Call SHGetImageList in Go

Question

I'm trying to call SHGetImageList in Go in order to extract icons from .EXE files. The problem is that I don't know how to create/pass an "IImageList2 interface" in Go, which is something SHGetImageList requires.

I've tried miscellaneous things for a few hours, but it all results in the same E_NOINTERFACE error. Basically they're all "shots in the dark" ([]byte array to see if I could receive any "data" at all, an actual interface{} in Go containing the same functions as the IImagelist2 interface defined by MSDN, etc). If it is of any relevance, I do have a working version of this in C# using something along the lines of http://www.pinvoke.net/default.aspx/shell32.shgetimagelist, but I simply have no real clue on how to "translate" that to Go. Any help would be much appreciated.

Example Go code below, with some info and links to MSDN in the comments.

package main

import (
    "fmt"
    "syscall"
    "unsafe"
)

var (
    shell32 = syscall.MustLoadDLL("shell32.dll")

    // https://msdn.microsoft.com/en-us/library/windows/desktop/bb762179(v=vs.85).aspx
    procSHGetFileInfo = shell32.MustFindProc("SHGetFileInfoW")

    //https://msdn.microsoft.com/en-us/library/windows/desktop/bb762185(v=vs.85).aspx
    procSHGetImageList = shell32.MustFindProc("SHGetImageList")
)

func main() {
    someExeFile := `c:\windows\explorer.exe`

    iconIndex := GetIconIndex(someExeFile)

    // The problem:
    HRESULT, _, _ := procSHGetImageList.Call(
        uintptr(SHIL_JUMBO),
        uintptr(unsafe.Pointer(&IID_IImageList2)),

        // I don't know how pass/create an "IImageList interface" in Go,
        // or if it's even possible without relying on CGO.
        // IImageList interface:
        // https://msdn.microsoft.com/en-us/library/windows/desktop/bb761419(v=vs.85).aspx

        // Currently there's just a pointer to an empty []byte so that the code will compile.
        // HRESULT naturally contains the error code E_NOINTERFACE (2147500034),
        // which makes sense seeing as I'm not passing a valid interface.
        uintptr(unsafe.Pointer(&[]byte{})),
    )

    fmt.Println(iconIndex, HRESULT)
}


const SHIL_JUMBO = 0x4

const shGetFileInfoLen = 3
const shGetFileInfoFlags = 16400 //(SysIconIndex|LargeIcon|UseFileAttributes)
// use SHGetFileInfo to get the icon index (only value we care about)
func GetIconIndex(fileName string) int {
    buf := make([]uint16, shGetFileInfoLen)
    ret, _, _ := procSHGetFileInfo.Call(
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(fileName))),
        0,
        uintptr(unsafe.Pointer(&buf[0])),
        shGetFileInfoLen,
        shGetFileInfoFlags,
    )

    if ret != 0 && buf[2] > 0 {
        return int(buf[2])
    }

    return 0
}

// From: "192B9D83-50FC-457B-90A0-2B82A8B5DAE1"
var IID_IImageList2 = &GUID{0x192b9d83, 0x50fc, 0x457b, [8]byte{0x90, 0xa0, 0x2b, 0x82, 0xa8, 0xb5, 0xda, 0xe1}}

// http://msdn.microsoft.com/en-us/library/windows/desktop/aa373931.aspx
type GUID struct {
    Data1 uint32
    Data2 uint16
    Data3 uint16
    Data4 [8]byte
}

UPDATE

The problem now is that it's exiting with an error(0xC0000005) when calling the Syscall to get the actual icon pointer.

package main

import (
    "fmt"
    "syscall"
    "unsafe"
)

var (
    shell32 = syscall.MustLoadDLL("shell32.dll")

    // https://msdn.microsoft.com/en-us/library/windows/desktop/bb762179(v=vs.85).aspx
    procSHGetFileInfo = shell32.MustFindProc("SHGetFileInfoW")

    //https://msdn.microsoft.com/en-us/library/windows/desktop/bb762185(v=vs.85).aspx
    procSHGetImageList = shell32.MustFindProc("SHGetImageList")

    ole32 = syscall.MustLoadDLL("ole32.dll")
    procCoInitialize = ole32.MustFindProc("CoInitialize")
)

func main() {
    someExeFile := `c:\windows\explorer.exe`

    procCoInitialize.Call()

    iconIndex := GetIconIndex(someExeFile)

    var imglist *IImageList
    hr, _, _ := procSHGetImageList.Call(
        uintptr(SHIL_JUMBO),
        uintptr(unsafe.Pointer(&IID_IImageList)),
        uintptr(unsafe.Pointer(&imglist)),
    )

