gecko-dev/js/ipc/JavaScriptShared.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sw=2 et 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/. */

#ifndef mozilla_jsipc_JavaScriptShared_h__
#define mozilla_jsipc_JavaScriptShared_h__

#include "mozilla/HashFunctions.h"
#include "mozilla/dom/DOMTypes.h"
#include "mozilla/jsipc/CrossProcessObjectWrappers.h"
#include "mozilla/jsipc/PJavaScript.h"
#include "mozilla/StaticPrefs_dom.h"
#include "js/GCHashTable.h"
#include "nsJSUtils.h"

namespace mozilla {
namespace jsipc {

class ObjectId {
 public:
  // Use 47 bits at most, to be safe, since jsval privates are encoded as
  // doubles. See bug 1065811 comment 12 for an explanation.
  static const size_t SERIAL_NUMBER_BITS = 47;
  static const size_t FLAG_BITS = 1;
  static const uint64_t SERIAL_NUMBER_MAX =
      (uint64_t(1) << SERIAL_NUMBER_BITS) - 1;

  explicit ObjectId(uint64_t serialNumber, bool hasXrayWaiver)
      : serialNumber_(serialNumber), hasXrayWaiver_(hasXrayWaiver) {
    if (isInvalidSerialNumber(serialNumber)) {
      MOZ_CRASH("Bad CPOW Id");
    }
  }

  bool operator==(const ObjectId& other) const {
    bool equal = serialNumber() == other.serialNumber();
    MOZ_ASSERT_IF(equal, hasXrayWaiver() == other.hasXrayWaiver());
    return equal;
  }

  bool isNull() { return !serialNumber_; }

  uint64_t serialNumber() const { return serialNumber_; }
  bool hasXrayWaiver() const { return hasXrayWaiver_; }
  uint64_t serialize() const {
    MOZ_ASSERT(serialNumber(), "Don't send a null ObjectId over IPC");
    return uint64_t((serialNumber() << FLAG_BITS) |
                    ((hasXrayWaiver() ? 1 : 0) << 0));
  }

  static ObjectId nullId() { return ObjectId(); }
  static Maybe<ObjectId> deserialize(uint64_t data) {
    if (isInvalidSerialNumber(data >> FLAG_BITS)) {
      return Nothing();
    }
    return Some(ObjectId(data >> FLAG_BITS, data & 1));
  }

  // For use with StructGCPolicy.
  void trace(JSTracer*) const {}
  bool needsSweep() const { return false; }

 private:
  ObjectId() : serialNumber_(0), hasXrayWaiver_(false) {}

  static bool isInvalidSerialNumber(uint64_t aSerialNumber) {
    return aSerialNumber == 0 || aSerialNumber > SERIAL_NUMBER_MAX;
  }

  uint64_t serialNumber_ : SERIAL_NUMBER_BITS;
  bool hasXrayWaiver_ : 1;
};

class JavaScriptShared;

// DefaultHasher<T> requires that T coerce to an integral type. We could make
// ObjectId do that, but doing so would weaken our type invariants, so we just
// reimplement it manually.
struct ObjectIdHasher {
  typedef ObjectId Lookup;
  static js::HashNumber hash(const Lookup& l) {
    return mozilla::HashGeneric(l.serialize());
  }
  static bool match(const ObjectId& k, const ObjectId& l) { return k == l; }
  static void rekey(ObjectId& k, const ObjectId& newKey) { k = newKey; }
};

// Map ids -> JSObjects
class IdToObjectMap {
  typedef js::HashMap<ObjectId, JS::Heap<JSObject*>, ObjectIdHasher,
                      js::SystemAllocPolicy>
      Table;

 public:
  IdToObjectMap();

  void trace(JSTracer* trc, uint64_t minimumId = 0);
  void sweep();

  bool add(ObjectId id, JSObject* obj);
  JSObject* find(ObjectId id);
  JSObject* findPreserveColor(ObjectId id);
  void remove(ObjectId id);

  void clear();
  bool empty() const;

#ifdef DEBUG
  bool has(const ObjectId& id, const JSObject* obj) const;
#endif

 private:
  Table table_;
};

