_ASSERT(NS_IsMainThread());

  if (AppShutdown::IsInOrBeyond(ShutdownPhase::XPCOMShutdownThreads)) {
    printf(
        "pref_SetPref: Attempt to write pref %s after XPCOMShutdownThreads "
        "started.\n",
        aPrefName.get());
    if (nsContentUtils::IsInitialized()) {
      xpc_DumpJSStack(true, true, false);
    }
    MOZ_ASSERT(false, "Late preference writes should be avoided.");
    return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
  }

  if (!HashTable()) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  Pref* pref = nullptr;
  if (gSharedMap) {
    auto result =
        pref_LookupForModify(aPrefName, [&](const PrefWrapper& aWrapper) {
          return !aWrapper.Matches(aType, aKind, aValue, aIsSticky, aIsLocked);
        });
    if (result.isOk() && !(pref = result.unwrap())) {
      // No changes required.
      return NS_OK;
    }
  }

  if (!pref) {
    auto p = HashTable()->lookupForAdd(aPrefName.get());
    if (!p) {
      pref = new Pref(aPrefName);
      pref->SetType(aType);
      if (!HashTable()->add(p, pref)) {
        delete pref;
        return NS_ERROR_OUT_OF_MEMORY;
      }
    } else {
      pref = p->get();
    }
  }

  bool valueChanged = false;
  nsresult rv;
  if (aKind == PrefValueKind::Default) {
    rv = pref->SetDefaultValue(aType, aValue, aIsSticky, aIsLocked,
                               &valueChanged);
  } else {
    MOZ_ASSERT(!aIsLocked);  // `locked` is disallowed in user pref files
    rv = pref->SetUserValue(aType, aValue, aFromInit, &valueChanged);
  }
  if (NS_FAILED(rv)) {
    NS_WARNING(
        nsPrintfCString("Rejected attempt to change type of pref %s's %s value "
                        "from %s to %s",
                        aPrefName.get(),
                        (aKind == PrefValueKind::Default) ? "default" : "user",
                        PrefTypeToString(pref->Type()), PrefTypeToString(aType))
            .get());

    return rv;
  }

  if (valueChanged) {
    if (!aFromInit && profiler_thread_is_being_profiled_for_markers()) {
      nsAutoCString value;
      aValue.ToString(aType, value);
      profiler_add_marker(
          "Preference Write", baseprofiler::category::OTHER_PreferenceRead, {},
          PreferenceMarker{}, aPrefName, Some(aKind), aType, value);
    }

    if (aKind == PrefValueKind::User) {
      Preferences::HandleDirty();
    }
    NotifyCallbacks(aPrefName, PrefWrapper(pref));
  }

  return NS_OK;
}

// Removes |node| from callback list. Returns the node after the deleted one.
static CallbackNode* pref_RemoveCallbackNode(CallbackNode* aNode,
                                             CallbackNode* aPrevNode) {
  MOZ_ASSERT(!aPrevNode || aPrevNode->Next() == aNode);
  MOZ_ASSERT(aPrevNode || gFirstCallback == aNode);
  MOZ_ASSERT(!gCallbacksInProgress);

  CallbackNode* next_node = aNode->Next();
  if (aPrevNode) {
    aPrevNode->SetNext(next_node);
  } else {
    gFirstCallback = next_node;
  }
  if (gLastPriorityNode == aNode) {
    gLastPriorityNode = aPrevNode;
  }
  delete aNode;
  return next_node;
}

static void NotifyCallbacks(const nsCString& aPrefName,
                            const PrefWrapper* aPref) {
  bool reentered = gCallbacksInProgress;

  gCallbackPref = aPref;
  auto cleanup = MakeScopeExit([]() { gCallbackPref = nullptr; });

  // Nodes must not be deleted while gCallbacksInProgress is true.
  // Nodes that need to be deleted are marked for deletion by nulling
  // out the |func| pointer. We release them at the end of this function
  // if we haven't reentered.
  gCallbacksInProgress = true;

  for (CallbackNode* node = gFirstCallback; node; node = node->Next()) {
    if (node->Func()) {
      if (node->Matches(aPrefName)) {
        (node->Func())(aPrefName.get(), node->Data());
      }
    }
  }

  gCallbacksInProgress = reentered;

  if (gShouldCleanupDeadNodes && !gCallbacksInProgress) {
    CallbackNode* prev_node = nullptr;
    CallbackNode* node = gFirstCallback;

    while (node) {
      if (!node->Func()) {
        node = pref_RemoveCallbackNode(node, prev_node);
      } else {
        prev_node = node;
        node = node->Next();
      }
    }
    gShouldCleanupDeadNodes = false;
  }

#ifdef DEBUG
  if (XRE_IsParentProcess() &&
      !StaticPrefs::preferences_force_disable_check_once_policy() &&
      (StaticPrefs::preferences_check_once_policy() || xpc::IsInAutomation())) {
    // Check that we aren't modifying a `once`-mirrored pref using that pref
    // name. We have about 100 `once`-mirrored prefs. std::map performs a
    // search in O(log n), so this is fast enough.
    MOZ_ASSERT(gOnceStaticPrefsAntiFootgun);
    auto search = gOnceStaticPrefsAntiFootgun->find(aPrefName.get());
    if (search != gOnceStaticPrefsAntiFootgun->end()) {
      // Run the callback.
      (search->second)();
    }
  }
#endif
}