    // These look OK
    fmt.Println(iconIndex, hr, imglist.Vtbl.GetIcon)

    var hIcon uintptr
    // GetIcon: https://msdn.microsoft.com/en-us/library/windows/desktop/bb761463(v=vs.85).aspx
    hr, _, _ = syscall.Syscall(imglist.Vtbl.GetIcon,
        uintptr(unsafe.Pointer(imglist)),
        uintptr(iconIndex),
        getIconFlags,
        uintptr(unsafe.Pointer(&hIcon)),
    )

    // Errors: "Process finished with exit code -1073741819 (0xC0000005)"

    fmt.Println("hIcon:", hIcon) // Never reaches this
}

// ILD_TRANSPARENT | ILD_IMAGE
const getIconFlags = 0x00000001 | 0x00000020

const SHIL_JUMBO = 0x4

const shGetFileInfoLen = 3
const shGetFileInfoFlags = 16400 //(SysIconIndex|LargeIcon|UseFileAttributes)
// use SHGetFileInfo to get the icon index (only value we care about)
func GetIconIndex(fileName string) int {
    buf := make([]uint16, shGetFileInfoLen)
    ret, _, _ := procSHGetFileInfo.Call(
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(fileName))),
        0,
        uintptr(unsafe.Pointer(&buf[0])),
        shGetFileInfoLen,
        shGetFileInfoFlags,
    )

    if ret != 0 && buf[2] > 0 {
        return int(buf[2])
    }

    return 0
}


// From: "46EB5926-582E-4017-9FDF-E8998DAA0950"
var IID_IImageList = GUID{0x46eb5926, 0x582e, 0x4017, [8]byte{0x9f, 0xdf, 0xe8, 0x99, 0x8d, 0xaa, 0x09, 0x50}}

// http://msdn.microsoft.com/en-us/library/windows/desktop/aa373931.aspx
type GUID struct {
    Data1 uint32
    Data2 uint16
    Data3 uint16
    Data4 [8]byte
}

type IImageList struct {
    Vtbl *IImageListVtbl
}

type IImageListVtbl struct {
    Add                uintptr
    ReplaceIcon        uintptr
    SetOverlayImage    uintptr
    Replace            uintptr
    AddMasked          uintptr
    Draw               uintptr
    Remove             uintptr
    GetIcon            uintptr
    GetImageInfo       uintptr
    Copy               uintptr
    Merge              uintptr
    Clone              uintptr
    GetImageRect       uintptr
    GetIconSize        uintptr
    SetIconSize        uintptr
    GetImageCount      uintptr
    SetImageCount      uintptr
    SetBkColor         uintptr
    GetBkColor         uintptr
    BeginDrag          uintptr
    EndDrag            uintptr
    DragEnter          uintptr
    DragLeave          uintptr
    DragMove           uintptr
    SetDragCursorImage uintptr
    DragShowNolock     uintptr
    GetDragImage       uintptr
    GetItemFlags       uintptr
    GetOverlayImage    uintptr
}

andlabs · Accepted Answer

Oh, I see the actual problem now.

        uintptr(unsafe.Pointer(&IID_IImageList2)),
...
var IID_IImageList2 = &GUID{0x192b9d83, 0x50fc, 0x457b, [8]byte{0x90, 0xa0, 0x2b, 0x82, 0xa8, 0xb5, 0xda, 0xe1}}

Your IID_IImageList2 is already a pointer. In your call, you're taking a pointer to that pointer, which means the address is used as the GUID. You should either do

        uintptr(unsafe.Pointer(&IID_IImageList2)),
...
var IID_IImageList2 = GUID{0x192b9d83, 0x50fc, 0x457b, [8]byte{0x90, 0xa0, 0x2b, 0x82, 0xa8, 0xb5, 0xda, 0xe1}}

or

        uintptr(unsafe.Pointer(IID_IImageList2)),
...
var IID_IImageList2 = &GUID{0x192b9d83, 0x50fc, 0x457b, [8]byte{0x90, 0xa0, 0x2b, 0x82, 0xa8, 0xb5, 0xda, 0xe1}}

That way, the GUID itself is used as the GUID, not its location in memory.

Call SHGetImageList in Go

Answers (2)

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