// Map JSObjects -> ids
class ObjectToIdMap {
  using Hasher = js::MovableCellHasher<JS::Heap<JSObject*>>;
  using Table = JS::GCHashMap<JS::Heap<JSObject*>, ObjectId, Hasher,
                              js::SystemAllocPolicy>;

 public:
  ObjectToIdMap();

  void trace(JSTracer* trc);
  void sweep();

  bool add(JSContext* cx, JSObject* obj, ObjectId id);
  ObjectId find(JSObject* obj);
  void remove(JSObject* obj);
  void clear();

 private:
  Table table_;
};

class Logging;

class JavaScriptShared : public CPOWManager {
 public:
  JavaScriptShared();
  virtual ~JavaScriptShared();

  void decref();
  void incref();

  bool Unwrap(JSContext* cx, const nsTArray<CpowEntry>& aCpows,
              JS::MutableHandleObject objp) override;
  bool Wrap(JSContext* cx, JS::HandleObject aObj,
            nsTArray<CpowEntry>* outCpows) override;

 protected:
  bool toVariant(JSContext* cx, JS::HandleValue from, JSVariant* to);
  bool fromVariant(JSContext* cx, const JSVariant& from,
                   JS::MutableHandleValue to);

  bool toJSIDVariant(JSContext* cx, JS::HandleId from, JSIDVariant* to);
  bool fromJSIDVariant(JSContext* cx, const JSIDVariant& from,
                       JS::MutableHandleId to);

  bool toSymbolVariant(JSContext* cx, JS::Symbol* sym, SymbolVariant* symVarp);
  JS::Symbol* fromSymbolVariant(JSContext* cx, const SymbolVariant& symVar);

  bool fromDescriptor(JSContext* cx, JS::Handle<JS::PropertyDescriptor> desc,
                      PPropertyDescriptor* out);
  bool toDescriptor(JSContext* cx, const PPropertyDescriptor& in,
                    JS::MutableHandle<JS::PropertyDescriptor> out);

  bool toObjectOrNullVariant(JSContext* cx, JSObject* obj,
                             ObjectOrNullVariant* objVarp);
  JSObject* fromObjectOrNullVariant(JSContext* cx,
                                    const ObjectOrNullVariant& objVar);

  bool convertIdToGeckoString(JSContext* cx, JS::HandleId id, nsString* to);
  bool convertGeckoStringToId(JSContext* cx, const nsString& from,
                              JS::MutableHandleId id);

  virtual bool toObjectVariant(JSContext* cx, JSObject* obj,
                               ObjectVariant* objVarp) = 0;
  virtual JSObject* fromObjectVariant(JSContext* cx,
                                      const ObjectVariant& objVar) = 0;

  static void ConvertID(const nsID& from, JSIID* to);
  static void ConvertID(const JSIID& from, nsID* to);

  JSObject* findCPOWById(const ObjectId& objId);
  JSObject* findCPOWByIdPreserveColor(const ObjectId& objId);
  JSObject* findObjectById(JSContext* cx, const ObjectId& objId);

#ifdef DEBUG
  bool hasCPOW(const ObjectId& objId, const JSObject* obj) {
    MOZ_ASSERT(obj);
    return findCPOWByIdPreserveColor(objId) == obj;
  }
#endif

  static bool LoggingEnabled() {
    return sLoggingEnabledByEnvVar || StaticPrefs::dom_ipc_cpows_log_enabled();
  }
  static bool StackLoggingEnabled() {
    return sStackLoggingEnabledByEnvVar ||
           StaticPrefs::dom_ipc_cpows_log_stack();
  }

  friend class Logging;

  virtual bool isParent() = 0;

  virtual JSObject* scopeForTargetObjects() = 0;

 protected:
  uintptr_t refcount_;

  IdToObjectMap objects_;
  IdToObjectMap cpows_;

  uint64_t nextSerialNumber_;

  // nextCPOWNumber_ should be the value of nextSerialNumber_ in the other
  // process. The next new CPOW we get should have this serial number.
  uint64_t nextCPOWNumber_;

  // CPOW references can be weak, and any object we store in a map may be
  // GCed (at which point the CPOW will report itself "dead" to the owner).
  // This means that we don't want to store any js::Wrappers in the CPOW map,
  // because CPOW will die if the wrapper is GCed, even if the underlying
  // object is still alive.
  //
  // This presents a tricky situation for Xray waivers, since they're normally
  // represented as a special same-compartment wrapper. We have to strip them
  // off before putting them in the id-to-object and object-to-id maps, so we
  // need a way of distinguishing them at lookup-time.
  //
  // For the id-to-object map, we encode waiver-or-not information into the id
  // itself, which lets us do the right thing when accessing the object.
  //
  // For the object-to-id map, we just keep two maps, one for each type.
  ObjectToIdMap unwaivedObjectIds_;
  ObjectToIdMap waivedObjectIds_;
  ObjectToIdMap& objectIdMap(bool waiver) {
    return waiver ? waivedObjectIds_ : unwaivedObjectIds_;
  }

  static bool sLoggingInitialized;
  static bool sLoggingEnabledByEnvVar;
  static bool sStackLoggingEnabledByEnvVar;
};

}  // namespace jsipc
}  // namespace mozilla

#endif