How to Safely Call the GetVolumeInformation WinAPI Function in Go Using the Unsafe Package?

How to Call the GetVolumeInformation WinAPI Function in Go

Problem:

When attempting to call the GetVolumeInformation function from within a Go program, an error occurs due to an unsafe pointer operation.

Background:

The GetVolumeInformation function retrieves information about a specified volume, including its name. It requires several input and output parameters to work.

Solution:

To resolve the error, it's crucial to understand the purpose and usage of the unsafe package in Go. The unsafe package allows direct manipulation of memory addresses, bypassing the type safety of the language. However, it should be used with caution.

One of the operations available for the unsafe package is to convert a pointer to a specific type to a Pointer, which represents a pointer to an arbitrary type. This flexibility allows for reading and writing arbitrary memory locations.

In the code provided, the error arose because the VolumeNameBuffer was passed to the GetVolumeInformation function using unsafe.Pointer(&lpVolumeNameBuffer). This cast attempts to convert the string variable to a Pointer.

Revised Code:

To address the issue, the code can use an array of uint16 (the size of which is determined by syscall.MAX_PATH) to receive the volume name and pass it as an argument to the GetVolumeInformation function. This approach avoids the need to use Pointer and ensures type safety.

<code class="go">import (
    "fmt"
    "syscall"
    "unsafe"
)

func main() {
    var RootPathName = `C:\`
    var VolumeNameBuffer = make([]uint16, syscall.MAX_PATH+1)
    var nVolumeNameSize = uint32(len(VolumeNameBuffer))
    // Other parameters...

    kernel32, _ := syscall.LoadLibrary("kernel32.dll")
    getVolume, _ := syscall.GetProcAddress(kernel32, "GetVolumeInformationW")

    var nargs uintptr = 8
    ret, _, callErr := syscall.Syscall9(uintptr(getVolume),
        nargs,
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(RootPathName))),
        uintptr(unsafe.Pointer(&amp;VolumeNameBuffer[0])),
        uintptr(nVolumeNameSize),
        // Other parameters...
        0)
    fmt.Println(ret, callErr, syscall.UTF16ToString(VolumeNameBuffer))
}</code>

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