How do I use Win32's GetRawInputDeviceList in Go? - pointers

Question

I'm trying to use the GetRawInputDeviceList function in Go and I keep getting the following error:
The parameter is incorrect.
Per the official documentation: the first parameter needs to be an array of RAWINPUTDEVICELIST structures for the devices attached to the system. I don't quite understand what combination of unsafe.Pointer, pointer arithmetic(?), and other things I need to do in order to get this to work correctly.
I found this Medium article that offers some guidance, but it's not directly applicable to my use case. I don't have enough experience working with pointers and manual memory management to apply it to my problem. I don't know how to translate this C++ example to Go, and I got so desperate that I tried to convert a working VBA solution to Go with no success.
I have two questions regarding this matter:
How do I convert an array of structs in Go to the appropriate type expected for a Windows API call?
How do I convert the result of the Windows API call back to an array of structs with populated data?
Environment
Here's my system/language details:
macOS Mojave v10.14.6
Go v1.10.7 (required to run executables on Windows XP)
I'm targeting Windows XP, so I run the following command to compile it:
env GOOS=windows GOARCH=386 go1.10.7 build -o example.exe example.go
Code
Here's the code I'm trying to get working. I'm not doing anything with devices yet, but the goal would be to use the handle (DeviceHandle from rawInputDeviceList) to get information about the input device.
package main
import (
"fmt"
"syscall"
"unsafe"
)
// RAWINPUTDEVICELIST structure
type rawInputDeviceList struct {
DeviceHandle uintptr
Type uint32
}
var (
user32 = syscall.NewLazyDLL("user32.dll")
getRawInputDeviceListProc = user32.NewProc("GetRawInputDeviceList")
)
func main() {
dl := rawInputDeviceList{}
size := uint32(unsafe.Sizeof(dl))
// First I determine how many input devices are on the system, which
// gets assigned to `devCount`
var devCount uint32
_ = getRawInputDeviceList(nil, &devCount, size)
if devCount > 0 {
size = size * devCount
devices := make([]rawInputDeviceList, size) // <- This is definitely wrong
for i := 0; i < int(devCount); i++ {
devices[i] = rawInputDeviceList{}
}
// Here is where I get the "The parameter is incorrect." error:
err := getRawInputDeviceList(&devices, &devCount, size)
if err != nil {
fmt.Printf("Error: %v", err)
}
}
}
// Enumerates the raw input devices attached to the system.
func getRawInputDeviceList(
rawInputDeviceList *[]rawInputDeviceList, // <- This is probably wrong
numDevices *uint32,
size uint32,
) error {
_, _, err := getRawInputDeviceListProc.Call(
uintptr(unsafe.Pointer(rawInputDeviceList)),
uintptr(unsafe.Pointer(numDevices)),
uintptr(size))
if err != syscall.Errno(0) {
return err
}
return nil
}

Answer 1

First, the ERROR_INVALID_PARAMETER error is cause by the last parameter: cbSize, According to the document, it should always be set to size of RAWINPUTDEVICELIST.
Then you will pass the compiler but still get the runtime error. because you have passed a pointer of array.
The following code works for me:
package main
import (
"fmt"
"syscall"
"unsafe"
)
// RAWINPUTDEVICELIST structure
type rawInputDeviceList struct {
DeviceHandle uintptr
Type uint32
}
var (
user32 = syscall.NewLazyDLL("user32.dll")
getRawInputDeviceListProc = user32.NewProc("GetRawInputDeviceList")
)
func main() {
dl := rawInputDeviceList{}
size := uint32(unsafe.Sizeof(dl))
// First I determine how many input devices are on the system, which
// gets assigned to `devCount`
var devCount uint32
_ = getRawInputDeviceList(nil, &devCount, size)
if devCount > 0 {
devices := make([]rawInputDeviceList, size * devCount) // <- This is definitely wrong
for i := 0; i < int(devCount); i++ {
devices[i] = rawInputDeviceList{}
}
// Here is where I get the "The parameter is incorrect." error:
err := getRawInputDeviceList(&devices[0], &devCount, size)
if err != nil {
fmt.Printf("Error: %v", err)
}
for i := 0; i < int(devCount); i++ {
fmt.Printf("Type: %v", devices[i].Type)
}
}
}
// Enumerates the raw input devices attached to the system.
func getRawInputDeviceList(
rawInputDeviceList *rawInputDeviceList, // <- This is probably wrong
numDevices *uint32,
size uint32,
) error {
_, _, err := getRawInputDeviceListProc.Call(
uintptr(unsafe.Pointer(rawInputDeviceList)),
uintptr(unsafe.Pointer(numDevices)),
uintptr(size))
if err != syscall.Errno(0) {
return err
}
return nil
}