iunknown.go

// +build windows

package clr

import (
	"fmt"
	"syscall"
	"unsafe"

	"golang.org/x/sys/windows"
)

type IUnknown struct {
	vtbl *IUnknownVtbl
}

// IUnknownVtbl Enables clients to get pointers to other interfaces on a given object through the
// QueryInterface method, and manage the existence of the object through the AddRef and Release methods.
// All other COM interfaces are inherited, directly or indirectly, from IUnknown. Therefore, the three
// methods in IUnknown are the first entries in the vtable for every interface.
// https://docs.microsoft.com/en-us/windows/win32/api/unknwn/nn-unknwn-iunknown
type IUnknownVtbl struct {
	// QueryInterface Retrieves pointers to the supported interfaces on an object.
	QueryInterface uintptr
	// AddRef Increments the reference count for an interface pointer to a COM object.
	// You should call this method whenever you make a copy of an interface pointer.
	AddRef uintptr
	// Release Decrements the reference count for an interface on a COM object.
	Release uintptr
}

// QueryInterface queries a COM object for a pointer to one of its interface;
// identifying the interface by a reference to its interface identifier (IID).
// If the COM object implements the interface, then it returns a pointer to that interface after calling IUnknown::AddRef on it.
// HRESULT QueryInterface(
//   REFIID riid,
//   void   **ppvObject
// );
// https://docs.microsoft.com/en-us/windows/win32/api/unknwn/nf-unknwn-iunknown-queryinterface(refiid_void)
func (obj *IUnknown) QueryInterface(riid windows.GUID, ppvObject unsafe.Pointer) error {
	debugPrint("Entering into iunknown.QueryInterface()...")
	hr, _, err := syscall.Syscall(
		obj.vtbl.QueryInterface,
		3,
		uintptr(unsafe.Pointer(obj)),
		uintptr(unsafe.Pointer(&riid)), // A reference to the interface identifier (IID) of the interface being queried for.
		uintptr(ppvObject),
	)
	if err != syscall.Errno(0) {
		return fmt.Errorf("the IUknown::QueryInterface method returned an error:\r\n%s", err)
	}
	if hr != S_OK {
		return fmt.Errorf("the IUknown::QueryInterface method method returned a non-zero HRESULT: 0x%x", hr)
	}
	return nil
}

// AddRef Increments the reference count for an interface pointer to a COM object.
// You should call this method whenever you make a copy of an interface pointer
// ULONG AddRef();
// https://docs.microsoft.com/en-us/windows/win32/api/unknwn/nf-unknwn-iunknown-addref
func (obj *IUnknown) AddRef() (count uint32, err error) {
	debugPrint("Entering into iunknown.AddRef()...")
	ret, _, err := syscall.Syscall(
		obj.vtbl.AddRef,
		1,
		uintptr(unsafe.Pointer(obj)),
		0,
		0,
	)
	if err != syscall.Errno(0) {
		return 0, fmt.Errorf("the IUnknown::AddRef method returned an error:\r\n%s", err)
	}
	err = nil
	// Unable to avoid misuse of unsafe.Pointer because the Windows API call returns the safeArray pointer in the "ret" value. This is a go vet false positive
	count = *(*uint32)(unsafe.Pointer(ret))
	return
}

// Release Decrements the reference count for an interface on a COM object.
// ULONG Release();
// https://docs.microsoft.com/en-us/windows/win32/api/unknwn/nf-unknwn-iunknown-release
func (obj *IUnknown) Release() (count uint32, err error) {
	debugPrint("Entering into iunknown.Release()...")
	ret, _, err := syscall.Syscall(
		obj.vtbl.Release,
		1,
		uintptr(unsafe.Pointer(obj)),
		0,
		0,
	)
	if err != syscall.Errno(0) {
		return 0, fmt.Errorf("the IUnknown::Release method returned an error:\r\n%s", err)
	}
	err = nil
	// Unable to avoid misuse of unsafe.Pointer because the Windows API call returns the safeArray pointer in the "ret" value. This is a go vet false positive
	count = *(*uint32)(unsafe.Pointer(ret))
	return
}