Goroutines, Callbacks and sync.WaitGroup

With the following code:

package main

import (
    "github.com/davecgh/go-spew/spew"
    "sync"
    "time"
)
func callbackWithTimeout(cbFunc func() ([]byte, error), timeout time.Duration) {
	defer wg.Done() //I don't want this function to know about sync.WaitGroup
	time.Sleep(timeout)
	d, e := cbFunc()
	spew.Dump(d)
	spew.Dump(e)
}
var wg sync.WaitGroup
func main() {
	wg.Add(1)
	go func() {
		cbFunc := func() ([]byte, error) {
            //I feel like I should be able to defer here instead
			return nil, nil
		}
		callbackWithTimeout(cbFunc, time.Duration(4*time.Second))
	}()
	println("some line")
	wg.Wait()
}

In function callbackWithTimeout, I don't want to use defer wg.Done() because it's not callbackWithTimeout()'s concern to wg.Done(). How do I go about implementing such a thing? i.e., remove any sync.WaitGroup in callbackWithTimeout? I have a bit of problem understanding the separation of concerns here as a callback'er function should not have to know about waitgroups but in this case it seems, I have no other choice?

I feel like it should be a caller's responsibility to wg.Done() (which in this case is the cbFunc) but lack any concise reference to documentation or ideas on how to implement it in Go because by definition, all a callback function does is call the function back. So, where I am doing it wrong?

Silly assumptions were made by yours truly during refactoring. Working code below. Many thanks.

package main

import (
	"errors"
	"github.com/davecgh/go-spew/spew"
	"sync"
	"time"
)

func callbackWithTimeout(cbFunc func() ([]byte, error), timeout time.Duration) {
	time.Sleep(timeout)
	d, e := cbFunc()
	spew.Dump(d)
	spew.Dump(e)
}

func main() {
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		callbackWithTimeout(func() ([]byte, error) {
			b := []byte{1, 2, 3, 4}
			e := errors.New("error123")
			return b, e
		}, time.Duration(2*time.Second))
	}()
	println("some line")
	wg.Wait()
}

May be like this?

package main

import (
	"sync"
	"time"

	"github.com/davecgh/go-spew/spew"
)

func callbackWithTimeout(cbFunc func() ([]byte, error), timeout time.Duration) {
	time.Sleep(timeout)
	d, e := cbFunc()
	spew.Dump(d)
	spew.Dump(e)
}

func main() {
	var wg sync.WaitGroup

	wg.Add(1)

	go func() {
		defer wg.Done() // move it here
		cbFunc := func() ([]byte, error) {
			//I feel like I should be able to defer here instead
			return nil, nil
		}
		callbackWithTimeout(cbFunc, time.Duration(4*time.Second))
	}()

	println("some line")

	wg.Wait()
}