Bug 803376 - Allow wrappers to be reused (r=bholley)

js/src/jsapi-tests/testBug604087.cpp

@@ -56,7 +56,8 @@ PreWrap(JSContext *cx, JSObject *scopeArg, JSObject *objArg, unsigned flags)
 }
 
 static JSObject *
-Wrap(JSContext *cx, JSObject *objArg, JSObject *protoArg, JSObject *parentArg, unsigned flags)
+Wrap(JSContext *cx, JSObject *existing, JSObject *objArg,
+     JSObject *protoArg, JSObject *parentArg, unsigned flags)
 {
     js::RootedObject obj(cx, objArg);
     js::RootedObject proto(cx, protoArg);

js/src/jsapi.h

@@ -1950,10 +1950,15 @@ typedef JSBool
 /*
  * Callback used to ask the embedding for the cross compartment wrapper handler
  * that implements the desired prolicy for this kind of object in the
- * destination compartment.
+ * destination compartment. |obj| is the object to be wrapped. If |existing| is
+ * non-NULL, it will point to an existing wrapper object that should be re-used
+ * if possible. |existing| is guaranteed to be a cross-compartment wrapper with
+ * a lazily-defined prototype and the correct global. It is guaranteed not to
+ * wrap a function.
  */
 typedef JSObject *
-(* JSWrapObjectCallback)(JSContext *cx, JSObject *obj, JSObject *proto, JSObject *parent,
+(* JSWrapObjectCallback)(JSContext *cx, JSObject *existing, JSObject *obj,
+                         JSObject *proto, JSObject *parent,
                          unsigned flags);
 
 /*

js/src/jscompartment.cpp

@@ -193,9 +193,12 @@ WrapForSameCompartment(JSContext *cx, HandleObject obj, Value *vp)
 }
 
 bool
-JSCompartment::wrap(JSContext *cx, Value *vp)
+JSCompartment::wrap(JSContext *cx, Value *vp, JSObject *existing)
 {
     JS_ASSERT(cx->compartment == this);
+    JS_ASSERT_IF(existing, existing->compartment() == cx->compartment);
+    JS_ASSERT_IF(existing, vp->isObject());
+    JS_ASSERT_IF(existing, IsDeadProxyObject(existing));
 
     unsigned flags = 0;
 
@@ -304,14 +307,25 @@ JSCompartment::wrap(JSContext *cx, Value *vp)
 
     RootedObject obj(cx, &vp->toObject());
 
+    /* See if we can reuse |existing| as the wrapper for |obj|. */
     JSObject *proto = Proxy::LazyProto;
+    if (existing) {
+        if (!existing->getTaggedProto().isLazy() ||
+            existing->getClass() != &ObjectProxyClass ||
+            existing->getParent() != global ||
+            obj->isCallable())
+        {
+            existing = NULL;
+        }
+    }
 
     /*
      * We hand in the original wrapped object into the wrap hook to allow
      * the wrap hook to reason over what wrappers are currently applied
      * to the object.
      */
-    RootedObject wrapper(cx, cx->runtime->wrapObjectCallback(cx, obj, proto, global, flags));
+    RootedObject wrapper(cx);
+    wrapper = cx->runtime->wrapObjectCallback(cx, existing, obj, proto, global, flags);
     if (!wrapper)
         return false;
 
@@ -348,12 +362,12 @@ JSCompartment::wrap(JSContext *cx, HeapPtrString *strp)
 }
 
 bool
-JSCompartment::wrap(JSContext *cx, JSObject **objp)
+JSCompartment::wrap(JSContext *cx, JSObject **objp, JSObject *existing)
 {
     if (!*objp)
         return true;
     RootedValue value(cx, ObjectValue(**objp));
-    if (!wrap(cx, value.address()))
+    if (!wrap(cx, value.address(), existing))
         return false;
     *objp = &value.get().toObject();
     return true;

js/src/jscompartment.h

@@ -349,10 +349,10 @@ struct JSCompartment
     /* Mark cross-compartment wrappers. */
     void markCrossCompartmentWrappers(JSTracer *trc);
 
