open_windows.go

//go:build windows

package browser

import (
	"context"
	"fmt"
	"sync"
	"syscall"
	"unsafe"
)

var (
	kernel32            = syscall.NewLazyDLL("kernel32.dll")
	loadLibraryExW      = kernel32.NewProc("LoadLibraryExW")
	shellExecuteOnce    sync.Once
	shellExecuteW       *syscall.Proc
	shellExecuteLoadErr error
)

func openDefault(ctx context.Context, rawURL string) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	return shellExecuteURL(rawURL)
}

var shellExecuteURL = func(rawURL string) error {
	proc, err := loadShellExecuteW()
	if err != nil {
		return err
	}

	operation, err := syscall.UTF16PtrFromString("open")
	if err != nil {
		return err
	}
	target, err := syscall.UTF16PtrFromString(rawURL)
	if err != nil {
		return err
	}

	// ShellExecuteW returns a value greater than 32 on success. It uses the
	// user's registered URL handler directly, avoiding cmd.exe and PowerShell
	// quoting and availability issues.
	result, _, _ := proc.Call(
		0,
		uintptr(unsafe.Pointer(operation)),
		uintptr(unsafe.Pointer(target)),
		0,
		0,
		1, // SW_SHOWNORMAL
	)
	if result > 32 {
		return nil
	}
	return fmt.Errorf("ShellExecuteW failed (%d)", result)
}

func loadShellExecuteW() (*syscall.Proc, error) {
	shellExecuteOnce.Do(func() {
		name, err := syscall.UTF16PtrFromString("shell32.dll")
		if err != nil {
			shellExecuteLoadErr = err
			return
		}

		// Do not use syscall.NewLazyDLL("shell32.dll") here. Unlike kernel32,
		// shell32 is not on the standard library's internal system-DLL
		// allowlist. LOAD_LIBRARY_SEARCH_SYSTEM32 prevents DLL preloading from
		// the application or working directory without adding a dependency.
		const loadLibrarySearchSystem32 = 0x00000800
		handle, _, callErr := loadLibraryExW.Call(
			uintptr(unsafe.Pointer(name)),
			0,
			loadLibrarySearchSystem32,
		)
		if handle == 0 {
			shellExecuteLoadErr = fmt.Errorf("LoadLibraryExW shell32.dll: %w", callErr)
			return
		}

		shell32 := &syscall.DLL{
			Name:   "shell32.dll",
			Handle: syscall.Handle(handle),
		}
		shellExecuteW, shellExecuteLoadErr = shell32.FindProc("ShellExecuteW")
	})

	return shellExecuteW, shellExecuteLoadErr
}