gecko-dev/dom/bindings/SimpleGlobalObject.h

/* -*- 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/. */

/**
 * A simplere nsIGlobalObject implementation that can be used to set up a new
 * global without anything interesting in it other than the JS builtins.  This
 * is safe to use on both mainthread and worker threads.
 */

#ifndef mozilla_dom_SimpleGlobalObject_h__
#define mozilla_dom_SimpleGlobalObject_h__

#include "nsIGlobalObject.h"
#include "nsWrapperCache.h"
#include "js/TypeDecls.h"
#include "nsISupportsImpl.h"
#include "nsCycleCollectionParticipant.h"

namespace mozilla {
namespace dom {

class SimpleGlobalObject : public nsIGlobalObject,
                           public nsWrapperCache
{
public:
  enum class GlobalType {
    BindingDetail, // Should only be used by DOM bindings code.
    WorkerDebuggerSandbox,
    NotSimpleGlobal // Sentinel to be used by BasicGlobalType.
  };

  // Create a new JS global object that can be used to do some work.  This
  // global will NOT have any DOM APIs exposed in it, will not be visible to the
  // debugger, and will not have a useful concept of principals, so don't try to
  // use it with any DOM objects.  Apart from that, running code with
  // side-effects is safe in this global.  Importantly, when you are first
  // handed this global it's guaranteed to have pristine built-ins.  The
  // corresponding nsIGlobalObject* for this global object will be a
  // SimpleGlobalObject of the type provided; JS_GetPrivate on the returned
  // JSObject* will return the SimpleGlobalObject*.
  //
  // If the provided prototype value is undefined, it is ignored.  If it's an
  // object or null, it's set as the prototype of the created global.  If it's
  // anything else, this function returns null.
  //
  // Note that creating new globals is not cheap and should not be done
  // gratuitously.  Please think carefully before you use this function.
  static JSObject* Create(GlobalType globalType,
                          JS::Handle<JS::Value> proto =
                            JS::UndefinedHandleValue);

  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(SimpleGlobalObject,
                                                         nsIGlobalObject)

  // Gets the GlobalType of this SimpleGlobalObject.
  GlobalType Type() const
  {
    return mType;
  }

  // Gets the GlobalType of the SimpleGlobalObject for the given JSObject*, if
  // the given JSObject* is the global corresponding to a SimpleGlobalObject.
  // Oherwise, returns GlobalType::NotSimpleGlobal.
  static GlobalType SimpleGlobalType(JSObject* obj);

  virtual JSObject *GetGlobalJSObject() override
  {
    return GetWrapper();
  }

  virtual JSObject* WrapObject(JSContext* cx,
                               JS::Handle<JSObject*> aGivenProto) override
  {
    MOZ_CRASH("SimpleGlobalObject doesn't use DOM bindings!");
  }

private:
  SimpleGlobalObject(JSObject *global, GlobalType type)
    : mType(type)
  {
    SetWrapper(global);
  }

  virtual ~SimpleGlobalObject()
  {
    ClearWrapper();
  }

  const GlobalType mType;
};

} // namespace dom
} // namespace mozilla

#endif /* mozilla_dom_SimpleGlobalObject_h__ */