//===========================================================================
// Prefs parsing
//===========================================================================

extern "C" {

// Keep this in sync with PrefFn in parser/src/lib.rs.
typedef void (*PrefsParserPrefFn)(const char* aPrefName, PrefType aType,
                                  PrefValueKind aKind, PrefValue aValue,
                                  bool aIsSticky, bool aIsLocked);

// Keep this in sync with ErrorFn in parser/src/lib.rs.
//
// `aMsg` is just a borrow of the string, and must be copied if it is used
// outside the lifetime of the prefs_parser_parse() call.
typedef void (*PrefsParserErrorFn)(const char* aMsg);

// Keep this in sync with prefs_parser_parse() in parser/src/lib.rs.
bool prefs_parser_parse(const char* aPath, PrefValueKind aKind,
                        const char* aBuf, size_t aLen,
                        PrefsParserPrefFn aPrefFn, PrefsParserErrorFn aErrorFn);
}

class Parser {
public:
  Parser() = default;
  ~Parser() = default;

  bool Parse(PrefValueKind aKind, const char* aPath, const nsCString& aBuf) {
    MOZ_ASSERT(XRE_IsParentProcess());
    return prefs_parser_parse(aPath, aKind, aBuf.get(), aBuf.Length(),
                              HandlePref, HandleError);
  }

private:
  static void HandlePref(const char* aPrefName, PrefType aType,
                         PrefValueKind aKind, PrefValue aValue, bool aIsSticky,
                         bool aIsLocked) {
    MOZ_ASSERT(XRE_IsParentProcess());
    pref_SetPref(nsDependentCString(aPrefName), aType, aKind, aValue, aIsSticky,
                 aIsLocked,
                 /* fromInit */ true);
  }

  static void HandleError(const char* aMsg) {
    nsresult rv;
    nsCOMPtr<nsIConsoleService> console =
        do_GetService("@mozilla.org/consoleservice;1", &rv);
    if (NS_SUCCEEDED(rv)) {
      console->LogStringMessage(NS_ConvertUTF8toUTF16(aMsg).get());
    }
#ifdef DEBUG
    NS_ERROR(aMsg);
#else
    printf_stderr("%s\n", aMsg);
#endif
  }
};

// The following code is test code for the gtest.

static void TestParseErrorHandlePref(const char* aPrefName, PrefType aType,
                                     PrefValueKind aKind, PrefValue aValue,
                                     bool aIsSticky, bool aIsLocked) {}

MOZ_CONSTINIT static nsCString gTestParseErrorMsgs;

static void TestParseErrorHandleError(const char* aMsg) {
  gTestParseErrorMsgs.Append(aMsg);
  gTestParseErrorMsgs.Append('\n');
}

// Keep this in sync with the declaration in test/gtest/Parser.cpp.
void TestParseError(PrefValueKind aKind, const char* aText,
                    nsCString& aErrorMsg) {
  prefs_parser_parse("test", aKind, aText, strlen(aText),
                     TestParseErrorHandlePref, TestParseErrorHandleError);

  // Copy the error messages into the outparam, then clear them from
  // gTestParseErrorMsgs.
  aErrorMsg.Assign(gTestParseErrorMsgs);
  gTestParseErrorMsgs.Truncate();
}

//===========================================================================
// nsPrefBranch et al.
//===========================================================================

namespace mozilla {
class PreferenceServiceReporter;
}  // namespace mozilla

class PrefCallback : public PLDHashEntryHdr {
  friend class mozilla::PreferenceServiceReporter;

public:
  typedef PrefCallback* KeyType;
  typedef const PrefCallback* KeyTypePointer;

  static const PrefCallback* KeyToPointer(PrefCallback* aKey) { return aKey; }

  static PLDHashNumber HashKey(const PrefCallback* aKey) {
    uint32_t hash = HashString(aKey->mDomain);
    return AddToHash(hash, aKey->mCanonical);
  }

public:
  // Create a PrefCallback with a strong reference to its observer.
  PrefCallback(const nsACString& aDomain, nsIObserver* aObserver,
               nsPrefBranch* aBranch)
      : mDomain(aDomain),
        mBranch(aBranch),
        mWeakRef(nullptr),
        mStrongRef(aObserver) {
    MOZ_COUNT_CTOR(PrefCallback);
    nsCOMPtr<nsISupports> canonical = do_QueryInterface(aObserver);
    mCanonical = canonical;
  }

  // Create a PrefCallback with a weak reference to its observer.
  PrefCallback(const nsACString& aDomain, nsISupportsWeakReference* aObserver,
               nsPrefBranch* aBranch)
      : mDomain(aDomain),
        mBranch(aBranch),
        mWeakRef(do_GetWeakReference(aObserver)),
        mStrongRef(nullptr) {
    MOZ_COUNT_CTOR(PrefCallback);
--> --------------------

--> maximum size reached

--> --------------------

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