Ultralight Workaround for Favicons - Windows 10

win.go

// +build windows

package main

import (
	"os"
	"syscall"
	"unsafe"
)

var (
	_user32                = syscall.MustLoadDLL("user32.dll")
	procEnumWindows        = _user32.MustFindProc("EnumWindows")
	getProcessIdFromWindow = _user32.MustFindProc("GetWindowThreadProcessId")
	loadImage              = _user32.MustFindProc("LoadImageW")
	sendMessage            = _user32.MustFindProc("SendMessageW")
)

func LoadImage(hwnd syscall.Handle, lpsz *uint16, uType uint, cxDesired int, cyDesired int, fuLoad uint) (len uintptr, err error) {
	r0, _, e1 := syscall.Syscall6(loadImage.Addr(), 6, uintptr(hwnd), uintptr(unsafe.Pointer(lpsz)), uintptr(uType), uintptr(cxDesired), uintptr(cyDesired), uintptr(fuLoad))
	len = r0
	if len == 0 {
		if e1 != 0 {
			err = error(e1)
		} else {
			err = syscall.EINVAL
		}
	}
	return
}

func SendMessage(hwnd syscall.Handle, msg uint, wParam int, lParam uintptr) (len int32, err error) {
	syscall.Syscall6(sendMessage.Addr(), 4, uintptr(hwnd), uintptr(msg), uintptr(wParam), lParam, 0, 0)
	return
}

func EnumWindows(enumFunc uintptr, lparam uintptr) (err error) {
	syscall.Syscall(procEnumWindows.Addr(), 2, enumFunc, lparam, 0)
	return
}

func GetProcessIdFromWindow(hwnd syscall.Handle, processId *uint64) (len int32, err error) {
	r0, _, e1 := syscall.Syscall(getProcessIdFromWindow.Addr(), 2, uintptr(hwnd), uintptr(unsafe.Pointer(processId)), 0)
	len = int32(r0)
	if len == 0 {
		if e1 != 0 {
			err = error(e1)
		} else {
			err = syscall.EINVAL
		}
	}
	return
}

func UpdateIcon() {
	name, _ := syscall.UTF16PtrFromString("icon.ico")
	zero := syscall.Handle(0)
	img, _ := LoadImage(zero, name, 1, 16, 16, 0x10)

	cb := syscall.NewCallback(func(h syscall.Handle, p uintptr) uintptr {
		var b uint64 = 0
		GetProcessIdFromWindow(h, &b)
		if b == uint64(os.Getpid()) {
			SendMessage(h, 0x80, 0, img)
			return 0
		}
		return 1 // continue enumeration
	})
	EnumWindows(cb, 0)
}

Use it by calling UpdateIcon() after creating an Ultralight window.