83 lines
3.1 KiB
Go
83 lines
3.1 KiB
Go
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package winbt
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// This file implements a COM object that can be used for various event
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// callbacks. In C++, it would use an ITypedEventHandler instantiation.
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import (
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"unsafe"
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"github.com/go-ole/go-ole"
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)
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// const void * winbt_getEventVtbl(void);
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import "C"
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// Event implements event handler interfaces (ITypedEventHandler). This is
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// therefore a valid COM object, derived from IUnknown.
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type Event struct {
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ole.IUnknown
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IID *ole.GUID
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Callback func(*Event, *ole.IInspectable)
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token uintptr
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}
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// NewEvent creates a new COM object for event callbacks. The IID must be the
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// IID for a particular event, which is unfortunately not included in the *.idl
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// files but has to be found in the relevant C++/WinRT header files.
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func NewEvent(iid *ole.GUID, callback func(*Event, *ole.IInspectable)) *Event {
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// Another way to find the IID is to print the requested IID in the
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// QueryInterface method below. The first queried IID is likely the one
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// that is the event interface IID.
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// The event must be allocated on the C heap, because it is not allowed to
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// retain a pointer on the Go heap after a non-Go call returns (e.g.
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// syscall.Syscall).
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event := (*Event)(C.malloc(C.size_t(unsafe.Sizeof(Event{}))))
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event.RawVTable = (*interface{})(C.winbt_getEventVtbl())
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event.IID = iid
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event.Callback = callback
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return event
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}
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// The two functions below implement IUnknown and an interface I couldn't
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// really get the definition of (possibly ITypedEventHandler, although
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// ITypedEventHandler is really a C++ template). The closest thing I could find
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// to documentation are the C++/WinRT headers and this mention by Kenny Kerr
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// (the original developer of C++/WinRT):
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// https://docs.microsoft.com/en-us/archive/msdn-magazine/2013/august/windows-with-c-the-windows-runtime-application-model
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// > [...] Fortunately, all of these interfaces are generated by the MIDL
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// > compiler, which takes care to specialize each one, and it’s on these
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// > specializations that it attaches the GUID representing the interface
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// > identifier. As complicated as the previous typedef might appear, it
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// > defines a COM interface that derives directly from IUnknown and provides
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// > a single method called Invoke.
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//export winbt_Event_QueryInterface
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func winbt_Event_QueryInterface(eventPtr, iidPtr unsafe.Pointer, ppvObject *unsafe.Pointer) uintptr {
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// This function must adhere to the QueryInterface defined here:
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// https://docs.microsoft.com/en-us/windows/win32/api/unknwn/nn-unknwn-iunknown
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iid := (*ole.GUID)(iidPtr)
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event := (*Event)(eventPtr)
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if ole.IsEqualGUID(iid, event.IID) {
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// This is us.
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*ppvObject = eventPtr
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return ole.S_OK
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}
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if ole.IsEqualGUID(iid, ole.IID_IUnknown) {
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// This is our parent. There are some limitations as to what we can
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// return here, but returning the *Event pointer is fine.
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*ppvObject = eventPtr
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return ole.S_OK
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}
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return 0x80004002 // E_NOTINTERFACE
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}
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//export winbt_Event_Invoke
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func winbt_Event_Invoke(eventPtr, senderPtr, argsPtr unsafe.Pointer) uintptr {
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// See the quote above.
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event := (*Event)(eventPtr)
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argsInspectable := (*ole.IInspectable)(argsPtr)
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event.Callback(event, argsInspectable)
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return ole.S_OK
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}
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