dom/bindings/DOMJSProxyHandler.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_dom_DOMJSProxyHandler_h
   8 #define mozilla_dom_DOMJSProxyHandler_h
   9
  10 #include "mozilla/Assertions.h"
  11 #include "mozilla/Maybe.h"
  12
  13 #include "jsapi.h"
  14 #include "js/Object.h"  // JS::GetClass
  15 #include "js/Proxy.h"
  16
  17 namespace mozilla::dom {
  18
  19 /**
  20  * DOM proxies store the expando object in the private slot.
  21  *
  22  * The expando object is a plain JSObject whose properties correspond to
  23  * "expandos" (custom properties set by the script author).
  24  *
  25  * The exact value stored in the proxy's private slot depends on whether the
  26  * interface is annotated with the [OverrideBuiltins] extended attribute.
  27  *
  28  * If it is, the proxy is initialized with a PrivateValue, which contains a
  29  * pointer to a JS::ExpandoAndGeneration object; this contains a pointer to
  30  * the actual expando object as well as the "generation" of the object.  The
  31  * proxy handler will trace the expando object stored in the
  32  * JS::ExpandoAndGeneration while the proxy itself is alive.
  33  *
  34  * If it is not, the proxy is initialized with an UndefinedValue. In
  35  * EnsureExpandoObject, it is set to an ObjectValue that points to the
  36  * expando object directly. (It is set back to an UndefinedValue only when
  37  * the object is about to die.)
  38  */
  39
  40 class BaseDOMProxyHandler : public js::BaseProxyHandler {
  41  public:
  42   explicit constexpr BaseDOMProxyHandler(const void* aProxyFamily,
  43                                          bool aHasPrototype = false)
  44       : js::BaseProxyHandler(aProxyFamily, aHasPrototype) {}
  45
  46   // Implementations of methods that can be implemented in terms of
  47   // other lower-level methods.
  48   bool getOwnPropertyDescriptor(
  49       JSContext* cx, JS::Handle<JSObject*> proxy, JS::Handle<jsid> id,
  50       JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc) const override;
  51   virtual bool ownPropertyKeys(
  52       JSContext* cx, JS::Handle<JSObject*> proxy,
  53       JS::MutableHandleVector<jsid> props) const override;
  54
  55   virtual bool getPrototypeIfOrdinary(
  56       JSContext* cx, JS::Handle<JSObject*> proxy, bool* isOrdinary,
  57       JS::MutableHandle<JSObject*> proto) const override;
  58
  59   // We override getOwnEnumerablePropertyKeys() and implement it directly
  60   // instead of using the default implementation, which would call
  61   // ownPropertyKeys and then filter out the non-enumerable ones. This avoids
  62   // unnecessary work during enumeration.
  63   virtual bool getOwnEnumerablePropertyKeys(
  64       JSContext* cx, JS::Handle<JSObject*> proxy,
  65       JS::MutableHandleVector<jsid> props) const override;
  66
  67  protected:
  68   // Hook for subclasses to implement shared ownPropertyKeys()/keys()
  69   // functionality.  The "flags" argument is either JSITER_OWNONLY (for keys())
  70   // or JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS (for
  71   // ownPropertyKeys()).
  72   virtual bool ownPropNames(JSContext* cx, JS::Handle<JSObject*> proxy,
  73                             unsigned flags,
  74                             JS::MutableHandleVector<jsid> props) const = 0;
  75
  76   // Hook for subclasses to allow set() to ignore named props while other things
  77   // that look at property descriptors see them.  This is intentionally not
  78   // named getOwnPropertyDescriptor to avoid subclasses that override it hiding
  79   // our public getOwnPropertyDescriptor.
  80   virtual bool getOwnPropDescriptor(
  81       JSContext* cx, JS::Handle<JSObject*> proxy, JS::Handle<jsid> id,
  82       bool ignoreNamedProps,
  83       JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc) const = 0;
  84 };
  85
  86 class DOMProxyHandler : public BaseDOMProxyHandler {
  87  public:
  88   constexpr DOMProxyHandler() : BaseDOMProxyHandler(&family) {}
  89
  90   bool defineProperty(JSContext* cx, JS::Handle<JSObject*> proxy,
  91                       JS::Handle<jsid> id,
  92                       JS::Handle<JS::PropertyDescriptor> desc,
  93                       JS::ObjectOpResult& result) const override {
  94     bool unused;
  95     return defineProperty(cx, proxy, id, desc, result, &unused);
  96   }
  97   virtual bool defineProperty(JSContext* cx, JS::Handle<JSObject*> proxy,
  98                               JS::Handle<jsid> id,
  99                               JS::Handle<JS::PropertyDescriptor> desc,
 100                               JS::ObjectOpResult& result, bool* done) const;
 101   bool delete_(JSContext* cx, JS::Handle<JSObject*> proxy, JS::Handle<jsid> id,
 102                JS::ObjectOpResult& result) const override;
 103   bool preventExtensions(JSContext* cx, JS::Handle<JSObject*> proxy,
 104                          JS::ObjectOpResult& result) const override;
 105   bool isExtensible(JSContext* cx, JS::Handle<JSObject*> proxy,
 106                     bool* extensible) const override;
 107   bool set(JSContext* cx, JS::Handle<JSObject*> proxy, JS::Handle<jsid> id,
 108            JS::Handle<JS::Value> v, JS::Handle<JS::Value> receiver,
 109            JS::ObjectOpResult& result) const override;
 110
 111   /*
 112    * If assigning to proxy[id] hits a named setter with OverrideBuiltins or
 113    * an indexed setter, call it and set *done to true on success. Otherwise, set
 114    * *done to false.
 115    */
 116   virtual bool setCustom(JSContext* cx, JS::Handle<JSObject*> proxy,
 117                          JS::Handle<jsid> id, JS::Handle<JS::Value> v,
 118                          bool* done) const;
 119
 120   /*
 121    * Get the expando object for the given DOM proxy.
 122    */
 123   static JSObject* GetExpandoObject(JSObject* obj);
 124
 125   /*
 126    * Clear the expando object for the given DOM proxy and return it.  This
 127    * function will ensure that the returned object is exposed to active JS if
 128    * the given object is exposed.
 129    *
 130    * GetAndClearExpandoObject does not DROP or clear the preserving wrapper
 131    * flag.
 132    */
 133   static JSObject* GetAndClearExpandoObject(JSObject* obj);
 134
 135   /*
 136    * Ensure that the given proxy (obj) has an expando object, and return it.
 137    * Returns null on failure.
 138    */
 139   static JSObject* EnsureExpandoObject(JSContext* cx,
 140                                        JS::Handle<JSObject*> obj);
 141
 142   static const char family;
 143 };
 144
 145 // Class used by shadowing handlers (the ones that have [OverrideBuiltins].
 146 // This handles tracing the expando in JS::ExpandoAndGeneration.
 147 class ShadowingDOMProxyHandler : public DOMProxyHandler {
 148   virtual void trace(JSTracer* trc, JSObject* proxy) const override;
 149 };
 150
 151 inline bool IsDOMProxy(JSObject* obj) {
 152   return js::IsProxy(obj) &&
 153          js::GetProxyHandler(obj)->family() == &DOMProxyHandler::family;
 154 }
 155
 156 inline const DOMProxyHandler* GetDOMProxyHandler(JSObject* obj) {
 157   MOZ_ASSERT(IsDOMProxy(obj));
 158   return static_cast<const DOMProxyHandler*>(js::GetProxyHandler(obj));
 159 }
 160
 161 }  // namespace mozilla::dom
 162
 163 #endif /* mozilla_dom_DOMProxyHandler_h */