gecko-dev/dom/bindings/CallbackObject.cpp

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

#include "mozilla/dom/CallbackObject.h"
#include "jsfriendapi.h"
#include "nsIScriptGlobalObject.h"
#include "nsIXPConnect.h"
#include "nsIScriptContext.h"
#include "nsPIDOMWindow.h"
#include "nsJSUtils.h"
#include "nsCxPusher.h"
#include "nsIScriptSecurityManager.h"
#include "xpcprivate.h"

namespace mozilla {
namespace dom {

NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(CallbackObject)
  NS_INTERFACE_MAP_ENTRY(mozilla::dom::CallbackObject)
  NS_INTERFACE_MAP_ENTRY(nsISupports)
NS_INTERFACE_MAP_END

NS_IMPL_CYCLE_COLLECTING_ADDREF(CallbackObject)
NS_IMPL_CYCLE_COLLECTING_RELEASE(CallbackObject)

NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(CallbackObject)
  tmp->DropCallback();
NS_IMPL_CYCLE_COLLECTION_UNLINK_END
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(CallbackObject)
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(CallbackObject)
  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mCallback)
NS_IMPL_CYCLE_COLLECTION_TRACE_END

CallbackObject::CallSetup::CallSetup(JS::Handle<JSObject*> aCallback,
                                     ErrorResult& aRv,
                                     ExceptionHandling aExceptionHandling)
  : mCx(nullptr)
  , mErrorResult(aRv)
  , mExceptionHandling(aExceptionHandling)
{
  // We need to produce a useful JSContext here.  Ideally one that the callback
  // is in some sense associated with, so that we can sort of treat it as a
  // "script entry point".  Though once we actually have script entry points,
  // we'll need to do the script entry point bits once we have an actual
  // callable.

  // First, find the real underlying callback.
  JSObject* realCallback = js::UncheckedUnwrap(aCallback);

  // Now get the nsIScriptGlobalObject for this callback.
  JSContext* cx = nullptr;
  nsIScriptContext* ctx = nullptr;
  nsIScriptGlobalObject* sgo = nsJSUtils::GetStaticScriptGlobal(realCallback);
  if (sgo) {
    // Make sure that if this is a window it's the current inner, since the
    // nsIScriptContext and hence JSContext are associated with the outer
    // window.  Which means that if someone holds on to a function from a
    // now-unloaded document we'd have the new document as the script entry
    // point...
    nsCOMPtr<nsPIDOMWindow> win = do_QueryInterface(sgo);
    if (win) {
      MOZ_ASSERT(win->IsInnerWindow());
      nsPIDOMWindow* outer = win->GetOuterWindow();
      if (!outer || win != outer->GetCurrentInnerWindow()) {
        // Just bail out from here
        return;
      }
    }
    // if not a window at all, just press on

    ctx = sgo->GetContext();
    if (ctx) {
      // We don't check whether scripts are enabled on ctx, because
      // CheckFunctionAccess will do that anyway... and because we ignore them
      // being disabled if the callee is system.
      cx = ctx->GetNativeContext();
    }
  }

  if (!cx) {
    // We didn't manage to hunt down a script global to work with.  Just fall
    // back on using the safe context.
    cx = nsContentUtils::GetSafeJSContext();
  }

  // Make sure our JSContext is pushed on the stack.
  mCxPusher.Push(cx);

  // Unmark the callable, and stick it in a Rooted before it can go gray again.
  // Nothing before us in this function can trigger a CC, so it's safe to wait
  // until here it do the unmark. This allows us to order the following two
  // operations _after_ the Push() above, which lets us take advantage of the
  // JSAutoRequest embedded in the pusher.
  //
  // We can do this even though we're not in the right compartment yet, because
  // Rooted<> does not care about compartments.
  xpc_UnmarkGrayObject(aCallback);
  mRootedCallable.construct(cx, aCallback);

  // After this point we guarantee calling ScriptEvaluated() if we
  // have an nsIScriptContext.
  // XXXbz Why, if, say CheckFunctionAccess fails?  I know that's how
  // nsJSContext::CallEventHandler used to work, but is it required?
  // FIXME: Bug 807369.
  mCtx = ctx;