-    bool wrap(JSContext *cx, js::Value *vp);
+    bool wrap(JSContext *cx, js::Value *vp, JSObject *existing = NULL);
     bool wrap(JSContext *cx, JSString **strp);
     bool wrap(JSContext *cx, js::HeapPtrString *strp);
-    bool wrap(JSContext *cx, JSObject **objp);
+    bool wrap(JSContext *cx, JSObject **objp, JSObject *existing = NULL);
     bool wrapId(JSContext *cx, jsid *idp);
     bool wrap(JSContext *cx, js::PropertyOp *op);
     bool wrap(JSContext *cx, js::StrictPropertyOp *op);

js/src/jsproxy.cpp

@@ -3143,6 +3143,23 @@ js::NewProxyObject(JSContext *cx, BaseProxyHandler *handler, const Value &priv_,
     return NewProxyObject(cx, handler, priv_, TaggedProto(proto_), parent_, call_, construct_);
 }
 
+JSObject *
+js::RenewProxyObject(JSContext *cx, JSObject *obj,
+                     BaseProxyHandler *handler, Value priv)
+{
+    JS_ASSERT(obj->getParent() == cx->global());
+    JS_ASSERT(obj->getClass() == &ObjectProxyClass);
+    JS_ASSERT(obj->getTaggedProto().isLazy());
+    JS_ASSERT(!handler->isOuterWindow());
+
+    obj->setSlot(JSSLOT_PROXY_HANDLER, PrivateValue(handler));
+    obj->setCrossCompartmentSlot(JSSLOT_PROXY_PRIVATE, priv);
+    obj->setSlot(JSSLOT_PROXY_EXTRA + 0, UndefinedValue());
+    obj->setSlot(JSSLOT_PROXY_EXTRA + 1, UndefinedValue());
+
+    return obj;
+}
+
 static JSBool
 proxy(JSContext *cx, unsigned argc, jsval *vp)
 {

js/src/jsproxy.h

@@ -318,6 +318,9 @@ NewProxyObject(JSContext *cx, BaseProxyHandler *handler, const Value &priv,
                JSObject *proto, JSObject *parent,
                JSObject *call = NULL, JSObject *construct = NULL);
 
+JSObject *
+RenewProxyObject(JSContext *cx, JSObject *obj, BaseProxyHandler *handler, Value priv);
+
 } /* namespace js */
 
 extern JS_FRIEND_API(JSObject *)

js/src/jswrapper.cpp

@@ -56,6 +56,21 @@ Wrapper::New(JSContext *cx, JSObject *obj, JSObject *proto, JSObject *parent,
                           obj->isCallable() ? obj : NULL, NULL);
 }
 
+JSObject *
+Wrapper::Renew(JSContext *cx, JSObject *existing, JSObject *obj, Wrapper *handler)
+{
+#if JS_HAS_XML_SUPPORT
+    if (obj->isXML()) {
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL,
+                             JSMSG_CANT_WRAP_XML_OBJECT);
+        return NULL;
+    }
+#endif
+
+    JS_ASSERT(!obj->isCallable());
+    return RenewProxyObject(cx, existing, handler, ObjectValue(*obj));
+}
+
 Wrapper *
 Wrapper::wrapperHandler(RawObject wrapper)
 {
@@ -357,7 +372,8 @@ Wrapper Wrapper::singletonWithPrototype((unsigned)0, true);
 /* Compartments. */
 
 extern JSObject *
-js::TransparentObjectWrapper(JSContext *cx, JSObject *objArg, JSObject *wrappedProtoArg, JSObject *parentArg,
+js::TransparentObjectWrapper(JSContext *cx, JSObject *existing, JSObject *objArg,
+                             JSObject *wrappedProtoArg, JSObject *parentArg,
                              unsigned flags)
 {
     RootedObject obj(cx, objArg);
@@ -967,6 +983,12 @@ js::NewDeadProxyObject(JSContext *cx, JSObject *parent)
                           NULL, parent, NULL, NULL);
 }
 
+bool
+js::IsDeadProxyObject(RawObject obj)
+{
+    return IsProxy(obj) && GetProxyHandler(obj) == &DeadObjectProxy::singleton;
+}
+
 void
 js::NukeCrossCompartmentWrapper(JSContext *cx, JSObject *wrapper)
 {
@@ -1063,25 +1085,32 @@ js::RemapWrapper(JSContext *cx, JSObject *wobj, JSObject *newTarget)
     // immediately cease to be a cross-compartment wrapper. Neuter it.
     NukeCrossCompartmentWrapper(cx, wobj);
 
