go + cgo and linking

i want to use the following c as Go's cgo:

#include <X11/extensions/scrnsaver.h>

main() {
  XScreenSaverInfo *info = XScreenSaverAllocInfo();
  Display *display = XOpenDisplay(0);

  XScreenSaverQueryInfo(display, DefaultRootWindow(display), info);
  printf("%u ms\n", info->idle);
}

build with:

gcc -o idle printXIdleTime.c -lX11 -lXss

i re-wrote that code for Go's cgo:

package tools

// #cgo pkg-config: x11
// #include <X11/extensions/scrnsaver.h>
import "C"

func GetIdleTime() (idleTime uint32) {
	var info *C.XScreenSaverInfo
	var display *C.Display 
	
	info = C.XScreenSaverAllocInfo()
	display = C.XOpenDisplay(0)

	defaultRootWindow := C.XDefaultRootWindow(display)

	C.XScreenSaverQueryInfo(display, defaultRootWindow, info)
	idleTime = info.idle

	return
}

tried to compile with:

go build -gccgoflags="-lXss -lX11"

however i'm getting linker errors:

> /tmp/go-build076004816/opensource.stdk/lib/tools/_obj/x11.cgo2.o: In
> function _cgo_c0e279f6f16e_Cfunc_XScreenSaverAllocInfo': ./x11.go:52:
> undefined reference to XScreenSaverAllocInfo'
> /tmp/go-build076004816/opensource.stdk/lib/tools/_obj/x11.cgo2.o: In
> function _cgo_c0e279f6f16e_Cfunc_XScreenSaverQueryInfo': ./x11.go:65:
> undefined reference to XScreenSaverQueryInfo' collect2: error: ld
> returned 1 exit status

what am i doing wrong?

This is how I got it to build. Note the #cgo LDFLAGS line which is probably what you are missing. I had to make a few other changes to make it build. It seems to be returning the right answer on my Linux machine!

package tools

// #cgo LDFLAGS: -lXss -lX11
// #include <X11/extensions/scrnsaver.h>
import "C"
    
func GetIdleTime() (idleTime uint32) {
	var info *C.XScreenSaverInfo
	var display *C.Display

	info = C.XScreenSaverAllocInfo()
	display = C.XOpenDisplay(nil)

	defaultRootWindow := C.XDefaultRootWindow(display)

	C.XScreenSaverQueryInfo(display, C.Drawable(defaultRootWindow), info)
    idleTime = uint32(info.idle)

	return
}

Note that this can be done with the native X Go Binding and the ScreenSaver extension:

package main

import (
	"fmt"
	"log"

	"github.com/BurntSushi/xgb"
	"github.com/BurntSushi/xgb/xproto"
	"github.com/BurntSushi/xgb/screensaver"
)

func main() {
	X, err := xgb.NewConn()
	if err != nil {
		log.Fatal(err)
	}

	if err = screensaver.Init(X); err != nil {
		log.Fatal(err)
	}

	root := xproto.Setup(X).DefaultScreen(X).Root
	info, err := screensaver.QueryInfo(X, xproto.Drawable(root)).Reply()
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("Idle: %d\n", info.MsSinceUserInput)
}

Outputs:

[andrew@Liger go] go run xscreensaver_idle.go 
Idle: 1040