  // Check that it's ok to run this callback at all.
  // FIXME: Bug 807371: we want a less silly check here.
  // Make sure to unwrap aCallback before passing it in, because
  // getting principals from wrappers is silly.
  nsresult rv = nsContentUtils::GetSecurityManager()->
    CheckFunctionAccess(cx, js::UncheckedUnwrap(aCallback), nullptr);

  if (NS_FAILED(rv)) {
    // Security check failed.  We're done here.
    return;
  }

  // Enter the compartment of our callback, so we can actually work with it.
  mAc.construct(cx, aCallback);

  // And now we're ready to go.
  mCx = cx;

  // Make sure the JS engine doesn't report exceptions we want to re-throw
  if (mExceptionHandling == eRethrowExceptions) {
    mSavedJSContextOptions = JS_GetOptions(cx);
    JS_SetOptions(cx, mSavedJSContextOptions | JSOPTION_DONT_REPORT_UNCAUGHT);
  }
}

CallbackObject::CallSetup::~CallSetup()
{
  // First things first: if we have a JSContext, report any pending
  // errors on it, unless we were told to re-throw them.
  if (mCx) {
    bool dealtWithPendingException = false;
    if (mExceptionHandling == eRethrowExceptions) {
      // Restore the old context options
      JS_SetOptions(mCx, mSavedJSContextOptions);
      mErrorResult.MightThrowJSException();
      if (JS_IsExceptionPending(mCx)) {
        JS::Rooted<JS::Value> exn(mCx);
        if (JS_GetPendingException(mCx, exn.address())) {
          mErrorResult.ThrowJSException(mCx, exn);
          JS_ClearPendingException(mCx);
          dealtWithPendingException = true;
        }
      }
    }

    if (!dealtWithPendingException) {
      // Either we're supposed to report our exceptions, or we're supposed to
      // re-throw them but we failed to JS_GetPendingException.  Either way,
      // just report the pending exception, if any.
      nsJSUtils::ReportPendingException(mCx);
    }
  }

  // If we have an mCtx, we need to call ScriptEvaluated() on it.  But we have
  // to do that after we pop the JSContext stack (see bug 295983).  And to get
  // our nesting right we have to destroy our JSAutoCompartment first.  But be
  // careful: it might not have been constructed at all!
  mAc.destroyIfConstructed();

  // XXXbz For that matter why do we need to manually call ScriptEvaluated at
  // all?  nsCxPusher::Pop will do that nowadays if !mScriptIsRunning, so the
  // concerns from bug 295983 don't seem relevant anymore.  Do we want to make
  // sure it's still called when !mScriptIsRunning?  I guess play it safe for
  // now and do what CallEventHandler did, which is call always.

  // Popping an nsCxPusher is safe even if it never got pushed.
  mCxPusher.Pop();

  if (mCtx) {
    mCtx->ScriptEvaluated(true);
  }
}

already_AddRefed<nsISupports>
CallbackObjectHolderBase::ToXPCOMCallback(CallbackObject* aCallback,
                                          const nsIID& aIID) const
{
  if (!aCallback) {
    return nullptr;
  }

  AutoSafeJSContext cx;

  JS::Rooted<JSObject*> callback(cx, aCallback->Callback());

  JSAutoCompartment ac(cx, callback);
  nsRefPtr<nsXPCWrappedJS> wrappedJS;
  nsresult rv =
    nsXPCWrappedJS::GetNewOrUsed(callback, aIID,
                                 nullptr, getter_AddRefs(wrappedJS));
  if (NS_FAILED(rv) || !wrappedJS) {
    return nullptr;
  }

  nsCOMPtr<nsISupports> retval;
  rv = wrappedJS->QueryInterface(aIID, getter_AddRefs(retval));
  if (NS_FAILED(rv)) {
    return nullptr;
  }

  return retval.forget();
}

} // namespace dom
} // namespace mozilla