-    // First, we wrap it in the new compartment. This will return
-    // a new wrapper.
+    // First, we wrap it in the new compartment. We try to use the existing
+    // wrapper, |wobj|, since it's been nuked anyway. The wrap() function has
+    // the choice to reuse |wobj| or not.
     JSObject *tobj = newTarget;
     AutoCompartment ac(cx, wobj);
-    if (!wcompartment->wrap(cx, &tobj))
+    if (!wcompartment->wrap(cx, &tobj, wobj))
         return false;
 
-    // Now, because we need to maintain object identity, we do a
-    // brain transplant on the old object. At the same time, we
-    // update the entry in the compartment's wrapper map to point
-    // to the old wrapper.
-    JS_ASSERT(tobj != wobj);
-    if (!wobj->swap(cx, tobj))
-        return false;
+    // If wrap() reused |wobj|, it will have overwritten it and returned with
+    // |tobj == wobj|. Otherwise, |tobj| will point to a new wrapper and |wobj|
+    // will still be nuked. In the latter case, we replace |wobj| with the
+    // contents of the new wrapper in |tobj|.
+    if (tobj != wobj) {
+        // Now, because we need to maintain object identity, we do a brain
+        // transplant on the old object so that it contains the contents of the
+        // new one.
+        if (!wobj->swap(cx, tobj))
+            return false;
+    }
 
     // Before swapping, this wrapper came out of wrap(), which enforces the
     // invariant that the wrapper in the map points directly to the key.
     JS_ASSERT(Wrapper::wrappedObject(wobj) == newTarget);
 
+    // Update the entry in the compartment's wrapper map to point to the old
+    // wrapper, which has now been updated (via reuse or swap).
     pmap.put(ObjectValue(*newTarget), ObjectValue(*wobj));
     return true;
 }

js/src/jswrapper.h

@@ -46,6 +46,8 @@ class JS_FRIEND_API(Wrapper) : public DirectProxyHandler
     static JSObject *New(JSContext *cx, JSObject *obj, JSObject *proto,
                          JSObject *parent, Wrapper *handler);
 
+    static JSObject *Renew(JSContext *cx, JSObject *existing, JSObject *obj, Wrapper *handler);
+
     static Wrapper *wrapperHandler(RawObject wrapper);
 
     static JSObject *wrappedObject(RawObject wrapper);
@@ -235,7 +237,8 @@ class JS_FRIEND_API(DeadObjectProxy) : public BaseProxyHandler
 };
 
 extern JSObject *
-TransparentObjectWrapper(JSContext *cx, JSObject *obj, JSObject *wrappedProto, JSObject *parent,
+TransparentObjectWrapper(JSContext *cx, JSObject *existing, JSObject *obj,
+                         JSObject *wrappedProto, JSObject *parent,
                          unsigned flags);
 
 // Proxy family for wrappers. Public so that IsWrapper() can be fully inlined by
@@ -270,6 +273,9 @@ UnwrapOneChecked(JSContext *cx, HandleObject obj);
 JS_FRIEND_API(bool)
 IsCrossCompartmentWrapper(RawObject obj);
 
+bool
+IsDeadProxyObject(RawObject obj);
+
 JSObject *
 NewDeadProxyObject(JSContext *cx, JSObject *parent);
 

js/xpconnect/wrappers/WrapperFactory.cpp

@@ -292,7 +292,8 @@ GetWrappedNative(JSContext *cx, JSObject *obj)
 }
 
 JSObject *
-WrapperFactory::Rewrap(JSContext *cx, JSObject *obj, JSObject *wrappedProto, JSObject *parent,
+WrapperFactory::Rewrap(JSContext *cx, JSObject *existing, JSObject *obj,
+                       JSObject *wrappedProto, JSObject *parent,
                        unsigned flags)
 {
     NS_ASSERTION(!IsWrapper(obj) ||
@@ -448,6 +449,9 @@ WrapperFactory::Rewrap(JSContext *cx, JSObject *obj, JSObject *wrappedProto, JSO
         }
     }
 
+    if (existing && proxyProto == wrappedProto)
+        return Wrapper::Renew(cx, existing, obj, wrapper);
+
     return Wrapper::New(cx, obj, proxyProto, parent, wrapper);
 }
 

js/xpconnect/wrappers/WrapperFactory.h

@@ -59,6 +59,7 @@ class WrapperFactory {
 
     // Rewrap an object that is about to cross compartment boundaries.
     static JSObject *Rewrap(JSContext *cx,
+                            JSObject *existing,
                             JSObject *obj,
                             JSObject *wrappedProto,
                             JSObject *parent,