gecko-dev/ipc/mscom/Interceptor.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/. */

#ifndef mozilla_mscom_interceptor_h
#define mozilla_mscom_interceptor_h

#include "mozilla/Move.h"
#include "mozilla/Mutex.h"
#include "nsTArray.h"
#include "mozilla/mscom/Ptr.h"
#include "mozilla/mscom/WeakRef.h"
#include "mozilla/RefPtr.h"

#include <callobj.h>

namespace mozilla {
namespace mscom {

// {8831EB53-A937-42BC-9921-B3E1121FDF86}
DEFINE_GUID(IID_IInterceptorSink,
0x8831eb53, 0xa937, 0x42bc, 0x99, 0x21, 0xb3, 0xe1, 0x12, 0x1f, 0xdf, 0x86);

struct IInterceptorSink : public ICallFrameEvents
{
  virtual STDMETHODIMP SetInterceptor(IWeakReference* aInterceptor) = 0;
};

// {3710799B-ECA2-4165-B9B0-3FA1E4A9B230}
DEFINE_GUID(IID_IInterceptor,
0x3710799b, 0xeca2, 0x4165, 0xb9, 0xb0, 0x3f, 0xa1, 0xe4, 0xa9, 0xb2, 0x30);

struct IInterceptor : public IUnknown
{
  virtual STDMETHODIMP GetTargetForIID(REFIID aIid, InterceptorTargetPtr& aTarget) = 0;
  virtual STDMETHODIMP GetInterceptorForIID(REFIID aIid,
                                            void** aOutInterceptor) = 0;
};

/**
 * The COM interceptor is the core functionality in mscom that allows us to
 * redirect method calls to different threads. It emulates the vtable of a
 * target interface. When a call is made on this emulated vtable, the call is
 * packaged up into an instance of the ICallFrame interface which may be passed
 * to other contexts for execution.
 *
 * In order to accomplish this, COM itself provides the CoGetInterceptor
 * function, which instantiates an ICallInterceptor. Note, however, that
 * ICallInterceptor only works on a single interface; we need to be able to
 * interpose QueryInterface calls so that we can instantiate a new
 * ICallInterceptor for each new interface that is requested.
 *
 * We accomplish this by using COM aggregation, which means that the
 * ICallInterceptor delegates its IUnknown implementation to its outer object
 * (the mscom::Interceptor we implement and control).
 */
class Interceptor final : public WeakReferenceSupport
                        , public IInterceptor
{
public:
  static HRESULT Create(STAUniquePtr<IUnknown>& aTarget, IInterceptorSink* aSink,
                        REFIID aIid, void** aOutput);

  // IUnknown
  STDMETHODIMP QueryInterface(REFIID riid, void** ppv) override;
  STDMETHODIMP_(ULONG) AddRef() override;
  STDMETHODIMP_(ULONG) Release() override;

  // IInterceptor
  STDMETHODIMP GetTargetForIID(REFIID aIid, InterceptorTargetPtr& aTarget) override;
  STDMETHODIMP GetInterceptorForIID(REFIID aIid, void** aOutInterceptor) override;

private:
  struct MapEntry
  {
    MapEntry(REFIID aIid, IUnknown* aInterceptor, IUnknown* aTargetInterface)
      : mIID(aIid)
      , mInterceptor(aInterceptor)
      , mTargetInterface(aTargetInterface)
    {}
    IID               mIID;
    IUnknown*         mInterceptor;
    IUnknown*         mTargetInterface;
  };

private:
  Interceptor(STAUniquePtr<IUnknown>& aTarget, IInterceptorSink* aSink);
  ~Interceptor();
  MapEntry* Lookup(REFIID aIid);
  HRESULT QueryInterfaceTarget(REFIID aIid, void** aOutput);
  HRESULT ThreadSafeQueryInterface(REFIID aIid,
                                   IUnknown** aOutInterface) override;
  HRESULT CreateInterceptor(REFIID aIid, IUnknown* aOuter, IUnknown** aOutput);

private:
  STAUniquePtr<IUnknown>    mTarget;
  RefPtr<IInterceptorSink>  mEventSink;
  mozilla::Mutex            mMutex; // Guards mInterceptorMap
  // Using a nsTArray since the # of interfaces is not going to be very high
  nsTArray<MapEntry>        mInterceptorMap;
};

template <typename InterfaceT>
inline HRESULT
CreateInterceptor(STAUniquePtr<InterfaceT>& aTargetInterface,
                  IInterceptorSink* aEventSink,
                  InterfaceT** aOutInterface)
{
  if (!aTargetInterface || !aEventSink) {
    return E_INVALIDARG;
  }

  REFIID iidTarget = __uuidof(aTargetInterface);

  STAUniquePtr<IUnknown> targetUnknown(aTargetInterface.release());
  return Interceptor::Create(targetUnknown, aEventSink, iidTarget,
                             (void**)aOutInterface);
}

} // namespace mscom
} // namespace mozilla

#endif // mozilla_mscom_interceptor_h